The downy mildew scouting program is sponsored by the Ontario Cucumber Research Committee. Field scouting in Norfolk County is managed by Tania Keirsebilck-Martin at the Norfolk Fruit Growers’ Association. Field scouting in Kent County is managed by Cheryl Trueman at the Ridgetown Campus, University of Guelph. We thank Elaine Roddy, OMAFRA vegetable specialist, for her guidance with implementing this program.
In 2016, Cheryl Trueman compared several different cucumber downy mildew control programs in plots at the University of Guelph Ridgetown Campus. These studies indicated that the highest level of control was achieved using a three product rotation of Orondis Ultra A+B, Torrent and Zampro.
Several different product rotations were compared including:
Bravo-only applied 6 times.
a high input strategy that focused on optimal control and resistance management: Orondis Ultra A+B; Torrent; Zampro; Orondis Ultra A+B; Torrent; Zampro.
a low-input strategy that focused on early control and resistance management, switching to lower-cost fungicides in the final weeks of harvest: Orondis Ultra A + B (plus Bravo); Torrent; Zampro; Bravo; Bravo; Bravo.
a single application of Orondis Ultra, applied early followed by the other targeted downy mildew fungicides (Orondis Ultra A + B; Torrent ; Zampro; Torrent; Zampro; Torrent).
Control – no fungicides applied
Leaf Area Infected
Single Orondis Ultra in rotation
Final yields for both the high input and single Orondis Ultra (in rotation) were both significantly higher than the Bravo only programs. The yields for the high input program, were significantly higher than all other treatments.
July 5th, 2016: cucurbit downy mildew was identified today in a processing cucumber field in Kent County, Ontario. Now that the disease is present in the great lakes region, growers should immediately move to a targeted downy mildew spray program.
Use only the downy mildew targeted products listed in the strategy. Research trials in Ridgetown, Simcoe and in the neighbouring states have shown these products to be the most consistent from year-to-year.
Rotate between all three of the targeted downy mildew products, starting with the most effective product, Orondis Ultra, and then rotate to either Zampro or Torrent within 7-days.
If you have any questions about the cucumber downy mildew control strategy, please call 519 674 1616 or email firstname.lastname@example.org
Do date there have been no confirmed reports of downy mildew in the Great Lakes region. However, activity does continue in the Southern US. The ipmPIPE website tracks the epidemic (figure 1) and also forecasts the potential spread of the disease.
Historically, downy mildew has arrived in this area in late-June to early July. We have found that using an early broad spectrum preventative fungicide program, staring at vine development, will result in better season long control of the disease. This is especially important if weather conditions turn wet and overcast, with storm originating in the Southern US.
If you suspect downy mildew in your cucurbit crop, please notify OMAFRA, your agri-business supplier or your grading station. Downy mildew is a community disease and open communication is vital to ensuring a healthy crop.
Due to the development of resistance and concerns about efficacy, Tattoo C and Presidio have been removed from the 2016 strategy. These products may provide suppression under low risk conditions, however research results indicate that they are not sufficient controls under higher disease pressure.
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.
Information for commercial vegetable production in Ontario