A Technical Report from The Bartlett Tree Research Laboratories
Scab is one of the most devastating diseases of ornamental crabapples and apples. If early spring weather conditions are optimum (warm and moist), hawthorn and mountain ash may also be seriously affected. Apple scab is caused by the fungus Venturia inaequalis which infects leaves, petioles and fruit of its host. Initial symptoms appear as olive-green, sooty spots on leaf blades and petioles on young, developing foliage.