Some agrometeorological aspects of pest and disease
management for the 21st century
Joyce Fox Strand
∗Statewide Integrated Pest Management Project, University of California, Davis,CA 95616-8621, USA
Abstract
In the 21st century increasing societal, environmental, and economic pressures will create a changing context for solving agricultural pest management problems. Interdisciplinary approaches to problem solving will be needed to meet goals such as mitigating environmental degradation associated with the use of farm chemicals, and increasing productivity by reducing insect and disease damage to crops, and reducing competition from weeds. Crop system models will provide useful frameworks in which to examine the interrelationships among plants, the pest complex, and the environment to determine the most appropriate management strategies to meet individual and societal goals. Improved techniques for managing pests, such as transgenic plants resistant to pests and diseases, new biological control agents, innovative cultural controls, biological pesticides, and additional information to improve efficacy of traditional chemicals, will require weather data and forecasts in order to be used, and climate information to determine their suitability for use. Climatic change, including global warming and increased variability, will require improved analyses that can be used to assess risks associated with existing and newly developed pest management strategies and techniques, and to gauge the impact of these techniques on productivity and profitability. Control recommendations will need to be evaluated for suitability in the farming system where they are to be implemented. Training in the basics of agrometeorological relationships and pest management disciplines will have to be supplied to agricultural meteorologists, extension personnel involved in this work, and farmers. Research to successfully develop the new technologies and the weather and climatic information required by the technologies must be approached by interdisciplinary teams that include agricultural meteorologists. © 2000 Elsevier Science B.V. All rights reserved.
Keywords:Agrometeorology; Pests; Diseases; Weeds; Pest management; Biocontrol; Cultural control
1. Introduction
As we enter the 21st century, agrometeorology for pest management must respond to a significantly in-creased demand for food, a need to reduce environ-mental degradation, and a need to assess new risks associated with a changing climate.
Pests, which include insects, mites, and other arthro-pods, diseases, nematodes, weeds, and vertebrates are major constraints to crop productivity by directly
dam-∗Fax:+1-530-752-6004
E-mail address:jfstrand@ucdavis.edu (J.F. Strand)
aging the crop and by causing plant stresses that de-crease yields. Worldwide, pre-harvest and post-harvest losses to insects, weeds, and plant pathogens are esti-mated at 45 percent (Pimentel, 1991); additional losses can be attributed to vertebrate pests. These losses occur even with the use of chemical pesticides and resistant varieties. Neither planting more productive varieties nor putting an increased land area under production can meet the need for food if yield and post-harvest losses due to pests remain at current levels.
While there is demand for higher productivity, there also is increasing pressure to reduce negative impacts of agriculture and its activities, including pest
management. Production practices have had negative impacts on crop ecosystems in regions of the world where highly intensive agricultural systems have been adopted. These impacts have included contamination of groundwater and surface water with nutrients and pesticide residues, and increasing resistance of insects and diseases to current methods of control. In pest management, the move toward environmental respon-sibility involves developing alternatives to chemical pesticides, developing more environmentally benign pesticides, and applying technology to reduce unin-tended effects of pesticides.
Climate change, including global warming and in-creased climatic variability, is likely to affect agricul-tural pest management. The impact these changes may have on the complex of pests that affect crops in spe-cific regions, on the persistence of pest problems, and on the efficacy of options available to manage pests will need to be assessed.
In the absence of pests, crop systems are complex and difficult to describe fully. Taking pests and dis-eases into account, the complexity incrdis-eases dramati-cally and an interdisciplinary approach is required to define the relevant issues and develop all of the signifi-cant components. Plant scientists, entomologists, plant pathologists, weed scientists, meteorologists, and soil and water scientists are needed to provide sound sci-ence for building the system accurately. Social scien-tists complete the team by helping to define the social, cultural, political, and economic factors that must be considered.
