Agricultural Development and Environmental Research: American and Czechoslovak Perspectives: Proceedings of a Bilateral Workshop (1987)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Recent Developments in Integrated Pest Management FRANK G. ZALOM University of California, Davis PESTICIDES AND THE ENVIBONMENT Agricultural crops in the United States are the target of several thousand pests including insects, plant pathogens, weeds, nema- todes, and vertebrates. Prior to the Second World War, relatively few chemicals were used for pest control and most were classified as either botanical or inorganic, depending on their origins. Production of pesticides in 1945 was less than 90 million kilograms. The develop- ment of synthetic chemicals during the war such as DDT, parathion, rnalathion, and 2,4-D resulted in a large increase in the production and use of pesticides. During the next 40 years, pest management became increasingly dependent upon chemicals, and pesticide pro- duction in the United States increased by a factor of ten. Despite this rise in pesticide use, it is estimated that approximately one-third of U.S. agricultural production is lost prior to harvest by the action of pests. Pesticide use worldwide has brought about many unforeseen environmental problems which affect not only the agricultural com- munity but the general population as well. Problems affecting agri- culture include pesticide resistance and secondary pest outbreaks. More than 350 species of insects, mites, and plant pathogens have developed genetic strains which can survive the application of one or more classes of pesticides. To control these resistant pests, higher rates of pesticides and more frequent applications are often used. At the extreme, when control of the pest by any method is no longer 137

138 possible, production of the crop in an affected area may cease. Be- cause pesticides kill beneficial organisms in addition to target pests, organisms that were under natural control may increase to damaging levels, requiring further pesticide intervention. Such a situation is referred to as a secondary pest outbreak. Pesticides have come to be regarded as a threat to the environ- ment and to human health by many individuals and organizations. There is reason for such concern. Some pesticides are highly persis- tent and can be found in the environment years after their use has ceased. Others can move readily through soil or water to become translocated beyond their original site of application. DDT is an example of a highly persistent pesticide which enjoyed wide agricultural use. DDT entered the food chain at microorgan- ism levels, becoming concentrated in the fatty tissue of organisms at higher trophic levels. In response to research relating DDT to abnor- mally thin-shelled eggs in birds and to cancer in laboratory animals, the U.S. Environmental Protection Agency (EPA) banned its use in 1972. However, DDT residues can still be found in the environment. Dibromochloropropane (DBCP) was a pesticide widely used to control nematodes. In 1977, DBCP was found to cause sterility in male workers exposed to the pesticide during its production. Subse- quently, DBCP was found in wells in some agricultural areas where it had been used. Apparently, DBCP could move through the soil to enter underground water supplies. Again, EPA moved to halt the use of this pesticide. About 40,000 people are treated for pesticide poisoning each year in the United States. The actual number is not known because most cases do not involve acute toxicity, and symptoms mimic those of common maladies. Most acute poisonings occur because of worker exposure in either the production or the application of pesticides. In response, there has been increased regulation to ensure the safe use of pesticides. INTEGRATED PEST MANAGEMENT Recognition of the problems associated with the use of pesticides has brought about the development of a systematic approach to con- trolling pests in the agro-ecosystem. Integrated Pest Management (IPM) is an interdisciplinary approach using multiple methods to maintain pest populations at tolerable levels. Developing an inte- grated pest management system requires an understanding of crop

