I have had a worm dangling from a silk tread that has been eating the foliage...

Asked October 22, 2014, 10:31 AM EDT

I have had a worm dangling from a silk tread that has been eating the foliage on my oak, dogwood and wild cherry trees for the last 2 springs. The trees affected have since died. Can you tell what they are and how to control them? Mechanicsville

St. Mary's County Maryland

1 Response

We can't say for sure what pest you are having trouble with, and if you would send us a digital photo attached to one of these emails next spring, we can give you a positive identification.

However, it sounds like cankerworms. These are common on oaks, though not so much on wild cherry or dogwood. They are a native insect, however and feed on many native trees. Their populations spike some years (not every year) and they can seriously defoliate a tree. Usually a tree can bounce back from one year of defoliation, but several years in a row will kill them surely.

Cankerworms are the larvae of a beetle. The best way to handle them is to spray Bt (Bacillus thuringiensis) in the spring when the leaves of the trees are 1/2 unfurled. Bt is an ingredient found in several products. If your trees are very large, your best bet is to hire a tree service company to spray them. Bt is a great pesticide because it does not harm your beneficial insects--which in turn eat your cankerworms.

You can also spray the trees while dormant with a dormant oil to kill eggs before they hatch.