Septoria Leaf Spot
On Dogwood

Symptoms:

The leaves become spotted with angular, dark brown leaf spots with a purplish margin. These spots appear after periods of hot humid weather and many times are caused by poor watering techniques. This disease does not generally harm the plant unless it is severe and it occurs for several years.

Disease Cycle:

Septoria sp. produces tiny pinpoint-sized fruiting bodies in the spots on the leaves. Spores can be spread by wind or rain. The fungus can overwinter in leaf debris.

Control:

No chemical control is necessary but you can use a general fungicide as a preventative in the spring and summer months. The best control is to remove leaf debris around the affected plants and when watering make sure you do not get water on the foliage.