Solutions to pest problems must be location, crop, and pest specific. Traditional techniques for manag-ing agricultural pests and diseases have depended on weather and climate information: Choices of crop, variety, and location are influenced by climate and climatic risk, and affect the pest complex likely to be encountered. During the growing season, many tactical pest management decisions are based on an-tecedent weather and forecasts. For example, good water management can reduce damage from insects, mites, or pathogens, and affect weed competitiveness; current and near future weather conditions determine suitability for making pesticide applications to control pests. Meteorological observations, forecasts, and out-looks, coupled with plant and pest observations, can help to predict the development of key pests and can be used to schedule control actions for preventing pest
development or protecting an infested crop. In some cases, farmers can modify the microclimate to affect a plant’s habitability for pests, for example through pruning to reduce humidity within the plant canopy and reduce the likelihood of infection from plant pathogens.
Integrated pest management (IPM) has been a re-sponse to the need for improving pest management and reducing the environmental impacts of chemical pesticides. Integrated pest management (IPM) is an ecosystem-based strategy that focuses on long-term prevention of pests or their damage through a com-bination of techniques such as biological control, use of resistant varieties, habitat manipulation, and modi-fication of cultural practices. Pesticides are used only after monitoring indicates they are needed according to established guidelines, and pest control materials are selected and applied in a manner that minimizes risks to human health, beneficial and nontarget or-ganisms, and the environment. Integrated crop man-agement (ICM) adds to IPM other components of the system, such as soil, fertility, and water management. To manage some aspects of the cropping system, such as long-term choices of location for planting, and between-season sanitation measures, managers rely on climatic descriptions. For in-season pest manage-ment, weather and forecasts are useful tools. Large scale regulatory control programs use both weather and climate information to plan and take preventive or emergency action to solve particularly damaging pest problems.
traditional techniques that can play a key role in pest management.
2. Biological and environmental system descriptions
Thorough descriptions of cropping systems being managed or studied are needed to explain the inter-actions among pests, plants, and environment, and to assess the efficacy of available controls for reduc-ing pest damage. Systems models or other prediction schemes can be used with appropriate biological, en-vironmental, economic, or other inputs to analyze the most effective management actions, based on accept-able control, sustainability, and assessment of eco-nomic or other risks. Even the simplest models must be tested to be ‘proven’, but validation over a wide range of conditions will be most important for models based on empirical rather than biological and physical processes, or where there is insufficient understanding and quantification of how interactions change under varying environmental conditions. This is the case for many plant disease forecasting models, while insect phenology models are more generally applicable to all environments.
Crop system models, when available, can be used to generate information on the status of the crop, its pests, and its environment under different scenarios, includ-ing different management options. The relative effi-cacy of a range of pest management techniques can be evaluated, and the risks and impacts on yield and profit analyzed before a recommendation is made or deci-sion is finalized. In practice, there are few examples of these models that include all the necessary compo-nents and can be used for practical decision making. However, individual crop and pest components have been developed and can be analyzed at the same time to give information that can improve decisions.
2.1. Weather and climate variables in pest management
The prediction schemes, or models, require ac-cess to weather and climate data, in addition to pest and plant data. The models usually require as inputs measurements of temperature, rainfall, and humidity, although other variables may be required either as
direct inputs or in computing values for variables not measured. For example, many crop disease agents require moisture for spore germination, but surface wetness is rarely measured from standard weather stations and is difficult to measure accurately even when instrumentation is available. Reliable algo-rithms are needed to compute leaf wetness duration from measured variables.
Depending on the use, weather variables may need to be measured at the field level, at regional stations, or on a broader scale. For many farm management actions, data representative of the field conditions are expected. Improved technology has made automated weather stations more available in recent years. In many developed countries, numerous regional net-works of automated agricultural weather stations have been established (Meyer and Hubbard, 1992). How-ever, these stations usually do not supply data that are representative of crop canopy environments, and it is unlikely that the number of these stations will ever be adequate to meet the needs of agricultural management even on a regional scale.
To improve the availability of information needed for pest and crop management, agricultural meteo-rologists need to explore alternatives to field-based monitoring. While it is difficult to relate accurately measurements from regional stations to field condi-tions, development of such relationships would ad-vance significantly the ability to use models and inte-grate weather into farm management schemes (Weiss, 1990). A promising approach used by Diak et al. (1998), combines net radiation from satellites, rainfall measured by NEXRAD, standard synoptic measure-ments, and detailed forecast models of the soil-canopy environment as inputs to a potato early blight pre-diction system developed by Pscheidt and Stevenson (1986). Developing relationships between in-field and remotely sensed data would be a very significant advance.
having the potential of reducing wheat yield and qual-ity and disrupting trade. Recently, ten-year temper-ature averages from 9068 stations across the United States were examined with reference to the conditions conducive to Karnal bunt development (maximum temperatures between 14 and 20◦C) and periods of plant susceptibility (anthesis and grain fill) as deter-mined from estimated planting dates and a wheat phe-nology model. The agency categorized probability of colonization as high, medium, or low, depending on the degree of intersection between reproductive plants and temperatures appropriate for infection (Sequeira, 1999).
