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GATHERING INFORMATION ABOUT CONTROL OPTIONS A successful control strategy for an invasive often begins with checking on-line and other data sources about manage- ment options for the target species. Successful methods used under similar conditions; that is, in similar habitats and cli- mates, are preferred. Because invasions and the effective- ness of control methods vary with local conditions, general statements about suitable control methods should be approached with caution. Experience-based reports of meth- ods used to control certain species and their effectiveness under specific environmental factors are essential for inva- sive species management. DOTs may benefit from using shared databases or having common points of contact on the Internet, to share and benefit from each otherâs experience and learning. Invasives management can greatly benefit by use of the best practices available and dissemination of experience and information. General Versus Species-Specific Control Methods The most successful invasive species control has been achieved with species-specific methods, which also have the least impact on nontarget species. In some instances, such as highly degraded habitats without any native species remain- ing, a more general method is acceptable. In these cases, a broad-spectrum herbicide, or bulldozing the ground, has lim- ited negative effects on native biodiversity. However, in less disturbed areas; for example, in particular nature reserves, the use of a species-specific method is highly recommended. Although DOTs strive to avoid reaching unacceptable levels of unintended consequences, impacts on nontarget species may be expected while carrying out such control measures. When control or eradication is successful, the reduced impact of the alien species on the native biodiversity normally outweighs the cost; native species that suffer losses during the control efforts typically rebound following the removal of the invasive species. In choosing a management strategy, DOTs usually consider: â¢ Legal requirements related to management of invasive species and particular regulations on herbicide usage, including those in health and safety legislation. â¢ Best methods that have been used for this target species. 38 â¢ The types of herbicides, baits, and equipment that are readily available and the ways by which further sup- plies can be obtained. Plant control may involve manual methods (e.g., hand- pulling, cutting, mowing, bulldozing, and girdling), herbi- cides, release of biological control agents, controlled use of grazing or browsing animals, prescribed fires, flooding, planting competitive native species, and other land manage- ment practices. Land invertebrate control may involve traps (e.g., light traps, pitfall traps, and pheromone traps), mechan- ical and physical means (e.g., hand-picking, removal, and destruction of host species), insecticides, biological control (e.g., fungi, other insects), and other specialized means (e.g., mass release of sterile males). Land vertebrate control may involve trapping, shooting, baiting, biological control, con- traceptives, or sterilization. Control of pathogens often focuses on hosts rather than measures directly orientated against the pathogen species. In some cases the hosts are eliminatedâthis is a preferred choice when the hosts are nonindigenous as wellâin others, including diseases of humans and domesticated animals, the hosts are vaccinated. Resistance of the host can also be induced or intensified. If vectors are a part of the pathogenâs life cycle, vector man- agement should be considered. Control of marine bioinva- sions is more difficult, although pathogens, pesticides, and hand-picking have been used. Prevention is generally considered the principle defense against marine invasive species, which are distributed by one principal pathway, the ship. Organisms in freshwater habitats can be controlled with mechanical, chemical, and biological measures and habitat management. Aquatic weeds can be harvested when floating on the surface, pulled out when rooted, or sprayed with herbicides. Biological control has been particularly effective against several water weeds in different parts of the world. For example, weevils have been used to control water lettuce in the United States and other countries. Fish-specific poison has been used in the eradication of several fish invasions. Another control option for fish is recreational or industrial fishing. Mos- quito larvae and pathogens vectored, and by extrapolation other freshwater insects, can be controlled by spraying chemicals or biological pesticides onto the infested water. The community of a freshwater system can be influenced by changes in the water quality and quantity in favor of native species (71). CHAPTER FOUR ROADSIDE CONTROL METHODS AND RESOURCES
39 Biological, cultural, physical, and chemical control meth- ods can be used to contain and eradicate invasives. Biological weed control includes the use of insects or pathogens. â¢ Physical control of invasive plant species includes till- ing, mowing, and burning areas to control invasives. â¢ Mechanical methods include hand-pulling and mow- ing, which can be effective in conjunction with other control methods. â¢ Chemical control of invasive species relies on herbi- cides and pesticides. â¢ Cultural control of invasives includes planting native grasses or competing plant species to force out invasive species. No individual method will control invasive species in a sin- gle treatment; diligence and persistence are often required over a number of years to bring infestations under control. In most cases, the best practice to manage an invasive species may involve a system of integrated management tailored for the species and the location. Thus, it is important to accumulate the available information, assess all potential methods, and use the best method or combination of methods to achieve the target level of control. These methods are usually combined in strate- gic planning to control invasives or in IVM or IRVM planning, as discussed in the previous chapter. All methods should include follow-up monitoring, treatments, and revegetation to prevent new infestations or resurgence of the target weed. All control methods, with the exception of classical bio- logical control, which is self-sustaining, need long-term funding and commitment. However, initial investments in developing biological control are largeâusually more than US $1 million. If the funding ceases, the population and the corresponding negative impacts will normally increase, in some cases leading to irreversible damage. Successful con- trol may be easiest to achieve in areas of lower density of the invasive species. The degree of success will vary with dif- ferent organisms, the ecosystem, the duration of the effort, the restoration effort, etc., and the optimum management strategies are location-specific and must be tested and fine- tuned for different areas. Control of nonindigenous invasive species aims for the long-term reduction in density and abundance to below an acceptable threshold. If prevention methods have failed and eradication is not feasible, managers will have to live with the introduced species and can only try to mitigate the negative impacts on biodiversity and ecosystems. In the short-term, because control appears to be a cheaper option than eradication, it is often the preferred method. Funding and commitment do not need to be at such high levels as for eradication programs, and funding can be varied from year to year depending on the perceived importance of the problem, political pressure, and public awareness. The DOT makes a decision to consider harm caused by the species under this threshold as acceptable with regard to maintenance objectives, costs, damage to biodiversity, and economy. Suppression of the invasive population below that threshold can tip the balance in favor of native competing species. The weakened state of the invasive species allows native species to regain ground and even further diminish the abundance of the alien species. In rare cases this might even lead to extinction of the nonindigenous species (especially combined with habitat restoration efforts to support native species and put intact natural systems back in place); how- ever, this is not the principle goal of control efforts (71). TAILORING TREATMENTS TO DEPARTMENT OF TRANSPORTATION FUNCTIONS AND DEVELOPMENT STAGES NYSDOT has tailored invasive species control procedures and methods to DOT functional areas and stages in the trans- portation planning, development, construction, and manage- ment processes. A number of these practices are described in the section on prevention in chapter three. For example, all NYSDOT capital projects and appropriate maintenance activities and roadside operations shall consider and address, as practical, the potential environmental effects of invasive species. This process and analysis includes, at a minimum: (1) an inventory of the project area, (2) consideration of potential environmental impacts, and (3) incorporation of appropriate preventive measures and control practices into project documents and activities. BIOLOGICAL CONTROL OF INVASIVE SPECIES Biological control is the intentional use of populations of specialized organisms, commonly referred to as natural ene- mies, against pest species to suppress pest populations. It involves introducing herbivores, parasites, predators, or pathogenic microorganisms to suppress a target plant or ani- mal pest. Biocontrol agents are living organisms that have specific requirements for growing and thriving. Under- standing the life cycle, habitat requirements, and mode of attack assists in finding a hospitable release site and allow- ing the user to integrate the biocontrols into other control efforts. Different Types of Biological Controls The aim of biological control is not to eradicate targets. In a successful biological control program, the invasive speciesâ population will be reduced to an acceptable level, but popula- tions of prey or host and natural enemies will remain present in a dynamic balance. Biological control can be successful in all habitat types and is often the only alternative for use in nature reserves and other conservation areas because of its environmental-friendly nature and the prohibition of pesticide use in many such areas.
As described by the Global Invasive Species Programme, biological controls may be categorized as follows (72): â¢ Pheromone traps, based on chemicals produced by the target species to attract other members of the same species, are species- or genus-specific in most cases, and allow the selective collection of the target species. Occasionally species may be controlled effectively by using high densities of traps, particularly in a small or restricted area. Therefore, if the pheromone is readily and cheaply available in large amounts, the release of high doses can interfere with mate location and mating. If the air is filled with the pheromone the insects are not able to detect and find a partner. This method is only feasible for small infestations. Generally, pheromone traps are more effective when used to monitor the pres- ence or abundance of a species. For instance, traps can be used for early detection of high-risk species. This may enable a rapid response action to attempt eradica- tion or containment. Traps can also be used to monitor the density of pest species, so that when the catches reach a certain threshold other control measures are triggered. The progress of an eradication program can also be followed by monitoring the density (and later the lack) of the target species. â¢ BiopesticidesâThese are biological pesticides based on beneficial insect and weed pathogens and entomopatho- genic (i.e., insect-killing) nematodes. Pathogens used as biopesticides include fungi, bacteria, viruses, and proto- zoa. Produced, formulated, and applied in appropriate ways, such biopesticides can provide ecological and effective solutions to pest problems. Most product development to date has been directed toward control of pests having direct economic impact, particularly for the control of pests of agriculture, forestry, and horticulture (caterpillars, locusts, various beetles, and weeds), and medical and nuisance pests (mosquitoes, blackflies, and flies). Most types of biopesticides are relatively specific to their target pests, and many are very specific. It is this specificity that makes their use attractive compared with broad-spectrum chemical pesticides. The most widely available and used biopesticides are various formula- tions of Bacillus thuringiensis, which can be used to control the larval stages of Lepidoptera (caterpillars), and selected Coleoptera (beetles) and Diptera (e.g., mos- quitoes and flies). â¢ Entomopathogenic nematodesâThese are increasingly available in specialized niche markets, such as horticul- ture, and are used to kill selected invertebrate pest targets. â¢ FungiâFor control of specific weeds (mycoherbicides or bioherbicides) various types of fungi have been available for some time, and the development of new ones is increasingly routine (see e.g., the International Bioherbicide Group website at http://ibg.ba.cnr.it/). These products are usually host-specific either as a result of the physiology of the fungus or because of the way they are used. This makes their use attractive in 40 many situations, but also means that the market is small, making them commercially less attractive than tradi- tional herbicides. Nevertheless, a niche market exists and could be developed to address specific conservation needs to control invasive alien plants, as part of a man- agement program. For example, the development and use of mycoherbicide products to be used for stump painting in the control of plants such as Rhododendron ponticum in Europe is under consideration. Fungi for control of insects is also a relatively new research area; however, products are now coming onto the market, notably Green Muscle, a formulation of Metarhizium anisopliae for control of locusts and acridid grasshop- pers (73). â¢ Pathogens for control of vertebratesâNot only can pathogens be used as biopesticides but there are also opportunities to use them against vertebrates. Unlike more traditional interventionist techniques, a disease might spread with little human assistance and remain effective for years. Potential pathogens must be care- fully screened for risks to other animals and humans. Thus, pathogens, such as chemical insecticides require significant preliminary testing and verification before use. â¢ Biological control of freshwater and marine targetsâ The opportunity to use biological control against plants, invertebrates, and vertebrates was described earlier. To date, no biological control project has been attempted against a marine invader, although studies on the suit- ability of several parasites against different organisms are underway; for example, specific parasitic castrators of crabs. â¢ Biological control of plant diseasesâThis is still a young science. Many plant pathogens colonize parts of the plant that are initially free of microorganisms. Suc- cessful biological control in such circumstances depends on rapidly colonizing these plant areas with nonpathogenic antagonists competing for the space. The principal antagonists used are saprotrophic fungi and antibiotic-producing bacteria. The biological con- trol agent will ideally outcompete the pathogen. This concept is altogether a rather different approach than the biological control projects against weeds, inverte- brates, and vertebrates. In some cases, less virulent strains of the same pathogen species can be used to replace the virulent strain physically or by transmission of the traits of the less virulent strain to the virulent one. As used today biocontrols are a relatively inexpensive and safe alternative to chemical or mechanical control. Some of the introductions made more than 100 years ago were of generalist predators, including vertebrates such as mongooses and cane toads, and these did have severe adverse affects on nontarget populations, including species of conservation importance. Such species would not be used today in biological control, and some of them are good examples of invasive alien species causing serious
41 problems. However, today the safety standards of biologi- cal control for invasive plants are very rigorous. It is a nor- mal requirement [e.g., International Plant Protection Con- vention (IPPC) Code of Conduct] to assess the specificity of all agents proposed for introduction. This involves extensive laboratory and field screening tests. An informed decision can then be made by the appropriate national authority taking into consideration the potential for any effects on nontarget organisms. In the United States, peti- tions for release of herbivorous biocontrol agents are reviewed by the Technical Advisory Group (TAG), which makes recommendations, whereas USDA, APHIS, and state regulatory authorities are responsible for issuing permits for importation, testing, and field release of biological control agents of weeds. Biological control can be divided into several approaches grouped under two headings: those that are self-sustaining and those that are not. Methods that are not self-sustaining (which all target insect pests) include: â¢ Mass release of sterile males to swamp the population with males that mate with females without producing any offspring in the next generation. â¢ Inducing host resistance against the pest. This approach is particularly relevant to agriculture where plant breed- ers select (or create) varieties resistant to diseases and insects. â¢ Biological chemicals; that is, chemicals synthesized by living organisms. This category overlaps with chemical control and whether to list a particular method in one or the other category is a question of definition; for ex- ample, while applying living Bacillus thuringiensis (known as âBTâ) is without doubt a biological control option; to which group the use of the toxins stored in the organism belong could be debatable. Other examples of chemicals in this group are rotenone, neem, and pyrethrum, extracted from plants. â¢ Inundative biological control using pathogens, para- sitoids, or predators that will not reproduce and survive effectively in the ecosystem. Large-scale or mass releases of natural enemies are made to react quickly to control a pest population. Self-sustaining biological controls include: â¢ Classical biological control, which at its simplest is the introduction of natural enemies from the original range of the target species into new areas where the pest is invasive. Invasive alien species are often controlled in their indigenous range by their natural enemies, but are usually introduced into new environ- ments without these natural enemies. Freed of their natural enemies, alien species often grow and/or reproduce more vigorously in the area of introduction. Natural enemies for introduction are selected on the basis of their host specificity to minimize or eliminate any risk of effects on nontarget species. The aim is not the eradication of the invasive alien, but to reduce its competitiveness with native species; hence reducing its density and its impact on the environment. â¢ Augmentation of enemies under pest outbreak condi- tions for an immediate control, when the enemy can reproduce in the new environment. The control agent is reared or cultured in large numbers and released. â¢ Habitat management can enhance populations of native predators and parasitoids; for example, the release or replanting of native alternate hosts and food resources. The most important of these is classical biological control. Conservation managers are beginning to realize that this method, if used following modern protocols such as the IPPCâs Code of Conduct for the Import and Release of Exotic Biological Control Agents (74), provides the safest and most cost-efficient approach to solving many invasive alien species problems. Biocontrol is typically a long-term, environmentally acceptable approach for the control of a target plant species. In comparison with other methods, classical bio- logical control is, when successful, highly cost-effective, permanent, and self-sustaining. It is ecologically safe owing to the high specificity of the agents used. The main disadvantages are the lack of certainty about the level of control that will be achieved and the delays until the estab- lished agents achieve their full impact. Biocontrol agents can take 5 to 10 years to become established and increase to numbers large enough to achieve control. However, with a potentially very positive benefitâcost ratio, the benefits of classical biological control normally outweigh the draw- backs and it represents the cheapest and safest option to date. Such a long-term control method is best initiated in low-priority areas, at sites where the use of other control strategies would be cost-prohibitive. Once control agents build high enough populations and spread easily, control methods with shorter effect times can be replaced by bio- logical control. A major problem is that there are many noxious plant species for which biocontrol agents are not available at the present time. Department of Transportation Biological Control Activities Almost one-third (13 state DOTs) of respondents are using biological controls to some extent. Biocontrols also have played a particular role in some DOTs in places where there is no operational need to control, such as some wetlands or where the area is inaccessible. Several DOTs have become very active in the use of bio- logical controls. NCHRP Synthesis of Highway Practice 341 on IRVM reports that biological control practices using her- bivorous organisms such as beetles and seed flies are in use
