All varieties of apple trees are susceptible to fungal diseases, which cause symptoms such as black spots to develop on leaves and fruit. These infections may also compromise the health of the tree itself.
Apple scab is caused by the fungus Venturia inaequalis, which also appears on the pear, mountain ash and hawthorn. Another type of fungal disease affecting the leaves of apple trees is frogeye leaf spot, which is known as black rot when it affects the fruit of the tree.
Apple scab causes brown or black spots on leaves and fruit. According to North Dakota State University, heavy black spotting on leaves often leads to defoliation or leaf loss. Fruit infected with apple scab is often malformed and undersized.
Frogeye leaf spot causes dark leaf spots likened in appearance to a frog's eye. Black rot causes black spots on fruit, which eventually rots completely. Tiny spores in black fruiting bodies appear on the surface of the branches.
Removing and destroying any dead or infected fruit or wood is essential in the control of fungal diseases. Applying fungicides may help prevent or control fungal diseases such as apple scab, black rot or frogeye leaf spot. Fungicide application is most effective when good sanitation practices are being used, according to Ohio State University.