Symptoms of Apple Scab on Fruit

Station # 1 – Apple Scab

 Read the following article on apple scabs.

 Observe the apple specimens.

 Answer all questions on your lab sheet.

Symptoms of apple scab on fruit. Photo by Jack Kelly Clark.

Apple scab, caused by the fungus Venturia inaequalis, 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, while severely infected leaves may turn yellow and drop from the tree. Fruit infections appear as brown, corky spots, 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 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.

TABLE 1. Susceptibility of Apple Varieties to Apple Scab. Susceptible Highly resistant

Bellflower Monroe Easy-Gro Mac-free Blushing Gold Mutsu Enterprise Prima Fuji Paula Red Florina Priscilla Gala Red Delicious Freedom Pristine Golden Delicious Rome Beauty Gold Rush Redfree Granny Smith Stayman Winesap Jon Grimes Sir Prize Gravenstein Winesap Jonafree Spigold Grimes Yellow Newtown Liberty Williams Pride Ida Red York Imperial Jonathan