Greenbug resistance management on sorghum with insecticide mixtures: a biological and economic analysis

Several tactics were evaluated for insecticide resistant greenbug, Schizaphis graminum (Rondani), control on sorghum. During the first 2 yr of this research, control by chlorpyrifos, carbofuran, and malathion and mixtures of the latter 2 chemicals plus piperonyl butoxide with chlorpyrifos were compared on sorghum. Chlorpyrifos provided < 60% control. The mixtures of chlorpyrifos + carbofuran or malathion provided good control of insecticide resistant greenbug. The mixture of chlorpyrifos + piperonyl butoxide provided mediocre control of resistant greenbugs. In 1996, an experiment was designed to evaluate the effects of greenbug population insecticide resistance ratio and preexposure of greenbugs to chlorpyrifos on control by mixtures of chlorpyrifos with carbofuran or malathion. About half of the plots were presprayed with chlorpyrifos (0.28 kg [AI]/ha) 4 d before applying individual insecticides or mixtures. Plots were infested with 2 ratios of resistant: susceptible greenbugs (1:3 and 3:1, respectively). Application of mixtures of chlorpyrifos + malathion provided best control followed by chlorpyrifos + carbofuran and chlorpyrifos. Prespraying greenbugs with chlorpyrifos did not affect their control with subsequent insecticide resistance management mixtures. The difference between the 2 ratios was significant with the lowest greenbug densities in plots dominated by susceptible individuals. There was a significant yield response to greenbug densities. The highest yields were obtained in plots sprayed with chlorpyrifos + malathion mixtures. When chlorpyrifos was applied to greenbug populations dominated by resistant aphids, yields were lower than in the infested control plots where greenbugs were not sprayed. Economic analysis of the data further demonstrated the advantage of the chlorpyrifos + malathion mixture for controlling insecticide resistant greenbug.