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Master Gardener’s: Powdery Mildew


Published: March 29, 2016 • By: UCCE Colusa County Master Gardeners

White powdery growth on leaves and shoots can be a sign of powdery mildew disease. This disease affects many plants. In some situations, fungicide treatments may be required.

  • Powdery mildew is common under warm, dry conditions.
  • Unlike many diseases, powdery mildew does not require moist conditions to grow.
  • Unlike many diseases, powdery mildew does not require moist conditions to grow.
  • Moderate temperatures (60 to 80 degrees) and shade favor the disease.
  • Symptoms can vary by plant species.
  • White powdery spots develop on both surfaces of leaves and expand as the infection grows.
  • Leaves gradually turn yellow or brown and fall off.
  • In some cases, leaves or shoots twist or distort.

Consider non chemical approaches.

  • Sprinkle infected plants with water. To prevent problems with other diseases, do this mid morning so moisture dries out rapidly. Adding a little soap to the water can increase control.
  • Fungicides may be needed for susceptible varieties of some plants.
  • Plants often requiring treatment include apples, caneberries, grapes, roses, and cucurbits.
  • Control mild to moderate infections with horticultural oil or plant based oils such as neem oil.

Prevent infections with wettable sulfurs, especially those in ready-to-use products that are formulated with soaplike surfactants. These products are ineffective if applied after the disease appears. Additional applications may be needed.
For more information on powdery mildew go to ipm.ucdavis.edu