Fall Webworms and Armyworms

Fall webworms have emerged early this year and typically seen in pecan and other trees this time of year. Fall webworms over-winter in litter under trees in the soil. The moths emerge during the evening hours and therefore are often overlooked. Fall webworm caterpillars are characterized by spider-like webs in the leaves of trees which become apparent in the summer and fall.

The moth of the fall webworm is medium size with a wing span up to 1 1/2 inches. They are snow white in color with black spots. The eggs of the fall webworm are tiny, round, and yellow. Hundreds (350-900) of eggs are laid on the underside of tree leaves. Then tiny, hairy caterpillars hatch that grow up to 1 3/8 inches long. Fall webworms feed on over 600 kinds of trees, shrubs and other plants. In North Carolina they seem to prefer pecan, persimmon, sourwood, and willow trees.

Fall webworms are considered a cosmetic pest. Since the caterpillars feed in mid- to late summer when the weather is hot and dry, their feeding usually does not damage the health of a tree. Fall webworms can be destroyed by pulling down the webs and stepping on the caterpillars. This is the preferred way of getting rid of these pests. Insecticides can be used if webs can be reached by the spray. Insecticides work best when caterpillars are small, thus should be treated as soon as the web is noticed. Some insecticides suggested would be a variety of the Bacillus thuringiensis (BT) products. BT is a naturally occurring bacterium that has been formulated as a bacterial insecticide that is safer for people and pets.

Fall armyworms can also be seen this tiem of year. Fall army worms eat the grass at the soil level so maybe difficult to detect. One way to check and see if you have fall armyworms is to take a bucket of water, add a couple of tablespoons of liquid dish washer detergent and pour it over an area about 3 by 3 feet. If you have fall army worms, they will come to the surface. Sevin and other similarly labeled products can be used for armyworms until the end of October.

For more information on fall webworms and armyworms contact the Master Gardener hotline at 237-0113 on Mondays, Wednesdays, and Fridays from 1-3 PM or by email at wilsonmastergardener@hotmail.com.

Date Created: 10/22/2004.