Weevil Research: New Chemistries and Old Predators

The alfalfa weevil complex is the most severe insect pest of alfalfa in California. Because weevil larvae are the first insect pests of the production year to require management actions consideration of possible effects on pest management for the rest of the season must be made. Organophosphate and carbamate insecticides have provided acceptable weevil control in the past. However, the occurrence of these pesticides in surface waters has led to an emphasis on alternatives. New classes of products have been registered and others are being considered for registration. Although these new products may facilitate protection of surface waters, they may not have the optimal properties for IPM in alfalfa. Compounding these problems is the out-dated threshold developed in the 1970’s used to determine the need for insecticide applications. This threshold of 20 weevil larvae per sweep was based on cultivars not grown anymore and hay values, production costs, yield expectations that are significantly different today than in the 1970’s. Studies were conducted in 2002 and 2003 to evaluate the fit of the new and old materials into a current alfalfa IPM program and to examine the impact of the alfalfa weevil complex on alfalfa productivity.