Onions, Garlic: Downy mildew
categories: Onions, Garlic Onions, Garlic Diseases Vegetables
last review date: 2022-12-07 12:00
Photo by: R.S. Byther
Biology
Downy mildew is a fungal disease affecting onions and related species, including weedy species. Leaves initially develop pale, elongate patches. The spots may be water-soaked at first, then later appear somewhat purplish. The spots become covered with a downy, grayish or white fungal growth. Affected leaves often die back. Bulbs of affected plants are smaller than normal and of poor quality. Infected bulbs may become shriveled and discolored in storage, or may sprout prematurely. Cool, damp weather favors spread of the disease.
Management Options
See "Using Integrated Pest Management (IPM) in the Landscape" for successful problem management techniques.
Non-chemical Management
Select non-chemical management options as your first choice!
- Plant disease-free materials in well-drained soils.
- Rotate crops. Do not plant onions and related crops into the same locations each year. Allow at least three years before replanting susceptible crops in a location which was previously diseased.
- Space plantings to provide good air circulation.
- Avoid overhead watering.
- Remove and destroy diseased plants and debris. Destroy or discard (do not compost) diseased materials.
- Control weeds in and around the garden.
Chemical Management
IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.
- Apply when plants are 4 to 6 inches tall and repeat at 7- to 10-day intervals.
- Copper products can damage foliage.
Approved Pesticides
Examples of pesticides that are legal for home use in Washington State are listed below.
The list may not include all products registered for this use.
WSU Extension programs and employment are available to all without discrimination.
Evidence of noncompliance may be reported through your local Extension office.