WSU Extension


Lettuce : Downy mildew
(revision date: 6/3/2014)

Lettuce downy mildew is caused by a fungus which survives the winter on wild hosts and weeds. Light green or yellowish areas on the upper leaf surface are in places where the fungus is growing as downy patches on the undersides of the leaves. Affected parts turn brown and leaves die. Older leaves are infected first. This disease is worse in damp, foggy weather and between 43 and 53 degrees F.
Management Options

Non-Chemical Management
  • Remove weeds from around garden areas.
Select non-chemical management options as your first choice!

Chemical Management

None recommended

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Caption: Lettuce downy mildew
Photo by: R.S. Byther
Caption: Downy mildew on upper leaf surface
Photo by: R.S. Byther