Bacterial blight of cotton is the most economically important disease of cotton in Nigeria. The disease is estimated to cause an annual yield loss of 10-20 percent. The development and use of resistant cultivars is the most economic means of disease control. Breeding cotton cultivars resistant to bacterial blight has been an integral part of the cotton improvement programme in Nigeria. Over the last 60 years, eight commercial cultivars varying in levels of resistance to bacterial blight were released. The current two commercial cultivars (Samaru 71 and Samaru 77) are presently susceptible to the evolution of virulent strains of the pathogen. Over the past two decades, six cotton hybrid pools (ASA, AASA, ACSA, RSA, RASA and SMSA) were developed and now form the genetic pool for the current cotton varietal improvement programme. Advanced breeding lines with improved levels of bacterial blight resistance, yield and fibre qualities have been identified within some of the hybrid pools. The recent introductions of the short-seasoned, multi-adversity resistant (MAR) cotton from Texas, U.S.A., and the cultivar S295 from Chad, will be valuable in reinforcing and enhancing the progress in developing cotton cultivars resistant to bacterial blight, other diseases, insect pests and environmental stresses in Nigeria

Western Kenya (Bungoma, Busia and Kakamega Districts of Western Province and Nandi and Siaya Districts of Nyanza Province) covers an area of more than 13 thousand km(2) with a population of nearly 3 million. It has high potential for agriculture and is one of the major bean producing areas of Kenya. The climate is mainly humid, sub-humid and semi-humid but the soils (Nitosols, Acrisols, Vertisols, Luvisols and Ferralsols) are relatively infertile. The agriculture is at subsistence levels, producing maize, bean, banana, sweet potato and local vegetables, with some sorghum, finger millet, groundnut, sugar cane, fruit trees, coffee and tea. Bean is found in pure stand or in association with other crops, mainly maize but also with sorghum, cassava, cotton, sugar cane, coffee or banana. The main constraints to bean production include diseases, insects, poor soil fertility, excessive and inadequate rainfall, inappropriate cultivars and labour shortage. Breeding offers the most appropriate solution to these constraints and the improvement of bean production in western Kenya.

Acurate identification of plant pest problems requires expertise in the agronomic or horticulture aspects of crop production and a sophisticated level of knowledge of the many problems (diseases, insects, toxicities, and deficiencies) that may affect crops. Diagnostic expertise developed over many years is lost almost overnight through changes in career or program direction or retirement. Expert systems which simulate the behavior of diagnostic consultants in interaction with users, offer the chance to capture this expertise before it is lost. Each system is composed of a knowledge base and an expert system shell. The knowledge base contains the collective diagnostic expertise (often encoded in the form of IF‐THEN rules) of interviewed specialists in plant pathology, entomology, and agronomy. The shell performs the reasoning and problem‐solving tasks (including searching the knowledge base for applicable rules) while directing questions and issuing diagnostic reports to the user. There are currently a large number of expert systems being developed, evaluated, and placed into use in the USA. These include systems for diagnosing disease and insect problems of apple, cotton, muskmelon, peach, peanut, potato, red pine, soybean, tomato, and turfgrass. Weed identification systems are also in progress. It will be necessary, if not crucial, for extension professionals to be actively involved in the ongoing development, evaluation, and implementation of such systems.

