Date: Wed, June 14, 2006

In this email look for the following:  Oak Blotch

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In the past couple of weeks we've seen a lot of damage to oaks - primarily to white oaks - by oak blotch leaf miners. These guys are caterpillars of a small moth, and they "mine" inside the leaves leaving brown or tan blotches. See a picture at http://ipm.ncsu.edu/current_ipm/06PestNews/06News9/cameraria5.gif

These irregularly shaped blotches gradually increase in size. There may be many blotches per leaf and the blotches may run into each other. As the growing boys feed the cupboard gets increasingly sparse, their cupboard being the green tissue of the oak leaves. They seem to be having a good year. As much damage as we are seeing now, many leaves may be almost completely brown in a few weeks. Leaves may drop early. And to make matters worse, there could be another generation or two of the insects.

Because of the size of the trees, control with insecticides is usually not practical. Because the insects are protected within the leaf, control with insecticides is not usually effective. The good news is that the damage is not likely to kill affected trees. These caterpillars are present every year; they just seem to be more numerous this year. But apparently the insect and the trees have been peacefully co-existing for longer than humans have been worrying about our trees.

Since the insect overwinters as a larva within the fallen leaves, there may be some benefit in removing and destroying leaves this fall. On the other hand, with as many oaks as there are around, there will probably be a plentiful supply of new caterpillars next year. But if the population dynamics espoused by ecologists have any credibility at all, there's a good chance that some predator or parasite will also increase in number to bring the caterpillar population back down a bit. Who knows, maybe some local chef will find a use for them! Just kidding, of course.

alcooke

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Al Cooke
Extension Agent - Agriculture
Chatham County Center
North Carolina Cooperative Extension Service
N C State University
PO Box 279
Pittsboro, NC 27312
919.542.8202, FAX 919.542.8246
al_cooke@ncsu.edu http://www.ces.ncsu.edu/chatham/staff/acooke/home.html