Rose: Downy mildew
Photo by: R.S. Byther
Biology
Downy mildew can affect leaves, stems, flower stems, and flower parts. The infection is usually found only on young growth.
On leaves, symptoms include purplish or brown spots, usually between veins, and yellow leaves with green spots. Infected leaves may drop off the plant.
Grayish fungal masses may be found on the underside of some infected leaves (unlike powdery mildew, which is white and found on both sides of leaves).
Symptoms on stems and flower parts can include small or large purple to black spots.
Small, infected twigs can be killed.
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 varieties that are less susceptible to the disease.
- Collect and destroy all fallen leaves from beneath plants.
- Prune and destroy all infected portions of plants.
- Space plantings and prune to provide good air circulation.
- Avoid overhead watering to help reduce humidity around plants.
Chemical Management
IMPORTANT: Always read and follow label directions when working with pesticides.
For more information on using pesticides visit :
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Focus on cultural control.
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Copper fungicides may have some efficacy, but may cause discoloration of foliage or blooms.
Approved Pesticides
If you choose to use a pesticide, some examples of products that are legal in Washington are listed below. Some products are labeled for just INDOOR or just OUTDOOR use, or may allow both uses. Be sure to choose a product appropriate for your situation. Always read and follow all label directions.
WSU Extension programs and employment are available to all without discrimination.
Evidence of noncompliance may be reported through your local Extension office.