The advantages of Integrated Pest Management (IPM) for farmers in developing countries have been clear for many years. It cuts production costs by reducing reliance on expensive agrochemicals, reduces hazards to both humans and the environment and, at the same time, stabilizes yields by ensuring the survival of natural enemies of major pests. Yet its use is not understood. Why is this so? The idea of integrated pest management is not new. The original definition envisaged 'applied pest control which integrates biological and chemical control. Chemical control is used in a manner which is least disruptive to biological control'. Many scientists would now regard such a definition as too restrictive and would view chemical control as a last resort when other methods fail to keep a pest in check. More recently, the concept of IPM has been applied to the integrated control of different types of pests (for example, insects, diseases and weeds) in the same crop. Although originally distinct, the two terms integrated control and IPM are now used almost interchangeably to imply both concepts. The essential features of IPM are straightforward, although their application in specific cases requires considerable understanding of the biology of the pests involved and their natural enemies. They include three important principles. Firstly, wherever feasible, control should rely on natural enemies of pests; methods that seriously disrupt natural regulation of pest populations should never be used. Secondly, natural enemies should be enhanced, either directly or indirectly, and plant resistance used to reduce the necessity for expensive chemical control. The third principle is that chemical control should be selective and should only be used as and when pest populations increase to a level above which serious economic loss will result. The last of these principles needs further explanation. In most cases, pest populations will be low following planting but, in the absence of adequate natural controls, will increase rapidly as the crop develops. However, up until a certain level, there will be little or no damage of economic significance to the crop. The population level at which significant economic damage is observed is known as the economic threshold for a given pest and only above this threshold is chemical control employed. In this way, natural enemies are allowed to build up and expensive chemicals are not wasted. The economic threshold is obviously a moving target and differs between crops, pest species and, since it is dependent on the market value of a given crop, between seasons. Nevertheless, use of economic thresholds has proved its value in reducing crop production costs and is now very widely used in pest control schemes. The components of integrated pest control The weapons available to the farmer are of four types; biological control, cultural control, selective pesticide use and plant resistance. Biological control using natural enemies of pests can be achieved through introduction of predators, parasites or diseases. Introduction (in some cases re-introduction) of natural enemies is now a familiar concept. Although there have been some spectacular successes, for example the control of prickly pear by the moth Cactoblastis cactorium in Australia and of cottony cushion scale on citrus in California, it should be said that less than half of all attempts at biological control by introduction have been successful. While the reasons for this are complex, it does emphasize the importance of retaining existing control agents through the rational use of pesticides. This is particularly true in the tropics where many crops face dozens of different pest species. Although the effect of any one member of this pest complex may be relatively minor, in combination they can cause drastic losses. To introduce specific predators or parasites for each pest would be totally uneconomic, even if they could be found; enhancement of existing natural enemies, many of which feed non-selectively, is a more sensible alternative. Cultural control, which involves manipulation of the crop and its surrounding habitat aims to increase the chance of survival of natural enemies or reduce that of the pests. One obvious technique is to practice mixed cropping rather than monoculture. This can both reduce the size of pest populations by limiting the food resource available and provide alternative refuges for natural enemies. Intercropping has similar aims but on a finer scale. Other techniques include the provision of refuges (not necessarily a crop species) or food sources for natural enemies. In some situations, complete weeding of the crop may reduce yields since 'weeds' can provide both refuges and food sources for natural enemies. Destruction of crop residues by removal or burning can sometimes be successfully used to interrupt the development of pests that have a resting stage in such residues. Selective pesticide use is another possible approach. The most important facet of selective pesticide use is employing economic thresholds to limit the amount of chemicals applied. However, modern developments in both pesticides and their application can also reduce the need to spray the crop. Several insecticides now available have some degree of inherent selectivity. An example is Endosulfan (Thiodan), which is effective against a wide variety of crop pests but which, at recommended