The fall webworm infestation in certain Oklahoma trees is here, even though it’s summer, with the first generation of pests wrapping up webs in trees. The fall webworm larva hatch from eggs deposited on tree leaves, mainly pecan, walnut, persimmon, and other fruit bearing trees. Some ornamental trees found in the landscape such as river birch, oak, and sweet gum can also be prone to attacks. My native pecan trees have been hit, although not too bad yet.
The caterpillar will eat the leaves while forming a web around the outside of branches. They will soon pupate in the forest floor or lawn and overwinter, hatching out later this year or next as small adult moths starting the cycle all over again.
The webs are an eyesore, but the caterpillars will rarely cause significant damage to trees.Trees don’t die from webworm invasions, unless there are other problems with the tree now or later. We don’t recommend treating with insecticides once the webs form, as the damage has been done by the time webs are present. Plus, it’s difficult for any insecticide applied to even penetrate the webs for effective control. A high pressure hose or a long stick may be used to knock the unsightly webs from tree branches, but otherwise, just let wind and weather take care of them. If you insist, our tree & shrub department can come out to spray for webworms, but the existing webs will not disappear. This will help prevent further damage for a few weeks, but a second generation may come later in early fall also.
In some cases, a systemic granular or liquid insecticide named imidacloprid, or Merit, can be applied in early spring under the tree. This insecticide is then absorbed by the roots and taken up into the tree to help control infestation. As the worms eat the foliage, small amounts of imidacloprid are absorbed to control the insect pest. Always follow label instructions when applying insecticides.