Apple scab is a foliar leaf disease caused by the fungus Venturia inaequalis.
Commonly impacted trees: crabapple, apple, hawthorn, cotoneaster, mountain ash, and pear.
If infected leaf litter gets wet in spring, spores are released and may be carried by wind or rain to infect new leaf and blossom tissue. However, spores can continue to infect throughout the season as long as temperature and humidity conditions are favorable. Symptoms include: Olive-green to black velvety spots with indistinct margins on leaves. Severe cases can lead to yellowing of the leaves and early defoliation. Olive-green to black lesions on the fruit turn brown and corky over time.
Fungicide applications at 2-week intervals beginning when new growth is expanding in the spring.