application rates, has little effect on the minute parasitic wasps that are important natural enemies of many pests. When used in ultra-low volume formulation for control of tsetse flies, this insecticide was found to have virtually no detectable effect on other insect populations. Insecticides that are based on hormonal growth regulators or on microbial agents also show some degree of selectivity in their action. Even more selectivity can be achieved by careful formulation and application of pesticides. Because systemic insecticides are taken up through the foliage or roots of the plant they are only available to the chewing or sucking insects that attack it. The same principle applies to insecticides that are encapsulated, wrapped in a coating of gelatine or similar inert substance. The tiny capsules adhere to the surface of the plant and the insecticide can only be taken up by biting insects that feed on the plant. This avoids risk to predators and parasites. New application techniques can reduce the amounts of pesticide required to achieve effective control. Ultra low-volume (ULV) spraying is now widely used, particularly for aerial application. A rotating nozzle breaks the spray up into a haze of minute droplets. The droplets are sufficiently small that they can pass directly into the insect's body through the spiracles, the pores through which insects, breathe, killing them more rapidly. In this way, the amounts of insecticide required for effective control can be drastically reduced, often by as much as one hundredfold. One disadvantage of ULV spraying is that the droplets are so small that they are blown away by even the lightest breeze, reducing effectiveness. An ingenious technique called electrostatic deposition avoids this problem by giving each droplet a minute positive electric charge. The surface of the plant has a small negative charge, attracting droplets to the plant cuticle, where they are deposited. The pesticide is effectively 'glued' to the plant by electric forces! A cheap, portable sprayer, using this principle has now been marketed and has proved extremely effective in the Third World, particularly for the control of cotton pests. Plant resistance is a further option in IPM. Plant breeding has played a crucial role in the prevention of crop losses due to diseases throughout the 20th century, and disease-resistance is a major objective in the development of new crop varieties. The concept of breeding for insect pest resistance is a more recent one but has had considerable success and is being actively pursued, particularly for tropical crops. A good example is the range of rice varieties developed at the International Rice Research Institute (IRRI) in the Philippines. IRRI has bred varieties resistant to four of the major insect pests of rice which are now very widely grown in S.E. Asia. Several varieties are available which combine resistance to three of the four major pests. Insect resistant varieties of cowpea, an important tropical pulse, have been developed at the International Institute of Tropical Agriculture (IITA) in Nigeria using advanced biotechnologies. Successes in integrated control One of the earliest examples of successful IPM comes from the Canete Valley in Peru, where from the 1940s, cotton was grown as a monocrop with extremely heavy use of insecticides. By 1955, yields plummeted following blanket application of organochlorine and organophosphorus insecticides which resulted in breakdown of natural biological control and the development of pest resistance. In 1956, the government introduced compulsory crop rotation and mixed cropping and enforced a return to older insecticides. One of these, lead arsenate, is a stomach poison which only kills insects that chew the plant and is ineffective against natural insect enemies. These measures were combined with regular inspection of the crop for pests so that insecticides were only used when pest populations exceeded the economic threshold. Cotton yields rapidly recovered to levels close to those before the crisis and the Canete Valley remains today, over 40 years later, a major cotton producing area of Peru. Integrated control of pests has not been widely used in Africa but there have been some successes. The common coffee mealybug was a major pest of coffee in Kenya where its populations had exploded due to resistance to persistent organochlorine insecticides and to loss of natural enemies. Restrictions on the use of these insecticides, combined with the introduction and dissemination of a minute parasitic wasp (Anagyrus sp. ) brought the pest back under control. Similarly, in Tanzania a major pest of sugar cane, the sugar cane scale insect, has been successfully controlled by carefully timed insecticide application in conjunction with the release of a ladybird beetle which preys specifically on the pest. Cassava, an important staple crop for some 200 million people in Africa, is seriously threatened by the cassava mealybug, accidentally introduced from South America 20 years ago. In this case, classical biological control is proving highly successful. A parasite of the mealybug, itself from South America, is released from the air and has successfully controlled the bug over large areas of West and Central Africa. In Asia, Indonesia experienced a severe reduction in rice yields in recent years due to the ravages of the Brown Planthopper. This has