on 0.5% to 2% of the ROWs in Florida, Illinois, Kentucky, Maryland, Utah, and Washington (67). Other examples include the following: â¢ Caltrans has research underway on biological controls for yellow starthistle and tumbleweed (Russian thistle, Salsola tragus) (75). â¢ NYSDOT and other DOTs use Hylobius sp. and Gal- rucella spp. beetles on large, dense stands of purple loosestrife (one-half acre or larger). Cornell University conducted extensive research before the selection of these particular species and prepared a generic EIS for its release throughout the state. These beetles feed exclusively on purple loosestrife (they will starve rather than eat any other plants), will reproduce after release, and can be harvested from prior release sites for use in other locations. Research is currently underway by Cor- nell University to identify and test effective biological controls for introduced common reed (Phragmites aus- tralis), garlic mustard (Alliaria petiolata), water chest- nut (Trapa natans), and Japanese knotweed (Fallopia japonica). â¢ In 1995, Mn/DOT launched its first school partnership in beetle rearing for roadside use, an educational and pub- lic awareness success story, after two beetle species released at a site in southern Ontario effectively reduced purple loosestrife infestation by more than 90% over 5 years, allowing native plant populations to extend their reach (L. Skinner, Minnesota DNR Coordinator, Purple Loosestrife Program). The Mn/DOT Office of Environ- mental Services uses beetles to control leafy spurge (72). â¢ Between 1997 and 1999, New Hampshire DOT and the Department of Agriculture (NHDA) monitored a beetle release at a mitigation site infested with purple looses- trife. By 2000, all loosestrife within and adjacent to the site was either dead or extremely stressed and dying, and none of the remaining live plants appeared to develop flowers and therefore seed. Self-sustaining populations of beetles were still found among the remaining looses- trife plants. Indigenous vegetation, likely from seed in the existing soil bank, filled the void and restored diver- sity. New Hampshire DOT and NHDA released beetles at 12 additional sites the following year (76). â¢ Michigan State Universityâs laboratory produces 150,000 beetles per year, which the Michigan DNR has been releasing on state game areas infested with purple loosestrife since 1994. The lab has trained local groups around the state to rear the beetles, and release and monitor their effect, leading to an expected 80% reduc- tion in density in 10 to 20 years. â¢ The Vermont Agency of Natural Resources and Ver- mont Agency of Transportation (VTrans) have mapped purple loosestrife populations and VTrans is testing three approaches: (1) the release of beetles without mowing or spraying; (2) mowing right after flowering begins for easy identification, yet not be mature enough to disperse seed; and (3) spraying (76). 42 â¢ Spotted and diffuse knap invasives can be controlled using one of 12 insect species cleared by USDA for use in the United States. In Tennessee, the DOT was able to reduce musk thistle (Carduus nutans) infestations by 95% with a biocontrol beetle (9). Biocontrol Resources on the Internet Information on biocontrols for various weeds can be found in Biological Control of Weeds in the WestâBibliography or at commercial weed biocontrol insectaries. Cornellâs Inva- sive Plant website on Biological Control of Non-Indigenous Species is dedicated to promoting and educating people about the biological control of nonindigenous plant species and the site lists plant species where biological controls are available for eastern North America. The Global Invasive Species Programme suggests the following sites: â¢ IPPC Code of Conduct for the Import and Release of Biological Control Agents (1996). â¢ Biocontrol News and Information. â¢ The Nearctic Regional Section of the International Organization for Biological Controlâs Biological Con- trol of Weeds Working Group. Other resources include the U.S. Army Corps of Engi- neers Noxious and Nuisance Plant Management Information System that covers: â¢ General Introduction to Biocontrol. â¢ General Concepts of Biocontrol and History of Bio- control. â¢ Benefits/Disadvantages to Biocontrol. â¢ Process of Biocontrol. â¢ Overall Herbivore Effects. â¢ Using Biocontrol Agents More Actively in Existing Control Programs. â¢ Specific Organism/Damage Descriptions: Overview of Collection Techniques. â¢ Descriptions of the Included Organisms and Their Associated Damage. Other web resources include: â¢ USDAâs National Biological Control Institute. â¢ Biological Control Virtual Information Center. â¢ 110 Years of Federal Biological Control Researchâ USDA. â¢ Biological Control of Non-Indigenous Plant Speciesâ Cornell University. â¢ Weed-Feeders Table of ContentsâCornell University. â¢ Biological Control: A Guide to Natural Enemies in North AmericaâCornell University. â¢ Biological Control: Important Tool for Managing Invasive SpeciesâUSDA.
43 â¢ Biological Control of Invasive Plants in the Eastern United StatesâUSDA Forest Service. â¢ Biocontrol of Forest Weeds, University of Hawai`i at Manoa. â¢ Western Rangeland Weeds Home â Management and Prevention â Methods of Weed Control â Biological Control of Weeds. â¢ Agricultural permits for weeds and biological control agentsâAPHIS. â¢ Biocontrol: Integrated strategies for sustainable con- trolâCanada. â¢ Biological ControlâBLM. â¢ Biological Control Agents by Target WeedâOregon DOA. â¢ Biological Control ProgramâWho We Are; Biological Control Program Facility Locations from the California Department of Food and Agriculture. â¢ Technical Advisory Group for Biological Control Agents of WeedsâAn independent voluntary committee formed to provide advice to researchers. TAG members now review petitions for biological control of weeds and provide an exchange of views, information, and advice to researchers and those in APHIS responsible for issu- ing permits for importation, testing, and field release of biological control agents of weeds (from APHIS). â¢ Cornell has set up a website with monitoring protocols for biological control of purple loosestrife, as well as protocols for garlic mustard (Alliaria petiolata), proto- cols for water chestnut (Trapa natans), and Phragmites (Phragmites australis) insect surveys. The final goal is to establish a database where results from different regions can be collected, stored, and made available through http://www.invasiveplants.net. MECHANICAL CONTROLS Mechanical control methods involve directly removing indi- vidual plant or animal invasives, either as a means for eradi- cation in small areas or as a means for controlling species density and abundance. It encompasses tractor mowing and can involve anything from complete tillage for reseeding to hand scythes, shovels, string trimmers, push mowers, prun- ing shears, etc., for weed control and desirable vegetation maintenance. Mechanical eradication methods can be effec- tive when the population of the invader is still small and is limited to a small area. Weeds that grow vigorously from cut plant parts or multiply vegetatively are more difficult to con- trol. The downside of mechanical methods is the labor requirements. Most manual work is expensive and has to be repeated. Plant parts of some species left in contact with soil may survive and grow. For example, Japanese knotweed, an invasive alien in Europe and North America, will regenerate from stem cuttings and rhizome fragments of less than 1 g. In many cases, introduced pests can be controlled or even eradicated in small-scale infestations by mechanical control; for example, hand-pulling weeds or hand-picking animals. An advanced method of mechanical control is the removal of plants by specifically designed tools and even machines, such as harvesting vehicles for water hyacinth-infested lakes and rivers. In some cases of very persistent plants growing on large open areas such as pastures, bulldozing may be necessary (77). Invasive plants can be cut or hand-pulled (see http:// tncweeds.ucdavis.edu/tools.html for some simple tools) and larger plants can be uprooted with the aid of tools such as winches, if necessary. The effectiveness of this tech- nique will vary considerably depending on the response of the weed. If there is no information available about the plantâs response to uprooting, some simple tests should be carried out to discover its effectiveness and ways to treat the residues; for example, composting or burning the uprooted material. Repeated cutting of a woody weed may eventually drain the resources stored in the root system and kill the plant. In many cases, combined cutting of the plant and painting the stem with a systemic herbicide proves to be more efficient. Specialized cutting tools that will apply a pesticide as they cut have been tested. Mowing of herbs and grasses may lead to the same result, when the plants are not adapted to heavy grazing. Annuals are especially susceptible if mown shortly before setting flowers, be- cause they will have used up most of their root reserves to produce the buds. Girdling can kill trees; cutting with a knife through the cambium of a tree trunk and removing 5 cm of bark will interrupt the flow of nutrients and kill the plant. Girdling alone may not suffice for rapidly killing those species where the water and nutrient movement are not restricted to the outermost layer of the trunk; however, an application of herbicide will speed up the process. Regarding fauna, control of most insect species depends on traps, which are more or less specific to insect groups or species-specific using pheromones. Sedentary species such as scale insects or mealy bugs can be killed by destroying their food plants. Trapping and shooting can be considered the âmechanicalâ or âmanualâ way of dealing with invasive vertebrates. Recreational hunting of game can be effective in keeping populations down to an accept- able level and can be a revenue source for other manage- ment activities in the area. It does, however, give rise to the concern that the invasive species then becomes a valuable commodity that should be preserved to continue to gener- ate this income. Furthermore, there are many instances where recreational hunting will not reduce the target pop- ulation sufficiently. Similarly, recreational hunting can be counterproductive as a result of amateur hunters creating a shy target population and not being skilled enough to reduce target species desired densities. Also, depending on the species, recreational hunters may select only mature trophy males as targets; this will have little or no impact on the reproductive capacity of the species. To reach the pre- determined target population level, it may be necessary to
employ professional hunters. Using animals such as dogs, which can be specifically trained to target individual inva- sive species, can be extremely successful in combination with shooting and other forms of control. Fencing is another option for containment of species, either cordoning off the species in a certain area or fencing off ecologically valuable land. One needs to be sure that the invasive species is not present on both sides of the fence. Mowing Maintenance roadside mowing, while essential for safety, operational, aesthetic, and environmental purposes, can, has, and does play a significant role in the introduction, spread, and proliferation of invasive plants. Mowing can serve as a control method for certain invasives during certain periods of their reproductive cycles, but repeated mowing and attention to timing will be required. Mowing is most effectively used in combination with other vegetation management and inva- sive species control techniques. Few studies have been conducted on the effects of mowing plant communities and invasive species. Just 30% of responding state DOTs reported that they are timing mowing to control invasive species. Slightly fewer (25%) say they will mow in some areas to minimize seed transfer. Reduced mowing practices were initiated as early as the 1950s. The Wisconsin DOT (WisDOT) was a pioneer in the cutbacks. Many more DOTs reduced mowing in the 1970s, when high energy costs forced vegetation managers to mow less and spot spray, with the positive consequence of increased wildlife habitat, enhanced natural beauty, mini- mized herbicide use, reduced maintenance dollars, and pub- lic acceptance (9). NCHRP Synthesis of Highway Practice 341 noted that state DOTs remain heavily dependent on mechanical control methods, with the bulk of states cutting more than 90% of their ROW, a smaller set having reduced mowing to 50% to 90%, and only Florida and Washington indicating less than 50% was managed using mechanical methods (67). Mowing should be carefully considered to ensure that the target species will not actually be spread by the prac- tice. Because mowing cuts the tops of plants, more buds may grow, producing more stems than before; however, continuous mowing when plant reserves are low can grad- ually deplete root reserves. If flower-feeding biocontrols are used, weeds can still be mowed at times when natural enemies are not feeding. One of the greatest advantages of mowing is the ability to quickly reduce seed production. Because drainage ditches, streams, and wetlands can rapidly spread invasive plants through the dispersal of seeds 44 and, to a lesser degree, plant parts, it is strongly recom- mended to control (herbicide, excavate, etc.) priority inva- sive plant populations in and adjacent to drainage ditches and streams, before mowing. This also will provide opera- tional benefits, because invasive plant populations in the drainage system that are âonlyâ mowed will immediately regrow and spread and therefore require additional mowing. Isolated (upland) roadside populations of invasive plants can be mowed with less chance of dispersing the plant seeds and parts to new areas. Nevertheless, mowing should always be done before seed maturation, which typically occurs later in the last half of the summer. Because mechanical mowing spreads invasive plant seeds and each segment of many invasive plants, including the rootstock, can vegetatively sprout a new plant, priority inva- sive plant species should be mowed with due consideration for the following factors (78): â¢ When mowing untreated or uncontrolled invasive plant populations, do so before seed maturation. â¢ Plan on mowing invasive plant populations two to three times per year, before seed maturation, for successive years, if mowing is the only control practice used. The âmowing onlyâ option should be used in locations that are not in or adjacent to drainage ditches and are inac- cessible or too large for other control options. â¢ Control small invasive plant populations comprised of tender, young plants with herbicide early in the sum- mer, before mowing, especially in and adjacent to drainage ditches. â¢ If invasive plant populations consist of large, mature plants, mow the plants before seed maturation, allow the plants to regrow to a height of 2 to 4 ft and then treat the area with foliar herbicide, especially in or adjacent to drainage ditches. â¢ Physically remove flower or seed heads (cut and bag) of small invasive plant populations before mowing, espe- cially in and adjacent to drainage ditches. â¢ Physically remove the rootstock (mechanically exca- vate) of small invasive plant populations before mow- ing, especially in and adjacent to drainage ditches. â¢ Control large purple loosestrife plant populations with biocontrol beetles (Hylobias sp. or Galrucella spp.) before mowing. Beetle releases will take several years to significantly reduce purple loosestrife populations. â¢ If mowing occurs after seed maturation, hand clean, with brush or broom, the upper parts of contaminated mowing equipment before moving to new locationsâ especially uncontaminated locations. This is especially important for purple loosestrife, because each mature plant is capable of producing up to 2.5 million viable seeds. â¢ Take care to minimize scalping and rutting during mow- ing operations. These situations can be avoided by prop- erly adjusting the equipment and avoiding operating
45 equipment directly in wet areas or rough terrain. Any scalped or rutted areas should be immediately seeded and mulched. Any badly rutted areas should be repaired, seeded, and mulched. â¢ Use of optional mowing equipment, such as âover-the- railâ boom-type mowers, may be necessary in some sit- uations to reach invasive plants. The Montana State University Extension Service has compiled a number of recommendations on mowing to man- age invasive species, which are summarized in many of the upcoming sections (79). Identify Targets and Communicate with Relevant Parties When mowing to reduce invasive species, recommended practices include: â¢ Identifying invasive species that can and should be controlled by mowing (at least in part), identifying the location of patches, and determining thresholds when mowing should occur for these areas (such as when patch area exceeds a certain size). â¢ Identifying invasive species that should not be mowed or conditions under which they should not be mowed to avoid inadvertently spreading these invasives. â¢ Communicating with other maintenance staff to avoid mowing areas soon after or just before spraying, and to avoid mowing areas of leafy spurge and other species that spread with mowing. Time Mowing to Suppress Invasive Species Properly timed mowing can suppress some invasive species while favoring desired methods if used in conjunction with other methods. Timing is based primarily on the growth stage of the plants to be mowed and secondarily on the growth stage of the desired plants. If desired vegetation cover is inadequate (usually less than 20%), revegetation is likely to be necessary. Some desired plants, such as grasses, have equal amounts of growth above and below ground. When grasses are defo- liated during the growing season, this stress reduces vigor and the ability to maintain competitiveness, and to allow grasses to produce seed for next yearâs stand it is best to mow when these plants are dormant. Caution should be exercised, because mowing during the weedsâ seeding period can facil- itate seed dispersal. Establish Mowing Frequency Mowing frequency for invasive species control should depend on precipitation and the mowing tolerances of the vegetational function of relative growth rates, leaf replace- ment potential, and the plantâs ability to increase photosyn- thesis after mowing to compensate for leaf loss. Particularly important are the number, location, and source of growing points on plant stems. An effective mowing strategy mini- mizes the removal of growing points of desired plants and maximizes removal of growing points of weeds. For annual, biennial, and taprooted perennials the fre- quency of mowing depends primarily on precipitation. A sin- gle midsummer mowing after flower production can reduce or eliminate seed production and shift the balance in favor of desired species in areas with little or no summer rain. In one study, 78% control of diffuse knapweed (Centaurea diffusa) was achieved after mowing to a 2-in. height each month dur- ing the growing season (no mention of revegetation context). However, as summer rains increase, regrowth potential increases, and mowing may increase plant vigor and seed production similar to pruning. In this case, additional mow- ing is necessary. Rhizomatous weeds usually require more frequent mow- ing. Repeated mowing is considered an effective control of rhizomatous weeds in alfalfa and many pastures. In one study, mowing alfalfa two times per year reduced Canada thistle 86% after one year and 100% after 4 years. In other studies, mowing three or four times per year nearly elimi- nated Canada thistle within 3 years. Other studies have sug- gested that mowing Canada thistle kept stands in check but did not eliminate the weed. Mowing of large infestations is a long-term commitment. Some weeds, such as those that spread through rhizomes (a prostrate stem growing beneath the soil surface) have large energy storage capacities. During the first few years, mow- ing these weeds can stimulate shoot production from root buds and increase stem densities. However, over time, fre- quent mowing at each early flowering stage can affect under- ground reserves and eventually reduce stem densities. In addition to Canada thistle, rhizomatous invasive species include Dalmatian toadflax (Linaria dalmatica), leafy spurge, ox-eye daisy (Chrysanthemum leucanthemum), Russian knapweed (Acroptilon repens), and whitetop or hoary cress (Cardaria draba). Set Mower Height Most grasses can tolerate short mowings once dormant. If the dominant vegetation has not yet shifted to invasive species and still contains adequate grass cover, mowing should gen- erally be timed so the weeds are at the flowering stage and the grasses are dormant. When the dominant vegetation is a noxious weed, MDT recommends mowing 2 in. high when the weed is at the flowering stage. However, in some cases, inva- sive species will reach the appropriate stage for mowing, but the grasses have not reached dormancy. If so, MDT recom- mends mowing the weeds at a height above the desired plants.
