What can I do about an infestation of inch worms?

Asked May 1, 2015, 6:58 AM EDT

Looks like my third year of inch worm infestation is underway. My land is very wooded with lots of 150-year-old beech trees, and it's the understory of hornbeams that get completely denuded by the worms. These trees were looking very weak and decrepit last year; I just don't think they'll survive a third. Am I the only one with this much damage? And my woods are 5 acres, so spraying all of the understory would be close to impossible (and how effective would spraying be?).

Charles County Maryland cankerworms

1 Response

Yes, the fall cankerworms have emerged. I first noticed them over the weekend and they have been very active since then in different parts of the county.

As far as chemical controls, there is no way to reach the canopy with a spray, and spraying the understory would not appreciably reduce their populations. There is not much that you can do to control them in such a large area. If you have a shorter specimen tree in your yard that you want to protect, you can use a product containing B.t. (brand names include Dipel and Thuricide). That is effective only on caterpillars.

The tree will likely grow new leaves later in the season. However, the loss of leaves to the cankerworms can weaken trees and make them more susceptible to other insects and to environmental stresses. See the links for more information.