Leaves and twigs become covered with a white, powdery substance that is actually the mycelium of the fungus. Mycelia are the vegetative parts of the fungus, consisting of branching, threadlike filaments. Early infections may cause curling and twisting of young shoots. Fungicides can be used for control, but resistant cultivars are available. Of course, a cultivar that has resistance to the major diseases of crabapple is useless unless it has desirable horticultural characteristics.
Crabapples come in various sizes and shapes.
Some cultivars produce flowers on the current year's growth, others on the previous year's growth. Also, some cultivars bloom every year, whereas others bloom only every other year. It is possible to select cultivars that are both aesthetically pleasing and have disease resistance. In Virginia, scab resistance is the most important type of resistance. Unfortunately, the literature on disease-resistant cultivars of crabapple is confusing.