Mowing above the height of actively growing grasses allows seed production and unrestricted growth; this maintains the vigor needed to minimize reinvasion. Defoliating the weeds reduces seed production and vigor, increasing resources avail- able for neighboring grasses. Spotted Knapweed: A Case Study Montana State University performed a study on the effec- tiveness and timing of 15 different mowing strategies for spotted knapweed, showing that mowing can greatly reduce or diminish seed production and adult spotted knapweed den- sity. The mower was set at 10 in. height to cut the bolted knapweed plants while passing over the grasses. The study found that the most effective time to mow spotted knapweed was during the flowering stage. Mowing at this time decreased adult density by approximately 85%. Seedling density also was slightly reduced. Grasses were only decreased by the most aggressive mowing treatments. Integrating Mowing with Other Management Methods Although mowing will not eradicate invasive species, it can stress them, greatly reduce seed production, and help give native plants a competitive edge. The pervasiveness and com- plexity of invasive species, combined with their cost of con- trol, makes an integrated management plan necessary, because an IVM strategy seeks to use the most economic, ecologic, and environmentally effective combination of principles, practices, technologies, and systems to meet noxious weed management goals and objectives. Although little research has been con- ducted on incorporating mowing into an integrated plan, expe- rience provides some practical hints. Some evidence suggests that combining mowing with herbicides can enhance perennial weed control. For example, mowing two or three times a year consistently enhanced Canada thistle control following appli- cations of picloram, picloram 2,4-D, clopyralid 2,4-D, and dicamba (79). Mowing may also be combined with herbi- cides over several years. Most invasive species grow low to the ground after long-term repeated mowing. In these cases, peri- odic control through herbicides can remove plants that have adopted their growth form to frequent mowing. Department of Transportation Mowing Policies and Programs Eleven state DOTs have developed conservation mowing and spraying programs to protect native communities, minimize maintenance costs, and control invasives. NYSDOTâs conser- vation mowing program is among the most well known. North Carolina DOT (NCDOT) has developed a Clear Zone Improvement Program (C-ZIP) initiative, which relies on native grasses and forbs. Fourteen state DOTs (35% of respon- dents) have employed reduced mowing widths (one-mower 46 width) as a statewide standard to control costs and preserve native communities. TxDOT is among those that have marked many areas as âno mowâ to facilitate their return to native vegetation. A few states, such as Alaska and Vermont, noted that their roadsides consist primarily of native vegetation. Alaska Department of Transportation and Public Facilities indicated that the agency sometimes specifies just adding fertilizer and allowing the site to naturally revegetate. More information about DOT mowing practices may be found in the Guide to Environmental Stewardship Practices, Procedures, and Policies for Highway Construction and Maintenance (80) available at AASHTOâs Center for Environmental Excel- lence. A selection of these practices, with invasive species control components, is included here. Alabama Department of Transportation Mowing Program to Reduce Cogongrass In Alabama, mowing is restricted in cogongrass areas during seed head production, mowing is to progress from areas without cogongrass infestations into areas with cogongrass infestations, and mowers are to be cleaned of all vegetative propagules before leaving cogongrass-infested areas. North Carolina Department of Transportation Mowing Program Modifications to Encourage Wildlife Native and Rare Plant Species NCDOT implements its mowing program with an environ- mental perspective to encourage wildflowers, protect rare or endangered plants and protect or create wildlife nesting areas. Currently, NCDOT protects more than 35 populations of rare plant species growing along its roadsides. Endangered plant populations are marked with white-topped wooden stakes, an indication to mowers that the area is off-limits during the growing season. These areas are managed on a site-by-site basis according to their individual needs. Man- agement strategies to control invasive woody vegetation include mowing during the dormant season, hand pruning, and prescribed fire. NCDOT cooperates with the North Car- olina Wildlife Commission in posting and managing small game wildlife habitat areas in the ROW. Properly timed cleanup mowings enhance wildlife habitat (81). New York State Department of Transportation Stewardship Mowing Practices General NYSDOT mowing guidelines are outlined in the agencyâs Mowing Limits Manual, Highway Maintenance Subdivision Operational Guidelines, and Environmental Handbook for Transportation Operations. The Mowing Lim- its Manual addresses safety, water quality and erosion, sedi- mentation control, appearance and screening, landscape plantings and woody vegetation, and natural revegetation.
47 NYSDOTâs Environmental Handbook for Transportation Operations outlines stewardship practices and expectations for mowing, which go beyond mowing reduction policies to address other environmental features in the ROW (82). In addition, NYSDOT is implementing Conservation Alternative Mowing Plans (CAMPs), which preserve safety and aesthetics while reducing invasive species and enhanc- ing native habitat. CAMPs involve identification of rich landscapes as part of the maintenance planning process, threshold values for several species and suitable habitat in the landscape, species or groups of species to be used as indica- tors, and the barrier effect of roads (83). CAMPs have been successfully developed and implemented on Interstates, expressways, and parkways at NYSDOT through a multidis- ciplinary team approach, culminating in the following guide- lines, using four zones that describe to the operators what management is expected in the different zones. A High Man- agement Zone is comprised of an intensely managed area immediately adjacent to shoulder or curb, a Frequently Mowed Zone next to it is mowed multiple times per year, an Annually Mowed Zone provides a transition between the Frequently Mowed Zone and No-Mow Zone (or left to regenerate naturally), and a No-Mow Zone is left in its nat- ural state or left to regenerate naturally. Mowing Management in Southern Quebec, Canada According to a study commissioned by the MinistÃ¨re des Transports du QuÃ¨bec, traditional methods of controlling vegetation along the agencyâs 2000 km of highway corridors in southern Quebec âresult in a boring landscape, deteriorate the various wildlife habitats, and impoverish wild plant life while generating high maintenance costs.â Recently, the agency has pursued the development of new maintenance methods, including elimination of multiple annual mowings, to improve the safety of the highway systemâs users, satisfy neighboring residents, beautify the landscape, and consider the plant life and wildlife present along the highways. The new approach eliminates multiple mowings except on the first 2 m from the pavement, which will be mowed more fre- quently to ensure highway safety (visibility) and better con- trol of the allergen, ragweed. The agency and its researchers have also been monitoring the slowly increasing biodiversity in the unmowed area since 1998 (84). Manual RemovalâPulling Weeds and Seed Head Cutting Pulling weeds by hand is practical and efficient on small, iso- lated patches of weeds. It has the advantages of low damage to other plants and minimal equipment cost. Hand-pulling is most effective on annuals and biennials that do not resprout from root fragments. The labor requirements often make hand-pulling impractical, but because perennial weeds can resprout from extensive root systems, hand-pulling has the potential to be ineffective as well. â¢ Pull plants when soils are moist and before seeds are produced to prevent additional spread of the weed. â¢ Try to remove the entire root system, because many weeds can resprout from remaining root fragments. â¢ Attempt to keep soil disturbance to a minimum. â¢ Ten DOTs (25% of respondents) said they used hand- picking of weeds in some areas. NYSDOT has done manual cutting of seed heads with bagging and disposal where further control is not possible. Tilling and Disking Tilling and disking mechanically removes weeds from the soil, slices through roots, or buries weeds. It is fast and effec- tive against a wide variety of weeds; however, it can only be used in crops, pastures, and some rangeland. It can also lead to loss of soil moisture, increased soil erosion, and mixing of seeds into soil, a potential problem because it is not usually followed by residual control. Tilling does not kill most perennial weeds, but deep tillage of taprooted plants in late fall can expose roots to deadly winter frosts and interfere with the translocation of nutrients to roots for storage. In many areas the disturbance caused by cultivation creates a niche for new weeds to become established. Cutting and Brushing Cutting is used primarily for woody plants. It minimizes soil disturbance and involves tools such as brush cutters, power saws, axes, machetes, hand-pruning tools, loppers, and clippers. Smaller shrubs can be cut with power mowers, string cutters, machetes, scythes, or weed whips. When plants are cut, roots remain intact and are helpful in stabilizing soil on steep terrain. To minimize resprouting, stems should be cut close to the ground under maximum drought conditions. The effectiveness of cutting largely depends on the plant species, stem diameter, time of cut, and age of the plant. For example, scotch broomâs ability to resprout declines with age. Cutting broom to the ground during dry months (usually after flowering) usually kills the plant, whereas cutting before flowering, although effective in preventing another seed crop, may result in resprouts and little mortality. Cleaning Mowing, Cutting, and Removal Equipment Equipment used for invasive species control, whether hand tools or power driven, should be cleaned before entering a new site and before leaving the site, to reduce transport of plant propagules and the potential for new invasive intro- ductions. This is particularly important for some invasives that produce millions of seeds.
