Page Title

Diagnosing Powdery Mildew

Body

Podosphaera leucotricha

Powdery mildew on the upper surface of a lilac leaf
Powdery mildew on the upper surface of a lilac leaf (Ward Upham, Kansas State University, Bugwood)

 

Symptoms

  • 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.
Apple leaves curled from powdery mildew
Powdery mildew can cause apple leaves to curl (Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org)
Red apples showing white powdery mildew
Powdery mildew on apple fruit (N.S. Luepschen, Bugwood.org)

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.