Types

• Mock orange is susceptible to two major diseases: bacterial blight and powdery mildew. Bacterial blight, caused by the bacterium Pseudomonas syringae, affects mock orange foliage and shoots. It favors wet and cool weather for infection. Powdery mildew is a fungal disease that affects foliage and flowers during wet weather.
  
  

Identification

• Bacterial blight symptoms consist of water-soaked spots on foliage that cause leaf death, defoliation and underdeveloped plant growth, reports the Oregon State University Extension. Symptoms of a powdery mildew infection include white powdery fungal growth on leaves and flowers, leaf curl, stunted leaf growth and leaf drop. The disease rarely kills plants but is more of an aesthetic concern, reports the University of Illinois Extension.
  
  

Control

• The Oregon State University Extension website recommends avoiding excess moisture buildup and removing infected branches and leaves to prevent a severe bacterial blight infection. Bactericides are an effective way to control severe infections. Increase air circulation and avoid excess moisture buildup to prevent a powdery mildew infection. If infection is severe, fungicides can be used.