PHYSICAL METHODS Physical methods of invasive species control include cover- ing, burning, grazing, and changing abiotic factors. Covering Covering plants deprives them of the sunlight needed for growth and hastens plant decomposition by contact with soil microbes. Less cover is used (mulching) when trying to fos- ter new germination. â¢ Materials used to cover plants should block all light. Common materials include thick black plastic, black geotextile fabric, and mulches. Black geotextile mats are often used under highways, as landfill lining, and in landscaping projects. â¢ Before covering, cut, burn, or mow the weed close to the ground to reduce biomass and to put stress on the plants. Treatment sites require regular monitoring to detect and repair torn fabric. Although covering can be very useful, it has several draw- backs. Unless the material is biodegradable, the cover must be removed after the treatment. In addition, the amount of time needed to kill weeds varies and will need to be experi- mentally determined. Caltrans is testing two types of solid matsâDurotrim, a 1-in.-thick black matting made of recycled rubber tires, and Weedender, a light-green product made of recycled plastic bottles that is approximately 1/4-in.-thick, and a liq- uid soil sealer called Polypavement, which binds to the soil making it impervious to plant growth and erosion. The prod- uct from recycled plastic bottles is so light that it requires workers to secure it to guardrails. Although Caltrans has used all the products before, the test is the first time the agency has applied the weed control products simultaneously in one area for a side-by-side comparison of effectiveness with no herbi- cide use. Caltrans District Five is experimenting with the use of native grasses and organic materials, such as wood chip mulch and corn gluten meal, to test their effectiveness in mit- igating the growth of invasive weed species. The tests are also assessing community response to the look of the products, ease of application, and cost relative to herbicide application. According to Caltrans project management, other potential benefits that may be realized by the test include (85): â¢ Minimizing traffic congestion by eliminating lane clo- sures associated with more traditional vegetation con- trol activities. â¢ Enhancing worker safety by reducing the frequency of on-site work on the highways. â¢ Minimizing fire concerns by eliminating vegetation overgrowth. â¢ Improving drainage by removing weeds around drainage facilities. 48 â¢ Promoting visibility of traffic, highway structures, and wildlife. â¢ Reducing the need for herbicides. Controlled Burns Eight percent of DOTs are using controlled burns to restrict invasive species and foster native revegetation. Controlled burning or prescribed fire is a carefully planned and con- trolled fire conducted to manage natural areas such as prairie, oak savanna, wetlands, and oak woodlands. Prescribed or controlled burns have been used by land managers for more than 25 years in modern history and for hundreds of years by Native American tribes. The fire kills the above-ground parts of shrubs and small trees. In certain environments the practice of prescribed burning can change the vegetation cover in favor of native plant species, thereby decreasing population levels of weeds. Pre- scribed burning is particularly appropriate for restoring or maintaining fire-adapted or fire-dependent species and nat- ural communities. Many invasive plants are not adapted to fire and ecological burning may be an effective tool for con- trolling these species. Fire has been used quite frequently to manage invasive alien species in the United States and to stimulate natural vegetation in areas adapted to fire. For example, The Nature Conservancy has used controlled burns to eradicate Aus- tralian pine (Casuarina equisetifolia) in pine forests and other fire-tolerant communities in the United States, but less frequently elsewhere. Spot treatment is also possible; for example, early in the growing season babyâs-breath (Gyp- sophila paniculata) can be burned with a hand-held propane torch. Prairie plants grow more vigorously when built-up plant materials and shade are removed. Spring fire uncovers the soil, warming it sooner and extending the growing sea- son. Roadside areas across the United States are the site of important remnant native grassland habitats, many of which can be enhanced by management by fire. Many invasive plants are not adapted to fire; therefore, ecological burning may be an effective tool for controlling these species. How- ever, land managers must first determine if fire is a natural component in the plant community in question and if pre- scribed fire can be expected to help meet site goals. The context should be carefully evaluated to avoid notable failures and so that desirable species may be pro- moted rather than invasive species. For example, an Aus- tralian study of roadside burning noted that non-native plants were spread into adjacent woodland and that native species decreased (86). It should be remembered that the growth of some invasive alien plants, such as garlic mustard in wood- lands of the northeastern United States is stimulated by fire. In other areas, fires can cause disturbance and create estab- lishment sites for new weed infestations.
49 Only trained and experienced people should undertake prescribed burning owing to the many health and safety risks involved. Smaller infestations can be controlled with the aid of a flamethrower. The risks of a large-scale fire limit the use of these tools, especially in dry climates. Given these ecological and logistical challenges, prescribed burning may not be an appropriate method if considered for invasive species control only. It is best suited to a site where restoration and maintenance of fire-dependent or fire-tolerant communities are primary conservation goals. Controlled Burn Practices and Consideration Fire intensity, continuity, and duration are factors to consider in the success of a treatment. Controlled burning offers the following benefits (72): â¢ Controls invasives and woody invaders, â¢ Stimulates the growth of many native prairie plants, â¢ Removes thatch, â¢ Recycles nutrients, and â¢ Warms the soil and gives warm season plants an earlier start. After two growing seasons, planted prairies need to be burned annually for the next several years to become well-established (mature prairies with no serious weed prob- lems may need burning only once every 2 to 4 years) (87). Recommended practices include the following: â¢ Always use caution when burning. â¢ Check local fire and air quality regulations and obtain permits. â¢ Try to burn or mow only one-third of the prairie area each year to preserve over-wintering insects, their eggs, and pupae. â¢ Always plan fire safety into plantings, even if you are not going to use burn management. Prairie fires inten- tionally or accidentally set during fall or spring dor- mancy can burn very rapidly. â¢ Use any existing features such as roads, driveways, streams, lakes, or mowed lawns as fire breaks. â¢ In addition to paths through a prairie, also include a wide path around the perimeter. â¢ A mowed lawn buffer 20 ft in width between buildings and prairie is advised. â¢ An alternative to burning is to mow in late fall after seeds set or preferably in early spring (late March to mid-April). Sites that are too wet in spring need fall mowing when soil is dry. â¢ If burning does not occur periodically, cuttings need to be removed to avoid a thatch layer buildup. â¢ Do not cut and then burn large quantities of plant mate- rial (creating thick piles) or you will sterilize the soil beneath. â¢ Revegetation after a fire is important in reducing bare ground and preventing the establishment of other weeds. Before undertaking a controlled burn, staff must be prop- erly trained and plans developed. Planning considerations should include: â¢ Traffic safetyâany burning plan must include smoke management provisions for safety purposes. â¢ Weather conditions. â¢ Equipment. â¢ Staffing. â¢ Timingâburning is most beneficial from mid-April to early May for warm season grasses. Controlled burning is practically explained by Wayne Pauly in his How to Manage Small Prairie Fires (88). The Missouri Department of Conservation recommends the following practices for controlled burns, drawing on Paulyâs work: While fire management requires training and knowledgeable individuals, it takes âas little as a few hundred dollars in equipment, including drip torches, rakes, and safety clothing. . . . Roadside prescribed burns are easy. The road is one fire break and the others can be a mowed field of harvested hay or lawnsâ (89). Staff under- taking burns should be forewarned that corn stubble and older fence posts smolder. More detailed information on controlled burns for inva- sive species management may be found in the Center for Invasive Plant Managementâs on-line resource: âFire as a Tool for Controlling Non-Native Invasive Plantsâ (90). The review âfocuses on the intentional use of fire, alone or inte- grated with other methods, to control exotic plants in North America.â Additional information regarding proper burning procedures can be obtained from the Fire Management and Research Program at The Nature Conservancy or state resource agency. The Texas Parks and Wildlife Department uses an on-line burn plan form for controlled burns on state property and provides a Sample Burn Plan. Controlled Burning or Hay Removal as Roadside Grassland Management Alternatives to Mowing Mn/DOT and the University of Minnesota have been explor- ing whether mowing can be as effective as yearly burning at encouraging native prairie grasses and discouraging botani- cal invaders. A research team investigated the effects of burning and mowing on three separate test areas, examining above-ground vegetation and below-ground fungal commu- nities, as well as measuring changes in various soil parame- ters. Findings and recommendations were as follows (91): â¢ Prescribed burning has the strongest effects on plant community composition and was the most effective
method to increase above-ground plant biomass in a restored tallgrass prairie. Burning especially favors warm season grasses and legume species, although it also favors certain annual species. Also, when immediate grass cover is desired, burning is the best maintenance technique available to increase grass- land productivity. â¢ When burning is not an option, haying may be the next best alternative. The addition of lime may be important to consider on restorations of former agricultural lands. â¢ Adding lime to hayed prairie may help benefit the cool season plants, native and exotic. â¢ Spring haying is an acceptable alternative to spring burning, although its effects are less dramatic than the burn. In particular, haying does not favor warm season grasses as extensively and may not damage cool season species as thoroughly as burning. Spring haying did not control exotic species. â¢ Burning and haying provided the greatest increase in arbuscular mycorrhizal fungal structures, which may correspond to the increases in plant growth on these treatments. In prairie restoration, addition of arbuscular mycorrhizal inoculum appears to provide long-term benefits. â¢ The effect of mowing the prairie in the spring is similar to that of no management on the plant community. It is only useful for the control of woody species. Mowing may temporarily decrease nitrogen mineralization rates. This may help to prevent invasive species, but is not likely to do so if mowed annually. â¢ Frequent burning or haying should be done to prevent the accumulation of inorganic soil nitrogen, which may favor many weedy species. If haying is used instead of burning soil, pH should be tested periodically to detect acidic soil, Although this did not become apparent on this experiment, it may occur on long-term hayed grass- lands. Acidification may lead to decreases in certain plant populations or losses in productivity. â¢ The process of removing litter seems to be the most important cause of the ecosystem response to prescribed burning. Hayed plots are the most similar to burned plots in terms of soil moisture, temperature, and litter quantity. Hence, litter removal by haying will likely be a sufficient practice to replace prescribed burning at many sites. Department of Transportation Examples of Controlled Burning for Invasive Species Management A number of midwestern state DOTs use controlled burns. Illinois DOT attempts to use burns if the timing is right. The agency mows if burning is not an option and uses chemicals as necessary. In California, 5 acres of highway ROW were targeted to learn more about prescribed burns as a management tool. The 50 Bear Creek Botanical Management Area, one of the last examples of Upland Wildflower Fields in California, con- tained a plant community remnant with more than 200 native California plant species. After careful planning, Caltrans District 3 employees coordinated the safe passage of vehicles and the California Department of Forestry and Fire Protec- tion conducted the burn. The key target was yellow starthis- tle, which had invaded half the site within a short time. Observations following the fire have shown the prescribed burn to be more effective than the preceding years of mow- ing, spot spraying, and hand-pulling of starthistle; however, the state is attending to air quality issues (9). Infrared Treatments for Managing Invasive Species Infrared technology uses radiant energy (heat) to kill unwanted vegetation. Intense heat generated by liquid propane coagu- lates plant proteins and bursts cell walls, killing seedling plants and destroying the tops of established vegetation. Repeated treatments at regular intervals deplete the root reserves of established plants and lead to their decline and eradication. In a study by ODOT, infrared treatments were applied at three rates (eight, six, and four treatments per year) along Oregon highways and compared with shoulders treated with herbi- cides and unmanaged control sites. Results suggested that infrared technology can keep vegetation under control on roadway shoulders; however, timing of treatments to plant growth cycles, weather, and fire conditions is critical (92). Grazing Grazing is a biological alternative to mowing and has been considered a physical method, a biocontrol method, or a habitat management method. Continual grazing of the tops of young plants can retard plant development and seed formation and can gradually deplete root reserves. Because animals might prefer to eat nearby grasses in lieu of the target weed, they may be enclosed in a fenced-off, weedy area. This invasive species control method works best where the plants that are to be preserved are adapted to grazing; that is, they are either adapted to high populations of large herbivo- rous mammals or prevalent in human-made habitats such as pastures and heathland. Conversely, unmanaged grazing often favors alien plants, because grazing can preferentially remove native vegetation leaving alien plants, especially toxic species, to grow under reduced competition, leading to a monotypic stand of an alien plant. The following are four classes of grazing management plans that can be used for weeds in general: â¢ Seed removal involves grazing the weed in the spring to remove the bracts and flowers, and perhaps again in
51 late summer. This type of grazing prevents seed set, but does little to reduce the root system. â¢ A multiple pasture rotational system is a properly timed, rotational grazing system that continuously defoliates the target weed throughout the growing sea- son. This eliminates seed production and causes limited stress on the root system. It is useful when large infes- tations occur over many acres. â¢ Intensive rotational grazing involves grazing the plant in the spring until it is completely defoliated and then rotating the animals to the next pasture. In late summer each pasture is grazed a second time. This method places optimum stress on the plant, which decreases plant vigor and carbohydrate reserves. â¢ Continuous grazing, for approximately 4 months, allows goats or sheep to graze throughout the grow- ing season, thus preventing weeds from recovering and maximizing stress on the root system and its reserves. Allow animals to graze weeds only before they flower and set seed. If this is impossible, contain animals for 7 to 14 days in a holding area before moving them to noninfested areas. Habitat management with grazing mammals can be a suit- able option to obtain the desired plant cover. Goats and sheep are economical and do not pose the environmental dangers of applying chemicals. If confined, Angora and Spanish goats will trample or browse virtually any vegetation within a fenced area. Desirable trees or shrubs can be protected with light-weight flexible fencing (93). Maintenance managers have âhiredâ goats for control of broadleafed invasive species control in California, Montana, Nevada, and New Mexico, among other places. Caltransâ Technology Transfer newsletter described several examples (94). In 2000, a Billings Public Utilities Department mainte- nance mechanic hired a pair of angora goats to munch on a par- ticularly abundant yellow-flowered noxious weed that grows along the banks of the Yellowstone River. The goats showed a preference for the top part of the leafy green perennial where flower buds form, preventing blooming and subsequent spread. The goats continue to be used to clear around drainage facilities in Billings. It was found that goats eat whitetop, Canada thistle, spotted knapweed, leafy spurge, and bindweed. The Billings Public Utilities Department has also used the goats as part of an integrated bio-control management program in conjunction with introduction of Aphthona lacertosa flea beetle, which attacks the leafy spurge root systems. In Albuquerque, approximately 1,000 goats were brought in to clean up weeds along the Rio Grande. The district biol- ogist reported that âtightly managed and limited use of goats is a really good and ecologically sound way to manage veg- etation without having to use herbicides or fossil fuel for mowersâ and leave the native grasses to flourish. The state of New Mexico plans to use goats to clear more than 1,200 mi of canals, drains, and ditches, which would normally be cleared using costly electrical equipment, herbicides, and manual (human) labor. The goats provide a way to do this that is more cost-effective, saves energy, and safeguards the environment (94). Denverâs naturalist attempted something similar, but encountered problems stemming from the sheer logistics of trying to mobilize 50 to 275 goats in an urban environment, as well as unleashed dogs that chased the goats. Nevada uses a combination of grazing with goats, careful herbicide application, mowing, and seeding with annual plants. Along the Truckee River, goats that were put out to graze on whitetop weeds infesting the floodplain ate approx- imately 75% of the young, tender regrowth. Such efforts have done much to control the growth and spread of weeds. In Montana, BLM found that grazing sheep controlled approximately 90% of the leafy spurge weed over a 4-year period. Without sheep, the Bureau was spending $40 to $50 per acre on herbicides for weed control; today, with the help of the sheep, there is only a need for minor spot applications of herbicides. In Wyoming the DOT estimates that sheep grazing the land costs $18.80 an acre to maintain, compared with $185 to $310 an acre using herbicide, and $350 an acre to control growth through hand-cutting and mowing (94). In Rackerby, California, Goats Unlimited raises small New Zealand âKikoâ goats just for controlling weed growth. Their goats are serviced out to assist with rejuvenation, ero- sion control, and restoration projects, as well as creating fire- breaks and clearing ditches. Goats can help an agency reduce its dependence on fossil fuels and, because goats, unlike mowers, do not start brush fires with sparks from their motors, they have been used extensively since the fires of 1990 in the OaklandâBerkeley Hills area to safely manage the growth of undesirable vegetation by clearing dense undergrowth, including the highly flammable manzanita. Numerous agencies in the Bay Area now employ the goats for vegetation control. In the Sacramento area, 350 goats are clearing an acre a day. In San Luis Obispo, flood control managers have used goats to clear drainage channels along the Arroyo Grande Creek. Goats, traditionally mountain dwellers, do well on steep terrain, which poses a challenge for workers with power mowers. Also, the goats will con- tentedly âworkâ any time of day or any day of the week. For large groups of goats, goatherds are sometimes required (94). Changing Abiotic Factors Most invasions of nonindigenous species are caused or at least favored by human disturbance of the ecosystems. In these cases, a mitigation of negative effects by the invasive species could be achieved by changes in the human behavior that has led to the invasion. An example would be a change in the quan- tity of nutrients and/or water available for plants, which would alter the plant community. In some cases, invasive aquatic organisms can be controlled by improving the water quality,
