Key Features
- Defoliation
- Light brown leaf spots
- Black bumps in spot centers
Symptoms
Mycosphaerella fungi cause light brown spots on the upper surface of host leaves. These spots develop grey to tan centers as the leaf tissue dies and the fungus begins producing spores. The spores are formed in the tiny black bumps in the center of each spot. Severe infections may cause defoliation. Several years of defoliation may lead to a decrease in the number of leaves that emerge the following year.
Biology
The fungus survives on leaf litter from plants infected the previous season. Warm, wet spring conditions promote spore production and dispersal. Spores require high relative humidity or water on the leaves to infect and cause disease. Spots expand and the fungus produces spores within the necrotic, tan center of the lesion. These spores may be splashed to healthy tissue, spreading the disease. Mycosphaerella leaf spot rarely poses a threat to the plants health and survival. Note: The sexual stage of the fungus is called Mycosphaerella. The asexual phase of the fungus was historically named based upon what it looked like (morphology) and include names like Cercospora, Septoria or Cylindrosporium. For this reason, these diseases may be called Mycosphaerella. If you are confused, you understand the situation as well as the experts.
Management Recommendations
Whenever possible, reduce overhead water, and keep leaves as dry as possible. Correct fertilization, irrigation, and soil drainage will increase plants' natural defense against the disease. Remove and destroy all infected plant debris to reduce the spread of disease and number of overwintering spores. No chemical controls are recommended for the control of Mycosphaerella leaf spot.
Effective Pesticides
Active Ingredients include: Captan, Chlorothalonil, Copper salts, Propiconazole, Thiophanate-methyl
Resources
- Not satisfied with ID? Contact the Purdue Plant and Pest Diagnostic Lab
- Sign Up for the Purdue Landscape Report
