Keep Watching for Alfalfa Weevils in Northern Counties

May 28, 1999
Much of the first crop of alfalfa has been cut in southern and central Illinois, and harvest is upon us in northern Illinois. Growers should keep watching for alfalfa weevils, either on the first crop or in the stubble as the second crop greens up. Alfalfa weevil activity was relatively intense for about 3 weeks this spring, and some economic infestations linger. However, Matt Montgomery, Extension Unit Assistant/Crop Systems in Sangamon and Menard counties, found some alfalfa weevil larvae infected with the fungus Zoopththora phytonomi. The cool, wet weather has been ideal for the development of epizootics of this natural control factor. Unfortunately, the fungus did not keep weevil densities from reaching economic levels in many fields. Nevertheless, the presence of discolored weevil larvae curled around alfalfa stems or leaves suggests that the disease could be having an impact. Before making a decision to spray an insecticide, try to determine whether alfalfa weevils are healthy or diseased.

For the best management strategies for alfalfa weevils, including early cutting and suggestions for insecticides, refer to issues no. 6 and no. 8 (April 30 and May 14, respectively) of the Bulletin. Take note of harvest intervals if an insecticide is used.--Kevin Steffey

Author: Kevin Steffey