Alfalfa webworm, Loxostege commixtalis.
Adult alfalfa webworm
Alfalfa webworm egg masses.
Webworm larva on soybean
There are two species of webworm in Kansas, the garden webworm and the alfalfa webworm, and both will also attack soybeans. The larvae are slender, greenish, black-spotted caterpillars that produce significant amounts of webbing on the foliage. Later instars exhibit three dark spots on the side of each segment, each possessing one to three bristle-like hairs. A light stripe also runs down the middle of the back. These insects overwinter as pupae in the soil. Pigweeds are a preferred host plant of the garden webworm and herbicide applications can sometimes force the movement of larva into adjacent fields. There are at least four generations annually. Larvae are usually the most abundant in late July to mid-August, but may cause damage through September. Early cutting will often eliminate the problem. However, if the crop is more than two weeks from cutting, and 25 to 30 percent of the terminals are becoming webbed, one of the following sprays should be used. Use sufficient gallonage and pressure to thoroughly cover and penetrate the foliage.
Please refer to the most recent version of the Alfalfa Insect Management Guide for specific control alternatives.
Page last updated 10/29/2013 by J.P. Michaud.