Apple: Cytospora canker

Biology

The fungi which cause Cytospora canker attack through wounds on twigs and branches. The disease can spread to healthy tissues after the initial infection. Initial cankers are small, but enlarge quickly and may streak up and down the stems without girdling. The cankers may also girdle twigs, resulting in dieback above the infection site and causing “flags” of dead material to appear in the canopy. The leaves on the dead twigs turn color and droop, but often remain attached. The canker itself appears as a dark, sunken area of dead bark and wood. Pinhead-sized black fruiting structures of the fungi often erupt through the bark and produce reddish tendrils or droplets of spores in wet weather. Spores are easily spread by wind, rain, and insects. The cankers are often perennial, enlarging through several seasons.

Management Options

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

• Avoid wounding trees.
• Provide proper planting sites and culture. Healthy trees are more resistant to disease and winter injury.
• Control insect and disease problems to minimize injuries.
• Prune out and destroy infected tissues during dry weather. Make cuts at least 12″ below visibly infected area. Sterilize pruning tools frequently.
• Rake and destroy twig debris.
• Correct pruning practices minimize injury and improve wound healing. For more information see PNW 400, Training and Pruning Your Home Orchard, or contact your WSU Master Gardeners or county Extension agent.

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.

• None recommended.