RESIDUAL ACTIVITY OF LAMBDA-CYHALOTHRIN AGAINST BEAN LEAF BEETLE (COLEOPTERA, CHRYSOMELIDAE) IN SOYBEANS

Bean leaf beetle, Cerotoma trifurcata (Forster), is the most consisten tly important pest on soybeans (Glycine max [L.] Merr.) in the North C entral region of the United States. Its major impact is from pod feedi ng by the 2nd generation in late August/early September. Although most insecticides registered for control of this insect have a short pre-h arvest interval, others such as permethrin cannot be used against the 2nd generation because of the long time period (60-d pre-harvest inter val) before the crop can be harvested following application. A newly r egistered pyrethroid lambda-cyhalothrin has a 45-d pre-harvest interva l on soybean and was tested for long-term efficacy against second gene ration bean leaf beetle. Three weekly applications were made beginning in mid-August in field-grown soybeans, after which bean leaf beetles were sampled until mid-September. Data on pod feeding were recorded on 2 successive weeks in September. All weekly applications of lambda-cy halothrin provided significantly greater control of bean leaf beetles until plant maturity in late September. Pod feeding also was limited b y lambda-cyhalothrin. When a large 2nd generation of bean leaf beetles is anticipated, a single application of lambda-cyhalothrin provides l ong-term control if applied at the beginning of the emergence of the 2 nd generation beetles.