Adult alfalfa weevils become active and start laying eggs as soon as temperatures exceed 48°F. Alfalfa weevil eggs develop based on temperature, or accumulating degree days, and hatching can start around 200-300 degree days. Start scouting alfalfa fields south of Interstate 80 at 200 degree days and fields north of Interstate 80 at 250 degree days. Based on accumulated temperatures since January, weevils could be active throughout southern and central Iowa (Figure. 1).
Iowa State University
Hodgson, Erin W., "Alfalfa Weevils Active Throughout Southern and Central Iowa" (2017). Integrated Crop Management News. 2431.
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