MANHATTAN, Kan. – Handpicking is an effective way to control bagworms through much of the year. But, it’s often incomplete, due to the bags’ site-matching camouflage and sheer numbers.

"Spraying can be an unsuccessful control, too, unless you time it right and do it thoroughly," said Ward Upham, K-State Research and Extension horticulturist.

In Kansas, the year’s new bagworms usually begin to leave the protection of their mother’s bag in late May. Although a bit smaller than a pinhead, they immediately start feeding and spinning a silk "coat." Most remain near their birthplace, but some may also ride to other plants on the wind and a string of silk.

"That’s when they’re least likely to be noticed, yet most vulnerable to controls," Upham said. "So, we typically recommend Kansans spray for bagworms in June, to give all the year’s eggs time to hatch."

Bacillus thuringiensis is an effective control for June applications, he said. Other insecticides commonly used for bagworms include Orthene, Dursban, malathion and Sevin.

Through summer, the worms’ "coat" gradually becomes a 1- to 2-inch long bag that’s studded with leaf fragments. It provides increasing amounts of camouflage and protection as the larvae grow and consume increasing amounts of needles or leaves.

"By August, applying controls can be a waste of time and money, because the larvae become so large and tough. Plus, that’s when they begin to stop feeding and seal themselves in – to hang like a Christmas tree ornament and work on becoming an adult," Upham said.

The adult males (small, clear-winged moths that look like a wasp) emerge in September. They mate with the females – who stay in their bag and lay eggs, protected from any control except handpicking.