Diagnosing Powdery Mildew
- Apple leaves develop grayish-white spots or blotches that appear powdery.
- Symptoms are most common on the upper surfaces of leaves but may also appear on the lower surface.
- Leaves may curl and appear distorted.
- Powdery mildew on fruit manifests itself as streaks or russetting.
Management and other important facts
- Powdery mildew is common on leaves and usually does not affect plant health.
- The disease is more likely to occur when the relative humidity is high but does not require rainfall for the disease to develop.
- Prevent the disease by planting apple trees in full sun with good air circulation.
- Prune crowded branches to improve air flow.
- Fungicides are usually not necessary but in severe cases wettable sulfur, thiophanate-methyl or chlorothalonil may be applied.
Authors: Esther McGinnis and Aaron Bergdahl
This website was supported by the U.S. Department of Agriculture’s (USDA) Agricultural Marketing Service through grant 14-SCBGP-ND-0038.
Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the USDA.