Apple scab is a fungal disease that affects apple trees. It causes olive to brown spots on leaves, petioles, blossoms, and fruit. If left untreated, it can cause extensive defoliation and weaken trees over multiple years. The fungus overwinters in fallen leaves on the ground, so removing and destroying infected leaves and fruit in the fall helps prevent the disease the following year. An effective treatment is to apply fungicide sprays three times per year at bud break and again 3-4 weeks later for follow up applications, as fungal diseases require properly timed prevention. Once apple scab appears, it cannot be removed but future spreading can be prevented through ongoing fungicide use.