Fall webworms overtake trees

Wednesday, September 23, 2015

Experts 
recommend pruning to get rid of pests

Area residents may have noticed a drastic change in trees lately, as they are losing leaves and covered partially or completely with webbing, giving them an unsightly, ghost-like appearance.

The cause is fall webworms.

A sign that fall has arrived, the webworms, a type caterpillar which transforms into a moth, like to invade walnut, hickory, persimmon and wild cherry trees, but pestilize many species of forest, shade, fruit and ornamental trees throughout southwest Missouri. The trees may be completely defoliated and covered in webbing by hundreds of caterpillars making their homes on outer tree branches, and continued infestations can potentially threaten trees.

Although unsightly, experts are not overly-worried about damage, as trees will soon be losing their leaves due to the fall season.

"This is one of the worst years I've seen in a long time," said Tim Schnakenberg, regional agronomy specialist. "Walnut trees especially are at risk, sometimes Hickory. I have seen a few trees that are completely defoliated as a result of these web worms. It really stands out in the fall because they're always on the outside of the trees, so they're very easily seen. They have a very tight web that protects them, in fact so much so that insecticides have a hard time getting inside to reach them.

"The appearance looks awful and ugly. It's definitely not good, but it's so late in the season most arborists don't get overly-concerned about it. The tree probably will come back out just fine next spring."

Schnakenberg suspects moisture may be the cause for excessive webworms taking up residence in so many trees this year.

"When things are lush and green all summer long, these moths are attracted to those areas," he said.

Beginning in spring and throughout early summer, adult webworms, also called tent caterpillars, emerge from the ground or just below the soil surface, where they wintered as pupae in cocoons. Fully-grown caterpillars are about an inch long. They are typically light-colored and covered with tiny bumps from which come tufts of long, light-colored hairs. The head is either black, orange or red. Hundreds of eggs are laid on the undersides of leaves, then newly-hatched larvae begin to spin webbing over the tree foliage on which they feed. As the larvae grow, they make even bigger webs, giving trees a translucent, ghost-like appearance. After leaving the tree, they feed prior to pupating and going into the soil to start the process over again.

If homeowners are concerned, Schnakenberg suggests pruning.

"We do recommend pruning them out, and then destroying the web with the worms inside," he said. "I wouldn't go to a lot of great lengths and deform the tree as a result.

"If you're concerned about it, go ahead and take a board with a nail on the end to open up the web up and you might be able to spray something inside it, but we're just about a month away from the first frost, and for that reason, most aren't as concerned about trees losing their leaves because it's going to happen anyway."

Patrick Byers, horticulture specialist with the University of Missouri Extension, also recommends pruning if homeowners are bothered by the webworms.

"To control webworms, you need to prune them out and destroy small webs," he said. "You can also use a labeled insecticide to protect valuable trees."

Schnakenberg said webworms are sometimes confused with eastern tent caterpillars, which come out in early spring and weave webs on the inner parts and nooks of tree branches, verses outer branches like webworms in the fall.

"It looks worse than it is," he said.

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