Short- and medium-range forecasts of required variables make models useful planning tools. For control of some insects and diseases, improved fore-casts with longer lead times could reduce dependence on pesticides. Many crop diseases are routinely con-trolled by preventive fungicides applied at regular in-tervals determined by the residual action of the active ingredient. Fungicide use sometimes can be reduced by using a disease ‘forecasting’ or ‘risk assessment’ model that evaluates conditions to determine suit-ability for infection. However, for some diseases detecting the occurrence of favorable conditions may not allow time for control action. For example, with downy mildew (Bremia lactucae) of lettuce, infection can occur only 48 h after an appropriate period of wetting, so by the time the advice is conveyed to the farmer there may not be time to control disease by applying a preventive fungicide, and often no chem-ical with curative properties is available (Scherm and van Bruggen, 1993). For such diseases, a forecast of surface wetness duration can give farmers better lead time to take action for preventing disease. In the United States and the Netherlands, commercial firms are applying mesoscale modeling techniques to fore-casting disease and insect development, and producing gridded products for regional and on-farm planning and pest management (J. Russo, personal commu-nication). While short- and medium-range forecasts can assist with in-season decision making, quantifica-tion of climatic variability and long-lead forecasting are needed to help farmers make strategic choices such as the crop to grow, variety to plant, or planting date. Many insects, diseases, and weeds are persistent features and annual decisions can be made to assess their potential impact on yield. An example would be
predicting weather conditions favoring outbreaks of a pest at a susceptible crop growth stage, based on risk assessments of long-term weather patterns such as El Niño events. Varieties or planting dates could then be adjusted or the choice made to diversify in response to the level of risk the farmer is willing to accept.
3. Pest management options
Initial selection of the crop to grow and the most ap-propriate variety for a particular location is one of the keys to successful pest management. The location and the climate of the region determine naturally occur-ring stresses on the crop and the pest complex likely to be encountered. Selection of resistant varieties, ro-tation crops, crops for interplantings and cover crops is important for successful crop production with min-imal inputs of chemical pesticides and fertilizers.
3.1. Resistant varieties
Traditional and transgenic resistant varieties must be suited to the climate where they are to be used. While most expression of genetic resistance is not dependent on meteorological factors, in some cases exposure to local conditions can cause loss of resis-tance. Low temperature effects have been reported for some sorghum genotypes resistant to Schizaphis graminum, the greenbug (Starks et al., 1973); Sosa and Foster (1976) reported the loss of resistance to Hessian fly (Mayetiola destructor) in wheat when ex-posed to temperatures above 18◦C. Shading decreases stem solidness and density in some wheat varieties, which reduces their resistance to the wheat stem sawfly (Roberts and Tyrrell, 1961). Improvements in host plant resistance have the effect of making plant protec-tion less dependent on weather (Meeussen and War-ren, 1989). However, when several pests must be con-trolled and other characteristics must be incorporated into locally adapted varieties, host plant resistance will be insufficient to take care of all the pest management issues facing farmers and must be used in combination with other techniques.
3.2. Crop rotation and intercropping
Crop rotation has long been a standard pest man-agement technique and continues to play an important role. Rotation suppresses soil-borne insects, nema-todes, and pathogens through host deprivation. Weed control can be achieved by selecting a rotation crop with superior competitiveness under the microcli-matic environment, or with allelopathic effects on field weeds.
Intercropping is another strategy to reduce insect and weed pests. Insects may feed preferentially on the second crop, or it may provide a more favorable habitat to increase natural enemies. An interplanted crop may provide weed control by allelopathy, smothering, or reducing competition from the weed. Obiefuna (1989) showed that melons interplanted at a density of 5000 per ha significantly reduced weed growth in plantains, and allowed a 7-month delay in manual weeding.