resulted from excessive use of insecticides, to many of which the planthopper now shows resistance. By 1986,100,000 hectares of rice had been destroyed by this pest alone, despite 4 to 5 applications of insecticide in each growing season. In 1988, the Indonesian government took the decision to ban the use of 57 different types of insecticides and to reduce severely the use of the recommended Carbamate insecticides. This has allowed populations of natural enemies to recover and to provide adequate control of the planthopper. Between 1986 and 1988, average yields of rice in Indonesia increased from 6.1 tonnes per hectare to 7.4 tonnes per hectare, a gain of 21% in two years. Considering this was achieved simply by reducing the amount of insecticide applied, and, thus, production costs, the advantages of rational insecticide use had been confirmed. As a result, FAO is now planning experimental programmes of integrated rice pest control in 6 other countries in the region. The problems IPM is not a panacea and, as with biological control, there have been failures as well as successes. Clearly, IPM requires that farmers have a better knowledge of both the pests and their natural enemies than is the case with simple chemical control. It is also difficult for farmers to 'do nothing' until the pest reaches an economic threshold, even though it is clearly present in the crop. This is particularly true if, previously, they have been advised to spray at the first signs of the presence of pests. Neither can IPM be used against all types of pests. It has proved impossible to devise schemes for highly migratory pests, such as locusts, and soil nests. such as termites. The future of integrated control IPM is used on only a very small proportion of the world's crops. Apart from the problems mentioned above, the rapid development of synthetic pyrethroid insecticides since the 1970s has largely overcome the problems of pest resistance to earlier insecticides. Nevertheless, the need for more rational pest management will grow. The problem of pest resistance will not simply go away (some insects already show resistance to pyrethroids) and the cost of agrochemicals, which are largely oil-based, is likely to continue to rise sharply. Several of the components of IPM are now widely used in crop protection in the industrialized countries. Crop surveillance, combined with the use of an economic threshold for chemical control, is now widely used in such crops as cotton, alfalfa, tobacco and many fruit crops. And biological control has proved particularly successful for glasshouse crops, where chemical control poses particular problems and where there is good environmental control. What, then, is the likely future of IPM in the tropics ? The need for food security has lead to greater emphasis on sustainable agriculture, within which IPM can play a crucial role. It has proved most successful where farmers have sufficient resources and education to exploit the possibilities of longer term control strategies, but there are many developing countries, particularly in Africa, where this does not yet apply. In the medium term, it is likely that more rational use of insecticides, based on crop surveillance, is likely to increase, if only for economic reasons. Whether this will develop into fully integrated control in the longer term will probably depend more on economic and political factors than on purely technical considerations. Above all, successful introduction of IPM depends critically on reasonably stable and fair prices for agricultural produce, both staple foods for home consumption and cash crops for export. | The advantages of Integrated Pest Management (IPM) for farmers in developing countries have been clear for many years. It cuts production costs by reducing reliance on expensive agrochemicals, reduces hazards to both humans and the environment and,...

Over the centuries, farmers in the tropics have survived through good and bad years, in balance with the environment. But today population pressure on the land precludes practices that enable the environment to recover from extensive cropping systems. As a result the forests are dying, the soil is disappearing, the desert is spreading. Destruction of natural resources - the soil and vegetation cover - due to constant clearance of new ground as a result of exponential population growth, destroys the balance of the environment and mortgages the means of future production. The productivity of the land, both in terms of yields and of the intensity of cultivation, must be improved. But this raises a fundamental question. What are the effects on the environment of intensive agricultural practices? Does agricultural intensification adversely affect the environment or is it a means of preserving it? What are the ultimate consequences of non-intensification? Should we intensify agriculture in the tropics or not? Can one compare the situation in the Third World to that in the industrialized countries where large quantities of agrochemicals are regularly used to produce uneconomic surpluses? Shifting cultivation has in the past, allowed the population of tropical countries to maintain a balance between their needs and the resources of the natural environment. In the course of its history, traditional agriculture has evolved gradually over centuries in a stable human environment. Such conditions no longer exist. As V