By Scout Nelson
Alfalfa producers across the Upper Midwest are facing increasing challenges from alfalfa weevil populations during the 2026 growing season. Longer feeding periods and concerns about insecticide effectiveness are making pest management more difficult and increasing the importance of careful field monitoring.
Anthony Hanson, Regional Extension Educator, University of Minnesota Extension - Field Crops Integrated Pest Management, highlighted that alfalfa weevil continues to be one of the most important insect pests affecting forage production. The pest damages plants by feeding on leaves, reducing crop quality and yield during critical growth stages. Larvae create holes in leaves and can leave fields with a gray or frosted appearance when infestations become severe.
The insect typically completes one generation each year. Larvae emerge in spring and feed heavily on alfalfa before developing into adults. While adult weevils are often present later in the season, they generally cause little economic damage compared to the larval stage.
Researchers and producers have observed an extended feeding season in recent years. Some fields experience damaging populations beyond the first harvest and into second-cutting regrowth periods. This trend requires growers to continue scouting fields longer than in previous years and remain alert for additional feeding activity.
Regular field scouting remains the foundation of successful management. Producers are encouraged to inspect plants for feeding damage, count larvae, and evaluate whether economic thresholds are reached before making treatment decisions. Early detection allows farmers to select the most effective and economical management strategy.
Timely harvesting is often one of the best management tools available. Cutting alfalfa at the appropriate growth stage can reduce larval populations and limit further crop injury. Harvesting may provide benefits similar to insecticide applications in many situations.
Another growing concern is the possibility of reduced effectiveness of some pyrethroid insecticides. Reports of control failures have increased in certain areas, raising concerns about potential resistance. Because of this, experts recommend rotating insecticide groups when treatments are necessary and avoiding unnecessary applications.
Integrated pest management practices, including scouting, threshold-based decisions, harvest timing, and careful insecticide use, continue to provide the best long-term approach for protecting alfalfa yields and preserving future control options.
Photo Credit: gettyimages-0shut0
Categories: Minnesota, Crops, Hay & Forage, Alfalfa