As in 2025, degree-day accumulations for Kansas alfalfa weevils are well ahead of normal across the entire state (Table 1). As air temperatures continue to increase, it is recommended that scouting for weevil activity should be occurring right now in all regions of the state. There are confirmed reports of weevil activity and evident pin-holing in south central Kansas and along the Oklahoma border.
Alfalfa weevil degree days are a great way to estimate what might be going on in the field and serve as a useful tool to know when to time scouting. Alfalfa weevil eggs begin hatching after 300 degree days have accumulated (Table 2). Since we cannot determine if eggs present were laid the previous fall or the current spring, in Kansas, scouting should start after 180 degree days have accumulated since January 1.
Be aware of insecticide resistance - while warmer spring temperatures allow for faster alfalfa weevil development, be aware that dramatic temperature drops can slow down alfalfa growth, making the plants unable to keep up with feeding damage. Treatment may be warranted in shorter fields between 3 and 7 inches tall when feeding is evident on the top inch of growth, and 1 to 2 larvae are present. If a field is treated, it is important to verify that the expected amount of control was achieved. In 2020, populations of alfalfa weevil resistant to lambda-cyhalothrin (Warrior II, Karate, Demand, etc.) were verified in northwest and southwest Kansas and Oklahoma.
While this resistance has not appeared to become a widespread problem for Kansas producers, a couple of fields reported in central Kansas last year where lambda-cyhalothrin had reduced efficacy. Oklahoma continues to have resistance statewide. Numerous products are available for alfalfa weevil control in Kansas for reference refer to our on-line “Alfalfa Insect Pest Management Guide”. When making management decisions, it is important to rotate modes of action, as this is an effective way to prevent the development of resistance.
For the most up-to-date alfalfa weevil degree day accumulations, visit the Kansas Mesonet Alfalfa Weevil Degree Day Calculator (https://mesonet.k-state.edu/agriculture/degreedays/).
Information provided by Anthony Zukoff, Extension Entomology – Garden City.
Stacy Campbell is a Crop Production Extension agent in the Cottonwood District (which includes Barton and Ellis counties) for K-State Research and Extension. You can contact him by e-mail at scampbel@ksu.edu or by calling 785-628-9430.