Alfalfa weevil development is running ahead of the crop this spring in Wisconsin, and state entomologists are urging producers to begin scouting. Krista Hamilton of the Wisconsin Department of Agriculture, Trade and Consumer Protection told Brownfield that egg hatch has just started in parts of southwestern Wisconsin. One week early, she said, compared with a typical year.
Hamilton said initial egg hatches are showing up from Grant County over toward Rock County, but larvae are still sparse in fields right now. She warned that if someone used a sweep net today they would likely not find many larvae because the eggs are only beginning to open. Egg hatch in SW is the current pattern, Hamilton said, and observers should note that insect development is ahead of plant development.
Growing degree units indicate the hatch will push north and east over the coming days, and the department’s crop survey team is preparing to sample first-cut alfalfa early. Hamilton expects hatch to move into Iowa, Crawford and Vernon counties to the north and into Columbia County to the east in the next week. Scouting starts next week, she told Brownfield, as surveyors begin systematic sampling of first-crop fields.
Where to scout
Producers should focus scouting on first-crop stands and watch for early-stage larvae in fields that warm faster or have south- or southwest-facing slopes. Because larval populations can build quickly, checking multiple spots across a field with a sweep net and noting alfalfa height and vigor will help time any needed control measures. Hamilton emphasized comparing insect stage to plant growth before deciding on treatment.
Hamilton also noted alfalfa weevils have already been reported across the border in Illinois and in parts of Iowa, so southwestern Wisconsin’s early finds fit a broader regional pattern this spring. Growers in adjacent counties should expect hatch to appear soon and factor that into their cutting plans and pest-management scouting schedules.
Crop surveyors with the state will begin sampling first-crop alfalfa next week to map hatch progression and advise on thresholds and timing, providing county-level updates as they collect results. This coordinated sampling will inform any recommended actions for producers in affected counties.
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