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Dogwood Anthracnose

June 21, 2000

No, I have not seen this disease in 2000. It has been active in parts of Kentucky and is a potential threat to dogwoods in Illinois, so it is important to be aware of symptoms. Not every spot and burn of the leaf edges are a problem on this host. Dogwood anthracnose, however, can be quite damaging if left untreated.

Dogwood anthracnose is easily confused with spot anthracnose, a more common but less damaging disease of dogwoods in Illinois. The spot anthracnose fungus will infect leaves, young shoots, and fruit. It causes small spots with purple borders. Dogwood anthracnose causes leaf spots and stem cankers and may kill shoots. The infected leaves may have brown spots with purple borders that are usually larger than those of spot anthracnose (1/2 inch in diameter versus 1/4 inch in diameter). The edges of the leaves may be necrotic and spread until the entire leaf is dead. These brown leaves often remain attached for a month or more. If you suspect that leaf symptoms resemble dogwood anthracnose, examine larger branches for cankers by peeling back the bark in infected areas. Look for twigs dying back, especially in the lower crown. In very humid conditions, infected leaves and twigs produce tiny fruiting bodies with masses of spores, which are used to confirm the disease in the lab.

Spot anthracnose usually does not require fungicide sprays for control unless conditions remain favorable for prolonged periods. Dogwood anthracnose is difficult to control once it has caused significant dieback. Maintain optimum conditions for growth and recovery: water during drought stress of 2 weeks, avoid overhead irrigation, apply a mulch over the root system, and improve air movement around trees (through pruning of surrounding vegetation) to minimize infections and encourage drying of foliage. Prune and discard infected branches and shoots. Rake up fallen leaves. Avoid high nitrogen fertilization, which encourages succulent, susceptible vegetation.

Dogwood anthracnose has devastated dogwood populations in wooded parts of the eastern and northwestern United States, and the disease has been confirmed in our neighboring states of Indiana, Mis-souri, and Kentucky. We have seen some cases of dogwood anthracnose in Illinois as well, but the disease is not as prevalent in Illinois, partially because of our weather conditions and partially because of how we use our dogwoods in the landscape. The disease is prevalent in moist, humid areas in dense forests where plants do not dry out quickly. In Illinois, we tend to use our dogwoods as specimen trees in the landscape. Such sites are usually exposed to sun and good air flow, so foliage dries quickly. In fact, positive cases of this disease have been found more often in wooded sites than in the landscape.

For pictures and more information about dogwood anthracnose, consult the Web site at http://dogwood. ag.utk.edu/. This site was developed by the dogwood working group at the University of Tennessee. Work has been ongoing for many years.

Author: Nancy Pataky


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