Kansas Farmers Advised to Scout for Alfalfa Weevils

Changing weather patterns may increase risk of early-season weevil damage to alfalfa crops

Mar. 19, 2026 at 6:09pm

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With a warmer start to spring, Kansas State University researchers are urging alfalfa farmers to closely monitor their fields for signs of alfalfa weevil larvae activity. Alfalfa is one of Kansas' most valuable crops, and weevil infestations can cause significant damage if not caught and treated early.

Why it matters

Alfalfa is a crucial crop for Kansas, generating hundreds of millions in annual revenue. Weevil infestations, if left unchecked, can severely impact yields and quality. Early detection and proper management are key to protecting this important agricultural resource.

The details

Alfalfa weevil larvae typically become active around 300 growing degree days. Producers should look for pinholing and skeletonization of leaves at the top of the alfalfa plants, which indicates weevil feeding. The recommended scouting method is to cut 30-50 random stems, shake them in a bucket, and count the average number of larvae per stem. Treatment may be warranted if there are 1-2 larvae per stem in 3-7 inch tall plants, or 4 larvae per stem in 8-14 inch plants with 30% feeding damage.

  • Alfalfa weevil larvae typically become active around 300 growing degree days.

The players

Anthony Zukoff

A Kansas State University Extension entomologist who is advising alfalfa farmers on monitoring and managing alfalfa weevil infestations.

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What they’re saying

“Cold, dry weather that slows or hinders the growth of alfalfa may make it more at risk from serious weevil damage early in the season as the plants may not be able to keep up with weevil feeding.”

— Anthony Zukoff, Extension Entomologist

“Very tiny larvae typically are not active until around 300-degree days have accumulated. Spraying too early, before threshold, likely will require additional spraying before the first cutting.”

— Anthony Zukoff, Extension Entomologist

What’s next

Producers should continue to monitor their alfalfa fields and be prepared to treat for alfalfa weevils if thresholds are reached. They should also consider rotating to a different insecticide mode of action if a product was ineffective the previous season.

The takeaway

Early detection and management of alfalfa weevils is crucial for Kansas farmers to protect their valuable alfalfa crops. By closely scouting fields and acting quickly when thresholds are met, producers can minimize the impact of this pest and preserve alfalfa yields and quality.