The Q&A Archives: Diseased Dogwood

Question: My dogwood tree has large 'scabs' on the bark, and when I break a piece off, there are tiny black bugs underneath. I'm wondering if this will kill it or spread to other plants, or if there is a treatment for it? Thanks

Answer: I'm going out on a limb here - but I think the bugs are secondary to the real problem with your dogwood. A disease called anthracnose is common with dogwoods. The symptoms include small, purple-rimmed spots or large tan blotches on the leaf, with the entire leaf eventually turning brown. Twigs may die back several inches, or all the way to the main stem. Eventually cankers appear on limbs and the trunk of the tree. The fungus thrives in cool, moist weather, and since dogwoods prefer to grow in the dappled shade of larger trees, this can create cooler, more humid conditions than in full sun, increasing the disease problems.

To save an infected tree, prune out cankerous branches as soon as they are noticed. To protect new growth and reduce the amount of leaf spot infection spray a fungicide such as copper sulfate three times in spring while the new growth is still succulent and most likely to get infected. Spray once at bug break and then twice again, at 10 day intervals, preferably after a rain.

If you need to replace your flowering dogwood, there are anthracnose resistant trees, but they are crosses between Cornus florida and Cornus kousa such as the Constellation series.

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