Kansas alfalfa growers are dealing with what may be the state’s worst-ever infestation of webworms.

"People who have three to four decades of experience with this are saying they’ve never seen anything like this before," says Randy Higgins, Kansas State University entomologist. "Billions of these larvae are continuing to raise havoc in eastern Kansas and reports also are starting to come in from western regions."

Higgins says webworms are green to yellow caterpillars measuring up to an inch long. They have three prominent black spots and one or more hairs on each side of each segment. The black spots are arranged in a triangle. Each worm has a light stripe down the center of its back.

Webworms feed on green portions of alfalfa leaves, leaving a network of veins to dry and turn brown. They also feed on certain weeds – especially pigweeds – and occasionally, soybeans.

Some growers have sprayed or cut early to curb the defoliation. But webworms produce several generations per season, so the problem likely will persist until late in the year, says Higgins.

The problem has been exacerbated by hot, dry weather. Some alfalfa didn’t get more than 8-10" tall before blooming or being defoliated by webworms. Those stands likely weren’t able to recharge stored carbohydrates, and may be susceptible to winterkill. Also, growers may have difficulty establishing fall-seeded alfalfa because of the worms, according to Higgins. Learn more about webworms at www.oznet.ksu.edu/entomology/extension/KIN.htm