Use of climatic risk assessment can help us to understand the probable effects of selecting different varieties, rotation crops, and intercropping strategies. Environmental limits of the plants must be known to determine the success of the primary or alternative crop in the specific environment.
3.3. Cultural and biological controls
In-season cultural practices related to pest manage-ment are influenced by antecedent and near future weather, and these often low-technology control meth-ods are likely to remain commonly used tools as part of an overall strategy for managing pests. Examples are monitoring for pests and damage, cultivation, and irrigation. Late-season or early-season pest problems may be avoided by planting shorter season varieties or manipulating the time of planting or harvest, but the weather risks must be evaluated against the expected yield reductions due to pests.
Manipulation of planting date is of prime impor-tance as a pest management tactic, to render the crop less vulnerable to the pest. Early or delayed planting can be effective where the length of the growing sea-son exceeds the time required to produce the crop. A farmer can avoid the egg-laying period of the pest, get the crop past a susceptible stage before attack, create a shorter period of susceptibility, have the crop ma-ture before the pest is abundant, or synchronize the pest with its natural enemies and climatic conditions that would adversely affect the pest. The date can be adjusted to take advantage of temperature or tropical wet and dry seasons to disrupt the pest’s life cycle. For example, weeds can be allowed to emerge and then be controlled by cultivation or herbicides before the crop is planted. In temperate climates, early plantings of some crops can take advantage of cooler conditions and a problem nematode’s period of inactivity, as in the example of sugar beets and the sugarbeet cyst ne-matode (Heterodera schachtii) (Roberts and Thoma-son, 1981).
Strepto-myces scabies; nematodes such as several root-knot nematode species (Meloidogyne spp.) and lesion ne-matodes (Pratylenchus spp.), and numerous weeds, e.g., bermudagrass, barnyardgrass, nightshades, and some pigweed species. Highest temperatures occur when days are long, air temperatures are high, skies are clear, and there is no wind across the plastic to dis-sipate the trapped heat (Elmore et al., 1997). Climatic descriptions can identify areas where solarization is likely to be successful.
Biological pest control options include methods that preserve or increase populations of natural enemies of target pests. Environmental limitations are a constraint to the effective use of many biological agents, or the successful introduction of new agents against pests in-troduced into a new environment. To fight an intro-duced pest, a standard technique is to look at the pest’s native environment to find biological agents that con-trolled it there, but which have limits compatible with the pest’s new location. Cover crops and nursery crops can provide habitat with a microenvironment different from the surroundings, and which may be more suit-able for the growth and reproduction of the biocon-trol agent. One of the largest successful classical bio-logical control programs has been the introduction of the parasitoidEpidinocarsis lopeziagainst the cassava mealy bug,Phenacoccus manihoti, throughout much of Africa (Herren and Neuenschwander, 1991).
In other cases the biocontrol agent must be rein-troduced periodically through inoculative releases. Through rearing in artificial environments, the phe-nology of the natural enemy can be manipulated to match the susceptibility of a target pest, so mass re-leases of the natural enemies will match the pest’s susceptible stage. A related technique is mass release of sterile insects, which also must be timed to co-incide with the life cycle of the target population. Releases of sterile males are used in conjunction with chemical sprays to eradicate Mediterranean fruit fly (Ceratitis capitata), which is repeatedly in-troduced into California and Florida in the United States.
3.4. Chemical and biological pesticides
Under the intensification of agricultural production, inputs in the form of chemical pesticides have been heavily used where farmers could afford them. These
pesticides often affect air and water quality, and there is significant social pressure to reduce reliance on these chemicals. However, under many circumstances pesticides are a necessary part of pest management, and are likely to continue to be one of the ways that higher productivity can be achieved, particularly in the shorter term; where pesticides are used steps must be taken to assure their safe and effective application. Biological pesticides, including products based on bacteria, viruses, fungi, and nematodes, have been developed and are becoming more widely available. While these products are more environmentally be-nign than chemical pesticides, their efficacy also depends on appropriate application.
