Miami Valley Trees Under Attack from Mimosa Webworm

Honeylocust trees in the Miami Valley and Cincinnati area are being affected by an infestation of mimosa webworm caterpillars. These pests spin sticky webs around the tips of branches, consuming the top layer of foliage and causing brown leaves.

The mimosa webworm has three generations per year, with the third generation's damage being the most noticeable. The caterpillars are a tannish brown color and almost an inch in length, producing black spots or frass inside their silk nests. They won't kill a tree but can be a nuisance.

Colleagues of the entomologist have been seeing this infestation for a while now, and it's believed to be a result of a few years of favorable conditions for the pests. The good news is that these caterpillars don't harm the trees, just make them look unsightly.

There are pesticides available to spray on affected areas, but experts recommend selecting the proper one as general caterpillar sprays can kill beneficial predators. Biorational pesticides like spinosad and azadirachtin, along with the bacteria Bt, can be effective when used properly.