Anthracnose
Apiognomonia spp., Colletotrichum spp., Gloeosporium spp., Kabatiella spp., Discula spp.
Key Features
- Wilt or prematue defoliation
- Dead sunken areas on stems
- Expanding spots on leaves
Symptoms
Early infection of young, immature leaves often results in dead and/or deformed leaf margins as well as dead, irregularly shaped spots that tend to form along the veins. Heavily infected leaves may appear misshapen and curled. Mature leaves are more resistant to infection. Older leaves develop small, brown spots when infected in the summer during wet weather. Dead spots may develop on twigs and small branches and develop into small cankers. Infections are most abundant in the lower portion of the trees. Severe infections may result in defoliation; When severe defoliation occurs in the spring, trees usually produce a new flush of leaves. Dieback results when twigs are killed by cankers or repeated defoliation. Tiny bumps (fruiting bodies) may be seen within or underneath the dead areas. A hand lens or magnifying glass is usually required to see these.
Biology
Wet weather, promotes infection of all these pathogens. The fungus survives between seasons on infected branches, twigs, fallen leaves, and in the crown of perennials. In the spring, spores are blown or splashed from stem spots to developing leaf and twig tissue. Infected leaves may shrivel and fall, while infected young twigs or stems can be girdled and killed. High relative humidity and leaf wetness are required for these pathogens to cause new infections. Symptoms are most severe in the lower canopy where humidity is highest and leaves are not dried by the sun.
Management Recommendations
Anthracnose may be ugly, but does not cause permanent damage to well established, vigorously growing trees. Proper watering, mulching, and sanitation procedures will reduce damage caused by anthracnose. Raking and destroying leaves in the fall and pruning dead or dying branches will reduce the number of new infections the following year. Trees should be pruned only during dry weather. Spring fertilization of severely stressed trees can improve tree vigor. Trees that have been severely stressed from repeated defoliation, or are newly transplanted, may benefit from chemical control. Fungicide application should begin at bud break to protect new growth. Repeat applications according to the fungicide label during cool wet weather. Read the label carefully and apply only as directed. Application to large trees requires special equipment to ensure adequate coverage.
Effective Pesticides
Active Ingredients include: Chlorothalonil, Copper salts, Myclobutanil, Propiconazole, Tebuconazole, Thiophanate-methyl
Resources
- Not satisfied with ID? Contact the Purdue Plant and Pest Diagnostic Lab
- Sign Up for the Purdue Landscape Report
