Black Spots on a Forsythia Bush

Identification

• Forsythia shrubs are susceptible to bacterial blight caused by Pseudomonas syringae. The bacteria are more active in wet, rainy weather. Forsythia shrubs exposed to prolonged moisture exhibit worse symptoms.

Damage

• Initial symptoms of disease include appearance of small, black spots on foliage. The spots are often irregularly shaped and brown in color. As the infection spreads, it leads to blossom dieback and cankers on stems. Black or brown lesions also appear on flowers. Infected tree areas often start to ooze sap in wet weather.

Management

• All infected plant areas should be removed. Pruning during wet weather may cause the spread of bacteria. Plants must be spaced to ensure adequate air circulation and light. Overhead sprinklers should be avoided. Cankers on the trunk of the shrub indicate a chronic stage of disease, signaling the necessity to remove plant entirely.