Is your nut-laden pecan tree suddenly developing a “bald spot?” Dr. Charles Allen of San Angelo said he and his colleagues from Central and South Texas have been getting a number of reports over the past few weeks of pecan trees suddenly being denuded.

Walnut caterpillars are often mistaken for webworms, but they don’t make a web, though they do a lot of the same things. They typically hit our region in the fall and are capable of defoliating whole trees.

Walnut caterpillars are fairly large, up to an inch or longer, dark colored with lines down the body, and they are very fuzzy or actually hairy. The caterpillars feed on the leaves of pecan, hickory and walnut trees, which Allen said are all closely related. The eggs are laid next to each other and are bright white and reflective.

The tree may look perfect with just a limb or two eaten bare, which he says is not a major issue. But if the tree has lots of egg clusters, chances are it will soon have lots of caterpillars.

Major defoliation is always a concern, but depending on the time of the year, may not be a big problem for the tree. Leaves become less and less functional as we move further into fall. We’re getting close to that point right now, so you may not need to do anything to control the caterpillars.

For those who do want to apply some level of control, Allen said observant homeowners can take advantage of the caterpillar’ habits. As the caterpillars mature, they move down the trunk of the tree, making them easier to spray.  

“You can treat the caterpillars as they reach the rough bark on the trunk. Hose-end sprayers using a contact insecticide approved for walnut caterpillars are very effective, though the rate of delivery and label information.

 A good way to scout for impending populations is to go out at night and shine a flashlight into the tree, and those white egg masses will really shine. After the eggs have hatched, typically the caterpillars clump up on a few leaves and as they get a little older, they’ll spread out from there.  

Having the caterpillars is an annual thing, but it’s not an annual thing everywhere. It tends to be pretty sporadic in this part of the world. Closer to the Gulf Coast, it’s more common every year.

This is not a bad pest to have, most of the time, because it attacks late in the season when the leaves are about to lose their utility. And whether you do or don’t take an action to control them, it doesn’t make much difference one way or the other when they occur late. As each day passes from now through the end of October, those leaves are less and less valuable to the tree.