Here’s how to manage late winter tent caterpillars

Eastern tent caterpillars crawling on top of their webby tent, location and date unspecified | Photo courtesy of, St. George News

FEATURE — Start this year’s tree pest management with a stroll through the landscape. As you enjoy the scenery, be sure to look for any unwelcome pests that may be overwintering on the twigs of trees. 

Western tent caterpillars do their work in trees along on the Halfway Wash Trail in St. George, Utah, on April 17, 2020. | Photo by Chris Reed, St. George News

Look for and remove egg masses of tent caterpillars now through spring. These clusters of eggs look like shiny blobs of mud surrounding the twigs. Each egg mass contains hundreds and in some cases thousands of eggs.

The forest tent caterpillar is the most widely distributed tent caterpillar. It attacks a variety of trees that vary with the region. Check any sugar maples, aspen, cherries, apples, oaks, birch, ash, alder, elm, basswood or water tupelo trees growing in your landscape.

Trees may suffer damage when large populations of these caterpillars devour the majority of the tree’s leaves for several years in a row. This can result in reduced tree growth, top dieback and tree mortality. There are several natural predators of this insect pest so working with nature is a great way to help reduce damage.

Remove the egg masses found on small twigs that are more easily reached on smaller trees. After the eggs hatch, look for the caterpillars in a silken mat, not a tent like the other tent caterpillars. Remove the young caterpillars from branch tips or squash those resting on the main stem in the evening or on cool days.

You may also see similar egg masses of the Western or Eastern tent caterpillars depending on where you live. Their egg masses look similar to those of the forest tent caterpillar. Remove the egg masses of these tent caterpillars in spring before the eggs hatch.

Once the eggs hatch, the caterpillars begin forming a webby tent in the crotch of the tree. As they feed and grow, the tent expands. They remain in the tent during the hot part of the day and rainy weather.

Knock the tents, caterpillars and all, out of the tree when the majority of caterpillars are in the tent. Smash or dump the caterpillars in a can of soapy water.

Do not burn the tents. This old practice is hazardous and the fire can severely damage the tree, much worse than the insects.

Control is usually not needed on healthy and established trees. If you decide to intervene, consider using an organic insecticide with the active ingredient Bacillus thuringiensis var. kurstaki (Btk). It is effective when applied to the tents soon after they start to form and when the caterpillars are small. Just spray the tent and the surrounding 1.5 feet of leaves. These products only kill caterpillars and will not harm other insects or birds feeding on these pests.

When working with nature, we have help from predatory insects and songbirds when managing these and other garden pests. Taking time this winter for a bit of prevention can go a long way in reducing damage from tent caterpillars.

Copyright Melinda Myers, LLC, all rights reserved.

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