Powdery Mildew

Blackberries are seldom severely infected by powdery mildew. It is occasionally a serious problem on susceptible varieties of red and black raspberries, especially the Black Hawk and Latham varieties. Infected plants may be stunted and less productive.

Symptoms and Disease Cycle

The disease is caused by the fungus Sphaerotheca macularis, which overwinters in infected cane tips and dormant buds. When temperatures reach 50 to 60°F, the spores are discharged and spread by wind. The characteristic sign of this disease is a white, powdery growth, primarily on the underside of the leaves. Infected leaves are dwarfed and twisted and have a yellow appearance on the upper surface. Powdery mildew is favored by warm weather without rainfall and is most serious in years and plantings with poor air circulation.

Disease Management

Unlike with most fungi, free water will reduce the incidence of this disease. Plant disease-resistant varieties when possible. Removing suckers that are infected with powdery mildew and pruning canes in the spring to a desirable height can reduce sources of the disease. Practices that allow good air circulation, such as cane thinning, proper plant spacing, and maintaining narrow rows, can be helpful in control. Apply fungicide sprays (see Table 7.5) when symptoms first appear, usually from midsummer through fall. If powdery mildew was severe in black raspberries the previous season, begin fungicide sprays in mid-June. Three to four applications might be required.

The important insects and diseases to be controlled, except for viruses, are listed in the right-hand column of this spray schedule. Always consult the label before making pesticide applications. Labels vary greatly among commercial products of the same material. It is important to refer to the label for the best timing and application rates when applying pesticides. Also read the text for information on cultural practices to minimize the application of pesticides. Due to a wide array of various products containing the same active ingredient, for insecticide recommendations, when appropriate, the active ingredient is listed instead of the name of the formulated product.

Table 7.5. Pesticide recommendations for brambles. (Follow all instructions and application rates listed on pesticide labels.
Time to Spray
Suggested Materials
Pests to be Controlled
Dormant (blackberries) - before buds open
Lime sulfur
Anthracnose, cane blight, powdery mildew, rust
Delayed Dormant - just as buds begin to open
Lime sulfur Anthracnose; spur blight on raspberries; powdery mildew, rust, and cane blight on blackberries
New shoots 8 inches long
Sulfur; Malathion; Esvenvalerate
Anthracnose; Botrytis, cane blight, and spur blight on raspberries; fruit worms; plant bugs
Petal Fall
Sulfur; Carbaryl plus Rotenone or Pyrethrum Anthracnose; Botrytis, cane blight, and spur blight on raspberries; fruit worms; rose chafer; aphids; mites; plant bugs
Preharvest Sulfur Fruit rots
Midharvest Sulfur Fruit rots
Postharvest Malathion plus Carbaryl Aphids, if present; Japanese beetles