Apply all chemicals according to directions on the label. Highly susceptible crabapple varieties may lose most of their leaves, which weakens the tree and reduces flowering the next year. The disease begins on the leaf as a purple speck that enlarges to have a brown or tan center, which looks like a frog s eye. Heavily infected leaves drop from the tree. Limbs may have slightly sunken, reddish brown areas called cankers.
Infected fruits begin with tiny red or purple spots occurring opposite the stem end.
After a few weeks the spots enlarge and have alternating zones of black and brown. The rot eventually affects the entire fruit, which wrinkles, mummifies and often remains attached to the tree. The fungicides captan and thiophanate-methyl are effective if applied early and at regular intervals throughout the season. They often occur together, even though they are each a distinctive disease. Although unsightly, the fruit is still edible.