It interferes with the proper functioning of leaves, reduces shoot growth, reduces fruit set, and produces a netlike russet on the fruit of some cultivars. It is often a serious problem in apple nurseries. Flowers do not develop normally, are likely to be greenish white, and produce no fruit. On leaves of new shoot growth symptoms of powdery mildew are feltlike, white patches on the margins and lower surfaces.
Infected leaves curl upward and soon become covered with a powdery coating of spores.
New infections of succulent leaves and growing shoots reduce the size of the entire shoot. By midsummer, leaves and shoots may turn brown. As these buds open in spring, all of their parts become covered with a powdery coating of spores. The spores are windblown and infect new leaves, fruit, and shoots. Fruit infection takes place during and shortly after the blossom period.