Ugh! What’s nastier than a sack of crawly caterpillars hanging from your trees? How about a dozen of ‘em?
If you have fall webworms in your trees we can certainly empathize. This year they seem to be particularly abundant. But here’s the good news: they won’t cause any lasting harm to your trees, even if they eat every last leaf.
Why aren’t they a problem? At this stage in the season, the leaves have done most of their job of collecting energy for the tree; they are about to drop off shortly anyway. The caterpillars don’t damage the woody stems.
The damage from fall webworm is entirely cosmetic. A healthy tree will not be affected by webworms, even a heavy load of them. (An unhealthy tree may need to have any other issues that make it unhealthy addressed.)
The hairy caterpillars (eventually they become a non-descript white moth) have a particular fondness for fruit and nut trees. They have also been abundant on ornamental cherry, river birch and sourwood trees.
If you’d like to try to get rid of the bagworms you see just so you don’t have to look at them there are a few methods you can use for fall bagworm control assuming you can reach the webs.
Easiest is to break open the protective webs with a rake or stick. (Do not stand directly under the web while doing this unless you want caterpillar poo in your hair-don’t say we didn’t warn you.) Natural predators will happily feast on the caterpillars once they have access. You’re creating a bird buffet! The remaining webs themselves will eventually weather away.
If you want to pull the webs off completely the caterpillars can be dropped in a bucket of soapy water, which will smother them. Or just leave them on the ground—they won’t regroup to create a new web, and predators will still pick them off.
On a tree that can spare the branch tips, the webs can be pruned out, though this can be impractical when they occur high above the ground.
It is not necessary or recommended to spend the time, expense or environmental risk to control fall webworm with pesticides. Note also that while these late-appearing (August or later) caterpillars pose little or no risk of damage, caterpillars that appear early in the season (usually Eastern tent caterpillar) and threaten to defoliate more than 50% of a tree should be treated with bacillus thuringensis or other pesticides that target caterpillars. Early loss of too many leaves can cause issues, particularly on already-stressed trees.