addressing eutrophication and pollution problems, or even changing the quantity of water; for example, draining or a water-level regime adverse for the invasive species. Hunting and Other Use of Nonindigenous Species Continuous hunting can be used to control exotic species, such as deer, originally introduced for hunting purposes. There are two approaches: commercial hunting principally for meat and recreational hunting. Problems encountered trying to control an alien species through hunting usually relate to land ownership and the dis- tribution of the invasive species. Some species spread into suburban areas where hunting is not allowed. Many groups within the human population, particularly in developed coun- tries, find hunting morally unacceptable, and so it may decrease in popularity, thus allowing alien species formerly controlled by hunting to explode in numbers. Many other invasive species can be eaten or have edible fruits, which can be exploited for human consumption or as fodder for domesticated animals. In many parts of the world with high human density, invasive plants are also esteemed for their production of highly valued firewood or for other uses. A high percentage of introduced fish and crustacean species are fished either recreationally or on an industrial scale. A significant drawback of this approach as a control method is the promotion of an alien species as a food resource and the promotion of new industries depending on what otherwise might be better to eradicate. The market may provide an incentive for individuals to spread the alien species to as yet uninfested areas, or breed them in captiv- ity, from where they may eventually escape. Thus, the costs and benefits must be evaluated on a case-by-case basis. CHEMICAL METHODS Herbicides adversely affect the physiological activity and development of plants and are used to control vegetation by causing death or suppressing growth. These compounds, as active ingredients, are incorporated into a wide variety of commercial herbicide formulations for application to plants and to surrounding soil or water as sprays, granules, and liq- uid concentrates. Herbicides can be grouped on the basis of their chemical structure and physiological action or on the timing and method of their application. Chemicals with sim- ilar structure usually produce the same type of physiological reaction in plants and control similar species. Nonselective herbicides control all vegetation because they affect physio- logical processes common to all plant species. Selective her- bicides will damage only those groups of plants that carry the biological pathways they target. 52 Herbicides are the major method of invasive species con- trol in non-crop situations as well as in agriculture because they are relatively effective, reliable, cost-efficient, safe, and easy to use. In addition, some areas virtually require treatment by herbicides; eradicating vegetation that grows around and under a standard current guardrail is very diffi- cult without the use of herbicides. Nevertheless, human health concerns have encouraged public agencies in partic- ular to examine and encourage alternatives to herbicide use. In the past, extensively used broad-spectrum pesticides such as DDT had massive detrimental effects on the environment as well as human health; however, today these products are banned in most countries, and there are more specific prod- ucts on the market with fewer negative nontarget effects. Some insecticides, such as those based on chemical struc- tures similar to insect hormones, can also be specific to target groups of insects. Other major drawbacks of herbicides are the high costs, the necessity of repeating an application, and the effects on nontarget species. Repeated use of pesticides also provides the selective pressure that enables many target species to evolve increasingly effective resistance to these chemicals. In response, either the dose has to be increased or a different group of pesticides has to be used, usually further increasing the control costs. There is also the possibility that indigenous peoples will oppose the use of toxins on their land; for exam- ple, where toxins may accumulate in sublethal levels in non- target species that may be an important food source for indigenous peoples. This latter concern is primarily true of persistent pesticides such as modern anticoagulants and the now largely obsolete organochlorine compounds. Selection of a pesticide to control an invasive species begins with a determination of effectiveness against the tar- get and all appropriate nontarget species that might come in contact with the chemical, either directly or through sec- ondary sources. Additionally, the environmental half-life, method of delivery, means of reducing nontarget species contact, demonstration of efficacy, and collection of data to ensure compliance with environmentally safe use (as set out by the regulatory bodies in the country where it will be used) must be evaluated. Most countries require pesticides to be registered for specific uses. Once identified, tested, and reg- istered, a pesticide can allow for the rapid control of a target species over large areas and, as a result, reduce the need for the personnel and costs for the traditional methods. Widely used application methods for herbicides include treatments of the bark of young trees or application of herbi- cide into the wounds created by girdling or cutting. This cut- stump application method, mentioned already in the section on mechanical control, is very effective against many woody plants. Herbicide can also be applied directly to the leaves of the invasive species by using a sponge, wick, or a syringe; however, a less specific and more common method is spray- ing of infested areas. As a general rule, foliar herbicides are
53 applied to young, tender, actively growing plants before flow- ering. If the plants are too mature for effective herbicide appli- cation, a common practice is to mow an invasive plant infes- tation, before seed maturation, allow the plants to regrow to a height of 2 to 4 ft and then apply the appropriate foliar herbi- cide. This process can weaken the plant and prevent spreading by seed, and maximize the effectiveness of the herbicide appli- cation. Owing to the vigorous nature of many invasive plants, especially knotweed and phragmites, this process may need to be repeated two or three times over consecutive years. Stem âcut and treatâ herbicide applications involve the cut- ting and removal of the growing plant stems and then the spot application of herbicide to the freshly cut surface of the remaining rooted portion of the stem. The herbicide will then be translocated down into the plantsâ root system. The âspotâ application can be accomplished with a swab or hand sprayer and should occur as soon as possible, but not more than 1 h from the time the stem is cut (within 15 min is preferred for best results). A common practice is to have one individual cut the stems while a second follows and applies the herbicide. It is important to mark which stems have been treatedâusing a marker dye is a common technique. This technique is recom- mended in situations where foliar treatments are not possible or effective, such as with Japanese knotweed. If stands of invasive plants extend beyond the ROW, a written release may be sought from the adjacent landowner to implement controls. All sites where herbicides are applied should be inspected 3 to 4 weeks post-application to assess success and to determine if natural revegetation by native or noninvasive plants is adequate or if additional restoration, for example, seeding and mulching, is required (95). Insecticides can be sprayed selectively on infested plants, plant parts, or indiscriminately over a large area. Application should always be as focused on the pest as possible; for example, spraying of the attacked plant part, at the most sus- ceptible time for the target, and limiting the use to the effi- cient dose to minimize side effects on other species. Pesticides are used against vertebrates primarily in baits; for example, bait stations for rats. Before using bait, small- scale experiments and observations can be carried out to determine which nontarget species might take the bait. With some ingenuity, it may be possible to develop bait stations that give easy access to the target species but prevent, as far as possible, other species from entering it. Naturally, a more target-specific bait station is easier to design for an ecosys- tem with no species similar to the target species. Chemical substances are used to mitigate diseases in humans and animals. Water and surfaces capable and sus- pected of disease transmission are treated with disinfectants to kill pathogens before entering their hosts. Chemical treatment offers one of the few options for control of marine invasive species, although its potential is limited. Herbicides (e.g., glyphosate and 2,4-D) have been used extensively around the world as a quick and effective means of controlling weeds in freshwater environments. However, because they are nonselective and more difficult to apply directly to the target plant in water, they are more likely to cause harm to nontarget species. The fish poison rotenone is frequently used to control fish species in ponds and other small water bodies. This method is efficient for the eradication of species; however, the nonselective character limits its use for large-scale infestations. DOTs are required to follow the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and other appro- priates laws and mandates when using herbicides or pesti- cides. DOTs are required to use all herbicides in accordance with label instructions, state and federal law (including adja- cent landowner notification requirements), and by or under the supervision of certified applicators. Herbicide Use as Part of an Integrated Vegetation Management Program Judicious use of herbicides is an important tool in invasive plant control efforts. IVM stresses the need for selectivity, restraint, and proper training and protections whenever her- bicides must be used. On the road shoulder and in other zones too, invasive species must be controlled to protect against the undesirable succession of plant communities, not only for the sake of the roadside zone itself, but also to prevent the road- side from becoming a refuge for invasive species and the source of further spreading. Chemical vegetation controls are used to protect preferred vegetation, to provide fire protec- tion, and to improve roadside appearance. In IVM programs, herbicides are considered transition tools that enable the manager to suppress weeds and replace them with desirable, competitive vegetation. Therefore, it is impor- tant to select the least-toxic, low-residual herbicide that is effective against the target weed and to apply it in a judicious manner. The Cooperative Extension Service, state agricultural experiment stations, or County Agriculture Commissioner should be consulted for specific herbicide recommendations and information on their use in particular localities. Responding to Public Concerns of Herbicide with Integrated Roadside Vegetation Management and Improved Stewardship Practice DOTs find themselves in the public spotlight over herbicide use. In integrating all the IRVM tools, FHWA has outlined the following recommended steps to follow before herbicide use (96): â¢ Evaluating each site to determine if invasives really present a problem. â¢ Spot mowing to prevent annual weed seed production.
â¢ Removing a [non-native species] and allowing desir- able species to reclaim the area. â¢ Prescribing burning of prairie communities to promote healthy vegetation. â¢ Using biological controls as alternatives. â¢ Frequent roadside management equipment cleaning to help reduce seed transfer. DOTs have also responded to public concerns with herbi- cide reduction and/or notification efforts (97). â¢ Caltrans pledged to decrease herbicide use by 50% between 1992 and 2000, and by 80% by 2012. District 1 governments can opt for no herbicide spraying. â¢ Iowa DOT controls invasives with herbicides only if mowing or other controls are not practical. Forty-one of 99 counties in the state participate in IRVM programs. â¢ NYSDOT set up a toll-free number for members of the public to find out about spraying plans. â¢ North Carolina, Oregon, and Washington State DOTs use IVM and offer no-spray agreements to adjacent landowners. WSDOT tracks and reports on reductions in herbicide usage. Reducing Herbicide Application and Cost with Innovative Sprayers A number of DOTs have been active in developing the best technology for roadside vegetation control. Herbicide spray- ing helps eliminate unwanted vegetation; however, typically, 80% to 90% of the sprayed chemical misses its mark and is wasted, according to horticultural scientists at North Car- olina State University. Recent research and development work by Purdue University led to the commercial production of an equipment system that can electronically identify indi- vidual invasives within its path and deliver a prescribed targeted application of herbicide in a single pass over the roadside. Treatment of various invasives often requires the use of different herbicides. Sprayers must have the capacity to spray more than one chemical at a time, negotiate rough terrain, and apply herbicides safely and in a way that pre- serves the environment. Purdueâs technology and the other following examples reduce the amount of herbicide needed and DOT costs (98): â¢ Iowaâs Clinton County oversees a commercial roadway management system that uses a sprayer-mounted com- puter connected to a GPS receiver to record the place- ment of multiple herbicides. The countyâs objective is to integrate data from years of mapping to target neces- sary spraying and avoid sensitive areas. â¢ Small sensors can be used on trucks or other equipment to pinpoint the location of an undesirable plant and then target and spray the weed with herbicide. Each sensor views a 12-in.-wide area. The unit will spray only weeds and not bare ground. Several Caltrans districts are using the sensors. A side-mounted strip of sensors 54 at the rear of a vehicle lets the unit target and spray roadside weeds at 10 mph. Using the sensors cuts her- bicide amounts and costs by 50% to 80% compared with broadcast or manual spot spraying. The sensors have their own light source so they can be used at night when traffic is light. Units with the sensors need only the driver, reducing work hours required as well. â¢ At North Carolina State University, Drs. Jim Burton and Walter Skroch developed an herbicide applicator that can be attached to weed mowers. The unit applies a film of chemicals to the weed stem as the plant is cut by the mower. From 70% to 90% of the herbicide is absorbed into the plant to prevent future growth. The applicator, called the Burch Wet Blade, is designed for use on rotary roadside weed cutters. A reservoir mounted on the cutterâs deck holds the premixed chem- ical solution. A pump regulates an adjustable flow of the chemical through the spindle shaft and out along the blade to an opening on the cutting edge. âWhen you cut the plant, its vascular system sucks in the herbicide and sends it plantwide,â Burton says. The system is a closed one that never sprays into the open air, which is safer for the operator. Mn/DOT tested four sprayer designs, each of which saved money compared with traditional sprayer use, according to a report by Claudius Toussaint, Mn/DOT Office of Mainte- nance Operations Research. Savings of up to $65,000 per sprayer were cited (99). â¢ The B & B Ditch Sprayer 300 prototype contains a 300-gal. oval-shaped plastic tank and a sprayer equipped with two spray booms, each consisting of drop nozzles and providing a 60 ft spray pattern. The spray boom has an innovative spring-loaded feature. Although this system had the lowest net savings of the four tested sprayers, it offered a rate of return of 360%. â¢ The Wanner Innovative Sprayer system includes an 850- gal. stainless-steel tank, with spray material dispensed from the tank and delivered to the spray nozzles by means of a pumping system. Spray booms consist of drop noz- zles and end-mounted boom-buster roadside nozzles. Additionally, there is a single straight stream nozzle mounted on the end of the boom. The system is also equipped with drop nozzles, which are used for spraying road shoulders. All spray nozzles are remotely controlled from the truck cab. The Wanner sprayer is more econom- ical for use in large districts or in areas with extensive road miles, owing to its capability for applying herbicides at high speeds and accurate amounts. The large size of the supply tank is also a factor in the sprayerâs ability to ser- vice large areas. The rate of return was measured at 76%. â¢ The Micro-Track Spray System, a multiple-injection spray system with console monitors, can be connected to any size of supply tank. The system is capable of spraying up to five different herbicides simultaneously, and the supply tank, chemical tanks, pumps, monitors,
