Powdery mildew on apple leaves. Figure 2 . Russetting of apple caused by powdery mildew.
Powdery mildew can be a problem on susceptible apple and flowering crabapple cultivars in Kansas.
The disease is especially severe on Jonathan apple and can result in shoot dieback, death of flower buds, and russetting of fruit. The disease first appears in the spring on fruit buds and new shoot growth. Low winter temperatures may kill infected flower buds. Those that do develop typically break bud several days later than normal and are covered with a white dusty growth of the fungus. The leaves on infected shoots also develop white patches and become distorted.