Answer: Without seeing the problem, it's difficult to diagnose. However, the most common problem with apples in your area is a fungal disease called apple scab. Apple scab, caused by the fungus Venturia inaequalis, occurs on apples and crabapples (Malus spp.). In late fall and early spring, fungal reproductive structures, appearing as round black pimples, develop primarily on infected leaves from the previous year. Spores are released from these structures in the spring and blown by wind or splashed by rain to new growth on nearby trees. There they start new infections. The fungus may infect and colonize the leaves, fruit, petioles, and blossoms of the tree, with symptoms commonly observed on the leaves and fruit. Later in the spring, these primary infections produce secondary spores which infect other leaves and fruit. These secondary infections may continue throughout the growing season during wet periods.
Symptoms on infected leaves initially appear as velvety brown to olive colored spots. Later, these spots turn black. Heavily infected leaves, with many spots, may turn yellow and drop from the tree. Fruit may also be infected, initially displaying lesions similar to those appearing on leaves. Later these lesions become brown and corky. Severe infections cause fruit to mature unevenly and crack.
Apple scab does not seriously harm apple trees. However, heavy defoliation causes apple trees to be less attractive, reduces growth and yield, and increases susceptibility to winter injury. During dry seasons, apple scab may be controlled through cultural practices. These practices include sanitation procedures, proper pruning, and watering during dry periods. Rake fallen leaves in autumn to reduce the number of spores available for infection the following spring. Prune suckers and branches in the crown to improve air circulation so leaves dry quickly. Perform annual pruning in late winter through early spring (February to early April, depending on environmental conditions).
To confirm the diagnosis, take an affected apple to your local Master Gardener Clinic or nursery. If this is the problem, there is a series of fungicide applications you can make to avoid the problem in the future.
Good luck with your apple trees!
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