Friday, April 6, 2012

Spot Anthracnose of Dogwood

Spot anthracnose on dogwood in Holly Springs, NC (Wake Co.) on 04 April 2012.
Photo by Mike Munster

Spot anthracnose of dogwood is a perennial problem on one of our loveliest landscape plants. This photo was taken to represent the several questions about this disease we’ve had over the last two weeks. The red to tan spots can be barely noticeable from a distance, but when numerous they can severely stunt and deform the showy "petals", which are actually modified leaves called bracts. Leaf, fruit, and twig infections can also occur. The fungus responsible for the damage is known scientifically as ElsinoĆ« corni. It overwinters in twigs and fruits, and spores infect the bracts in the spring if moisture is present. Fortunately, flowering dogwood is the only plant on which this disease is significant, and the overall health of the tree is not at risk. This disease is very different from “dogwood anthracnose”, caused by the fungus Discula destructiva. In North Carolina this more serious disease occurs only in the mountains.

Susceptibility to spot anthracnose varies among dogwood cultivars. See the table of dogwood cultivars from our Department of Horticultural Science, and their guide to dogwood care. Not much can be done to prevent spot anthracnose, but promoting good air circulation in the vicinity of dogwood trees may be beneficial. Avoid dense plantings or low-lying sites, and prune out dense growth. We generally do not recommend chemical control for tree diseases in the home landscape, where the correct equipment is not generally available. Also, once you see symptoms like those in the photo, it’s too late to get any benefit from a fungicide spray this spring. Looking ahead to next year, a professional applicator may be able to help protect high-value, high-profile trees. Be aware that a protectant spray program may involve spring, summer, and fall applications. Contact your local county cooperative extension service for more information.