Statewide Alfalfa Weevil Scouting Week 4

Alfalfa weevil pressure appears to be winding down for the season. Many of the fields that county educators have been scouting have been sprayed to control the alfalfa weevil populations that exceeded the action threshold this spring. Even fields that did not have alfalfa weevil populations that reached the action threshold are declining due to the natural maturation of the pest. Some early-stage larvae can be found in fields, but pupal cocoons are readily found in many alfalfa stands. Larvae progressing to the pupal and adult stages are no longer an economic concern for alfalfa, so a treatment to a declining population is not likely to be an economically sound decision. Table 1 provides the scouting numbers that our team saw last week. Larvae counts are generally lower with many counties unable to report numbers due to spray applications or harvest. It is important to emphasize that your field may be different than what we are seeing, so it is important to scout and use the recommendations in Table 2 to gauge control response.

Table 1: County alfalfa weevil scouting reports for May 4 – May 10

Table 2. Alfalfa Weevil Threshold Recommendations

As we get closer to harvest, be sure to account for harvest restrictions that are attached to an insecticide application. Be sure to read and follow the pesticide label to make an effective application. An additional resource that is helpful is the OSU/ MSU IPM Guide. If there is alfalfa weevil population present at harvest, it is good practice to scout the regrowth a few days after harvest to make sure the alfalfa weevils are not persisting into the second cutting.