Key Features
- Defoliation
- 1/4 inch diameter leaf spots
- Dark spots with light centers
Symptoms
Cercospora leaf spot is often referred to as frogeye leaf spot due to the small (under 1/2 inch), brown to purplish-black spots with light brown or tan dead centers. Older lesions may have tiny black specks within the dead center; this is where spores are produced. The centers of these spots may crack and fall away from the leaf, creating a shot-hole effect. Each species of Cercospora can only infect a few host species, however, there are many species of Cercospora.
Biology
Cercospora survives on leaf litter from plants infected the previous season. Spores landing on a susceptible host in the presence of high relative humidity or water on the leaves are likely to infect and cause disease. Lesions 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. Cercospora leaf spot rarely poses a threat to the plants' health and survival.
Management Recommendations
Resistant cultivars are available for some host species and should be planted in sites where Cercospora leaf spot is a severe and recurring problem. In existing plantings, 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 Cercospora infected plants and plant debris to reduce the spread of disease and number of overwintering spores. Cercospora rarely poses a threat to plant health, thus fungicide use is not recommended. Several fungicides are available for sites with repeated, severe infections. Always read and follow the directions on the product label.
Effective Pesticides
Active Ingredients include: Chlorothalonil, Copper salts, Sulfur, Thiophanate-methyl
Resources
- Not satisfied with ID? Contact the Purdue Plant and Pest Diagnostic Lab
- Sign Up for the Purdue Landscape Report
