Peak Alfalfa Weevil Season Starts In North

Surveys to assess alfalfa pest populations and distribution are underway, according to the Department of Agriculture, Trade and Consumer Protection.

As expected for early June, alfalfa weevil larvae, pea aphids, and plant bugs are currently the most abundant insects.

Sampling across Columbia, Dane, Green, Jefferson, Rock, and Sauk counties indicates alfalfa weevil larval counts range from 0.1-4.8 per sweep. The average is approximately 3.9 larvae per sweep. Estimates of leaf tip feeding were above the 40 percent economic threshold in over half (55 percent) of the fields surveyed in the past week. This signals that cutting the first crop should be a priority for the next rain-free window.

The peak weevil damage period is in full swing from Madison to Eau Claire, according to DATCP. In areas north of Wausau, weevil feeding intensifies in the week ahead (June 7-13). More weevil grubs will enter the most destructive third and fourth instars.

DATCP advises cutting alfalfa as soon as the weather permits to avoid damage by the larger late-stage weevil larvae. Feeding damage by alfalfa weevil and other pests can still happen under windrows if hay cannot be baled shortly after cutting.

Alfalfa regrowth should be checked for signs of weevil injury up to five days after harvest and until new growth of the second crop is established.