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Management of downy mildew in field cucumber with biopesticides

Project Code: BPI09-030

Project Lead

Peter White - Agriculture and Agri-Food Canada


This project, part of the North American Free Trade Agreement (NAFTA) Biopesticides Initiative, aimed to evaluate the efficacy of biopesticides in the control of downy mildew. A similar project was conducted at the same time through the United States Interregional Research Project #4 (IR-4) program under the lead of Margaret Tuttle McGrath (Cornell University).

Summary of Results


Downy mildew caused by Pseudoperonospora cubensis is a serious disease of cucumber. Once established, the disease can spread rapidly causing significant loss of fruit quality and yield of cucumber. The downy mildew pathogen primarily infects the leaves, resulting in decreased photosynthesis. During favourable environmental conditions the pathogen can defoliate plants and destroy entire fields within a week. Fruit of infected plants are usually undersized and misshapen. They are also more likely to develop sun scald which further reduces their quality. The management of downy mildew is successful when cultural practices are integrated with registered fungicides. However in organic production the use of copper fungicides does not provide a satisfactory level of control, and there is also a need for lower risk products in conventional cucumber production.


Trials were conducted in Ontario in 2009 for control of downy mildew in pickling cucumbers (Cucumis sativus) cv. Fancipak. Commercial products Serenade ASO® (Bacillus subtilis), Regalia MAX® (Reynoutris spp. extract), Milstop® (potassium bicarbonate), and Timorex Gold® (tea tree oil) were applied seven times at the rates of 9.3 litres per hectare, 0.25% volume per volume (v/v), 5.6 kilograms per hectare and 0.5% (v/v), respectively. All treatments were replicated 4 times in a randomized complete block design. Disease incidence and disease severity were assessed at various dates after the first treatment.


Results from this trial showed that none of the biopesticides provided season long control of downy mildew in cucumbers. However, Regalia MAX® and Milstop® did numerically reduce the downy mildew severity following the first two applications. No phytotoxicity effects were reported from this trial.

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