Apple Scab

Characteristics

Apple scab is a fungal disease that affects foliage, flowers, and fruits on apple trees. This disease overwinters in infected leaves that fall off the tree in autumn. During spring, spores are produced in the fallen, dead leaves. When it rains spores become airborne and easily contaminate the new growth on apple trees.

Signs & Symptoms

Lesions appear on the upper and lower sides of leaves, usually developing first on the lower side. The lesions start out as velvety brown to olive green. Over time, the olive green lesions turn dark brown to black. The number of lesions on leaves varies depending on the season, tree variety, and tree vigor. Lesions on older leaves are typically raised, dark green to gray brown, and cause cupping on the underside of the leaf. Leaves that are heavily infected with scab will curl, shrivel, and fall from the tree.

Small black spots will develop on fruit. As these spots grow and become older, the center loses the velvety appearance and becomes brown, corky and scabby. Heavily infected fruit becomes deformed and cracked when infected at an immature stage. The entire fruit is susceptible to scab, but lesions tend to cluster around the bottom end of the fruit.

Treatment & Recommendations

To help reduce apple scab, clean up leaves in the fall by raking, or using leaf blowers to keep leaves away from the base of the affected tree. Frequent pruning of trees allows for better airflow through the canopy, and helps reduce the amount of apple scab on a tree.

Fertilizer and proper nutrition of trees is very important in maintaining tree health. Healthier apple trees are less prone to infection.

Talk with one of our arborists about plant health care for your apple trees.