WSU Extension


Common Diseases
Armillaria root rot 
Botrytis blight (Gray mold) 
Crown gall 
Dead roots 
Downy mildew 
Dwarf mistletoe 
Leaf spots and blights 
Nectria cankers 
Phytophthora root rot 
Powdery mildew 
Pseudomonas bacterial canker 
Root rots 
Sclerotinia white mold 
Sudden oak death 
Tubercularia canker 
Verticillium wilt 

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Caption: Lettuce downy mildew
Photo by: R.S. Byther
Common Diseases : Downy mildew
(revision date: 4/30/2013)

Downy mildew is a fungal disease of tender green tissues including leaves and shoots. Infected leaves show areas of slightly chlorotic to purplish red to dark brown discoloration on the upper surface. A light gray-brown feltlike growth develops on the undersides of infected leaves. Infected tissues become necrotic, and eventually die. Wet, humid conditions favor disease development. Under favorable conditions, the disease can spread quite rapidly, and the entire plant can droop and die. Many vegetables, ornamentals, flowers, and other plants including grapes and cereal crops are susceptible to downy mildew infections.
Management Options

Non-Chemical Management
  • Destroy infected plants and debris.
Select non-chemical management options as your first choice!

Chemical Management

Fungicides may be effective in managing downy mildew in certain situations. However, the fungicide must be registered for the host plant. Contact your county extension agent for additional information.


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Caption: Lettuce downy mildew
Photo by: R.S. Byther
Caption: Downy mildew on pansy
Photo by: R.S. Byther
Caption: Downy mildew on pansy
Photo by: R.S. Byther