Fall Webworms

You may not want to think of fall during July and August, but the signs of fall are already here. From mid-July through the end of August you will see an increase in the number of long web like structures on the tips of tree branches. This problem is caused by an insect called fall webworm.

Fall webworms emerge as early as the beginning of June, although they generally don’t reach their peak until August. The silken webs spun by fall webworm often contain leaf litter, casts of immature insects, and hundreds of white, hairy caterpillars. The webs will enlarge to lengths of up to 3 feet by the end of the season. After several weeks of feeding, the caterpillars will emerge from the webs, crawl down to the soil, and spin cocoons. Depending on the weather there can be as many as three given generations per year. They will over winter in cocoons and emerge the following year to lay eggs in the tree. Each caterpillar can lay between 300-900 eggs.

Although the webs found in trees are unsightly and cause much concern for homeowners, fall webworms will rarely cause much longterm damage to a tree. They will cause the tree to partially defoliate, however it is rare for the damage to be extensive enough in one year or even in several consecutive years to cause severe damage or death to the tree.

Homeowners who wish to control fall webworms face a few challenges, most notably how to reach the webs on very tall trees. Most of the time, this is difficult or impossible. Those webs that can be reached can be removed with a stick or by hand, and caterpillars inside the webs can be removed with a stick or otherwise disposed of. Pesticides such as Orthene or Bacillus thuringiensis (Dipel) can be sprayed, but again, reaching the higher webs will be difficult for most homeowners. In addition to these options, any leaves or other plant material that falls to the ground below an infected tree in the fall should be raked up and disposed of, as this will likely decrease the amount of webworms present the following year.

All in all, fall webworms are a problem that looks much worse than it is. While no one enjoys the site of multiple webs covering their favorite tree, they pose little longterm threat to the tree and are more of a visual nuisance than a truly damaging pest.