Other environmental conditions affect the effi-cacy of pesticide applications. The moisture status of the plant affects uptake and winds affect coverage. Extreme temperatures may affect the action of the pesticide, or cause it to be phytotoxic to the plant. Some biological pesticides made from viruses and fungi may be inactivated when exposed to sunlight, and fungi and nematodes may require moisture to be effective.
Recent research has shown that in some cases the environmental requirements may be modified. For ex-ample, in the case of pathogenic biocontrol agents that require free moisture for spores to germinate, the ad-dition of oils and emulsions can minimize the require-ment (Weidermann, 1996). Research into other means of modifying the environments or environmental re-quirements could improve the efficacy of introduced biological control agents.
3.5. Management of migratory pests
Effective management of a migratory pest is based on warnings and forecasts of its changing distribution. This requires an understanding of the migration pro-cess and the effects of the weather on it. In addition, monitoring and mapping need to provide a regularly updated stream of field data (Pedgely, 1993).
It is best to prevent the migration if possible, ap-plying preventive techniques to sources of pests or to insects in migration. This can be effective when the source area is small enough to be managed at one time. There have been several operational preventive management schemes developed, notably oriental migratory locust in China, blackfly in West Africa, and screwworm fly in North America (Pedgely, 1993).
Desert locust is a migratory pest in Africa with the potential to devastate crops over large regions. The pest is feared both for its destructive capacity and the constant threat to the region. Locust survival and pop-ulations are greatest with frequency of sufficient rain-fall, where rain is enhanced by run-off and flooding, and where vegetation and soils provide suitable habi-tats. Prevention of outbreaks by destroying flightless nymphs is desirable, but often emergency measures are taken to control the swarms of adults (Prior and Streett, 1997). Forecasts of wind fields and convergence zones can identify paths of the locusts as they move from one
area where rain has fallen to another (Skaf et al., 1990), and swarms in flight can be systematically tracked and sprayed. A formal locust watch program in African countries has been developed to forecast desert locust movement, and the program includes not only moni-toring for the locusts, but also 5-day forecasts of wind fields and rainfall at ground level and 850 hpa to gen-erate a forecast for invasion. The program utilizes a regional approach requiring international cooperation and free exchange of observations and forecasts of lo-cust movement (Kellou et al., 1990).
Fungal spores also may be transported over long distances by winds. One recent operational application for tobacco blue mold uses a trajectory model to fore-cast the position in space and time of a spore cloud center for 2 days following release from a source. Me-teorological factors considered are temperature, cloud cover, and rainfall related to sporulation at the source, UV related to survivability of the spores during trans-port, and rain along the path that would relate to de-position and rainout (Main, 1998).
4. Effects of climate change
5. Extension and training
The output scenarios resulting from models and other quantitative tools must be transformed into man-agement recommendations. The recommendations must be reasonable for the farming system where they are to be applied, they need to be communi-cated within a time frame that action can be taken, and must be understandable to the farmer. The output may require expert analysis, unless the technique is of sufficient simplicity for less technical interpretation. Local goals and attitudes about risk need to be under-stood and coupled with model output. Understanding of the interaction among various farming practices is also an important component of the analysis lead-ing to a recommendation. If the expected results of various options, and the risks associated with them, can be conveyed to the decision maker to show the impact of the options, the recommendations will be more meaningful.
The interdisciplinary nature of integrated crop or pest management requires that both extension person-nel and agrometeorologists be exposed to the foun-dations of related disciplines and the workings of the systems that are developed. Training needs to include understanding of data collection, how to integrate the data with the crop-pest system description, conditions under which tools might fail, and how the recom-mended practices fit into the actual system. Farmers need to be given training in how best to integrate new information into their farming activities but should also be given a basic understanding of agrometeoro-logical relationships to augment their own observa-tions and experiences.
6. Needs related to agrometeorology and pest management
In pest management, strategies and techniques that contribute to groundwater and surface water pollu-tion and other pesticide issues, including food safety, need to be replaced with others that reduce or elim-inate undesirable impacts. Alternatives to techniques that contribute to atmospheric ozone depletion, such as in-season and post-harvest uses of some fumigants, or that reduce air quality are also needed. Where
biotech-nology is proposed as a pest management solution, appropriate methods of development and deployment that address concerns about the safety of the tech-niques must be developed and agreed on. These and other societal concerns will need to be identified as a basis for setting the agricultural research agenda for the 21st century, and many of the issues will be global in nature (Ruttan, 1996).
