Apple Scab

Apple scab is a fungal disease caused by the fungus Venturia inaequalis, which affects leaves, fruit and twigs.

While most common in apple trees, both pear and hawthorn are also frequently infected by the fungus. Outbreaks will be most severe following particularly wet and cool spring conditions.

The fungus overwinters on fallen leaves and begins to develop spores in the spring prior to bud break. The spores are then transported by wind, rain or other physical means to infect tender, developing leaves, twigs and fruit. Once the fungal infection is established in the newly forming tissues, more spores are produced and spread to other areas of the tree.

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  • Common Symptoms
    • Infection is commonly evidenced first by brownish-green spots on the leaves or fruit. As the infection progresses, the spots on the fruit become darker and more prominent and take on a somewhat fuzzy texture. When infection is severe, leaves will turn yellow and drop off. Fruit will become deformed and/or drop off prior to ripening.

    • We recommend a trunk injection with a systemic fungicide, either PHOSPHO-jet or Propizol Fungicide.

      PHOSPHO-jet inhibits fungal cells while eliciting a plant health response from the tree. It promotes stronger, tree cells, root development, and triggers the tree’s natural defense mechanisms making it more resistant to infection with quicker recovery time.

      Propizol will have more direct and aggressive activity against the fungus itself and is recommended if infection is chronic or particularly severe.

    When To Treat
    • The best results will be achieved when PHOSPHO-jet or Propizol are applied prior to infection. Applying PHOSPHO-jet or Propizol in the fall will minimize or prevent infection the following spring. If applying in the spring, it should be applied as early in the spring as possible, before or at bud break.

      If treating an established infection, Propizol is recommended as a first treatment, with subsequent treatments of PHOSPHO-jet as necessary. Assess tree health prior to treatment.

    What To Expect After Treatment
    • Tree recovery will be proportional to the severity of the infection at the time of treatment. PHOSPHO-jet will elicit a plant health response that helps trees endure the infection and look healthier and more robust.

    References And Photo Credits
    • Header Image taken by: Joseph OBrien, USDA Forest Service,

      Leaves infected taken by: Joseph O’Brien, USDA Forest Service,

      Defoliation taken by: Mary Ann Hansen, Virginia Polytechnic Institute and State University,

      Olive Green taken by: Srdjan Acimovic, Arborjet Inc.