Key Features
- Chlorotic or browning leaves
- Defoliation
- Brown or black spots on leaves
Symptoms
Marssonina causes leaf spots and dead spots on stems. Leaf spots first appear in the spring during periods of wet weather, expand and may grow together as the season progresses; this gives the appearance of very large leaf spots or entire sections of dead leaf tissue. Spots may be brown or black and are sometimes bordered by a yellow halo. Dead, sunken spots may be observed on small stems late in the season. Spores are produced on tiny brown bumps within leaf and stem lesions. Marssonina leaf spot may be impossible to distinguish from other leaf spot and anthracnose diseases without microscopic analysis. Samples may be sent to a plant disease diagnostic clinic for confirmation.
Biology
Marssonina overwinters in the cankers (stem spots) it forms on small stems. Spores are produced in the spring and summer when temperatures increase and rain is frequent. Spore release and infection is highly dependent on wet leaves caused by rain, dew, irrigation, or even high humidity under warm conditions. Marssonina leaf spot rarely causes long-term damage to its host. Severe infections may result in defoliation or a poor flush of leaves the following spring.
Management Recommendations
Replace susceptible trees with resistant species or varieties in locations with repeated, heavy infections. Pruning out cankered stems and destroying infected leaf litter after fall leaf drop are the most effective controls for this disease. Maintaining plant health through irrigation and proper fertilization are often enough to promote healthy growth even in the presence of the disease. Irrigating landscapes in the morning will allow leaves to dry throughout the day. Dense plantings of susceptible trees may be thinned to slow the disease. Chlorothalonil is labeled for the control of Marssonina leaf spot. Always follow the instructions on the product label. With large trees, pruning cankered branches and treating with fungicides is not always feasible or safe.
Effective Pesticides
Active Ingredients include: Chlorothalonil
Resources
- Not satisfied with ID? Contact the Purdue Plant and Pest Diagnostic Lab
- Sign Up for the Purdue Landscape Report