Drachoussoff underlined, (1) 'one should not overestimate the ability of traditional agricultural systems to evolve. They can adapt to rapid but slight changes, or to those that are profound but slow. But change is now both rapid and profound (for example, in a population with a high growth rate and galloping urbanization), and these systems cannot support traditional cultural practices and conserve the soil, water and vegetation resources.' Is it better to build a dam or use chemical fertilizers, and deal with their drawbacks, rather than to pillage the last forests to gain a few thousand hectares of new land thus passing on the problem to the future generations? All these questions arise from a central preoccupation: how can developing populations avoid a terrible dilemma - to eat today at the risk of dying tomorrow or to make sacrifices and preserve the future? Is the development of food production compatible with the protection of the environment? Water, fertilizers, agrochemicals and mechanization are among the most important elements of modern agriculture. Most would agree that their intensive use has consequences for the quality of the environment. It is therefore important to review the impact of agricultural intensification in the tropics. Water: large or small-scale projects The example of the irrigated area of Gezira in the Sudan demonstrates the problems, even today, of large-scale irrigation schemes with major infrastructure requirements. The Gezira is the oldest and, at present, the largest irrigated area in Africa. During the last 12 years, yields of cotton have fluctuated around half a tonne per hectare and cereal yields have remained between one, and one-and-a-half tonnes per hectare. These can hardly be considered high yields in irrigated agriculture. However, since the rainfall of the region rarely reaches 400mm per year, and in some years an almost complete absence of rain precludes any harvest, it must be recognized that the Gezira scheme has provided, for almost half a century, subsistence for an environmentally underprivileged population. It is a fact that the large quantities of insecticides required to grow cotton cause pollution of soil and water. Thirty million dollars' worth of insecticides and six million dollars' worth of herbicides are used each year and their effects are felt by the population. It is clear that projects of this size can be damaging to the environment and this should be taken into consideration at the decision-making and planning stage. On the other hand, small-scale irrigation in the Sahel consists of many small developments fed by pumped ground-water. Successes have been achieved: in addition to providing water for the people these developments have permitted profitable agricultural activities, such as fruit growing and market gardens, tree nurseries and construction of watering points for livestock. In short, these schemes have been instrumental in rational development of the region. The effect of such developments on the environment is, at first sight, very positive. But the ill-considered use of ground water is not without consequence for future supplies of water. The increase in boreholes, has, unfortunately, resulted in chaotic management of the grazing areas with profound effects on the environment. Plant cover has been considerably impoverished, disappearing in many places over large areas around watering points and leading to wind erosion. Boreholes, combined with improved veterinary services have led to a rapid increase in livestock numbers. The herds are then forced to move south where the same practices which originally led to desertification in their countries of origin are repeated. It should be noted that, during the past ten years, remarkable successes have been obtained with a number of small-scale schemes entirely managed by the farmers themselves. (1) Spectacular results, with rice yields exceeding 10 tonnes per hectare in two growing seasons each year, have been recorded. These yields, which show the real potential of irrigation, should be compared with the yields from traditional cereal crops (millet and sorghum) which on average do not reach a half tonne per hectare. (2) Small-scale irrigation schemes in Madagascar have led to greatly increased productivity in traditional rice paddies, thanks to better water management in harmony with the social and ecological environment. Agrochemicals The industrialized countries use large quantities of chemical fertilizers and often optimum application rates have been exceeded. Furthermore, optimum rates of application from an economic standpoint do not correspond to those required to maintain the balance of the environment. In the African context, however, if lack of purchasing power has averted the drawbacks of overuse of fertilizers, it has also denied the continent the benefits of their rational use. In tropical countries, improved soil productivity resulting from fertilizer use has other advantages: increased biomass, better soil cover and, consequently, reduced risk of erosion and better preservation of soil organic matter derived from leaves and roots. Considering that agricultural losses due to pests amount to 30% of production, it is clear that pest control is essential, including the use of chemical products. But chemical pesticides have their drawbacks. They are expensive, dangerous to store and have a limited shelf-life. If