Crabapple: Scab

Biology

Scab of crabapples is caused by the same fungus which causes scab on apple and hawthorn. The disease infects during wet weather in the spring and initially causes small, pale, watersoaked spots on the leaves. The spots enlarge and darken, first to olive-green then to black. Leaves may become distorted and often drop, sometimes resulting in severe defoliation of susceptible trees. Scab can also affect fruit, with pinhead spots enlarging to velvety olive then black blotches. The disease is most favored by cool, wet conditions and overwinters in infected plant debris.

Management Options

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

Non-chemical Management

Select non-chemical management options as your first choice!

• Many crabapple cultivars are resistant to scab including ‘Bob White’, ‘Centennial’, *’Christmas Holly’, ‘David’, ‘Indian Summer’, ‘Jewelberry’, *’Molten Lava’, ‘Ormiston Roy’, *’Professor Sprenger’, ‘Profusion’, ‘Red Jewel’, and *’White Angel’. Malus floribunda, and M. Tschonoskii are also resistant. (*rated as good to excellent scab and powdery mildew resistance. See EB1809.)
• Plant in full sun.
• Avoid overhead irrigation.
• Rake and destroy fallen leaves.

Chemical Management

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

• Pesticide recommendations are for flowering (non-edible) crabapples.
• Apply at pre-pink, pink, calyx.
• If scab was a problem last year, begin at green tip.
• 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 Fung-onil Multi-Purpose Fungicide Concentrate
  Active ingredient: chlorothalonil [EPA registration number: 60063-9-4]
• Bonide Infuse Systemic Disease Control
  Active ingredient: propiconazole [EPA registration number: 100-773-4]
• ferti-lome Liquid Systemic Fungicide II R-T-Spray
  Active ingredient: propiconazole [EPA registration number: 53883-184-7401]
• GardenTech Daconil Fungicide Concentrate
  Active ingredient: chlorothalonil [EPA registration number: 67572-82-71004]
• Ortho Max Garden Disease Control Concentrate
  Active ingredient: chlorothalonil [EPA registration number: 239-2522]
• 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