Raspberry: Powdery mildew
Photo by: R.S. Byther
Biology
Powdery mildew is a fungal disease which can affect leaves, shoot tips, new canes, and fruit of red and black raspberries, blackberries, and hybrids including ‘Logan’ berries. Leaves show pale green to watersoaked spots on the upper surface, with corresponding patches of white, powdery fungal growth on the lower surface. Infected young leaves do not expand properly, curling upward at the margins and becoming stunted and deformed.
Shoot tips may be entirely covered with fungal growth. Severe infections cause the shoots to become spindly and weak and may stunt the whole plant. Fruit may become covered with the fungus, fail to reach full size, and die.
Small, black fungal structures may be present in the white mats on leaves and stems later in the season. Powdery mildew development is favored by warm, cloudy, humid weather. The fungus overwinters in infected buds.
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 resistant varieties. The red raspberries ‘Chilcotin’, ‘Meeker’, ‘Nootka’, ‘Sumner’, and ‘Willamette’ are reported to be resistant to powdery mildew.
- Space plantings, prune, and train to provide good air circulation and reduce humidity.
- Carefully cut out and destroy or discard (do not compost) diseased suckers in the spring.
Chemical Management
IMPORTANT: Always read and follow label directions when working with pesticides.
For more information on using pesticides visit :
- Sulfur sprays may burn foliage in warm weather.
- Apply first spray of sulfur or potassium bicarbonate when first blooms open, then weekly until all fruit is set.
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.