Fungal diseases apple scab

Fungal diseases are grouped according to the type of disease (or symptoms) that they cause, such as mildews, molds, or rots. Most spread from plant to plant in the form of spores. Some, like clubroot, have dormant spores that can remain viable in the soil for 40 years or more. The fungus that causes apple scab overwinters on infected debris such as leaves on the ground. Fungal diseases are more common in warm, damp conditions, which allow the spores to move freely in moist air and on a film of water on the surface of leaves. 

This fungal disease overwinters in leaf debris, and in severe cases in twig lesions, and is spread to new leaves in spring by wind and rain. Apple scab is worse when the weather is cool, wet or overcast in spring and early summer, especially at flowering time. 

Fungal disease similar to apple scab (q.v.) but infection also often occurs on bud scales. Scab is worse in cool, wet periods in spring and early summer. 

Phenylmercury acetate is excellent for seed treatment and, in addition, is an eradicant leaf fungicide against apple scab (prebloom period) and against the fungal diseases of rice (Frohberger, 1969). 

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