Residual efficacy of three spinosad formulations against Psorophora columbiae larvae in small rice plots.

Experiments were conducted to determine the residual efficacy of both a briquette and a granular formulation (2 rates) of a numbered spinosad compound against Psorophora columbiae larvae in small rice plots. Comparisons were also made between the numbered compounds and labeled granular and briquette formulations of methoprene. Both rates of the spinosad granules had the highest initial efficacy (100% control), with the spinosad briquette being the least effective. However, 1 wk after treatment, the spinosad briquette was equally effective to both spinosad granules, suggesting a slow release in the briquette. The experimental briquette and the high rate of the experimental granules had the most residual activity, providing over 80% control for 33 days posttreatment. The granular methoprene formulation was the least residually effective compound, providing only 12% control at 7 days posttreatment.