Apple scab is a common fungal disease that infects both the leaves and fruit of the apple. It causes lesions and splitting. Apple Scab can lead to premature defoliation, resulting in less flowering and greater susceptibility to other diseases.

For region-specific information, please contact your local Giving Grove partner. If you would like more information like this sent straight to your inbox, consider subscribing to The Serving, The Giving Grove’s quarterly newsletter.

Causes:

  • A fungus that infects the leaves and fruit of apples.

  • Fungus harbors in leaves infected the prior year and overwinters on the orchard floor.

  • The timing and degree of infection depend on the amount of remaining leaves that are wet, the rain volume, and air temperature.

Symptoms:

  • Apple scab causes grayish-brown spots on leaves and hard, rough lesions on fruit

  • Small, raised, fuzzy, olive-colored spots will first appear on the leaves surrounding fruit clusters

  • Causes grayish-brown spots on leaves and hard, rough lesions on fruit

  • The fruit lesions can lead to the fruit splitting open and rotting

Timing:

  • Initial leaf infections take place early in the growing season around bloom time (March-April)

  • Secondary infections occur with fruit formation.

  • Ideal temperatures for infection are 60-75°F (16-24°C).

How to Avoid:

  • Purchase varieties that have a higher degree of resistance or immunity to apple scab. Click here for a list of suggested varieties.

  • Throughout and after the growing season, keep the orchard floor clear of fallen leaves to reduce the spread of the disease.

  • Sanitize pruning equipment between trees.

How to Treat:

  • Sulfur can be sprayed just before bloom time and then every 7-10 days during infection periods.

  • 5% solution of Urea or other nitrogen fertilizers sprayed on the ground in the fall will encourage decomposition of fallen leaves and prevent the spread of spores.

Why it Matters:

Apple Scab can lead to premature defoliation, which can lead to less flowering the following spring and greater susceptibility to other diseases. Entire fruit crops can be lost.

Sources: MyIPM, Pennsylvania State University Extension, Kansas State Research and Extension, University of California IPM, Patrick L. Byers, Horticulture Specialist, and Michael Phillips, “The Holistic Orchard.”