Impact of Water Management on Efficacy of Insecticide Seed Treatments Against Rice Water Weevil (Coleoptera: Curculionidae) in Mississippi Rice

Two experiments were conducted at the Delta Research and Extension Center in Stoneville, MS, during 2011 and 2012 to determine the impact of water management practices on the efficacy of insecticidal seed treatments targeting rice water weevil, Lissorhoptrus oryzophilus Kuschel. Larval densities and yield were compared for plots treated with labeled rates of thiamethoxam, chlorantraniliprole, and clothianidin and an untreated control. In the first experiment, plots were subjected to flood initiated at 6 and 8 wk after planting. Seed treatments significantly reduced larval densities with the 8-wk flood timing, but not the 6-wk flood timing. Overall, the treated plots yielded higher than the control plots. In the second experiment, the impact of multiple flushes on the efficacy of insecticidal seed treatments was evaluated. Plots were subjected to zero, one, or two flushes with water. All seed treatments reduced larval densities compared with the untreated control. Significantly fewer larvae were observed in plots that received one or two flushes compared with plots that did not receive a flush. All seed treatments resulted in higher yields compared to the untreated control in the zero and one flush treatments. When two flushes were applied, yield from the thiamethoxam and clothianidin treated plots was not significantly different from those of the control plots, while the chlorantraniliprole treated plots yielded significantly higher than the control. These data suggest that time from planting to flood did not impact the efficacy of seed treatments, but multiple flushes reduced the efficacy of thiamethoxam and clothianidin.