|Synopsis on Integrated Pest Management in Developing Countries (NRI, 1991, 20 p.)|
22. IPM is firmly rooted in biology and ecology. It seeks to harness indigenous regulatory mechanisms for pest population control and exploit physiological and behavioural characteristics of pest species in their management. It also emphasizes the adaptation of indigenous 'well-adapted' or 'robust' cropping systems in the development of more productive agriculture. Such an approach demands a detailed understanding of the characteristics of agro-ecosystems and their dynamics in response to intervention.
23. An adequate knowledge base is generally lacking and much research has been confined to too few components of the system to predict the effects of control strategies. This is particularly relevant in the case of the farmers' situation. Farmers are nationally reluctant to adopt technology when they are unsure how it will fit within/disrupt their system. Since it will be virtually impossible for the crop protection specialist to anticipate the full effect of a given technology on an individual farmer's system, a choice, or 'menu' of technologies should be on offer from which the farmer can choose and with which further experimentation can be carried out on-farm.
24. Increasing concern is now being expressed about our ability to characterize pest organisms. As methods of control become more specific and sophisticated it becomes more important to distinguish variability in order to ensure that the appropriate method is applied. The rationale is clear for management of host plant resistance and pesticide resistance; evidence is accumulating that the host specificity of parasitoids is much greater than previously recognized. The adaptation of research outputs from molecular biology to provide accurate, simple field diagnostics is a high priority.
25. Technical constraints limit the effectiveness of IPM component technologies. The disfavour with which pesticides have been viewed has tended to discourage research in the public sector into improved application technology, better targeting in space and time, and higher standards of pesticide management.
Ultra low volume (ULV) application technology involves the pesticide being dissolved in volatile solvent oils then atomized by feeding them on to a rapidly spinning disk. The cloud of spray produced by this 'rotary atomization' is then allowed to drift downwind on to the crop. Wider swaths can be sprayed because oil-based droplets evaporate more slowly than water droplets. Some of the disadvantages of ULV spraying such as increased dermal toxicity, patchy spray cover and in some cases greater application costs, led to the development of very low volume (VLV) spraying which combines the advantages of wettable powder with ULV rotary atomization technology. VLV spraying has been particularly successful against cotton pests in The Gambia.
26. With few exceptions, the farmer still uses approaches to and methods for pesticide application that have been current for 20 years. There is almost universal recognition that pesticide use will continue and probably increase. If this is to be the case improved techniques are essential to safeguard the effectiveness of other control technologies. Low and Ultra-low Volume techniques, which could provide massive benefits in economy, safety and ease of use have not yet been well adapted for use by peasant farmers.
27. This is often related to plant architecture and some application specialists have grave doubts that much further progress is possible without, for example, crop breeding for appropriate physical characteristics.
28. Host plant resistance has made a major contribution as 'seed-borne technology' requiring minimal change in farmer practice. Even in low input farming, yields have been improved and stabilized. The major challenge is in countering the selection of pest populations able to neutralize the characters conferring resistance; this depends upon strategic deployment of resistant cultivars and the identification of polygenic resistance. An empirical approach through screening is no longer enough; the underlying mechanisms must be characterized and classified. The ability to create transgenic plants can then be fully exploited.
In Indonesia between 1979 and 1983, Host Plant Resistance (HPR) in rice (IR-36) to brown plant hopper (Nilaparvata lugers) was vital to suppression of the pest. It was difficult however to maintain wide resistance in varieties that are also optimal for yield quality and sale price. In 1981, two rice varieties were released with the same genes for resistance to N. lugens as IR-36. These varieties did not, however, carry other genetic material to confer more lasting resistance. Within two and a half years both varieties became susceptible to N. lugens attack.
29. Biological control is one of the fastest growing and potentially productive areas of IPM technology. The term is used here in its modern sense to cover the use of all biological or biologically derived agents. Classical biocontrol based on release of exotic or supplementation of indigenous natural enemies has had striking successes but is heavily constrained as an IPM component by problems of rearing and supply, particularly for insects. Bacteria, viruses and their toxins have presented similar difficulties compounded by problems of formulation, application, persistence and potential side effects.
Within ten years of its accidental introduction into Africa from South America, cassava mealybug was a major pest. For subsistence farmers who did not use chemicals, a biological control solution was considered the best option. Researchers found a small wasp, Epidinocarsis lopezi, which was not only a parasite of, but a host feeder on, cassava mealybug. Mass rearing and distribution techniques were developed at IITA; by 1987 E. lopezi was established in 90% of Africa's cassava-growing region. Estimates of reduction in losses range from 50% to 90%.
30. The use of behaviour-modifying chemicals has found wide application, particularly with insect pheromones, as a tool of great importance in a number of pest management systems. Pheromones may be used directly in pest control but perhaps play an even more important generic role in facilitating pest monitoring, the fundamental requirement of IPM. Here the constraint lies in identifying appropriate, cost-effective methods for field deployment and in relating catches to action thresholds.
In Egypt, control of cotton pests such as Pectinophora sp. by slow release pheromone formulations has resulted in increased honey production as well as an increase in boll weight. Moreover, the cost of pheromone formulations are 20% lower than insecticide.