The premature leaf drop will weaken the trees somewhat, but will usually not kill them. The damage is mainly aesthetic. Heavily defoliated trees are unattractive. However, heavy defoliation in several successive years can weaken susceptible crabapples and predispose them to additional damage, such as winter injury. Apple scab may be prevented by the application of fungicides, such as captan and chlorothalonil, starting as soon as leaf growth appears until about the middle of June.
Infections are less likely to occur with the arrival of warmer, drier weather in early summer.
Sanitation also plays an important role in controlling apple scab. Raking and destroying the leaves as they fall will help control the disease next season. The fungus overwinters on partially decayed leaves. Pruning to open up the tree canopy and speed drying of the foliage may also be helpful. However, the best control for apple scab is to plant scab resistant varieties.