Blackberry (Rubus spp.)-Powdery Mildew

Cause Podosphaera macularis (formerly Sphaerotheca macularis) , a fungus. Powdery mildew causes fruit loss in some Pacific Northwest plantings each year. 'Boysenberry' is very susceptible while 'Loganberry' is less susceptible; however, most other blackberries and their hybrids are generally not affected by this disease.

Powdery mildew also attacks 'Munger' black raspberry, 'Himalaya', and some other blackberries. The 'Puyallup' red raspberry is very susceptible, so powdery mildew may be a limiting factor with that cultivar. 'Canby', 'Fairview', 'Haida", 'Skeena', 'Wakefield', and 'Washington' are sometimes infected. 'Amity', 'Cascade Bounty', 'Chilcotin', 'Heritage, 'Rudi, 'Sumner', and 'Willamette' are resistant.

Symptoms Whitish-gray, powdery growth on foliage and fruit. Infection on the lower surface of a leaf may cause the upper surface to look mottled or blotchy with light-green areas. Severe mildew retards, dwarfs, and distorts plant parts and makes fruit unsalable. Young fruits fail to size properly, wither, and die.

Cultural control

  • Do not plant close to wooded areas that might shade the field.
  • Remove wild blackberries from around the field.
  • Plant more-resistant cultivars.
  • Remove any infected primocanes that occur late in the season.
  • Create an open plant canopy to improve air circulation and increase light penetration.

Chemical control

  • Dormant spray.
    • Rex Lime Sulfur Solution (28%) at 6 to 12 gal/100 gal water. 48-hr reentry. O
    • Sulforix at 3 gal/100 gal water. 48-hr reentry.
  • Apply during the season just before or when disease first appears. Repeat every 10 to 14 days as needed. Tank-mix and/or alternate products from different groups with different modes of action to prevent the build-up of resistant fungi. Minimize the use of any one group during the growing season.
    • Abound at 6 to 15.5 fl oz/A. Do not apply with silicone-based surfactants. May be applied on the day of harvest. Group 11 fungicide. 4-hr reentry.
    • Cabrio EG at 14 oz/A. Use before symptoms are anticipated. May be used on the day of harvest. Group 11 fungicide. 12-hr reentry.
    • Cinnerate at 13 to 32 fl oz/100 gal water. 4-hr reentry. O
    • Horticultural Mineral Oils. Generally effective at 1% to 2% volume to volume. Necrotic foliage may result if applied within 10 days of any sulfur application. Do not tank-mix with copper-based products when fruit is present. Do not use during freezing temperatures, above 90°F, or when plants are under heat or moisture stress. Do not use when foliage is wet because good coverage is essential. 4-hr reentry. O
      • JMS Stylet Oil at 3 to 6 quarts/100 gal water.
      • SuffOil-X at 1 to 2 gal/100 gal water.
      • Trilogy at 1% of spray volume but do not exceed 2.5 gal/A. Not registered in Oregon.
    • Kaligreen (82% potassium bicarbonate) at 2.5 to 3 lb/A. Might be used to supplement a normal program when powdery mildew is first observed. Do not mix with acidifying agents. Easily washed off leaves so thorough and frequent coverage is essential. 4-hr reentry. O
    • Luna Tranquility at 13.6 to 27 fl oz/A. May be used day of harvest. Group 7 + 9 fungicide. 12-hr reentry.
    • Monterey Bi-Carb Old Fashioned Fungicide at 4 teaspoons/2 gal water. H
    • M-Pede at 1 to 2 gal/100 gal water. Do not use within 3 days of sulfur sprays, and do not mix with hard water. 12-hr reentry. O
    • Oso SC at 6.5 to 13 fl oz/A. May be applied on the day of harvest. Group 19 fungicide. 4-hr reentry. O
    • Ph-D WDG at 6.2 oz/A plus an adjuvant. May be applied on the day of harvest. Group 19 fungicide. 4-hr reentry.
    • Prev-Am at 50 fl oz/100 gal water. Do not use above 90°F or when plants are under heat or moisture stress. 24-hr reentry.
    • Prolivo 300 SC at 4 to 5 fl oz/A. Can be used day of harvest. Group 50 fungicide. 4-hr reentry.
    • Pristine at 18.5 to 23 oz/A. Do not use with any other tank additive. Can be used day of harvest. Group 7 + 11 fungicide. 12-hr reentry.
    • Propiconazole-based fungicides are registered. Do not use within 30 days of harvest. Group 3 fungicides. 12-hr reentry.
      • Bumper 41.8 EC at 6 fl oz/A.
      • PropiMax EC at 6 fl oz/A.
      • Tilt at 6 fl oz/A.
    • QuiltXcel at 14 to 21 fl oz/A. Do not use within 30 days of harvest. Sprayers should not be used on apples. Group 3 + 11 fungicide. 12-hr reentry.
    • Rally 40 WSP at 1.25 to 3 oz/A. Applications may be made up to the day of harvest. Group 3 fungicide. 24-hr reentry.
    • Regalia at 1 to 4 quarts/A. Use on 7-day intervals. May be used day of harvest. Does not benefit from the addition of an adjuvant. Group P5 fungicide. 4-hr reentry. O
    • Rex Lime Sulfur Solution (28%) at 0.5 to 1.25 gal/100 gal water. 48-hr reentry. O
    • Sil-Matrix at 1 to 4 quarts/100 gal water plus a nonionic surfactant. Can be applied up to the day of harvest. 4-hr reentry. O
    • Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate for Gardens at 0.67 fl oz/gal water. May be applied up to the day of harvest. Group 3 fungicide. H
    • Sulfur-based products have good efficacy. Do not use within 2 weeks of an oil spray. Group M2 fungicides. 24-hr reentry. O
      • Cosavet-DF (80% sulfur) at 6 to 12 lb/A.
      • Kumulus DF (80% sulfur) at 6 to 15 lb/A.
      • Microthiol Disperss (80% sulfur) at 6 to 15 lb/A. Do not use a spreader-sticker.
      • Lilly Miller Sulfur Dust at 1 Tbl/gal water. Do not use within 30 days of an oil spray. H

Biological control

  • Aviv (Bacillus subtilis strain IAB/BS03) at 10 to 30 fl oz/100 gal water. Do not tank mix with more than one product. Unknown efficacy. Preharvest interval not specified. 4-hr reentry. O
  • LifeGard WG (Bacillus mycoides isolate J) at 4.5 oz/100 gal water. Does not have direct activity on pathogens but stimulates host defenses. Unknown efficacy. 4-hr reentry. O
  • Serenade ASO (Bacillus subtilis strain QST 713) at 2 to 4 quarts/A. Active ingredient is a small protein. 4-hr reentry. O
  • Sonata (Bacillus pumilis strain QST 2808) at 2 to 4 quarts/A. May be applied up to and including the day of harvest. 4-hr reentry. O

Reference Harvey, N., and Xu, X.M. 2010. Powdery mildew on raspberry is genetically different from strawberry powdery mildew. Journal of Plant Pathology 92:775-779.