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Saturday - October 06, 2007

From: Burke, VA
Region: Mid-Atlantic
Topic: Diseases and Disorders, Pests, Trees
Title: Possible disease on Eastern Redbud
Answered by: Barbara Medford

QUESTION:

Our Eastern Redbud appears to be suffering from our recent drought. The leaves are turning brown in July/August on a few branches. A few black spots appear on the leaves before they turn brown. Other smaller Redbuds in our yard do not seem to be affected. Is this a disease, a drought protection strategy or both?

ANSWER:

We're assuming that what you have is Cercis canadensis (eastern redbud), as that is the only one in our Native Plant Database that is found naturally in Virginia. Plants native to an area are much more likely to do well in that area, which is why the Lady Bird Johnson Wildflower Center is focused on promoting and preserving plants native to North America.

This Florida Cooperative Extension Service website on the redbud has a great deal of information about the culture of the Eastern redbud, as well as some of the common causes of problems. The only reference we found to black spots on the leaves was in reference to too much rain, so that's probably not your problem. The Eastern redbud can be both an understory tree or stand in full sun, but if you've had a dry, hot summer and the tree in question is in full sun, it may be stressed by that. If that's the case, hopefully some deep watering by sticking a hose down in the surrounding soil and turning on a slow drip for an hour or so will help.

So much for the weather being the problem. How about disease and/or critters? Borers can attack the trunks of older or stressed trees. To prevent this, keep the plant vigorous, which is what you're trying to do in the first place. Scale insects can infest the tree, and can cause sooty mold, which might explain the black spots on the leaves of your tree. Webworms may defoliate parts of the tree in summer and fall. The caterpillars are the larval form of the tiger moth, and they build ugly web nests in the spring or fall. Ugly as they are, they rarely cause any lasting damage. Probably the biggest problem in redbuds is canker. Bark in the canker turns black and a crack forms between diseased and healthy brk. The fungus enters through wounds or dead and dying branches. There is no chemical control, but spread can be at least slowed down by pruning out diseased branches. And, finally, verticillium will attack and kill Eastern redbud.

So, now that we've convinced you that your tree is a rooted Emergency Ward, let's just hope that cooler weather, more water, maybe at least some cloudy days for shade will begin to perk up the patient.

Cercis canadensis