Control of Insect Vectors to Prevent Virus Infection of Rice Plants1

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Abstract
The rice crop in Asia suffers serious losses from several insect pests and their control is essential for obtaining better crop yields. Also, some of the long-known rice problems often described as physiological diseases have in recent years been identified as leafhopper- and planthopper-transmitted virus diseases. This paper describes experiments to devise techniques for protecting the crop from the vectors and thus prevent virus spread. Greenhouse experiments with several insecticides showed that carbaryl, phosphamidon, and phorate when applied to the soil surface killed the rice green leafhopper, Nephotettix impicticeps Ishihara, feeding on the plants, and had longer residual effects than foliar treatments. This leafhopper is the vector of tungro, the commonest virus disease of rice in the Philippines. In field experiments these compounds, applied to the soil surface or paddy water at a rate of 3 kg per hectare, effectively controlled the leafhopper population, prevented virus infection, and increased rice yields up to 6-fold. Lindane, although effecting a significant degree of control, was not so effective as carbaryl, phosphamidon, and phorate. Of these, phorate was most effective and had the longest residual period. A combination of 2– kg per hectare each of lindane and carbaryl, when applied at 30- and 15-day intervals, respectively, provided highly effective Asiatic rice borer. Chilo suppressalis (Walker), and leafhopper control, prevented virus infection, and increased yields. Insecticidal effectiveness declined as the rate of application was reduced for either insecticide. In large-plot experiments a combination of lindane and carbaryl treatments at 30- and 15-day intervals, respectively, each at 3 kg per hectare, provided more effective insect control and re suited in greater yield increases than weekly sprays with 0.04% endrin.

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