used unwisely they are also hazardous to the environment. Experience has shown the dangers of accumulation of toxic residues both for humans and for the environment. Integrated pest control offers encouraging prospects for methods of crop protection that are less likely to alter the natural environment. These methods integrate chemical control with cultural practices, plant breeding and biological control. In view of me limits of intensive chemical control as well as those of biological control alone, integrated pest management rests on a thorough understanding of the interactions between pests, plants and beneficial organisms. Mechanization In Africa, whereas 80% of the population is involved in agriculture, food production levels remain inadequate. Therefore the profitability of labour must be improved. Agricultural mechanization has considerable prospects in this field so long as it is managed efficiently. Care must be taken not to leave fields badly cleared, insufficiently ploughed, and without protection against erosion or without restoration of organic matter. Mechanization should aim at maximizing the use of arable land, promoting the use of other production factors and it should lead to the improvement of crop performance. In regions with livestock, draught power is undoubtedly the type of mechanization most widely available and with the least financial risk since it requires a small investment and a minimum of family labour. Use of draught animals is, with penning of livestock for manure production, one of the best ways of integrating livestock and crop production. These two aspects of agriculture can be complementary rather than competitive. However, draught power has its limitations. It is difficult to implement in farming communities with no livestock tradition and it is limited by animal diseases. On its own it does not allow the mechanization of all cropping practices. Productivity levels are only modest. Mechanization with tractors helps to alleviate problems due to labour shortage when the interval between harvesting and planting of another crop is very short. This method can be highly profitable by increasing the number of harvests per cycle and when rainfall is poor, it makes it possible to use the whole area available. Perhaps the greatest advantage of tractorization is that it enables farmers to extend the area under crops where a lot of land is available or where it is too difficult to cultivate by hand or draught power because of compacted soi1. The consequences of agricultural intensification for the environment were examined during a one-day meeting in Brussels in June 1990, which was organized jointly by the Academie Royale des Sciences d'Outre-Mer de Belgique and CTA. The main conclusions reached were: - that agricultural intensification leads to economies in land use which are indispensable if the environment is to be saved and restored, and - that there would be no point in protecting the environment by intensive crop practices if these practices lead to other forms of environmental deterioration. The experience of the industrialized countries shows that over-intensification is as harmful to the quality of life and the environment as excessive population growth combined with extensive farming in developing countries. There are no miraculous solutions to agricultural problems. But there is a range of methods that research workers can offer to farmers. However, the excessive use of one method over another, can lead to imbalances and result in the deterioration of the environment. In fact, each of these methods represents a single stone within a whole building and good agriculture requires proper integration of each method with all the other production factors. Good agriculture leads to an increase in production and thus, to economical land-use. It results therefore in the conservation of the natural heritage and safe-guarding the future. Like industrialized countries, developing countries undeniably have the right to agricultural intensification. In the present population context, it is a right to survival. One can only hope that they will not commit excesses that will in turn jeopardize their future. Intensification is of course expensive. 'I'd rather fell some trees than buy fertilizers' said an African; but intensification can be a profitable investment. Nowadays, the disastrous consequences of extensive farming, linked to overpopulation, in the tropical world are evident. In many industrialized countries, it is easy to foresee the even more disastrous consequences of the excesses of intensive commercial agriculture. Faced with problems that can already be identified, if the new farmers of the Third World repeat the same errors, they will be responsible for mortgaging their future for ever. References: *(1) Strategies Alimentaires et Nutritionelles. Concepts - Objectifs - Practiques. Proceedings of a workshop. Edited by R Dellere and J J Symoens, CTA, Academie Royale des Sciences d' Outre-Mer. *(2) Perimetres irrigues villageois en Afrique Sahelienne, J Hecq and F Dugauquier, CTA, 1990. *(3) Petite hydraulique agricole a Madagascar, J Hecq and F Dugauquier, CIA, 1990 | Over the centuries, farmers in the tropics have survived through good and bad years, in balance with the environment. But today population pressure on the land precludes practices that enable the environment to recover from extensive cropping...