55 and nozzles are all mounted on one unit. No trailers are needed. The Micro-Track sprayer had the highest rate of return, 1,142%. â¢ The SCS 750 can independently control the liquid, granular dispensing systems, and overall hydraulic system at the same time. If spot spraying is needed, each chemical can be controlled by a manual switch. Hand-spraying attachments are also available for spot spraying. The spray rate is controlled by a wheel-driven speed sensor. Visual and audible alarms alert the operator to any deviation from the programmed rate of application. Measurements can be calculated using the metric or U.S. measurement systems. Calibrations and weather information are stored in the 10-year memory capacity. A compact printer is plugged into the 750 console to obtain a readout of the daily activ- ities. The SCS 750 sprayer had the highest net annual savings along with the advantage of being able to monitor, tabulate, and print out all vital statistics (areas, dosages, weather conditions, application rates, and so on). Washington State Department of Transportation Efforts to Minimize Herbicide Use Through Integrated Roadside Vegetation Management As a single government body, DOTs are often the largest users of herbicides in the state and therefore have drawn criticism for this from environmental groups. WSDOTâs strategy for dealing with the public concern regarding her- bicide use has been to implement IRVM through the agencyâs local crews at the field level, increase the account- ability of the program, and minimize herbicide use over time by working to establish desirable, low-maintenance plant communities that will naturally preclude the estab- lishment of undesirable plant species. WSDOT is develop- ing roadside vegetation management plans for each of its 24 maintenance areas. As of 2005, WSDOT had developed and implemented such plans for approximately one-third of the stateâs 7,000-centerline-mile system. Complete cover- age is scheduled by 2007. In dealing with the most sensi- tive and controversial areas to date, WSDOTâs IRVM approach has incorporated the following: â¢ Planningâdevelopment of an IRVM plan that contains an inventory of roadside management features and pro- vides specific documentation on how WSDOT will treat various aspects of the roadside. â¢ Communicationsâmeetings and ongoing dialogue with interested individuals, groups, local governments, tribes, and neighboring landowners to discuss, negoti- ate, and decide on specific roadside vegetation man- agement policy and practice. â¢ Researchâcommitments to conduct research to seek out and analyze alternatives to herbicide use where they exist, through both design and construction and maintenance. â¢ Partnershipsâinclusion of local volunteers in research, planting and roadside restoration, and weed control pro- jects. Also, working with local governments and tribes to develop local solutions and share information. â¢ WSDOT makes information on WSDOT herbicide use, including need and risk, available for the public on-line through the agencyâs Gray Notebook of accountability measures. There are currently six counties in Western Washington that maintain their road systems without the use of herbi- cides. WSDOT developed a Comparison of Roadside Main- tenance PracticesâImpacts of Herbicide Use on Cost and Results. The findings show that to preserve the same level of service WSDOT maintenance currently delivers, without the use of herbicides, the overall cost of roadside vegetation management would be close to double. WSDOT found that most of the cost increase from herbicide elimination comes from maintenance at the road shoulder. In most cases, WSDOT keeps this area vegetation free; however, in the six counties that do not use herbicides, grass is allowed to grow up to the edge of pavement. Further research will be con- ducted in the coming years for road shoulder maintenance in areas throughout the state. Mn/DOT Position Statement on the Use of Herbicides Mn/DOT Position Statement on the Use of Herbicides states the agencyâs commitment to using the least toxic, efficacious pesticides available for control- ling identified pest species. Herbicide selection and use should be based upon scientific information, including but not limited to, efficacy on targets to be controlled, environmental fate, and toxicity. Selection and use of herbicides is further governed by state and federal laws and regulations. Herbicides selected and used are to be applied by licensed applicators except as allowed in the herbicide policy guidelines adopted here under. All appli- cations should be in accordance with applicable laws, regula- tions, and label instructions. On-Line Sources of Information The following is a guide to the use of various herbicides for the management of noxious and nuisance plant species. â¢ Overview and Using the Corpsâ Plant/Herbicide Identi- fication System. Herbicides by Plant. Plant lists are organized by habitat type as well as the list of all plants contained in the system. A related herbicide list is included as well. â¢ Safe Herbicide Handling in Natural Areas: A Guide for Land Stewards and Volunteer Stewards, Upkeep and Maintenance of Herbicide Equipment: A Guide for Natural Area Stewards, and an example of Stan- dard Operating Procedures for Herbicide Use, includ- ing a contingency plan in case of spills as well as a
generalized check sheet. All by The Nature Conser- vancy staff. â¢ Crop Data Management Systems MSDS SheetsâThe Crop Data Management Systems website provides Material Safety Data Sheets (MSDS) for fertilizer and pesticide products of North American manufacturers. â¢ Herbicide Recommendations: Rangeland Rights-of- WayâEasy-to-use table describing how and when to treat specific weeds with herbicides [Yellowstone County (Montana) Weed Department]. â¢ Development of Weed Resistance as Affected by How Frequently a Herbicide Is AppliedâFact sheet explain- ing a strategy for decreasing selection pressure by her- bicides on weed communities (Western Society of Weed Science). â¢ Herbicide Resistant WeedsâThe development of herbi- cide resistant weeds is described along with strategies to prevent development (University of NebraskaâLincoln). CULTURAL CONTROLS Cultural control methods introduce and manage desirable plants and covers to control invasive species and other unde- sirable plants. Many native plants are poor competitors in their early stages of growth; however, once established, they can crowd out most other plants with minimum management. Pre- vention measures may also be considered cultural controls, and are covered in detail in chapter three. Nine DOTs (23% of respondents) mentioned that they are using cultural control methods; however, the percentage may be considered higher when altered DOT processes and procedures are considered. Cultural controls include land management practices that inhibit weed growth and prevent conditions that lead to weed establishment. For instance, planting and maintenance activ- ities can be modified to reduce weed infestations. Attention to suitable seedbed preparation and proper fertilization can help prevent colonization by weeds. Planting in narrow rows reduces bare ground and increases the shaded area between rows, further decreasing potential weed habitat. Many agencies are using native grasses to control inva- sive species, because their dense, deep root systems inhibit weed growth. Both Minnesota and Iowa DOTs have found success in controlling invasive species and Canada thistle, in particular in Minnesota, using native grass stands (72). Department of Transportation Use of and Research on Prevention Practices and Native Revegetation Review and Pretreatment of Construction and Materials Sites Preconstruction planning and treatment to reduce infesta- tions of invasives is on the upswing. Nine DOTs (23% of 56 respondents) reported that all construction sites are reviewed for invasive species before opening. WYDOT is among five that are working at pretreating construction zones before soil disturbance. WYDOT is attempting to develop a more aggressive pit assessment and treatment program with local Weed and Pest districts. These sources have been identified as having the greatest potential for spreading invasives. At NDOT, a staff biologist surveys material source sites for invasives. When invasives are found, a management plan is developed in cooperation with the local BLM weed coordinator or botanist. Environmental Services is developing standard noxious weed control BMP specifications for weed manage- ment on material and project sites. Eight other DOTs (23% of respondents) also ensure that dirt and gravel sources are evaluated. In addition: â¢ More than one-third of DOTs (17) specify weed-free mulches on all projects. Inert mulch products such as straw or wood fiber are used in sensitive areas by 11 DOTs (28% of respondents). â¢ Twenty-one state DOTs (53% of respondents) specify on project plans and bid contracts that seed and sod sources must be free of invasive species and/or weeds. Possible solutions to the problem of weeds that are intro- duced by animal feed or mulches contaminated with weed seed are discussed in âCertified Weed Free Forage: An Emerging Program for Western Statesâ (100). Protection of Native Populations Intact communities of native species both suppress invasives and shelter rare species. Thirty-eight percent of responding DOTs (15 states) are now screening for the presence of rare plant communities in the work zone or ROW. In 13 states, areas in need of special management are identified by resource agencies or the state NHP. NCDOT, like many others, works cooperatively with their state Department of Environment and Natural Resources, in-house botanists, and others to identify and protect state and federally endangered plant and animal species found on its ROWs. ODOT has labeled special management areas that indicate the types and timing of maintenance techniques that are to be done. Because WisDOT hires county highway departments to per- form highway maintenance, the agency has let several con- tracts to manage and restore high-quality remnant plant com- munities discovered on the ROWs. Management plans are often developed to inventory and ensure appropriate man- agement of special areas. Ten DOTs (25% of respondents) have mapped and tracked protected communities on the statewide DOT ROW. Staff at 14 DOTs (35% of respondents) identified spe- cial management areas, which are managed accordingly by
57 maintenance employees. As Illinois DOT noted, commit- ments are added to plans and DOT staff are trained on how to maintain these areas through mowing, herbicide applica- tions, and burning. Protected species are identified and restricted maintenance practices are incorporated to protect the endangered species; construction practices are also altered to minimize disturbances of native plant communi- ties whenever possible. In several states, special vegetation management programs have been developed to protect Karner Blue Butterfly habitat, including mowing date restrictions and native blue lupine and butterfly weed restoration planting and seeding. LADOTD has taken high- value remnant strips in several districts and moved them just beyond the ROW, with the consent of the owners of that property and following discussions regarding proper management. If moving them is determined not to be an option, LADOTD marks the site to prevent herbicide appli- cations or mowing at the wrong time of the year. In most cases, DOTs are undertaking these conservation measures without knowing the total acreage of high-quality forest, wetland, or native grassland remnants they have or are protecting in the ROW. Just 15% of those responding (6 states) could provide such an estimate if asked. More than one-third of DOTs (43% of respondents, 17 states) identify native and rare plant communities in EAs and EISs. In par- ticular, Hawaii DOT indicated that most of their protected areas have been identified as a result of EAs, EISs, and spe- cial management areas. Vehicle Cleaning Practices Vehicle and equipment cleaning procedures and practices are typically used to minimize or eliminate the discharge of pol- lutants from vehicle and equipment cleaning operations into storm drain systems or watercourses, and to minimize trans- port of invasive species. Twenty-three percent of responding DOTs (9) reported that they ensure vehicles are washed before and after use to control the spread of invasive species. Caltrans is among the DOTs that have developed an exten- sive set of construction vehicle cleaning environmental stew- ardship practices (101). Revegetation Some DOTs are undertaking research to identify what vegeta- tion establishment methods work best in their states and ecore- gions. Studies on compost usage have been undertaken in the West and Midwest, from Texas in the south to Idaho in the north. The Nebraska Department of Roads research results will be used to develop technical guidelines for vegetation establishment on roadway shoulders. The project is examining the interaction effects of seed priming, type of mulch, and level of irrigation on soil movement and establishment of the short grass mixture on the foreslope of roadway shoulders; the inter- action effects of composted manure applications and a 6- to 12-in. compacted buffer strip between the paved shoulder and the seedbed on soil movement; and establishment of the short grass mixture on the foreslope of the roadway. Delaware DOT is also publishing a vegetation management manual, in con- junction with the agencyâs tree preservation policy for a Liv- able Delaware (102). Soil Management on Construction Sites Soils management on construction sites is an important factor in invasive species control. Just 12 state DOTs (30%) reported that they stockpile desirable and uncontaminated topsoil to facilitate revegetation. Topsoil has become a commodity that contractors often strip and sell. In addition to removing native cover that may effectively compete with invasive species and opening new pathways for infestation, the change in soil char- acteristics that may occur with loss of topsoil can also bolster invasives. One Florida study on roadside soils and invasive species suggested that disturbance alone may not increase the presence of invasive species, but that a change in soil charac- teristics through the addition of clay and limerock from road construction may enhance invasion (103). Claassen et al. (104) have performed a number of studies on topsoil usage and compost, with funding from FHWA and Caltrans. Their work and recommendations augment that of DOT handbooks, and are summarized in AASHTOâs Envi- ronmental Stewardship Practices, Procedures, and Policies for Highway Construction Maintenance. Among its many helpful recommendations are for DOTs to test nitrogen content in soils and ensure slow-release of amendments over 3 years, use compost instead of commercial fertilizer, and ensure that compost amendments have adequately decom- posed. Where topsoil is not available other amendments can be used; the quantity and quality of the nitrogen materials applied is critical. The nitrogen release should be slow enough to keep plant-available nitrogen at modest levels; however, the total amount of nitrogen amended should be high enough so that the site does not run out before the plant community is well established. For example, the nitrogen amendment should be able to support 3 to 5 years of plant growth. Con- trolled release of nitrogen is important because excessive nitrogen availability promotes weedy annual grass growth, drying out the site and crowding slow growing perennials. Although the maintenance of moderate, sustained nitrogen levels may be achieved from commercial, slow-release fertil- izer sources, the inclusion of organic matter in the amendment is also important to improve the hard setting and poor water holding capacity of low organic content materials. Biomass associated with compost has been more effective than nitro- gen amendments that were evenly distributed throughout the profile (0â30 cm) or applied deeply within the profile (20â30 cm) (105). Studies of plant communities established on âproblem soilsâ amended with commercial fertilizers have shown vigorous initial growth; however, that vegetative cover often becomes sparse or nonexistent within several years
58 â Pavement edge treatmentâuse of topsoil and low- growing native grass species in place of unvegetated crushed rock along the edge of pavement. â Soil amendmentâuse of compost and mulch as amendments to raw mineral soils on cut and fill slopes. â Weed control during constructionâensuring ade- quate funding, specifications, and inspection provi- sions to prevent weed transport and establishment during construction. â Establishment of desirable low-maintenance vegeta- tionâplanting and effective establishment of native shrub and tree community on the back slopes and areas away from the traffic lanes. â¢ If all these recommendations can be carried out effec- tively, the only maintenance requirements will be occa- sional selective removal of weeds and undesirable trees and brush. With proper care for the planted materials over time, maintenance requirements should decrease as the roadsides become more established. Similar to WSDOT, Caltrans performed a study on how to successfully implement an IVM program in its diverse ROW corridor network. The main goals of the study were to develop better processes for roadside design and consideration of long-term maintenance (life-cycle costs) and develop strate- gies that satisfy safety, environmental quality, herbicide reduction, cost-effectiveness, and public perception goals. Caltrans decided that process revisions were necessary to Cal- trans Design, Project Development Procedures, Construction, and Maintenance manuals. In particular, cross-functional teams of skilled district and/or headquarters staff, such as landscape architects and landscape specialists, were recom- mended to ensure that life-cycle maintenance and corridor management issues are considered throughout project devel- opment. In addition, Caltrans decided that ROW corridor master plans needed to be developed to map out a future vision for ROW corridors in the state, because of the close relationships between vegetation management, stormwater management, scenic resources, environmentally sensitive areas, and many other issues, recognizing the relationships of these issues and determining how they are affected by high- way design and management. The master plans characterize each roadway segment, indicating aspects such as invasive species, scenic resources, environmentally sensitive areas, special status species, adjacent land use, projected average daily traffic, and other factors, and prescribe the objectives for the roadway. The master plans are to be coordinated with fed- eral, state, and local jurisdictional agencies to optimize resources and ensure consistency with other developed plans. The ROW corridor master plans enable: â¢ Designers to consider the predetermined and cultural issues associated with a corridor segment. â¢ Landscape architects to reference native species and establish overall site-specific objectives for highway plantings. (106). In addition to transportation-related studies, those of fertilized mine reclamation spoil observed that revegetated areas tended to be highly productive for 2 to 5 years, followed by a sharp decline in plant growth and nutrient availability (107). Reapplication of topsoil to subsurface materials enhanced reestablishment of vegetation by increasing nutri- ent availability, water holding capacity, and microbial activ- ity (108). Compost can be used to replace the organic matter and nutrients and can act as a surface mulch to protect against erosion, extreme temperatures, and drought (109). Long-term nitrogen release rates from most yard waste compost materials approached the nitrogen release rates of moderately fertile soils. Composts were shown to be able to regenerate the nitrogen availability characteristics of low- nutrient substrates that have been stripped of topsoil organic matter. Well-cured composts and co-composts (biosolids blends) approached the nitrogen release rates of highly fer- tile soils. Compost application provides longer nitrogen release duration compared with chemical fertilizer and also provides organic materials for improved infiltration and microbial activity. Potential compost sources and soils at the site should be analyzed before amendment, because compost products and the soils that are to be revegetated vary in fer- tility and water availability. Shoulder Grading DOTs are teaching maintenance staff that shoulder grading is not acceptable as a method of vegetation or invasive species control. Shoulder grading is only promoted as a means of refining lateral support for the road. Managing the Roadside as an Asset: Value Engineering and Invasive Species Prevention With the advent of modern herbicides, prevention as a weed management technique has been neglected. WSDOT discov- ered the following through the agencyâs value engineering work: â¢ Some of the biggest problems in relation to roadside vegetation management and invasive species control stem from inadequate consideration of soil conditions, restoration of desirable roadside vegetation, and weed control in design and construction. â¢ Through the value engineering study, WSDOT identi- fied a series of recommendations that, if implemented, could result in improved weed control and reduced her- bicide use over the long term; in effect, reducing the roadside maintenance requirements over the life cycle of the highway. â¢ Recommendations resulting from this study for improv- ing weed control and reducing long-term vegetation maintenance requirements through design and con- struction were grouped into four categories.
