Evaluation of Dichlorvos for Insect Control in Stored Rough Rice2

Abstract

Dichlorvos was evaluated as a direct-spray application at 5, 10, 15, and 20 ppm in comparison with malathion at 14 ppm for insect control in rough rice. Jar tests and small-bin tests were used. Jar tests revealed short-term protection by dichlorvos against infestation by rice weevils, Sitophilus oryzae (L.), and lesser grain borers, Rhyzopertha dominica (F.). Confused flour beetles, Tribolium confusum Jacquelin duVal, were controlled immediately after treatment but not at subsequent intervals. Dichlorvos was more effective than malathion in reducing rice weevil emergence. While high moisture content of the rice at the time of treatment adversely affected the duration of protection, it had no obvious immediate effect, because nearly complete control of the rice weevil was obtained at the time of treatment. This control occurred in jar tests and in small bin tests. Residues on rough rice were as high as 7.3 ppm 24 hr after treatment, but in 30 days they were 0.87 ppm on rough rice, 3.1 in hulls, 0.41 in bran, 0.03 in brown rice, and 0.02 in milled rice.