Efficacy of reduced rates of chlorantraniliprole seed treatment on insect pests of irrigated drill-seeded rice.
Background: For the past decade, insecticidal seed treatment has been the most widely used control tactic against insect pests of rice (Oryza sativa L.) in the USA. Seed treatments are used primarily to control the most economically important early-season pest of rice, the rice water weevil (Lissorhoptrus oryzophilus Kuschel). This study was conducted to evaluate the efficacy of reduced rates of chlorantraniliprole seed treatment against the rice water weevil, fall armyworm (Spodoptera frugiperda J.E. Smith), and sugarcane borer (Diatraea saccharalis F.) under field and laboratory conditions. Concentrations of chlorantraniliprole in plant tissues were determined at vegetative and reproductive developmental stages of rice plants. Results: Chlorantraniliprole seed treatment reduced the densities of rice water weevil larvae relative to non-treated controls even at rates 75% lower than the label rate. Increased mortality of fall armyworm larvae was observed at reduced seed treatment rates relative to a non-treated control. Chlorantraniliprole seed treatment increased the mortality of sugarcane borer larvae at all rates relative to controls and the mortality was consistently higher in larvae that were fed stems from treated plants at the vegetative developmental stage than larvae that were fed stems from plants at the reproductive stage. Concentrations of chlorantraniliprole in plant tissues increased with seed treatment rate and decreased with plant age. Conclusion: This study has shown that reduced chlorantraniliprole seed treatment rates can provide adequate control against the rice water weevil, fall armyworm, and sugarcane borer, particularly at early developmental stages of rice plants.