Leaf Rollers

In Austin, it's oak leaf roller season. Every year, live oaks are visited by these small, green caterpillars. Some years, it seems like a plague. This year, I have not seen many yet, but there may still be time.

Most people notice these things when they start dangling from the trees. They will hang by a single strand of web, similar to a spider's web. For those of us who find tiny, green worms really creepy, this can be a very difficult time. Walking to the car or mailbox means dodging worms and webs left and right. Often, after I've been working among them, I feel something tickle me hours later and absentmindedly squash one of the caterpillars onto my fingers. It's not very pleasant, but really it's no big deal for the trees in most cases.

Today I didn't see any caterpillars, but I did see the signs they were around. These photos show how the moth gets its name. On the right is a healthy branch next to one with all the leaves affected. Below is a closeup of some affected leaves. If you pry open those curled leaves, you will find inside either a larva or the remains of a cocoon that one made.

We usually get a few calls every year asking what to do about these critters. In the heavy years, we tend to get a lot of calls. But, except in severe cases, there really isn't much cause for action. The caterpillars eat some of the leaves, and some people get really creeped out, but things quickly run their course and the problem solves itself. The birds feast during heavy years, leading to light infestation the following year.

If a tree is so covered that it seems likely to suffer from the leaf damage, treatment would be the same as for any worm or caterpillar. I recommend spraying with Bt (Bacillus thuringiensis), which is deadly to larvae but pretty harmless otherwise. It still is wise to take care with Bt, since it does not discriminate between nasty larvae and caterpillars of desirable, pollinating moths and butterflies. Stronger pesticides are available, of course, but they would be overdoing things in this case. The Bt will do the job, and if it misses a few, they will be gone soon regardless.