Scab

Scab starts as tiny, pinhead-sized pale spots on new spring leaves, then darkens to olive or brownish black over a week or two. The spots enlarge irregularly, often showing a velvety black center with white halos. On fruit, you see raised brown or black circular areas that later develop a corky, cracked appearance. Infected leaves curl, become distorted, and drop early, sometimes defoliating the tree by mid-summer. This disease is especially problematic west of the Cascades where spring rains provide the moisture scab fungus needs to spread rapidly.

Scab overwinters on fallen leaves and requires at least 9 hours of leaf wetness at 59-77°F to infect. Western Washington's cool, wet springs create ideal conditions; you may see 8 or more infection periods per season here. Plant resistant cultivars like Liberty, Akane, or Chehalis apples when possible. If you already have susceptible trees, rake and destroy fallen leaves in fall, shred leaves to speed decomposition, and reduce overhead watering to keep foliage dry. Starting fungicide treatments at bud break (before visible symptoms) is necessary for disease management on susceptible varieties.