The heavy defoliation will weaken the trees somewhat, but will usually not kill them. The damage is mainly aesthetic. Heavily defoliated trees are unattractive. Apple scab may be prevented by the application of fungicides, such as chlorothalonil, when growth first appears. Repeat at 7 to 10 day intervals until about the middle of June.
Sanitation also plays an important role in controlling apple scab.
Raking and destroying the leaves as they fall helps control the disease next season. The best way to avoid apple scab problems is to plant scab resistant varieties. The following crabapple varieties perform well in Iowa and also possess good to excellent resistance to apple scab. However, they will lose considerable foliage whenweather conditions are ideal for scab. Spring Snow' isone of the few crabapple varieties that produces little or nofruit.