59 â¢ Maintenance personnel to be aware of environmentally sensitive areas and prescribe best management practices. â¢ Systematic upgrades and retrofits of facilities as new designs become available. â¢ Cooperative management efforts with local public works agencies. In their alternatives analysis of different vegetation man- agement methods, Caltrans found that one of their top-ranking alternatives was the use of preferred vegetation species, because roadside environments often favor invasives and are not supportive of native species. Caltrans identified the plant- ing of species that do not require ongoing maintenance and do not threaten adjacent resources or safety as one of the best strategies for minimizing vegetation control problems. Revegetation Through Restoration of Native Species Most weeds are opportunistic and become established fol- lowing a disturbance or opening in the canopy. Therefore, it is very important to cover the soil with dense, vigorous veg- etation to prevent the establishment of invasive species. Because weed treatments often disturb the soil, open the canopy, or leave bare soil, revegetation after treatments is crucial in suppressing weed seedlings and preventing weed infestations from reoccurring. Although restoration efforts have certain elements in common, each invasion and area is unique. Revegetation and restoration projects need to be based both on general principles and site-specific considera- tions and analysis. Monitoring programs are necessary to track the success of control and restoration efforts and to ensure that the area is not reinvaded. Executive Order Mandates Regarding Native Species Restoration E.O. 13112 requires federal agencies to âprovide for restora- tion of native species and habitat conditions in ecosystems that have been invaded.â In the long run, such restoration areas should require little to no maintenance. According to NCHRP Synthesis of Highway Practice 341 (67), on average, 58% of DOTsâ newly planted acreage requires no significant maintenance work on a perpetual basis; 23% indicated that less than 20% of the newly planted acreage requires signifi- cant maintenance work on a perpetual basis. Approximately one-quarter of responding state DOTs were aiming for 90% to 100% of planted acreage requiring no significant mainte- nance work on a perpetual basis. Restoration is an integral component of comprehensive prevention and control programs for invasive species that may keep invasive species from causing greater environ- mental disturbances. Revegetation with native species pro- vides better adaptation to the site and a more natural appear- ance than introduced species, which would have the potential to escape into the natural environment. An earlier Federal Executive Memorandum on beneficial landscaping became effective in April 1994, encouraging the use of native plants as much as practicable on all federal lands and in all feder- ally funded projects. In 2000, this Executive Memorandum was incorporated into Executive Order 13148 on the Green- ing of Government. Executive Order 13148 also required agencies to purchase âenvironmentally preferable and recy- cled content products, including compost and mulch that contribute to environmentally and economically beneficial practicesâ (110). FHWA Recommendations for Designing with Native Vegetation FHWA recommends the following considerations and spec- ifications in designing with native vegetation (9): â¢ Use natural region maps commonly available from the stateâs NHP instead of cold hardiness zones when designing with native plants. Visit native plant pre- serves that can serve as references for plantings. The NHP can recommend sites. â¢ Use seed mixes specific to the different conditions on the site. Dry conditions may be present on sandy slopes or forest edges and wet conditions in ditches, requiring different or adjusted mixes in these areas. â¢ Eradicate invasives from the site before planting. â¢ Consider a line item for the contractor to control inva- sives and clean equipment. â¢ Plant as much diversity as possible, unless an adjacent native seed source exists. â¢ Match site microclimates with distinct seed mixes as much as practical. â¢ Specify a locally grown or collected source if possible. Most native species will establish more easily if locally grown or collected. â¢ Order native seed when the contract is let to prevent unwanted substitutions. â¢ Limit bids to experienced contractors and approved vendors for these projects. â¢ Separate the planting contract from the general contract for best timing. â¢ Extend the establishment period to 3 years. â¢ Learn appropriate seed test criteria and seeding rates to avoid waste. â¢ Plan for seed collection and plant salvage if native rem- nants will be disturbed by the project. Department of Transportation Revegetation PracticesâSurvey Results As part of their commitments to reduce invasive species and to develop attractive and sustainable roadside environments that are better for native species and agency budgets, many DOTs are turning to native revegetation projects and plans.
The survey for this project found that 44% of DOTs reported that they rely on native grasses and forbs. Primary actions DOTs have taken to implement the use of native grasses and forbs in erosion control, landscaping, and revegetation include those shown in Figure 5. The percent- age DOTs that indicated use of this action is included. â¢ Required seed mixes have been designed for a variety of ecoregions and slope aspectsâ43% of respondents (17 states). â¢ Special provisions are included in contracts for partic- ular projectsâ45% of respondents (18 states). â¢ DOT policies or agency-wide design specifications require the use of native speciesâ38% of respondents (15 states). â¢ Landscape architect comments on landscape plans dur- ing reviewsâ33% of respondents (13 states). â¢ Vegetation and revegetation is performed according to a statewide or regional vegetation planâ18% of re- spondents (7 states). Policies or Plans Specifying Native Revegetation Policies or plans specifying native revegetation are already in place in 17 states (43% of responding DOTs). Another 10 states (25% of respondents) have plans specifying native revegetation on some projects or corridors. A statewide plan for native revegetation is in the process of being developed at five state DOTs (13% of respondents), Hawaii, Minnesota, Montana, New Hampshire, and New York State. States indi- cated that they believed their plans were generating results. Increasingly, plans are being developed in coordination with other agencies. For example, Connecticut DOT has coordinated with the stateâs Department of Environmental Protection and the National Resource Conservation Service to ensure that the DOTâs revegetation policies and agency- wide design specifications are in agreement with those of the resource agency. In a few other cases, state DNRs or agri- culture departments are developing plans in conjunction with DOTs or on which DOT plans will be based. Some state DOTs have been pursuing native revegetation or relying on native species in their seed mixes for 20 years or more (WYDOT and Nebraska Department of Roads). WisDOT used the 1987 Surface Transportation and Uniform Relocation Assistance Act (STURAA) to fund the ongoing use and preservation of native plants. STURAA contains a mandatory requirement that native wildflower seeds or seedlings or both be planted as part of landscaping projects undertaken on the federal-aid highway system. At least one- quarter of one percent of the funds expended for a landscap- ing project must be used for native wildflowers. WisDOT established a waiver that allows the agency to avoid planting native wildflowers where doing so would be inappropriate, 60 and save the unused funds for larger projects in the future. WisDOT also creates or preserves native plant conservation sites where possible to serve as conservation banks for unavoidable impacts. Caltrans manages and is adding to 20 Botanical Manage- ment Areas (BMAs) throughout the state, which harbor âsig- nificant native vegetation remnants that are self-sustaining, botanically diverse, and provide aesthetic enhancements to the roadside environment.â The areas help the agency satisfy STURAA requirements. Since 2003, Caltrans districts have been asked to âidentify and program native landscape restoration projects with a goal to develop sustainable rural landscapesâ programs as âhighway planting restorationâ in the state operations budget (111). An ecologically based program of roadside vegetation design and management seeks to produce low-maintenance, self-sustaining plant communities. WSDOT defines sustain- able roadsides as those roadsides that are designed and main- tained with the intent of integrating successful operational, environmental, and visual functions with low life-cycle costs (112). The use of native plants planted in the right location is integral to achieving such a sustainable system. This requires good stewardship practice in design. â¢ Include a landscape architect in the design development process to improve the design, environmental, and visual quality of the roadsides, and chances of planting success. â¢ Consider construction requirements such as site accessi- bility and constraints such as contract timing in design documents. â¢ Ensure that invasive species are addressed and not incorporated in plantings. Check with the stateâs nox- ious weed control board for a list of invasive species in the state, if not available through the DOT. â¢ Review and comment on plans during development of specifications and engineering. Maintenance review (such as by the maintenance supervisor in charge of the contract area) is essential, because DOT maintenance crews often maintain landscape projects after installation. â¢ Have project partners review design documents and plant material selection before installation. Some projects have special partnership arrangements; for example, the DOT might require the project sponsor or partner to maintain plant communities. Project sponsors have included cities, counties, tribes, transit agencies, and other agencies, that can often contribute labor, funding, and materials. Seed Mixes Are Designed for Native Restoration More than one-third of state DOTs have seed mixes designed for all or most projects; 8 states (20%) design seed mixes for every project, and another 10 (25% of respondents) do so for most. Thirty-eight percent of responding DOTs have developed
61 seed mixes for each ecoregion. Thirty percent of respondents modify seed mixes for project microclimates. It is more common for custom mixes to be developed on capital projects; maintenance forces more often draw on standard seed mixes. Mn/DOT, PennDOT, and other DOTs have designed and specified special seed mixes for areas out- side of the standard highway construction slopes, including wetlands, wildlife habitat, and streambank mitigation. â¢ Design for project sites, ecoregions, and distance from roadwayâThirty-three percent of responding DOTs reported that seed mixes are not designed for each proj- ect. Another 5% noted that they do not yet have such mixes, but are developing them. Missouri uses three main seed mixes statewide, not divided by ecoregion but by distance from the road; one mix for the first 30 ft, another mix for the next 30 ft in urban settings, and another for beyond 30 ft in rural settings. â¢ Variable amounts of native grass and forbs per mixâ The amount of native grass and forb species per mix varies in some cases by state and landscape architect. Native seed portion of the mix ranges from 60% in Maryland to up to 100% in Rhode Island and Wiscon- sin. Of the states responding to this question, most were in the 85% to 90% range. For Caltrans, the pro- portion depends on the landscape architect designing the mix. 0 5 10 15 20 25 30 35 40 45 Pe rc e n ta ge o f r es po nd en ts Special contract provisions included for particular projects Required seed mixes designed for variety of ecoregions , slope aspects DOT policies or agency-wide design specs require use of native species Landscape Architect comm ents on landscape plans during reviews (Re-)Vegetation perform ed according to statewide or regional plan FIGURE 5 Survey results of DOT revegetation practices.
â¢ Available expertiseâSeed mix customization requires a certain amount of ecological or botanical expertise. Forty-three percent of responding DOTs believe that they have adequate expertise available in their agency to cover the demand. Forty percent of responding DOTs indicated they could use more help in this area. Some DOTs said they had available expertise on staff, but that staff needed more time. Availability of Native Seed Sources Native seed sources are available in most states, although only 33% of responding DOTs stated that they have several sources available and an adequate supply. In five states, no native seed sources are available locally. Sources are insuffi- cient to meet demand in 13 other states (33% of respondents) (see Figure 6). Just over one-third of state DOTs are facing supply prob- lems in acquiring native seed. To address such needs, LADOTD developed a federal-aid project ($1.7 million over 5 years) to develop a wildflower seed bank pilot program using native species grown in state. LADOTD is also work- ing with three universities across the state to ensure that native species are developed for use on ROWs. Seed collection programs or seed banks are in place in six states (15% of respondents). Nine states (23% of those respond- ing) require certification for native seed sources. Four states specify certified native seed sources only (Arizona, Nebraska, New Mexico, and Texas). The Arizona DOT requires seed tests as well. Other DOTs, such as Iowa, give weighted preference to certified or source-identified seed or are just beginning to track where seed comes from. Virginia DOT indicated an inter- est in increased focus on germination rates for native seeds and/or ensuring noncontamination with invasive species, because germination rates for native species have presented a problem. Some DOTs are interested in harvesting more seed from native species on the ROW; however, at least one DOT indicated an interest in not being mandated to use wild- harvested seed because it could hamper revegetation efforts. Primary Obstacles in Greater Use of Native Species Primary obstacles indicated by DOTs in employing greater use of native species are length of time to establish and cost of desired materials and/or available agency funding. In each case, 17 states (43% of respondents) cited these as key obstacles. In addition to cost and establishment, multiple states found the fol- lowing to be primary obstacles (see also Figure 7): â¢ Availability of plant material or desired seed mixesâ 16 states (40% of respondents). â¢ Limited research regarding what worksâ15 states (38% of respondents). 62 â¢ Publicâs desire for ornamentals or other non-natives considered more aesthetically pleasingâ15 states (38% of respondents). â¢ Acceptance/education internally or among contrac- torsâ12 states (30% of respondents). â¢ Contracting process and lack of control over contrac- torsâ schedulesâ8 states (20% of respondents). â¢ Other agency requirementsâ15% of respondents. For example, WYDOT believed that federal resource agen- cies have recently held back native revegetation efforts in some areas by requiring untested, wild harvested plant materials to be used on federal lands. â¢ No answerâ15% of respondents. DOT vegetation management personnel also identified the following as problematic: â¢ Intense invasive seedbanks in some cases adjacent to the ROW. â¢ Contract language for establishment of native grass within contract because the work required is dynamic and changing with the seasons; that is, âadaptive management.â â¢ Weed control during establishment period requires a greater investment than field maintenance resources can provide. â¢ Adjacent land owners mow, hay, and spray plantings. â¢ Outdated temporary seed mixes. â¢ Commitment from the department. â¢ Roadside turf mixes generally end up looking the same after years because it is difficult to maintain a prairie strip without prescribed burns. 0 5 10 15 20 25 30 35 Pe rc e n ta ge o f R es po nd en ts Se ve ra l s ou rc es a va ila bl e, a de qu at e su pp ly So ur ce s in su ffi cie nt to m ee t de m an d Ce rti fic at io n re qu ire d fo r n a tiv e se e ds /s ou rc es Se ed c ol le ct io n pr og ra m /b an k in p la ce N on e av a ila bl e lo ca lly /in -s ta te N on e av a ila bl e/ kn ow n FIGURE 6 Native seed source availability.