Much information is needed to build new pest man-agement systems. Some essential areas for research and extension are the following:
• Techniques for studying insect, plant and pathogen biology, and packaging them as quantitative fore-cast tools are reasonably well known, but research is needed on the range of economic pests, and ef-forts need to be launched to implement the resulting information.
• In the case of migratory pests, biological informa-tion must be coupled with trajectory or three dimen-sional mesoscale models that will yield information for warning and after-the-fact analysis.
• Appropriate techniques to relate standard observa-tions to field condiobserva-tions need to be developed.
• Improvements are needed in our knowledge of how to use remote sensing not only to monitor weather conditions but also to monitor pest infestation and injury.
• Research must provide the environmental tolerances of new resistant varieties, as well as the standard ar-ray of agrometeorological information such as crop water requirements.
• Data, maps and other descriptions are needed to
de-lineate suitable climates for introduced biological control agents, new plant varieties, and to antici-pate pest problems as production moves into new regions.
• Regulation and international cooperation will be necessary to manage migratory pests and make bor-der exclusion programs effective.
Perhaps the first challenge is to effectively extend what is already known. Many available techniques are underutilized even in developed countries, and significant reductions in pesticide use could be made through better field monitoring for pests, more effec-tive pesticide application timing and better systems for delivering pesticides to their target.
be understood. The agrometeorologist and agroclima-tologist have important roles to play in this interdis-ciplinary work to assure that appropriate factors are considered and that the impacts of weather, climate, and their variability are integrated into the decision packages. These systems should be simplified to have the broadest application, and where possible be based on readily available inputs, including meteorological measurements and climatic analyses. For best deci-sion making, the systems must produce information that can be used to evaluate the short- and long-term costs of management techniques to the environment, sustainability, and profitability.
Those who are developing and extending the in-formation must acknowledge that agriculture is not uniform worldwide, and that where a management system or set of techniques is being implemented, the local culture may influence the values and hence recommendations. Resource differences will mean differences in the ability to implement all components of a cropping system, so implementers must expect to integrate only those technologies that fit within local constraints. For many areas a broad range of options is needed rather than narrow technological packages that will not prove suitable for poor farmers (Blackie, 1994). Blackie (1994) suggests that too often the solu-tions have been improved breeding, with insufficient research into the actual crop and pest management techniques needed to ensure success. The local culture is also likely to influence the dissemination system, and must be taken into account to assure that infor-mation on techniques will reach the right participants. Agrometeorology in the 21st century will con-tinue to provide support to the biological disciplinary sciences through provision of data, consulting on data collection, weather and climatic analyses, and research into subjects such as crop microclimates. Agrometeorologists must work closely with other scientists to maximize their resources and useful-ness. In the United States, the research system has frequently failed to recognize fully the importance of agrometeorological activities, both the research and data collection or maintenance functions. With-out appropriate recognition and support within the research institutions, public or private, disciplinary scientists will not have sufficient information to build flexible, reliable, leading-edge tools for pest and crop management.
Acknowledgements
Several colleagues shared their ideas of the needs of agricultural meteorology as related to pest man-agement in the 21st century, and their contributions are very much appreciated. A. Weiss, J. Russo, E. Se-queira, E. Taylor, A. van Bruggen, P. Brown, T. Gille-spie, C.E. Main, J. Bailey, R. Grant, and W. Bland.
References
Blackie, M.J., 1994. Maize productivity for the 21st century: the African challenge. Outlook on Agric. 23 (3), 189–195. Diak, G.R., Anderson, M.C., Bland, W.L., Norman, J.M.,
Mecikalski, J.M., Aune, R.M., 1998. Agricultural management decision aids driven by real-time satellite data. Bull. Am. Meteorol. Soc. 79 (7), 1345–1355.
Elmore, C.E., Stapleton, J.J., Bell, C.E., DeVay, J.E., 1997. Soil solarization a nonpesticidal method for controlling diseases, nematodes and weeds. Univ. Calif., Div. Agric. and Nat. Res., Oakland, CA.
