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Frogeye Leaf Spot
SYMPTOMS: Small purple specks typically appear 1-3 weeks after petal fall. These specks then enlarge to 1/8" - 1/4" in diameter and become brown with a purple margin. Older spots become irregularly shaped or lobed, retain their purple margin, and appear brown with a light colored center. Small black dots may appear in the light centers of older spots on the upper leaf surface. Heavily infected leaves may turn yellow and fall off, especially on the Jonathan variety.
DISEASE CYCLE: The fungus overwinters in dead bark and mummified fruit. Spores are primarily dispersed in splashing rain; this commonly results in the development of cone-shaped zones of infected leaves beneath the source of spores (e.g., fruit mummies hanging in the tree, or dead twigs and branches). Although spores may be released during rainy periods throughout the season, leaf infections occur primarily around the time of petal fall. Warm temperatures (minimum 60 0F, optimum 75-80 0F) and adequate moisture are necessary for infection to occur.
SCOUTING: Examine 100 leaves from each tree scouted (20 leaves per 5 limbs) and record the number showing at least 1 spot. On your scouting form, note the presence of fruit mummies and dead wood above zones of infection. Black rot cankers often form in branches that were infected with fire blight the previous season. From records or from the grower, note whether or not fire blight was serious the previous season. Note leaf yellowing and leaf drop if it occurs.
Apple IPM web site created by Kerry Kirk - 2001 - Send questions or comments to Patty Lucas