63 â¢ Availability is sometimes controlled by contractors and vendors who bring in seed from too far away. â¢ Resource agency requirements in some cases for very localized seed collection. â¢ Confidence in ability to successfully establish erosion- resistant stands of native (warm season) grasses. â¢ Limited research for our climate and applications, seed availability, short planting seasons, and the plantsâ perennial nature (two seasons to establish). As indicated by Caltrans, non-native ornamentals con- tinue to be used in many landscaping projects, although native species increasingly dominate in nonlandscaped or rural revegetation projects. Thirty-eight percent of respond- ing DOTs reported that they do not rely on native grasses and forbs in erosion control, landscaping, and revegetation. For example, PennDOT noted that ânative plants are not always the best plant for the roadside environment.â How- ever, many of those DOTs that do not necessarily rely on the use of native species report that their use is increasing, new internal resources are being developed, and native seed sources are being located. Several states indicated that Clean Water Act Nonpoint Discharge Elimination System requirements and the need to achieve prompt ground cover and stabilization after construction worked against the use of native species. However, a number of those states are using mixtures of quick germinating species to avoid erosion and native species for longer-term revegetation. Missouri and Kansas DOTs described the use of seed mixes, including warm and cool season grasses, outside of the clear zone in rural areas of the state. All of the warm season grasses are native species. Mn/DOT reported that âalthough the pendulum shifted to nearly all natives in seed mixes during the late 90s, we have shifted to mixes that provide quick and reasonably sustainable cover; with the development of compatible and economical mixes of native cool season with warm-season grasses our goal is to increase our use of natives.â Communication difficulties emerge from time to time as well, especially in the absence of systems to prevent mishaps. Several DOTs mentioned areas revegetated in native grasses or wildflowers being inadvertently mowed. Resources to Assist Designers The following resources may assist designers. â¢ The Natural Areas Association, an international non- profit organization with a mission to preserve natural diversity, provides information on appropriate manage- ment of natural areas. â¢ Nature Serve Explorer is an online encyclopedia for 50,000 plants and ecological communities in the United States and Canada. With the common or scientific name of a plant, it is easy to locate the life history, distribu- tion map, and more. â¢ Center for Plant Conservation website offers a state-by- state directory of conservation contacts. â¢ Northern American Plant Society provides an easy way to contact state and provincial native plants plant societies. â¢ The Native Plant Initiative, an interagency coalition, has worked to share information and resources to improve public awareness, educate their own forces, increase planting success, and more. Their Plant Con- servation Alliance can be found online. 0 5 10 15 20 25 30 35 40 45 Pe rc e n ta ge o f re sp on de nt s Co st o f m at er ia l Le ng th o f t im e to e st ab lis h Av a ila bi lity o f m at er ia l Pu bl ic âs de sir e fo r o rn a m e n ta ls Li m ite d re se ar ch Ac ce pt an ce / e du ca tio n Co nt ra ct in g pr oc es s O th er a ge nc y re qu ire m en ts FIGURE 7 Obstacles to native seed use.
â¢ USDA Natural Resources Conservation Service pro- vides a national plants database. â¢ FWS provides a national list of plant species that occur in wetlands. DOTs have developed a variety of formal and informal resources and tools to assist designers as well. For example, Caltrans recognized that the successful establishment of ben- eficial and native species is dependent on a process of detailed site evaluation, selection of appropriate species, ade- quate site preparation, and choosing the proper planting tech- nique. To support the successful establishment of beneficial species, Caltrans developed a matrix that identifies and cate- gorizes more than 20 botanical, horticultural, and environ- mental factors that should be considered for determining the appropriateness and suitability of a given species for a spe- cific ROW segment. Research Needed Regarding âWhat Worksâ A number of DOTs requested more information on success- ful practices. DOTs noted the following needs: â¢ Warm season grasses that will quickly establish and provide a sufficient ground cover. â¢ Treatment of topsoil. â¢ For native seeding areas where burning is not feasible. â¢ Seed mix design with nonburn-dependent species. â¢ Best practices for timing and frequency of mowing and haying of traditional native mixes. â¢ Seed establishment of Cyperaceae species. â¢ Native seeding in sites with low precipitation, heavy infestation by non-natives, or steep slopes. â¢ Specific research for climate and applications, such as the northeastern United States or eastern Washington State. â¢ Guidance on controlling less desirable vegetation in areas earmarked for native grasses. â¢ Complete survey of what native grasses exist within the state and where they occur. â¢ List of species that survive in high salt and pollution areas. â¢ Information on the establishment, performance, and maintenance characteristics of native vs. non-native grass seed mixes. Iowa Department of Transportation Revegetation Program Controls Invasive Species Although many state DOTs have begun to mandate the use of native species when revegetating construction sites, Iowa DOT has extended their landmark IRVM pro- gram to annually revegetate approximately 2,200 acres of targeted roadside areas not connected to any con- struction projects. Another 3,200 acres of roadside on 64 construction sites are seeded annually with native grasses and forbs. Iowa DOT and many Iowa counties have shifted from tra- ditional roadside maintenance of a monoculture of exotic grass in favor of management regimes that restore native vegetation and reduce the use of herbicides and mowing. Iowa DOT has identified maintaining a healthy stand of native grasses as the best way to control invasives. These grasses have extensive roots that offer the toughest competi- tion to Canada thistle. In addition, plant diversity along the roadsides creates a strong plant community. Prairie plants can adapt to a wide range of soil types, moisture levels, and climactic conditions. Most prairie grasses and wildflowers grow best during hot, dry summer months, providing excel- lent erosion control during the fall and spring. Iowa DOT recently extended their landmark IRVM pro- gram to revegetate approximately 5,200 acres of roadside annually with native grasses and forbs. Forty percent of that acreage is restoration unrelated to construction (113). The program is documenting species diversity and wildlife benefits as well. Twelve roadside areas were surveyed for abundance and species richness of disturbance-tolerant and habitat-sensitive butterflies and compared with nearby roadside dominated by primarily non-native legumes and/or grasses. Species richness of habitat-sensitive but- terflies showed a two-fold increase on restored roadsides compared with grassy and weedy roadsides. Abundance increased five-fold for native grass and forb habitat over non-native. Tracking studies found that butterflies were less likely to exit the restored roadsides, indicating that mortality rates may be lower and offering preliminary evidence that roadsides have the potential to be used as corridors (114). SUMMARY OF DEPARTMENT OF TRANSPORTATION SURVEY RESULTSâPOPULAR AND INNOVATIVE CONTROL STRATEGIES The survey conducted for this synthesis heard from 40 state DOTs. Results are summarized here. â¢ Weed-free mulches are specified on all projects (17 DOTs, 43%)âCA, CO, IA, KS, MA, MN, MS, MT, NV, NH, NC, OR, RI, UT, VT, VA, WA. â¢ Specifications are in place on project plans and bid con- tracts that seed and sod sources must be free of inva- sives and weeds (21 DOTs, 53%)âAK, CA, CO, CT, IL, MA, MN, MT, NV, NH, NC, OH, OR, PA, RI, SD, UT, VT, VA, WA, WI. â¢ Inert mulch products such as straw or wood fiber are used in sensitive areas (11 DOTs, 28%)âCA, MA, MN, NV, NH, NC, NY, OR, RI, VA, WA.
65 â¢ Desirable and uncontaminated topsoil is stockpiled to facilitate revegetation (12 DOTs, 30%)âCA, MA, MN, MT, NV, NH, NC, OR, RI, VT, VA, WA. â¢ All disturbed areas are restored through application of grass seed and mulch within 2 weeks of disturbance (14 DOTs, 35%)âCT, IL, IA, MA, MN, MT, NH, NC, NY, OR, RI, VT, VA, WI. â¢ Biological controls (e.g., insects) are used (13 DOTs, 33%)âCA, MA, MN, MT, NH, NC, NY, OR, RI, UT, VT, WA, WI. â¢ Mowing is timed to control invasive species; that is, before seed maturity (12 DOTs, 30%)âIL, MA, MN, MT, NC, NY, OH, OR, PA, RI, WA, WY. â¢ All construction sites are reviewed (9 DOTs, 23%)â CA, CT, NV, NH, NC, RI, UT, VA WY. â¢ Handpicking of invasive species is employed in some areas (10 DOTs, 25%)âAK, CA, CT, FL, IA, MN, NV, NY, UT, WA. â¢ Mowing occurs in an order to minimize seed transfer (10 DOTs, 25%)âCT, IL, IA, MN, MS, NH, NC, NY, OH, RI. â¢ Native seed mixes use native grass and forb species (9 DOTs, 23%)âCA, KS, MA, MN, NH, OR, RI, UT, WI. â¢ Cultural control methods used (9 DOTs, 23%)âCA, IL, IA, MN, NH, NY, OR, WA, WI. â¢ Dirt and gravel sources are evaluated (9 DOTs, 23%)â MT, NV, NH, NC, NY, OR, RI, VA, WY. â¢ Vehicles are washed before and after use (9 DOTs, 23%)âCO, IL, KS, MT, NV, NY, NC, OR, UT. â¢ Native seed sources are specified and only regional eco- types are used (7 DOTs, 18%)âCA, KS, NV, NH, OR, RI, WI. â¢ All ROWs are reviewed and treated annually for inva- sives (6 DOTs, 15%)âMT, NC, SD, VA, WA, WY. â¢ Contract grown native plants have been used when eco- nomically justified (7 DOTs, 18%)âCA, MN, MT, NC, NY, RI, UT. â¢ Policies are in place and enforced to minimize disturbed and opened areas; that is, construction phasing (7 DOTs, 18%)âCA, IA, NH, NC, NY, RI, UT. â¢ Restoration (7 DOTs, 18%)âCA, IA, MN, NH, NY, OR, WA. â¢ Badly infested material is excavated and buried (6 DOTs, 15%)âCT, MA, MS, NH, NY, UT. â¢ Construction sites are pretreated before disturbance (6 DOTs, 15%)âIL, MN, NY, OR, UT, WA. â¢ For all projects and activities, consider impacts for pri- ority invasive plant and animal species (6 DOTs, 15%)âIL, NV, NH, NC, NY, OR. â¢ Controlled burning (4 DOTs, 10%)âCA, IL, MN, WA. â¢ Contractors are prequalified based on experience and quality of work (2 DOTs, 5%)âNH, NC. â¢ Grazing (1 DOT, 3%)âCA. â¢ Roadway shoulders are treated before scraping (1 DOT, 3%)âNV. DOTs also noted innovative models of methods, equip- ment, and bids they were using for specific species and more generally. â¢ A combination of prescribed fire and chemical control has proven most effective for camelthorn (Alhagi maurorum), and also for starthistle species (Arizona). â¢ Spray fescue in the fall with two additional applica- tions in the spring before planting native species (Indiana). â¢ Beetles for biocontrol on graveyard spurge (Euphorbia cyparissias) shows this nontoxic strategy to be effective (Minnesota). â¢ Stem injection for multiple species of knotweeds (Washington State). NYSDOT also noted syringe injec- tion of herbicides for invasive species control. More general recommendations, observations, and resources recommended by the state DOTs included: â¢ Use of a Brown Brush monitor (Minnesota and Wash- ington State). â¢ Soil resource evaluation researchâa final report to be posted on the Caltrans Landscape Architecture home page (California). â¢ Basal application crews included in the herbicide spray contracts (Pennsylvania). â¢ Using Thinvert spray carrier in place of water to increase the acres treated by a single tank (Pennsylvania). â¢ All 325 herbicide trucks are built in-house and much of the smaller specialized equipment is also built in-house on an as-needed basis (Texas). â¢ Properly timed use of slow release liquid fertilizer (Washington State). â¢ LADOTD has found that over-application of soil ster- ilants to eliminate problem species has opened up areas for other weeds to establish themselves, creating unattractive areas that require reseeding as soon as possible to help minimize treatment spots. â¢ WisDOT has been letting prairie remnant contracts using specifications in the manner typical of normal highway construction projects, and has found that a more flexible system would be more desirable. WisDOT is exploring the use of a Request for Proposal process that would describe expected outcomes and let the bidder describe how to accomplish them. When asked if their invasive species control strategies were limited by authority and/or funding, 10 DOTs (25% of respondents) said they were not limited by a lack of authority. Seventeen DOTs (43% of respondents) said that they were limited by a lack of authority. A larger num- ber of DOTs believed that their invasive species control strategies were hampered by inadequate funding. Only three DOTs indicated they did not feel that way (8% of respondents).
DEPARTMENT OF TRANSPORTATION ON-LINE ROADSIDE MAINTENANCE GUIDANCE, MANUALS, AND PROCEDURES State DOTs have created the following guidance, procedures, tools, and manuals that may be used by other DOTs: â¢ Caltrans guidance for E.O. 13112. â¢ Caltrans Roadside Management Toolbox and Informa- tion on development of the Roadside Toolbox of spec- ifications, tools, and guidance. â¢ Caltrans Highway Planting and Irrigation. â¢ Caltrans Maintenance Manual; Caltrans Highway Design Manual; and Caltrans Stormwater Quality Handbook, Project Planning, and Design Guide. â¢ FDOT Procedure #850-000-015-f, Roadway and Road- side Maintenance. â¢ Iowa DOT roadside management guide containing col- lections of plant profiles, characteristics, requirements, and how these species are used in roadside management. â¢ Mn/DOT seeding manual. â¢ Mn/DOT herbicide policy and the attached partial list of pests and possible control measures along with precautions. 66 â¢ Minnesota Best Practices Handbook on Roadside Vegetation. â¢ Mn/DOT Integrated Roadside Vegetation Management. â¢ MDT Statewide Integrated Weed Management Plan, 2003â2008. â¢ Nebraska Department of Roads Mowing Guidelines. â¢ Nebraska Department of Roads Roadside Chemical Usage Guidelines. â¢ NYSDOT Environmental Procedures Manual, Chapter 4.8, Invasive Species, 9/10/04. â¢ NCDOT Vegetation Management Maintenance Program. â¢ Oregon 2005 Noxious Weed Policy and Classification System. â¢ PennDOT Design Manual 2, Section 8.1 Planting Design. â¢ Pennsylvania Code Chapter 110: Noxious Weed Con- trol Law. â¢ WSDOT Roadside Classification Plan. â¢ WSDOT State Roadside Manual. â¢ Washington State IVM for Roadsides. â¢ WisDOT Best Practices for Control of Certain Invasive Plant Species. â¢ WYDOT Policy and Procedure Directive for Noxious Weeds and Construction Projects, P&PDIR98-02. â¢ Wyoming Weed Management Plan.