Herren, H.R., Neuenschwander, P., 1991. Biological control of cassava pests in Africa. Ann. Rev. Entomol. 36, 257–283. Kellou, R., Mahjoub, N., Benabdi, A., Boulahya, M.S., 1990.
Algerian case study and the need for permanent desert locust monitoring. Phil. Trans. R. Soc. Lond. B 328, 573–583. Main, C.E., 1998. North American Blue Mold Forecast Center.
Online available http://www.ces.ncsu.edu/depts/pp/bluemold/, 1 March 1998.
Meeussen, R.L., Warren, G., 1989. Insect control with genetically engineered crops. Ann. Rev. Entomol. 34, 373–382.
Meyer, S.J., Hubbard, K.G., 1992. Nonfederal automated weather stations and networks in the United States and Canada: a preliminary survey. Bull. Am. Met. Soc. 73 (4), 449–457. Obiefuna, J.C., 1989. Biological weed control in plantains (musa
AAB) with egusi melon (Colocynthis citrullusL.). Biol. Agric. Hortic. 6, 221–227.
Pedgely, D., 1993. Managing migratory pests. In: Isard, S.A. (Ed.), Alliance for Aerobiology Research Workshop Report. Alliance for Aerobiology Research Workshop Writing Committee, Champaign, IL.
Pimentel, D. (Ed.), 1991. CRC Handbook of Pest Management in Agriculture, Vol. 1, 2nd Edition. CRC Press, Boca Raton, FL. Prior, C., Streett, D.A., 1997. Strategies for the use of entomopathogens in the control of the desert locust other acridoid pests. Memoirs Entomol. Soc. Can. 171, 5–25. Pscheidt, J.W., Stevenson, W.R., 1986. Comparison of forecasting
methods for control of potato early blight in Wisconsin. Plant Dis. 70, 915–920.
Rice, E.L., 1995. Biological Control of Weeds and Plant Diseases, University of Oklahoma Press, Norman, OK.
Roberts, D.W.A., Tyrrell, C., 1961. Sawfly resistance in wheat. IV. Some effects of light intensity on resistance. Can. J. Plant Sci. 41, 457–465.
Roberts, P.A., Thomason, I.J., 1981. Sugarbeet Pest Management: Nematodes. University of California Division of Agricultural Sciences Publication, 3272, Oakland, CA.
Rosenzweig, C., Hillel, D., 1998. Climate Change and the Global Harvest, Oxford University Press, Oxford.
Ruttan, V.W., 1996. Research to achieve sustainable growth in agricultural production: into the 21st century. Can. J. Plant Pathol. 18, 123–132.
Scherm, H., van Bruggen, A.H.C., 1993. Sensitivity of simulated dew duration to meteorological variations in different climatic regions of California. Agric. For. Meteorol. 66, 229–245. Sequeira, R.A., 1999. Meteorological data and regulatory
applications in agriculture: application examples, data status, and future meteorological data and modeling needs. In: CAgM Report 77, Contributions from Members on Operational Applications in Agrometeoorology for the International Workshop: Agrometeorology in the 21st Century, Needs and Perspectives, Accra, February 1999, WMO, Geneva. Skaf, R., Popov, G.B., Roffey, J., 1990. The desert locust: an
inter-national challenge. Phil. Trans. R. Soc. Lond. B 328, 525–538.
Sosa Jr., O., Foster, J.E., 1976. Temperature and the expression of resistance in wheat to the Hessian fly. Environ. Entomol. 5 (2), 333–336.
Starks, K.J., Wood Jr., E.A., Teets, G.L., 1973. Effects of temperature on the preference of two greenbug biotypes for sorghum selections. Environ. Entomol. 2 (3), 351–354. Vasil, I.K., 1998. Biotechnology and food security for the 21st
century: a real-world perspective. Nature Biotechnol. 16 (5), 399–400.
Weidermann, G.J., 1996. Bioherbicides: limitations and promise. In: Proceedings of the 3rd National IPM Symposium/Workshop: Broadening Support for 21st Century IPM. US Dept. Agric., Environmental Research Service, Washington, DC, pp. 165–166.
Weiss, A., 1990. The role of climate-related information in pest management. Theor. Appl. Climatol. 41, 87–92.
