How to recognize the disease:
The diagnostic symptom of frogeye leaf spot are angular spots with light gray centres and distinct purple to red-brown margins. No chlorotic halos surrounding lesions are present. Leaf spots can be single or merge to form larger lesions. This can result in premature leaf drop. Lesions on stems and pod can occur later in the season, but they are less common and distinctive than lesions on the leaves. Seeds near pod lesions can be infected and develop conspcuous light to dark gray or brown areas.
The concentric pattern of light brown to tan center portions of the leaf spot ringed by darker purple margins is the origin the name “frogeye leaf spot.” Young leaves exhibit circular spots with indistinct purple edges about 2 weeks after petal fall. Many of the spots develop no further and a well-defined circular brown spot is present by summer. However, in other spots, there is secondary enlargement during the summer and the brown spots develop irregular discoloured lobes. Tiny black fruiting structures often develop in the center of the leaf spots. Extensive spotting of leaves initially causes chlorosis followed by early leaf loss.
Damage to apple trees and crabapple trees from this disease can be severe. Once the fruit stage sets in, the fruit is inedible and completely rotten. Cankers can become quite large, several feet in diameter and length, and can completely girdle and kill the tree itself, not to mention branches and twigs.
Read complete article: http://seedbuzz.com/knowledge-center/article/frogeye-leaf-spot
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