On May 15, I scouted a stand of alfalfa in Champaign County and found numerous third and fourth instar alfalfa weevil larvae by using a sweep net. By May 16, 461 degree days (base 48ºF) had accumulated since January 1, 2013 for Champaign. The average degree-day accumulation by this date for the preceding 11-year period is 510. So, we are just slightly behind this long-term average. Although larvae were numerous, I did not detect significant defoliation. I anticipate this will soon begin to occur. I encourage readers of this Bulletin to visit the on-line Pest Degree-Day Calculator maintained by the Illinois State Water Survey for degree-day estimates and projections for a variety of important insect pests.
Producers should consider a rescue treatment for alfalfa weevils when 25% to 50% of leaf tips are skeletonized and three or more weevil larvae can be found per stem. Following a cutting, a rescue treatment may be needed when larvae and adults are feeding on more than 50% of crowns and regrowth has been stunted.
For more information about the life cycle, injury, scouting, and management, please click on the link below.