Feasibility of Using Mycoherbicides for Controlling Illicit Drug Crops (2011) / Chapter Skim
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2 Biological Control of Undesirable Plants
2 Biological Control of Undesirable Plants
Pages 27-46
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From page 27... ...
Attention also is given to a conceptual framework for considering risks to animals and humans posed by biological control agents. Information on specific mycoherbicides against illicit drug crops is provided in Chapters 4 and 5.
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Bioherbicide (Inundative) Target plants Exotic, aggressive, widespread, Native or naturalized, generally generally perennials annuals Biological Exotic arthropods and pathogens Locally occurring pathogens control agents (a few insects)
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is mass-produced, formulated, made into a standardized product, and applied in a large dose to inundate the target plant in a manner similar to the application of chemical herbicides. For this approach to be successful in controlling an undesirable plant species in commercial crops, a high level of control of the target plant is required within a short period to reduce economic losses (Charudattan 1990; Weston 1999)
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. The use of those pathogens was regarded as an option for eradicating illicit-drug crops because of their purported ability to cause serious damage to the crops, their specificity and narrow host range (they would have minimal nontarget effects)
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; Morris et al. 1999 acutatum registration was allowed to lapse in 1991 because of budget cuts by the main user and the limited market for the product Currently, the Agricultural Research Personal communication, Andries Fourie, Council Plant Protection Research ARC-PPRI, Stellenbosch, South Africa Institute (South Africa)
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; Personal communication, Karen Bailey, gloeosporioides (Malva pusilla) in field crops registration is currently inactive Agriculture and Agri-Food Canada, f.sp.
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BioSedge First rust fungus to be registered as a Phatak et al. 1983 canaliculata (Cyperus esculentus)
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. However, it does not persist as spores in soil or rice irrigation water in the absence of the host plant for more than several months, so annual applications of Collego are necessary to provide acceptable levels of northern jointvetch control.
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Several fungal pathogens evaluated as potential mycoherbicides have been found to require at least 10 hours of moisture (generally from overnight dew formation) to cause disease at magnitudes that sufficiently damage the target plant (Boyette and Walker 1985; Makowski 1993; McRae and Auld 1988; Wymore et al.
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There has been no report of a plant exhibiting resistance to a mycoherbicide over time, as happens with chemical herbicides, but it is known that naturally resistant plant varieties or biotypes exist. For example, three leaf forms of rush skeletonweed (C.
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that are somewhat specific to their target pests. EPA may require an experimental-use permit for field-testing of microbial pest-control agents, including ones that are genetically altered or nonindigenous.
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. Toxicity and pathogenicity to nontarget organisms and environmental fate, which involves four tiers of testing (see Box 2-1)
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It has worked with various organizations in developing standards for testing of pesticides and guidelines for transport and release of biological control agents. At the international level, applicable guidelines and requirements for testing, approval, and application of mycoherbicides against illicit crops fall under the International Plant Protection Convention (IPPC)
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The standard delineates the responsibilities of the NPPOs of the exporting and importing countries to implement and document adherence to the standard. Those responsibilities include carrying out pest risk analysis of biological control agents before import or release; ensuring compliance with phytosanitary import requirements; overseeing appropriate documentation relevant to the export, shipment, import, or release of biocontrol agents; ensuring that biocontrol agents are transported appropriately; and encouraging the monitoring of released agents (Vapner and Manzella 2007)
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RISK TO NONTARGET PLANTS AND ORGANISMS This section reviews some aspects of the scientific literature regarding potential exposure pathways and risks to nontarget plants and organisms (ecological receptors) posed by the introduction of biological control agents and provides a conceptual model to describe the pathways at a specific site (insofar as that is possible given current data constraints)
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reviewed case studies demonstrating the nontarget effects of biological control agents and evaluated them in the context of theoretical work in community ecology. Their analysis suggests that the magnitude of the indirect effects on nontarget organisms is indirectly proportional to the abundance of the biological control agent; this suggests that the more efficacious agents are less likely to cause indirect effects.
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The studies demonstrate the feasibility and the level of effort necessary for analyzing risks associated with the application of a particular mycoherbicide in a specific area and risks to specific, local nontarget organisms. Recent reviews identify and categorize the information necessary for conducting risk assessments of biological control agents.
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It allows one to trace the physical exposure pathways (independent of geography) of toxins, spores, and vegetative bodies from a particular application method through potential physical transport mechanisms to potentially affected environments.
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Wetland, Soil Biological Transformation and loss Latent Competitive Colonization Loss Mutation Degradation FIGURE 2-1 An example of a generalized conceptual model for mycoherbicide exposure that traces the potential physical exposure pathways of toxins, spores, and vegetative bodies from a particular application method to the general classes of ecological and human receptors. Dotted lines and question marks show where there is likely to be a particular lack of information about a pathway.
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From page 46... ...
Unless a decision is made to develop only strains indigenous to the relevant crop-producing areas, a mycoherbicide based on a nonindigenous strain may require more comprehensive testing to assess the risk to nontarget plant species than would a mycoherbicide based on indigenous strains. The higher level of testing would be comparable with the current testing requirement for the release of a classical weed-biocontrol agent.
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