Research Update – Fungicide Efficacy on Downy Mildew in Cucumbers

Cheryl Trueman, College Professor, University of Guelph – Ridgetown Campus
Rachel Riddle, Research Technician, University of Guelph – Simcoe
Elaine Roddy, Vegetable Crops Specialist, OMAFRA

Over the past two years, there have been several changes in the efficacy of fungicides commonly used to control downy mildew in cucumbers. The results from field trials conducted by the University of Guelph reflect trends also observed in Michigan and North Carolina.

Figure 1 and Figure 2 show the results of the Ontario 2015 downy mildew fungicide trials conducted at Ridgetown and Simcoe. Note that in both trials, a significant decline was observed in the efficacy of both Presido 4SC and Tattoo C. Presidio preformed no better than the untreated control, while the results from Tattoo C were no different than chlorothalonil (Bravo Zn).

The Canadian Pest Management Regulatory Agency (PMRA) is currently evaluating a new active ingredient called oxathiapiprolin (Orondis Ultra). In both of the University of Guelph studies, oxathiapiprolin demonstrated good control against cucumber downy mildew. If approved, this product will provide a good option for rotation with currently registered downy mildew fungicides.

Figure 1. AUDPC (area under the disease progress curve) for leaf area affected by cucurbit downy mildew in cucumber cv. Vlasstar, Ridgetown, ON, 2015. Fungicides were applied on a 7-day interval July 7-Aug 4. Columns with the same letter are not significantly different from each other.
Figure 1. AUDPC (area under the disease progress curve) for leaf area affected by cucurbit downy mildew in cucumber cv. Vlasstar, Ridgetown, ON, 2015. Fungicides were applied on a 7-day interval July 7-Aug 4. Columns with the same letter are not significantly different from each other.

 

Figure 2. AUDPC (area under the disease progress curve) for leaf area affected by cucurbit downy mildew in cucumber cv. Vlaspik, Simcoe, ON, 2015. Fungicides were applied on a 7-day interval July 16-Aug 6. Columns with the same letter are not significantly different from each other.
Figure 2. AUDPC (area under the disease progress curve) for leaf area affected by cucurbit downy mildew in cucumber cv. Vlaspik, Simcoe, ON, 2015. Fungicides were applied on a 7-day interval July 16-Aug 6. Columns with the same letter are not significantly different from each other.

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