Select the following link for the Apple Scab Report.

Apple scab is a fungal disease causing symptoms of brown corky "scabs" on fruit and olive-brown to black leaf lesions that can cause serious defoliation of apple trees. Infections begin, for the most part, from inoculum overwintering in infected leaf litter from the previous growing season. In the spring, the overwintering fungal structures (called pseudothecia) speed up their development forming asci (or sacs) containing ascospores within the pseudothecia. When the ascospores are mature, both morphologically and physiologically, and the orchard floor leaves become wet, the spores are released and carried by air currents to infect both leaf tissue and fruits.

Ascospores begin to mature sometime after the "silver tip" phenological stage, during the "first green" stage, preceding "green tip". Please re-visit this page in the spring for a report on the development and release of ascospores.

Links

UW Plant Pathology Fruit Disease Information

West Virginia University Apple Scab Reference Page

West Virginia University Apple Scab Mills Table

Cornell Mills Table

Vermont Extension Ascospore Maturity Degree Day Model Table