Biological control is here to stay
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Hammond, Winfred. 1995. Biological control is here to stay . Spore 56. CTA, Wageningen, The Netherlands.
Permanent link to this item: http://hdl.handle.net/10568/47028
Agrochemicals are proving too expensive and difficult to obtain in many parts of Africa and, on occasions, their excessive use has proved counterproductive and even dangerous to farmers. Integrated Crop Management, using few or no agrochemicals and...
Agrochemicals are proving too expensive and difficult to obtain in many parts of Africa and, on occasions, their excessive use has proved counterproductive and even dangerous to farmers. Integrated Crop Management, using few or no agrochemicals and relying on biological pest and disease control, offers a safer and more economic approach for many resource-poor farmers. Agrochemical pest control appears to be a straightforward and attractive means of solving pest and disease problems. Under certain circumstances, it may help reduce economic losses to farmers in the short-term. But we have to realize that pest problems are complex and diverse, and therefore ecologically sound pest management could be more complicated, particularly for resource-poor farmers in developing countries. Before we make recommendations or take decisions we have to examine, assess and understand each situation. Many researchers and practitioners thought that most pest control interventions could be applied entirely externally with minimal or no involvement by farmers: biological and genetic control involving release of beneficial agents, and the use of sterile males, are examples. But even in these cases farmers' participation and knowledge is required to report pest and disease outbreaks and to monitor results of actions taken by external agencies. In general, for effective Integrated Pest Management farmers must be consulted and included in revising methodology options and their application from the outset. Whatever methodology we choose is going to be influenced by farmers' attitudes, preferences, resources, education and training. And farmers even in a small community differ! I believe that a priority area for educating farmers is in the impact of agrochemicals on beneficial organisms. Farmers cannot be expected to know that the pests that attack their crops are themselves susceptible, in many cases, to predators and infection by diseases; the interaction is at microscope level and beyond simple field observation. Therefore it is difficult for farmers to appreciate that what kills 'bad' organisms may also kill 'good' organisms and that by destroying beneficial organisms the faster reproducing pest species can re-invade the crop un-checked, except by a further application of biocide. This, of course, is the route to biocide dependence and we have seen its consequences in the production of cotton, citrus and many intensively cultivated high value fruit and vegetable crops. What are the options? Choosing pest and disease tolerant varieties, and planting pest and disease free seed or other planting material, is a good start. The planting into well-prepared fertile soil gives plants the vigour to withstand pest attack and even to make good pest damage. Interplanting or intercropping offers less opportunity for pest populations to build up to damaging levels while rotation avoids soil pests, such as nematodes, multiplying. If pests are spotted, farmers must be aided to determine the levels at which they are economically damaging; too often farmers spray at the first sight of an insect or pathogen on plants, an interaction which if left undisturbed might result in an acceptable balance between pest and predators. I can give an example from the Brong-Ahafo Region of Ghana where, a few years ago, grasshoppers invaded the cassava fields. Left alone it is unlikely that the grasshoppers would have done very much damage. But grasshoppers are highly visible and so is the damage they do, restricted though that damage may be. So the farmers sprayed the grasshoppers and killed them; but unknowingly they also killed an important predator, a predator of the cassava mealybug. Needless to say, very soon we had reports of a resurgence of mealybug from this area where previously the pest had been well under control from its beneficial agent. However, a perfect solution was found by spraying pesticides on the next generation of grasshoppers developing on surrounding Chromolaena weed, so killing the generation of grasshoppers before they matured enough either to migrate to the cassava crop or to continue their life-cycle. But getting farmers to focus onto the weed rather than the more obvious target, the cassava, is a challenge. Farmers need education and training in the benefits of biological and integrated pest management in other ways too. For instance, integrated pest management does not totally exclude use of all pesticides; rather it involves careful use of pesticides to achieve the objectives without over-kill - especially over-kill of beneficial organisms. Many farmers still do not fully understand cause and effect in some pest control strategies: in Côte d'lvoire I remember farmers observing that they had no cassava mealybug for two or three years, whereas previously it had been a serious problem for them. They knew chemical control was not responsible because with chemical control the pest kept coming back. They did not know that the control of mealybug had been achieved by the release of predators. In such a situation it is difficult for farmers to integrate 'our' strategy into 'their' farm management. Prior to the advent of agrochemicals farmers survived by using natural or biological pest control methods. There were occasional disasters due to pest or disease epidemics contributed to by weather and other natural factors. But for thousands of years good management incorporating biological control sufficed. I believe that biological control is here to stay and prospects for it are much greater than we have thought in the past.