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Apple scab is the most common fungal disease of apples and crabapples.
This disease can occur throughout the growing season and is most
severe during wet years. Although apple scab does not usually harm
trees, it may reduce fruit quality and overall yield.
The leaves, petioles, blossoms, and fruit may all be infected.
Symptoms are most commonly seen as dark velvety spots on the
upper leaf surface [1], while severely infected leaves may turn
yellow and drop from the tree. Fruit infections appear as brown,
corky spots[2], which may crack open.
To help control apple scab, remove fallen leaves and apples throughout
the growing season, and after harvest in the fall. Properly water,
fertilize, and mulch trees to maintain vigor. Also prune trees annually [3]
to increase airflow and reduce leaf moisture.
Fungicides may be needed during wet, rainy seasons. Those fungicides
containing captan are labeled for use on edible apples and crabapples.
Carefully read the label before buying, opening, and using fungicides.
Finally, when planting new trees, use varieties resistant to apple scab.
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[1]
[2]
[3]
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