I have been meaning to write this for some time now, but other things have taken my attention away. So, Dr. Wayne Porter beat me to it and posted this on his blog, “Gardening in Mississippi”. It has a great description of the insect and how much damage to the tree it actually does. I tell most folks that it does no harm to the large trees and is only a concern on small, young trees. Read on below for more details:
“It is not even fall and they are back! I am getting calls from people asking, “What is that web stuff on my pecan trees!” That stuff is the webbing created by the fall webworm.
The fall webworm appears on pecans in summer as well as in the fall. The fall webworms build larvae nests on the ends of branches. In our area they appear mostly on pecans and up to 90 other deciduous trees.
Damage is caused by caterpillars that eat leaves within the nest and enlarge the nest as they grow. Damage to the tree is seldom serious, but several severe infestations can defoliate and stress a tree, particularly small ones. The adult insect is a one inch, snowy white moth, with dark spots on its wings. The caterpillars are one inch long and covered with silky hair. Their color varies from pale yellow to green with a black stripe on the back and yellow stripe on each side. People usually do not notice the caterpillars until the large, white webs with skeletonized leaves appear.
Although the fall webworm is not considered a deadly pest it does gets lots complaints due to its ugly web that detracts from the aesthetic value of the tree.
You usually do not need to worry about losing your tree is because the webworms are eating leaves relatively late in the growing season. Therefore the defoliation is much less damaging to the tree than had it occurred earlier.
Control of this pest is rarely needed or even effective. You could use stick or high water pressure to break their silk web nest and expose them to their natural predators: birds, yellow jackets, and wasps. Also, you could prune infected branches and burn or otherwise destroy them. Some people attach some newspaper to the end of a long pole, set it on fire, and burn the webs in place.
If using pesticides for the webworm, there are a few that are effective. For severe infestations, spray nests and leaves with Sevin, permithrin, spinosad, or malathion, according to label directions. The best way to apply these chemicals is to spray them around the nest, on branches that the worms may spread to, and inside the nest after first breaking it with a stick. There is an organic product called “B.t.” (Bacillus thuringiensis), sold under the product name of Biotrol, Dipel, or Thurcide. To apply break up newly formed nests, then spray with B.T. in early evening during mid-summer when the caterpillar nests are small. B.t. is slow acting so be patient.
Natural control is preferred whenever possible so poke that hole in the web and let Mother Nature take charge.”