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.

I Don't Like Ike.

I visited my mother-in-law in Houston this week. Her trees still reflect the aftermath of Hurricane Ike. After years of careful pruning, and one rather arrogant ligth placed at teh highest possible point, a big storm took out a good bit of this Willow Oak (Q. phellos). She had the debris removed from her garage, along with another Willow Oak that already had a suspicious lean before the storm.

I am sad for the trees, including another Willow Oak in front, which suffered monir damage. The Live Oak (Q. virginiana) and the Water Oak (Q. nigra) appeared to be unharmed.








The worst trees I saw in Houston were not Ike victims, though. My anectdotal evidence (based on a few trips a year for the past 15 years or so) reveals Houston to be much harsher and out-of-date market for tree care. As in Austin, Crape Myrtles (Lagerstroemia indica) take the brunt of the topping. I'm not sure I've seen the crape myrtle in Houston yet that hasn't been topped at least once. But, sadly, other trees get topped, in Houston and everywhere. If you don't know why this is bad, visit ISA's page. The short version is, lopping off a large tree brance midstream takes a huge amount of energy away from the tree, creates a wound that will lead to extensive decay, which will make all the new growth from those topeed stems much weaker thatn the equivalent untopped liibs would have been.

Based on brief forays into trying to sell work to M-I-L's neighbors, I gather the market there is highly underinformed on proper tree care practices. The going rate for this kind of work is not sufficient to do the job right, so it routinely gets done wrong. The abyssmal state of construction protection that exists everywhere is, if anything, worse here. Stripping out the interior of trees ("lion tailing") is common in trees that haven't been topped. Line clearance is brutal (though not as bad as rural topping). Maybe the periodic hurricanes make it difficult to invest in trees there. Maybe I've been running into the wrong people there. But the trees I see in Houston are suffering, and they need an educated populace to demand a higher level of care for their urban forest.

I'll do my best to fix the trees in my M-I-L's yard, but I'm still busy working on Austin as far as the rest of it. I hope some Houstonian tree crusaders are on the rise.