Pictured: Sweeping an alfalfa field. Photo by K. Hamilton DATCP
Overwintered alfalfa weevil adults are resuming activity much earlier than in 2025. The 10-day forecast calls for the start of spring egg laying in southern Wisconsin alfalfa fields.
Minimum winter temperatures were not low enough to significantly reduce adult weevil winter survival, and it will be important to plan for sampling first-crop alfalfa in May. Based on Wisconet two-inch soil temperature data, adult weevils protected in alfalfa stubble or beneath leaf debris were probably not exposed to lethal cold temperatures below the 13°F threshold for this insect, even during the most intense cold period January 22-25.
DATCP’s alfalfa surveys are scheduled to begin the week of May 10-16 and crop advisors should likewise start checking fields for weevil larvae at that time, or as 300 degree days are reached across the state.
The earliest larvae are likely emerging in Grant County eastward to Rock County. A map showing current alfalfa weevil degree day accumulations is available on the UW-Extension Vegetable Disease and Insect Forecasting Network (VDIFN) site: https://agweather.cals.wisc.edu/vdifn?type=insect&model=alfalfa-weevil
Sign up for DATCP’s Field Notes: https://datcp.wi.gov/Pages/Programs_Services/FieldNotesNewsletter.aspx
