Fall webworm infests more than 100 different tree species in the United States and Canada including forest, shade and fruit varieties. The most notable sign of an infestation is the large white webs that encompass the tips of trees.
These webs are host to a colony of caterpillars that feed first on the leaves within the web and then, as they grow, enlarge the web to gain access to more foliage for food. Once they are prepared to go through metamorphosis they will leave the web and drop to the ground.
Eggs are laid on the underside of leaves in the spring in hair covered masses. Removal and destruction of these masses may prevent unsightly webs in the fall.
The caterpillar itself is usually yellow or green with a solid stripe on the back. Black or red spots can be found along the sides of the body with dark hairs protruding from the length of the caterpillar. While their colony is unsightly, their feeding usually does not cause damage to a tree as it occurs in the fall when trees are preparing for dormancy and leaves are less necessary.
Simple control methods that are often very effective are to remove the web from the tree and burn it immediately. If the limb is small then you can remove the entire branch or limb and burn that to kill the caterpillars.
Further control can be supplied from predators such as birds, rodents and other insects including a parasitic wasp. Tearing a hole in the web may help to facilitate feeding by predators although caterpillars may repair the damage so webs may need to be broken more than once.
Chemical control is not recommended as infestations are usually low. If a tree has an excessive number of webs there are several chemicals available for homeowners. Applications would have to be done inside the web so only those colonies within reach could be sprayed.
Sarah Denkler is a horticulture specialist
with University of Missouri Extension
in Dunklin County.