by Dr. James H. Blake, Director, Home & Garden Information Center, Clemson University, 2009
Hi, I'm James Blake, Director of the Clemson Extension Home & Garden Information Center. Today we're going to talk about a disease on dogwoods known as spot anthracnose.
We're in the South Carolina Botanical Garden on the campus of Clemson University beside a very large dogwood, which in some years is gorgeous, with beautiful white blooms, but this year it has a disease known as spot anthracnose caused by the fungus Elsinoe corni. This disease is the most common disease found on dogwoods, the flowering dogwood, Cornus florida.
It starts out as very tiny spots with a reddish or purplish border. The centers can turn tan in color and then fall out in some cases. The spots on the leaves are just like the spots on the bracts. They're small, 1-2 mm spots, with a reddish purple border and a tan center that may drop out leaving a hole.
The disease is most severe when we have high rainfall amounts as the flower buds are opening and as the leaf buds are opening. The fungus survives in the shoots and on the fruit. Then in the spring when we get the nice rainfall we get the severe disease symptoms.
This year the flower bracts are very distorted because of the severe disease. The leaves are just now beginning to emerge and if we have more rainfall as they emerge the disease will be severe on these as well.
Control of this disease is really hard to accomplish. In years when there is no rainfall, there is very little disease. In years like this, when we have high rainfall amounts, you need to rake up any fallen leaves and get rid of those. But unfortunately the disease survives in the shoots and is there next year. For control of this disease with fungicides, you would have to spray every 7-14 days from the beginning of the flower bud break until the leaves completely expand. So unless you have a specimen plant, fungicide control is not really practical. There are resistant varieties available which you should select such 'Cherokee Sunset', 'Cherokee Chief' and 'Weaver's White'.
Although this disease is severe this year it rarely reduces tree vigor. And next year if the rainfall is later in the year you may not see much of this problem.
For more information on gardening, landscaping, insect and disease problems on your plants, visit the Home & Garden Information Center web site at www.clemson.edu/hgic.
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