Fall insecticide treatments to manage spring infestations of alfalfa weevil (Hypera postica)

The alfalfa weevil, Hypera postica (Gyllenhal), is considered a severe pests of alfalfa throughout the state of Kansas. They are univoltine and are active during early spring and again in the fall. If timely insecticide treatments are not applied during the spring, alfalfa weevil larvae can significantly affect first-cutting yields as well as subsequent regrowth of alfalfa. Several management tactics have been utilized against these destructive weevils but only the use of synthetic organic insecticides have provided acceptable protection for the first spring cutting of the alfalfa crop. Preliminary studies during the 2011-2012 field season investigated the first-ever fall insecticide application in order to manage adult weevils. Following positive results, a full-scale study was implemented in the 2012-2013 season investigating the effects of fall application timing on spring alfalfa weevil infestations. Results have shown that late November applications significantly reduced populations of larvae in the treatment areas. However, while a statistical difference was present, the practical difference did not eliminate the necessity of applying spring chemical treatments. These data are presented along with a discussion of the expected outcomes for the 2013-2014 field season and the future success of the utilization of this strategy by Kansas farmers.