Key Features
- Irregular dead leaf spots
- Small black bumps in spots
- Wilt and premature defoliation
Symptoms
Ascochyta leaf blight causes dead leaf spots that appear late in a wet spring through midsummer. The spots are light brown in the center with a dark ring between dead and healthy tissue. The edges of the spots are often defined by leaf veins, creating an irregular, mosaic appearance. Small, black pustules can be seen within the spots. Severe infections, and infections on the stem, can result in blackening and wilting of leaves. On chrysanthemum, it causes a foliar blight that often occurs during warm, wet summers.
Biology
Ascochyta overwinters in the soil and on previously infected leaf litter. In the spring, spores are produced that are blown by the wind or splashed onto susceptible hosts. Infection can only occur during periods of high humidity or when there is standing water on the leaf surface. As spots develop, the fungus produces more spores that spread the disease to healthy tissue and plants.
Management Recommendations
Avoidance is the best approach to managing this disease. Purchase symptom free plants from reputable growers. Space plants at a distance that allows air circulation between them; thin dense canopies. Water in the morning when the plant's leaves and stems have the most time to dry and avoid overhead watering. The amount of disease can be greatly reduced by removing all susceptible hosts for 3 or more years.
Effective Pesticides
Active Ingredients include: Chlorothalonil, Copper salts, Thiophanate-methyl
Resources
- Not satisfied with ID? Contact the Purdue Plant and Pest Diagnostic Lab
- Sign Up for the Purdue Landscape Report
