Pesticides: a two-edged sword
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CTA. 1989. Pesticides: a two-edged sword. Spore 19. CTA, Wageningen, The Netherlands.
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Insects, diseases, and weeds account for 40% of the annual crop and harvest losses in the ACP countries. But the use of pesticides, the most commonly adopted remedy against these scourges, has its dangers both for man and environment The only way to...
Insects, diseases, and weeds account for 40% of the annual crop and harvest losses in the ACP countries. But the use of pesticides, the most commonly adopted remedy against these scourges, has its dangers both for man and environment The only way to reduce these risks to a minimum is to follow rigorously the instructions for use and use the new, less toxic products and alternative techniques that are becoming available. Crop pests are legion in the tropics, especially in humid zones where they can bring about a substantial destruction of the crops. Lower yields, loss of quality, and devastation of stores can almost halve the harvest each year in developing countries Protection of plants by spraying against pests (in conjunction with improved seed and fertilizer and better husbandry techniques) therefore remains a vital factor in increasing production in West Africa, improved spray treatment has increased the cotton yield by more than 200kg to 1000 kg/ha in 25 years. The use of pesticides, is considerably lower in developing countries than in industrialized nations, but is rising continuously. Africa still accounts for only 5% of world pesticide use but has increased consumption rune fold in a decade or so. However, Third World countries have a poor safety record, and so it is that agrochemicals are frequently condemned and referred to as Third World poisons and the scourge of pesticides. Nevertheless, despite the undeniable toxicity of these products, agriculture cannot manage without them at present. On the other hand, there is a long way to go before they are utilized most effectively and the risks to both population and ecology are reduced. Educating the conscience of international businesses For governments the first challenge is to control the import of plant sprays which are not manufactured locally. Very few ACP countries (Africa in particular) possess the facilities to test and pass these products as safe for use when correctly handled and applied. This lack of effective control opens the door to many abuses: the import of products which are unsuitable for the purpose, the sale of dangerous products which are banned or strictly controlled in other countries; and the criminal trade in useless substances of doubtful origin. International arganizations are currently seeking to coordinate legislation on sprays throughout Africa and in order to reduce the costs of such measures, regional groups have been suggested where safety measures taken and tests done in one zone would be valid in all countries with a simiar climate At the same time there have been moves to mobilize the conscience of the international pesticide trade. In 1985 the FAO adopted the Code of Conduct for the Distribution and Use of Pesticides. It has been ratified by numerous organizations including GIPAP which unites 1000 companies producing 90% of pesticides used in the world. This code, which is not compulsory, is the first step towards inducing a greater sense of responsibility on the part of firms and governments in improving the control of sprays between the producer and end-user. An updated and more precise version of the code, which will increase its effectiveness, is currently being: studied. Necessary precautions Certain countries, however, have already gone further. The European Community has recently issued an edict stipulating that importing countries must give their prior consent to any introduction of a banned or controlled chemical product before its export can be authorized. This clause is also being discussed at international level by the Pesticide Action Network (PAN). Indeed, even if the application of these directives is taking longer than their formulation, the first step has been taken. Both industrialists and nations have understood the weight of responsibility they bear. In order to help the importing countries the International Register of Potentially Toxic Chemical Products supplies information on the relevant regulations, and the OMS instructs on the safe usage of pesticides. Rigorous labelling of exports is also one of the good resolutions taken by producers. Risks remain, even if the import of safe and appropriate products can be guaranteed. Lack of care in handling and applying pesticides often causes serious accidents and illegal uses such as fishing and poaching, or even criminal purposes (poisoning suicide, abortion) all too often increase the mortality figures. As with any chemical product, the use of pesticides requires precautions to ensure the protection of those applying them, the safety of the consumers of the treated crops, and the preservation of the environment. Storing sacks of pesticides next to foodstuffs in poorly-ventilated depots, handling torn sacks or leaking drums without gloves, and spraying with faulty equipment are some of the most frequent causes of poisoning. The many risks of contamination demand that the basic rules of safety are followed implicitly. Simple precautions and procedures which are not always put into practice include not checking wind direction and strength and washing hands after application. This sort of negligent affitude is sometimes accompanied by careless application. It is imperative that manufacturer's instructions are followed exactly. A product that kills locust larvae may not necessarily be the right thing to apply to tomato plants and, when a farmer treats