VIETNAMESE farmers have halved the amount of pesticide they use on their rice fields after experimenting to find out if they really needed the chemicals. Agricultural experts from eight Asian countries will meet at the International Rice Research Institute in the Philippines next month to learn how such science down on the farm can improve farming.
Research at the IRRI, one of the 16 laboratories of the Consultative Group for International Agricultural Research, has shown that insects that eat leaves make little difference to the rice yield. 鈥淵ou can remove half a plant鈥檚 leaves, and it will make the same amount of rice,鈥� says Kong Luen Heong of the IRRI. The larvae of leaf-folder moths eat less than that, but 鈥渇armers all over Asia spray it, because it does such visible damage, they are sure it must be hurting yields鈥�.
So convinced are they, that spraying young rice against leaf-folders accounts for 30 to 50 per cent of all pesticides used by Asian rice farmers. 鈥淭hey come under pressure to spray through advertising on billboards, radio and TV,鈥� says Heong. 鈥淲hen we told them they didn鈥檛 need to, they just said, we鈥檝e been doing this for years, how can it be unnecessary?鈥� He says that the main obstacle to the introduction of integrated pest management, which combines biological control with minimal pesticide use, 鈥渋s that farmers don鈥檛 believe us鈥�.
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But when scientists from the IRRI and Cantho University in Vietnam met farmers in the fertile Mekong Delta, the farmers admitted they did not like spraying, and often felt ill afterwards. 鈥淭he insecticides they use are among the most toxic,鈥� says Heong. They include methylparathion, a highly toxic organophosphorus pesticide made locally, and insecticides from the European multinationals Bayer and Ciba.
鈥淪o we challenged the farmers to spray part of their fields, and leave the rest alone,鈥� says Heong. Not everyone took part, but when farmers saw that unsprayed rice gave normal yields, 鈥渢hey all stopped spraying鈥�. More than half the farmers in the delta province where the programme started have now got the message, says Heong, and 鈥渟ome are organising further experiments, to see if they need other pesticides鈥�.
Now that they are no longer spraying for leaf-folders, they may find they have little need of other insecticides. 鈥淪praying so early in the season killed the spiders, crickets and beetles that eat rice pests,鈥� says Heong. In a village in the Philippines which has also stopped spraying leaf-folders, there has been a proliferation of such predators, as well as frogs and fish which also eat rice pests. The return of the predators 鈥渕eans other insecticides may not be so necessary any more鈥�, says Heong. Insecticides account for 90 per cent of pesticides used on Asian rice.