Frogeye Leaf spot and black rot are caused by the fungi Cercospora sojina and Botryosphaeria obtusa. It occurs in three phases: leaf infection, fruit rot, and branch infections.

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Appearance:

Frogeye Leaf Spot

  • Fungus enters through the stomata on the underside of the leaves

  • Tiny, purplish specks on foliage that become larger over time (circular and 1/8 to 1/4 inch in diameter)

  • The center of the spots become dark with dark brown-purplish margins

  • Yellowing of leaves and fall prematurely

Black Rot

  • Fruit infection following the appearance of frogeye leaf spot.

  • Can begin in the blossom of developing fruit

  • Series of brown and black rings will appear as the decay expands, as well as black dots on fruit

  • Rotted fruit will dry up, shrivel, and mummify

Management & Treatment:

  • Sanitation is key to prevention

  • Prune diseased/dead twigs and branches; dispose of prunings properly (remove from orchard and/or burn)

  • Use proper pruning technique

  • Cut well below diseased tissues

  • Protect trees from injury

  • Utilize allopathic measures like copper to address the pathogen

Sources: Michael Phillips, “The Holistic Orchard” and University of Kentucky (College of Agriculture, Food & Environment).