It’s time to scout your alfalfa fields for plant damage!
Alfalfa weevil larvae are hatching in Wisconsin and are expected to begin impacting the Southern and Central regions on ~May 19th and the Northern region on ~May 26th.
Photo Credit: Krista Hamilton, Department of Agriculture, Trade & Consumer Protection, Wisconsin
Scouting
Walk a W-shaped pattern in the field. Hand-collect alfalfa stems or examine the tops of 50 alfalfa stems at random for signs of weevil feeding.
Treatment Threshold
The treatment threshold for first crop alfalfa is when 40% or more of your stems show signs of alfalfa weevil feeding and you are more than seven days from harvest.
While scouting for larvae with a sweep net is useful to identify the pest in the field, treatment thresholds are not based on the number of larvae per sweep.
If there is significant damage prior to the first cut, scout regrowth thoroughly to ensure weevil larvae are not damaging new stems or crown buds.
Integrated Pest Management Strategies
Timely harvest is often the best management strategy for alfalfa weevil. Beneficial insects such as parasitic wasps and predatory beetles effectively control alfalfa weevil populations. Chemical control may be warranted if damage exceeds the 40% alfalfa stem feeding threshold. Find more information about management strategies in this alfalfa weevil resource.
Additional Resources
Learn more about alfalfa weevil with UW-Madison Extension’s Managing Alfalfa Weevil in Wisconsin Alfalfa Fields resource.
Subscribe to the DATCP Pest Survey Program’s Field Notes newsletter for pest updates throughout the growing season.
If you found this information online, you can sign up for insect pest text alerts.
Last updated: May 14, 2025