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Seek Small Bagworms on Evergreens

Did you ever play hide-and-seek as a kid? I’m sure many of you did. A common landscape pest plays, well, just “hide” with us on our evergreens – the bagworm. The insect does it not by hiding in the traditional sense, but by utilizing camouflage. In June, while bagworms do the hiding, we need to do some seeking.

Even if you have never had bagworms, they can infest your evergreens, and before you know it you have damage from their feeding activities. This becomes disturbingly noticeable in “hotspots” of infestation in rural windbreaks, and in prominently featured evergreens in home landscapes.

Purdue entomologist Cliff Sadof said that homeowners should inspect trees in June for bagworm. “Bagworms can be controlled by spraying the foliage with insecticides after eggs have hatched and small bags are seen on the trees,” he said. These elusive pests can kill evergreens, their primary target.

“Early in June, the insects hatch from eggs which wintered in the old bags attached to tree branches,” said Sadof. “As soon as the young worms appear, they start to spin bags and continue to enlarge these they feed and grow.” He said they crawl partway out of the bags to feed, and when disturbed, they retreat safely inside. “New infestations start in June, but symptoms won't likely start until a month has passed,” he said.

Inspect your trees now for these small, newly hatched bagworms – miniature forms of old bagworms from last year. They may appear somewhat like a piece of fuzz that wiggles among the needles. “Bagworms can be controlled by spraying the foliage with insecticides after eggs have hatched and small bags are seen on the trees,” said Sadof. Typically, this is around mid-June in northern Indiana.

Many homeowners have been surprised to find these pests affecting their landscape trees and their windbreaks. When symptoms become obvious, the pests have typically been active for months. “Bagworms mature in late August or early September,” said Sadof. “At this time the bags are about 2 inches long and can no longer be killed by pesticides.” Late in the year the best advice is usually to hand-pick the bags off the tree and drown in a bucket of soapy water to stop the reproductive cycle.

“These bags, composed of silken threads and bits of foliage, look so much like a part of the tree that they may go unnoticed until extensive damage has occurred,” Sadof said. The bags become somewhat camouflaged because leaf material (needles) from the tree sticks to the bag, making it look like something that belongs on the tree. Resembling a small pine cone, it hangs in a manner similar to a Christmas tree ornament.

People sometimes confuse bagworms with tent caterpillars, insects that form cobweb-like structures, typically in fruit trees and shade trees rather than evergreens.

Infested trees can be treated in June using one of several common insecticides. Homeowners may wish to consider a biorational insecticide first. “The biorational materials will kill the caterpillars without killing the natural enemies of spider mites and scale insects that can cause additional damage to the plant,” Sadof said. Products containing Bacillus thuringiensis (Kurstaki) or Spinosad are examples of biorational insecticides available to homeowners.

Find Purdue Extension publication E-27-W, Bagworms, authored by Sadof at Purdue Extension’s Education Store: It contains pesticide options for homeowners and commercial applicators.

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