A new analysis of insecticide use in rice in the Philippines and Vietnam has found that a large proportion of the insecticides currently used are unnecessary. Researchers at the International Rice Research Institute and the Visayas State College of Agriculture in the Philippines and the Ministry of Agriculture in Vietnam interviewed over 950 farmers in selected areas of these countries to compare insecticide use patterns. However, insecticide use patterns in areas studied did not appear to reflect pest situations. In both sites, there were no serious pest attacks during the periods when the surveys were done. In Vietnam, farmers use insecticides to protect their crops from leaf damage in the early stages because they perceive that this damage can lead to yield loss.
Farmers often believe that insects are the main constraints to high yields.
Studies have shown, however, that such leaf damage does not reduce yields. Using insecticides in this manner can lead to a disruption of natural control mechanisms, which then require additional sprays against the secondary pest, the brown planthopper. The authors' evidence indicates that the results of such experiments may have influenced policy makers to assume that intensification of rice cultivation necessarily leads to increased pest losses and that high production is not possible without higher pesticide inputs. The authors conclude that these perceptions, although not necessarily true, have strongly influenced the rapid increase in insecticide use on tropical rice. A study in Indonesia has shown that when farmers reduced insecticide sprays on rice crops from more than four to about one per season, average yields rose from 6.1 to 7.4 tonnes per hectare.