Introduction Powdery mildew, caused by Podosphaera clandestina, is a significant disease affecting sweet cherries in British Columbia. It impacts foliage and fruit, occasionally resulting in complete crop losses. Fungicide applications are essential for its control. This blog explores the findings from a 2007 trial conducted in Creston, BC, to evaluate the effectiveness and tolerance of summer oil sprays for powdery mildew control in sweet cherries.

Overview The trial was initiated by the Creston Chapter Okanagan Kootenay Cherry Growers Association and led by Duane Holder of FarmQuest Consulting. The primary objective was to assess the effectiveness and tolerance of summer oil sprays in controlling powdery mildew. Three trials were conducted on commercial cherry orchards using Bionatrol-M (a vegetable-based oil from NTS Research) and Purespray Green (a petroleum-based oil from Petro-Canada).

Trial Design

  • Trial 1 & 3 (Lapins/Mazzard variety, covered system): Evaluated the impact of treatments under rain-covered conditions.
  • Trial 2 (Staccato/Mazzard variety, non-covered): Assessed the efficacy in a more susceptible late-season variety.

Treatments Applied:

  • Untreated Control
  • Cabrio (20 g/100 L)
  • Bionatrol-M (750 ml/100 L)
  • Purespray Green (750 ml/100 L)
  • Cabrio + Bionatrol-M
  • Cabrio + Purespray Green
  • Pristine (29.6 g/100 L)
  • Pristine + Bionatrol-M
  • Pristine + Purespray Green

Application Method:

  • Two spray applications were made with a handgun to run-off, followed by cover sprays using an airblast sprayer.

Results and Conclusions Trial 1 & 3:

  • Disease severity in untreated controls was 4% and 10.5%, respectively.
  • Treatments significantly reduced mildew incidence, with Bionatrol-M and Purespray Green showing effectiveness comparable to conventional fungicides.

Trial 2:

  • Disease pressure was low, making it difficult to differentiate the effectiveness of control among treatments.


  • No signs of phytotoxic effects were observed in any treatments.

Key Findings:

  • Summer oils, though not registered in Canada, showed potential in integrated pest management programs.
  • Bionatrol-M and Purespray Green were effective in reducing powdery mildew incidence, supporting their use as part of a fungicide resistance management strategy.

Conclusion The 2007 Creston trial demonstrates that summer oil sprays, such as Bionatrol-M and Purespray Green, can effectively control powdery mildew in sweet cherries. These findings align with practices in Washington State, where summer oils are integrated into pest management programs. Continued research on rates and timing under local conditions is essential to fully assess their efficacy.