Do you have these Necrotic Symptoms on your Apple Trees?

Dr. Keith Yoder (Virginia Tech Plant Pathologist, Winchester, VA), received several calls from growers regarding the necrotic leaf spot symptoms in the top two photos. These necrotic blotches occurred on Gala, Golden Delicious, and Cripps Pink (Pink Lady) and had defined concentric rings. The lesions start as purple spots, then growth with concentric rings that may eventually coalesce. Symptoms may appear on both old and younger leaves and leaves may yellow and fall off. Dr. Yoder tentatively identified the causal organism as Glomerella cingulata. Fruit rot symptoms caused by Glomerella cingulata, a stage of the bitter rot fungus, tend to be darker than those usually associated with bitter rot. Like typical bitter rot, the fruit rot caused by the Glomerella strain has a cone-shaped pattern of growth into the fruit.

The lower two photos are from Golden Delicious in a Penn State Fruit Research and Extension Center (FREC) research orchard. We have been diagnosing the disorder as necrotic blotch that could be due to some epiphytic pathogen in the orchard. I have been monitoring the effects of seasonal fungicide programs on the incidence of these symptoms on Golden Delicious, but have not found consistent effects.

Summary/Recommendation:

To manage this malady and to minimize disease pressure for next growing season, I agree with Dr. Yoder’s recommendation to reduce the source of overwintering inoculum in the orchard by good sanitation practices of removing prunings, shredding leaf litter with a flail mower or applying a foliar spray of urea at leaf drop and / or early spring.  This can also help in suppressing other diseases such as apple scab, Alternaria leaf blotch and other unknown leaf pathogenic organisms on the orchard floor.

Resources:

APS Journal

Tree Fruit Disease

Penn State