What is Apple Scab
What is Apple Scab
What is Apple Scab? Apple scab is a fungal disease caused by Venturia inaequalis that appears as olive-green to brown spots on leaves and fruit. It thrives in cool, moist conditions and spreads via spores from overwintering leaves. Management involves early-season fungicide sprays, sanitation to remove fallen leaves, and planting scab-resistant varieties.
- Cause: A fungus called Venturia inaequalis.
- Appearance: Olive-green, velvety spots that darken and become bumpy on leaves and fruit. On fruit, lesions may eventually crack.
- Hosts: Affects apples, crabapples, hawthorns, and mountain ash.
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Overwintering:
The fungus survives the winter in infected leaves that fall to the ground.
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Primary infection:
In spring, spores are released from the fallen leaves during wet periods, infecting new leaves and fruit.
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Secondary infection:
After the initial infection, the fungus produces “summer” spores on the new lesions, which can cause multiple new infections throughout the growing season whenever it is wet.
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Sanitation:
Remove and destroy fallen leaves in the fall to reduce the number of overwintering spores. Applying a urea solution to fallen leaves can help them decompose faster.
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Pruning:
Prune trees to improve air circulation and reduce long periods of leaf wetness.
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Chemical control:
- Apply fungicides according to label instructions, beginning at bud swell and continuing through the early season before rain events.
- Common active ingredients include captan, mancozeb, chlorothalonil, myclobutanil, and propiconazole.
- Organic options include sulfur or copper sprays and products containing Bacillus subtilis or Bacillus amyloliquefaciens.
- Apply fungicides according to label instructions, beginning at bud swell and continuing through the early season before rain events.
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Resistant varieties:Plant apple varieties that are resistant to scab to help reduce disease pressure.If you’re uncertain about the condition of your trees, give Johnson Ops Tree Care a call. One of our Certified Arborists will gladly meet with you to discuss your concerns. After an assessment, we will provide a personalized PHC (plant health care) plan to treat your trees.
