This disease does occur in Illinois but is not as common as in Kentucky and states to the south and east of us. Still, it is a potential threat to dogwoods in Illinois, and it is important to be aware of disease symptoms to make an early diagnosis and initiate the proper controls. Not every spot and burn of the leaf edges is a problem on this host. Dogwood anthrac- nose, 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 infects leaves, young shoots, and fruit. It causes small spots with purple borders. Dogwood anthracnose causes leaf spots and stem cankers, and it may kill shoots. The infected leaves may have purple-bordered brown spots that are usually larger than those of spot anthracnose (1/2-inch diameter versus 1/4 inch). 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. Under very humid conditions, infected leaves and twigs produce tiny fruiting bodies with masses of spores, which can be 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 that encourages succulent, susceptible vegetation.

We have not seen a large number of anthracnose problems in the landscape in Illinois. 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.

The following table, developed by Bruce Paulsrud at the University of Illinois, may help you sort out the diseases that may occur on your dogwoods. 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 on this disease has been ongoing for many years.

Table 1. Comparison of Some Diseases of Dogwood