Apple scab on applese

By Shuhrataxmedov (Own work) [CC BY-SA 3.0], via Wikimedia Commons

Apple scab can really harm the appearance of ornamental apple and crab apple trees. Like most plant diseases, it is caused by a fungus.  Apple scab becomes active on young foliage and fruit early in the spring.  It is more active in cool and wet springs.  Initially there are dark spots which appear on leaves. Trees which are highly susceptible to apple scab may actually lose much of their foliage by mid summer due to this disease.  This of course can weaken a tree. Fungicide applications beginning in the spring will help to manage this disease.  Removal of fallen leaf debris is recommended to reduce new infections.  If you want to purchase a new crab apple tree for your landscape, it is advisable to select a plant variety which will be resistant to apple scab disease.