139 and pest development and their interactions. It also requires knowl- edge of available control tactics. Both crop and pest development are directly impacted by environmental, cultural, and biotic factors. The responses to such factors are not well understood. Research on plant growth is an essential prerequisite to develop- ment of an IPM system. Plants respond to temperature and light by producing products of the photosynthetic reaction. These products are used by the plant to produce more leaf area, more structures on which to hold the leaf area, more root mass, and ultimately re- productive structures. Well-watered and properly fertilized plants complete this process more efficiently. Plants store excess photosyn- thetic product for periods when production does not exceed demand. In the case of perennial plants this excess product is used for renewal of leaf area during the subsequent season. Man cultivates plants either for their biomass or for their repro- ductive structures, depending on the crop. Pests compete with man for the plant structures and can injure plants by removing their pho- tosynthetic area, damaging their structure, reducing their nutrient and water uptake mechanisms, or interfering with their reproduction. The importance of plant injury resulting from a given pest is depen- dent upon the plant structure damaged, the extent of the damage, the relationship of the plant structure to growth and development at the time of damage, and the intended use, if any, by man of the plant structure. Pest population abundance is influenced by weather, available resources for growth and development, natural enemies, and the intervention of man. The abundance of a pest and the extent of the injury it causes at critical periods of a plant's development are key factors in determining when and if control actions should be taken. PEST CONTROL ADVISORS • Application of IPM principles requires specialized training. Al- though growers in the United States are fully capable of learning and then applying these principles and tactics, many growers, especially in California, are relying increasingly upon guidance from profes- sional pest control advisors in making pest control decisions. Pest control advisors must understand how pests, their natural enemies, and the crop interact with each other and also respond to changes in weather and management practices. They establish systematic field monitoring programs and take appropriate pest management actions

140 which are based upon pest and natural enemy population abundance, crop maturity and health, and established control action thresholds. In California, pest control advisors must pass an examination to be licensed by the state and must take continuing education classes to renew their licenses. Several studies have shown that pest control advisors utilizing IPM principles can reduce the level of crop damage, reduce the amount of pesticides used, and increase the net economic return to growers. QUANTIFYING PEST POPULATIONS Thresholds The application of appropriate tactics to control pests requires that the impact of the pests be determined. An assumption of IPM is that some level of pest infestation can be tolerated and that the crop system can be managed to keep the pest population from exceeding an injury level with unacceptable economic consequences. The approach varies with: • the relationship between the pest infestation and crop yield or quality; • the cost of the pest control tactic; • the amount of physical damage that can be prevented by the control measure; • the monetary value of the portion of the crop saved by the control measure; • the cost associated with failure to control the reproduction of the pest and the future consequences resulting from the residual population. Some pests in park and recreation areas and in urban environ- ments where they can affect public health are managed solely for economic reasons. In these situation, threshold levels vary directly with concerns over public health and welfare. Pest Monitoring Pest populations vary seasonally, geographically, spatially in a field, and spatially on a host because of various biotic and abiotic factors. It is usually not possible to sample all the pests in a given

141 situation. Therefore, the abundance of a pest must be estimated by representative sampling. Applying principles of sampling to the monitoring of pest populations in the field requires: • knowledge of the organism's distribution; • a defined sampling unit; • a practical and repeatable sampling method; • an optimal sample size at a given confidence level with acceptable levels of error; • a defined pattern of sampling. A considerable amount of research has been conducted recently to improve the reliability and reduce the time of pest sampling. This research involves absolute sampling to provide estimates of the to- tal population of an area, which can be accomplished by counting numbers of organisms directly on the sampling unit or by removing all organisms from a definable sampling area for counting. Devices that can be used to remove organisms include suction traps and rotary nets for aerial samples; beating devices, suction traps, emer- gence traps, brushing, and washing machines for foliar samples; and core samplers and emergence traps for soil samples. Relative sam- pling also provides estimates of population density that cannot be related to total density of organisms in a specific area, but rather only to other such samples. These relative population estimates can be useful in detecting the occurrence of an organism and its rela- tive abundance seasonally. Examples of such devices include sweep nets, sticky traps, water-pan traps, pitfall traps, light traps, and pheromone traps. Relative sampling methods are especially useful when they can be calibrated to an absolute method, or when they are used with phenological models of pest development. Sample size is dependent upon the variance between samples in relation to the mean value of the organisms that are counted. It is also dependent upon the confidence level and degree of precision desired. If more precision is required, more samples must be taken. This has a direct impact upon the time and expense of the monitoring program. Methods used to reduce monitoring time while maintaining a given level of reliability include binomial (presence/absence) sampling—as opposed to numerical sampling—and sequential sampling.