his fields with the product he has to hand or that is available at market, he risks poisoninghimself orothers with the crops and vegetables from his farm and garden. Such practices which are too common and difficult to control, can have disastrous consequences on the health of consumers by contaminatingfood products and polluting water supplies. Furthermore, farmers do not always get the desired results from products which have to be applied at a precise dose and at a certain growth stage of crop or pest in order to be effective against target species. Herbicides, whichare now more commonly used, must be applied at a certain stage in the development of the weed for it to be killed. Usually cash crops are treated with appropriate pesticides whereas food crops, the poor relations of agriculture, all too often have to make do with products originally intended for other crops grown for export. Farmers themselves are not always primarily responsible for this hazardous state of affairs; they are poorly educated, they do not always know how to use these toxic substances, and often have expectations of performance and safety based on exaggerated claims made by salesmen and even extension staff. Aware of these difficulties and concerned with profits, development agencies and large-scale agricultural enterprises are trying to train their employees in the correct use of pesticides. Information and training must be a number one priority for agrochemical suppliers right down to the instructor in rural areas. For the iUiterate, FAO and GIFAP have designed pictorial labels which can be understood by anyone. GIFAP has also published several manuals and posters on handling, storage, safety precautions, and what to do if poisoning occurs, and these have been translated into local languages. But nothing can take the place of on-the-spot demonstrations and practical training courses. Those who sell pesticides must ensure from the beginning that their products are properly used. Pesticides are a two-edged sword beneficial or hazardous according to the use made of them. Incorporating other means of control If the inevitable weapon against pests is a chemical one, it is no longer considered as the panacea, and today other techniques have been introduced to reduce the dependence on chemical products. The first pesticides to appear in the 1940s, the organochlorines. of which DDT is the best known, are now prohibited almost world-wide. Very long-lasting, they can cause lasting damage to the environment and to human beings. The carbarnates and organo-phosphorus compounds were the second generation. They were widely used in agriculture and although these were more easily degradable, they were nonetheless toxic to people and mammals. But it is the third generation insecticides, synthetic pyrethroids. which came on the market in 1975 which are now most widely used. These products are harmless to man and beast and to the environment, and at the same time extremely effective against crop pests, especially the Lepidoptera. Even though less toxic, they need be applied at low dose rates: where 1 kg DDT or 400g parathion were once necessary, now only 10g of deltamethrine would be required. Unfortunately, repeated use of these pyrethroids induces resistance to them in insects so the selection of insecticides must be varied to extend their useful life. A fourth range of compounds is about to come onto the market. These are growth regulators which act on an insect's metabolism and disturbs their development. These are very selective, toxic to their target organisms only, and are effective at a very small dosage. Thus a promising new insecticide, which modifies the transformation mechanism in locust larvae, seems likely to replace the controversial organo-chlorine, dieldrin. But the cost of producing these complex molecules is high, and it will still be several years before their use becomes general in developing countries. Other types of products mimic natural substances and may be used in order to avoid causing serious ecological imbalances. For instance it is possible to synthesize the chemical messages which determine insects' sexual instincts (pheromones), which attract pests to certain plants (kairomones), or which repel them (allomones). Some can be used in traps, sometimes combined with chemical sterilizing agents, to kill or interfere with breeding. An example of their use is where the pink bollworm is becoming more resitant to insecticides and so Egypt has used the sex pheromone of this worm' which attracts the male, prevents him finding the female, and thus inhibits reproduction. Microbiological warfare is being developed on many other fronts: bacteria, viruses and fungi, to which insects are naturally victim, are being formulated and sprayed on crops like chemical pesticides. Their use - as yet not fully developed - will allow the reduction of and perhaps even substition for chemical pesticides. Both biotechnology (see SPORE 18) and using other insects which are hostile to pest species are also possibilities which can be considered in addition to the treatments outlined. With this wide range of weaponry available to farmers to fight these age-old foes, the <<all-chemical solution>> is no longer the only option. An integrated campaign which combines complementary techniques of chemical and biological control seems to be the solution for the future. Although a pesticide-free future must be the goal, the usefulness of these substances to safeguard the meagre crops in developing countries cannot be denied. However it is possible to kill pests without poisoning mankind or nature if the use of pesticides is reduced to the minimum necessary and where products are chosen more selectively, and their correct use is safeguarded by education and training.
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