Looking up into pecan or sweet gum trees, you may have noticed webs around the tips of branches, as well as defoliation under the webs. It's probably an infestation of fall webworms.
In the South, the fall webworm uses many deciduous hardwoods trees, as well as some evergreen trees, as its host. Some favorite host trees of the fall webworm are hickory, pecan, persimmon and sweet gum.
The adult fall webworm, which is actually a moth at this life stage, is a medium-sized white moth with a wide body. Typically, the wings are marked with brownish to black spots. But as with most worm or caterpillar problems, it's not the adults that are the pests, but the larvae or caterpillars. The larvae of the fall webworm have an orange head and tubercles which are small bumps on the body. Full grown fall webworms can reach 1¼ inches.
Each year the fall webworm can produce three to four generations. The first generation begins in early spring, typically in April. The larvae of the last generation pupates in late October and early November.
The fall webworm feeds in groups. As the caterpillar becomes larger, they will construct large, loose, irregular-shaped silk webs, which will cover the twigs and branches of the host trees. These large, ugly webs can reduce the potential beauty of these shade trees.
While the caterpillars are in their self-made tents, they will begin to eat down to leaf skeletons the foliage of the area. As the worms continue to feed and grow larger, they will require larger quantities of food. The fall webworm will then begin to expand the size of its webbed area to encompass more foliage to consume.
The fall webworm does not usually kill trees, but an infestation can reduce the quality of the current season’s pecan crop and reduce the crop yields for the following season.
Many native insects will feed on the eggs of the fall webworm, while other insects will become parasites on the young larvae. Many different species of birds will also feed on the soft-bodied larvae.
If only a few webs are present on your pecan, hickory, persimmon or sweet gum tree, it is most economical to prune out the webbing and discard in the trash. If a homeowner chooses a chemical approach, several insecticides are available that offer great control.
The liquid formulas of Sevin or Carbaryl will control the fall webworm. If you prefer to use an organic insecticide, Bacillus thuringiensis (Bt) is an excellent option. Spraying should be done when the webs are first noticed and the larvae are small. The smaller the larvae, the better control the insecticide will give you.
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