142 Meteorology Weather controls many of the growth and developmental re- sponses of pests and crops. Knowledge of temperature and precipi- tation can be used in some cases to accurately predict their develop- ment. In general, growth rate is dependent upon temperature. More accumulation of heat results in faster development within specific thermal thresholds. Physiological time expressed as degree-days is a measure of accumulated heat. Several phenological models which are based on physiological time are being widely used in the management of pests and crops. Some of these models are very simple, providing information on the timing of such events as emergence after wintering and subsequent population dynamics. Others provide information on growth and maturation. Examples of insects often managed using phenology models include the oriental fruit moth (Grapholitha molesta), the codling moth (Laspeyresia pomonella), and the tomato fruitworm (Heliothis zea). Examples of crops managed with such models include tomatoes for processing and cotton. Disease prediction typically requires information on periods of wetness and innoculum density in addition to temperature. Ex- amples of diseases for which predictive models are available and commonly used include apple scab (Venturia inaequalis), late blight (Phytophthora infestans), and early blight (Alternania solani). Technological advances in electronics have made the acquisition and use of weather data more efficient. Automatic weather stations and data loggers with probes that sense various meteorological pa- rameters are available and are being used by public agencies and by some medium to large farms to gather and store weather information for use in making management decisions. In addition, at least three private companies have combined automated meteorological data ac- quisition with computer programs for specific applications and are marketing these microprocessor-based products as pest management tools for farmers and pest control advisors. MANAGEMENT TACTICS Tactics available for managing pests are generally divided into those that involve pesticides and those that do not.

143 Pesticides Pesticide uses in IPM are generally based upon information gen- erated by some form of monitoring. As IPM programs have become more widely adopted, there has been a trend away from using resid- ual, broad spectrum materials toward those that are intrinsically selective. An exception in the United States has been a trend toward increased use of residual, broad spectrum herbicides. Certain con- ventional pesticides are being used with specificity to some degree. Low dosages of the pesticide are applied in a manner which does not interfere with the activities of the natural enemies of the pests. Current research on insecticide development is focused on chem- icals to regulate insect growth such as juvenile and molting hormone mimics, on microbial insecticides, and on pheromones. Successful microbial insecticides, such as Bacillus thuringiensis and the codling moth granulosis virus, and pheromones used as mating disruptants must undergo a registration process similar to that for pesticides. Their specificity and the registration process have been factors in limiting the number of these materials commercially available. Biological Controls There are a number of approaches in using biological control agents. Conservation and enhancement utilize natural enemies that are already present in the crop system. Conservation is the avoidance of measures that destroy biological control agents, while enhancement is the use of measures that increase the longevity or abundance of natural enemies. Classical biological control—the importation and colonization of biological control agents—is used to combat pests which have become stablished in a new area in the absence of the agents. Augmentation—the propagation of large numbers of bio- logical control agents for release against specific pests at strategic times—is a third approach. Cultural Controls Cultural controls are modifications of the physical environment that reduce the survival or reproductive capacity of pests or their ability to attack crop plants. Common procedures include adjust- ment of tillage methods, restricted planting and harvest dates, and irrigation. Other approaches include the use of trap crops, cover

