Apple: Scab

Biology

Apple scab is caused by a fungus which also causes scab on crabapple and hawthorn. The first infections occur during wet weather in the spring. Initially, the disease causes tiny, pale, chlorotic, water-soaked spots on the leaves. The spots enlarge and darken to a dark, velvety, olive-green then to black. Leaves may become distorted, puckered, and mottled. Leaves may drop, sometimes resulting in severe defoliation of susceptible trees. Scab can also affect fruit. Fruits infected early in development show olive-green to brown, roughened or corky spots which may develop deep cracks. These apples are often misshapen. Fruits infected at later stages develop small black “pinpoint” scab spots while in storage. The disease is favored by cool, wet conditions and overwinters in infected plant debris. Refer to PNW0582 Apple Scab for more information.

Management Options

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

Non-chemical Management

Select non-chemical management options as your first choice!

• Plant scab-resistant varieties such as ‘Akane’, ‘Chehalis’, ‘Liberty’, ‘Paulared’, ‘Prima’, or ‘Tydeman Red’.
• Plant in full sun.
• Space plantings and prune to provide good air circulation and light penetration.
• Avoid overhead irrigation.
• Rake and destroy (do not compost) fallen leaves, or cover them with soil.
• The application of nitrogen to the leaves in the fall will enhance the decomposition of the fallen leaves.

Chemical Management

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

• Apply fungicides when leaves are separating, just exposing bud cluster.
• Repeat at 7-day intervals for three or more applications until weather dries.
• When in blossom, wait until 3⁄4 of petals have fallen before applying.
• Homeowners should not make foliar applications to trees over 10 ft. tall.
• Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Approved Pesticides

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.

• Bonide Fruit Tree and Plant Guard R-T-Spray
  Active ingredient: boscalid, lambda-cyhalothrin, pyraclostrobin [EPA registration number: 4-488]
• Captan 50% WP Fruit and Ornamental
  Active ingredient: captan [EPA registration number: 4-459]
• ferti-lome F-Stop Lawn and Garden Fungicide
  Active ingredient: myclobutanil [EPA registration number: 7401-505]
• Spectracide IMMUNOX Multi-Purpose Fungicide Spray Concentrate
  Active ingredient: myclobutanil [EPA registration number: 9688-123-8845]
• This list may not include all products registered for this use.

Additional Images