Field efficacy of wintertime insecticide applications against greenbugs, Schizaphis graminum (Rondani) (Hemiptera: Aphididae) on winter wheat (Triticumaestivum L.)

Winter wheat producers in Oklahoma often combine an insecticide with a top-dress application of nitrogen during late fall and winter to control existing greenbug populations. We evaluated the efficacy of three classes of insecticides applied in cold weather field conditions ranging from −13.3 to 28.9 °C from 2002 to 2004 for greenbug control in winter wheat in replicated small plots. Insecticides provided control ranging from 0% to 98%, but generally responded similarly to temperature. Percent control of greenbugs resulting from applications of dimethoate, chlorpyrifos and λ-cyhalothrin was correlated with maximum, minimum and average daily temperatures that occurred two days post-treatment. While percent control was unique for each insecticide, a combined regression of percent control against average daily temperature predicted that a 95% level of control would be achieved when post-treatment temperatures exceeded 13.6 °C. Rainfall that occurred post-treatment affected the efficacy of dimethoate but did not affect the other insecticides. Insecticide persistence was extended under cooler temperatures, allowing acceptable control 14 days post-treatment if temperatures warmed. The decision to apply insecticides should be made based on existing treatment thresholds for greenbug, but if treatment with an insecticide is warranted, winter wheat producers can expect reasonable control of greenbugs from insecticides applied during the winter, as long as post-treatment temperatures exceed 13 °C within the following 14 days.

► Winter wheat producers often include an insecticide with their top-dress fertilizer applications during the winter to save application costs. ► Results of field experiments showed that insecticide applications in winter during cold temperatures produced lower efficacy for control of greenbugs in winter wheat. ► While efficacy was generally lower if temperatures remained cold during the first two days post-treatment, greater efficacy generally resulted after 14 days. However, if temperatures were high during the first two days post-treatment, efficacy did not change from 2 days to 14 days. ► Analysis predicted that if temperatures exceeded 13 °C during the two weeks following the application, satisfactory control of greenbugs resulted. ► Winter insecticide applications may be justifiable in areas where temperatures are likely to exceed 13 °C within two weeks following the application if field inspections showed that economic thresholds for greenbugs have been exceeded.