144 crops, and mulches; crop rotations; crop residue destruction; removal of alternate hosts; and pest-free seed or transplanting stock. Host Plant Resistance Development of varieties which possess genetic defenses that reduce the susceptibility of plants to pests has led to one of the most widely used and most successful of all pest control tactics. Resistance can be ecological, physiological, or physical. Ecological resistance results from asynchronies between host plant and pest development. Tolerance—the ability of a plant to sustain relatively high levels of pest infestation without suffering damage or yield loss—and antibiosis—the suppression of a pest by reducing its vigor or developmental rate—are forms of physiological resistance. Non- preference occurs when a pest is either repelled or not attracted to a host plant. Genetic Controls The sterile male technique is the most successfully applied ge- netic control for insects. Researchers continue their attempt to use genetically-altered races of pests for autocidal control. SYSTEMS APPLICATIONS It is not possible to fully understand the complexity of inter- actions both within and between the crop, the pest complex, the natural enemy complex, and the environment. Thus, one area of integrated pest management research that has become increasingly important is the development of systems which attempt to define the development and interactions of various parts of the agro-ecosystem in mathematical terms. Phonological models discussed earlier are ex- amples of simple attempts to explain the physiological development of certain organisms in terms of a single factor: their exposure to the environment. Despite their simplicity, such models are being widely used for timing control actions and monitoring activities of pests for which they have been developed. Physiological models and multitrophic level models are more complex than phenological models and are intended to predict pop- ulation abundance, and often crop loss, in addition to timing. Such models have proven useful to researchers in clarifying the interactive processes within the agro-ecosystem. They have also been used to

145 develop economic threshold levels for various pests under a variety of conditions which would be difficult to duplicate in field research, and they can be helpful in identifying relevant areas of future research. Management models can assist in determining optimal man- agement strategies in field conditions specified through monitoring activities. Such models can be complex or simple depending upon the level of complexity required to project the event with a given level of accuracy. Expert systems represent a new area of research which holds promise for future management applications. IPM RESEARCH PROGRAMS IN THE UNITED STATES IPM research activities are conducted at the national, state, and local levels. On the national level, the U.S. Department of Agri- culture (USDA), EPA, and the National Science Foundation (NSF) provide major funding for IPM research. These agencies combined to fund the Huffaker Project (1972-1979) and later the Consortium for Integrated Pest Management (1979-1984) which focused on manage- ment systems for several major crops. The Agricultural Experiment Stations and the Cooperative Extension Services of the Land Grant colleges and universities continue to fund IPM research on a number of crops and environmental resources. The University of California received funding from the Califor- nia State Legislature in 1979 for a special project to develop and implement Integrated Pest Management systems on selected Cali- fornia commodities. This program has become a model for other interdisciplinary research programs. In addition to funding research, the University of California Statewide Integrated Pest Management Project employs a group of technical writers who have produced a series of IPM manuals. In addition, six Cooperative Extension IPM advisors have regional assignments. Finally, a computer staff developed and now maintains an IMPACT computer system which consists of large data bases of weather information and pest man- agement guidelines as well as useful programs for management and research. REFERENCES Croft, B.A., and S.C. Hoyt. 1983. Integrated management of insect pests of pome and stone fruits. New York: Wiley-Interscience. Flint, M.L., and R. van den Bosch. 1981. Introduction to integrated pest management. New York: Plenum Publishing.

146 Grape pest management. 1982. Univ. Calif. Div. Agri. Sci. Publ. 4105. Hall, D.C. 1977. The profitability of IPM: Case study for cotton and citrus in the San Joaquin Valley. Bull. Entomol. Soc. Amer. 23(4):267-74. Integrated pest management for alfalfa hay. 1981. Univ. Calif. Div. Agric. Sci. Publ. 4104. Integrated pest management for tomatoes. 1985. Univ. Calif. Div. Agric. Sci. Publ. 3274. McCarl, B.A. 1981. Economics of IPM: An interpretive review of the literature. Oregon State Univ. Spec. Kept. 636. Stern, V.M., R.F. Smith, R. van den Bosch, and K.S. Hagen. 1959. The integrated control concept. Hilgardia 29:81-97. Zalom, F.G., P.B. Goodell, L.T. Wilson, W.W. Barnett, and W.J. Bentley. 1983. Degree-days: The calculation and use of heat units in pest management. Univ. Calif. Div. Agric. Sci. Publ. 21373.