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
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.
By Cheryl Trueman, College Professor, University of Guelph – Ridgetown Campus and
Elaine Roddy, Vegetable Specialist, OMAFRA
We are getting many questions from growers with regards to the “best” fungicide program for managing cucurbit downy mildew. The early detection and subsequent wet weather conditions have resulted in higher-than-usual amounts of downy mildew in cucumbers and cantaloupe.
The Ridgetown fungicide efficacy trial was seeded June 24. Treatments applied July 7, 14, and 21. The first fungicide application was made prior to the first observation of symptoms. The following results are from the initial disease assessment, completed July 21 (Table 1). These results are preliminary. The completed trial will include at least three visual assessments and yield data.
These results indicate that among registered products, Torrent 400SC and Zampro are providing the highest level of control.
Table 1. Efficacy of fungicides for management of downy mildew in pickling cucumbers ‘Vlasstar’ at Ridgetown Campus, University of Guelph, July 21 2015.
Treatment (per Ha)
% Infected Leaves a, c, d
Leaf area affected (%) b, c. d
Bravo ZN (4.8 L)
Manzate Pro-Stick (3.25 kg)
Torrent 400SC (200 mL) + Sylgard (150 mL)
Tattoo C (2.7 L)
Presidio 4 SC (256 mL)
Zampro (1 L) +
Sylgard (150 mL)
A20942 (6 L)
Phostrol (5.8 L)
a Leaves in the whole plot were evaluated. The percentage of leaves infected was calculated based on the number of leaves in a representative 1 m section of the trial.
b Leaves in the whole plot were evaluated. The leaf area affected by downy mildew was estimated on symptomatic leaves only.
c Data was transformed for analysis using a log transformation; the original means are shown here.
d Numbers in a column followed by the same letter are not significantly different at P ≤ 0.05, Tukey’s HSD. Numbers highlighted in BOLD are significantly different than the nontreated control.
In general, insect pressure has been relatively low this year. However, over the past week we have noticed an increase in insect activity.
Start scouting for European corn borer at the mid-whorl stage, before the tassel begins to emerge from the plant. Look for flattened, white egg masses on the under surface of the leaves. Newly hatched larvae often hide in the developing tassel during the heat of the day. Window panes, pin-hole feeding and small amounts of saw dust-like frass are all signs of feeding. Optimal control occurs during the early stages of insect development, before the larvae enter the stalk. Young larvae range in colour from almost translucent to yellow to brownish, with a black head.
Last week’s confirmation of downy mildew in both Kent and Elgin was unusually early. Recent reports have also been made in Michigan and Ohio. As a result, we are in the unfortunate situation of having to “stay ahead” of the disease this year. Here are a few additional thoughts to help manage this aggressive disease in what appears to be a high pressure year.
Rotate! Research at Ridgetown Campus has shown that the “best” product does vary from year-to-year, and that all of the products have had years where they did not perform as well. To rely on one or even two products puts the crop at risk should one of those products fail, or if resistance develops. Use at least 3 different products from different fungicide groups.
If at all possible, spray BEFORE aforecast rain event. While several of the products have a limited amount of curative properties, they all work best when used preventatively.
If downy mildew is present in your field, shorten the spray interval. Especially if rain is forecast in the immediate future (see above).
All leaf material is susceptible to downy mildew infection, even the cotyledons. Begin a preventative program in new plantings as soon as they emerge.
Scout fields regularly, especially fields in which downy has not yet been identified. And by regularly, I mean daily! The disease can progress significantly in just a few days. I have seen fields go from “watersoaked” lesions to spore producing brown lesions in less than one day.
Ranman 400SC/Torrent 400SC
In response to the issue regarding the use of Ranman 400SC the PMRA has issued this response: “The RANMAN 400SC AGRICULTURAL FUNGICIDE (Reg. No. 30716) was recently amended to remove all uses except potatoes. With respect to product bearing the previous label,(i.e. just prior to the latest amendment), the PMRA would have no issue with this previously purchased product being used on cucumbers for the 2015 use season. Any purchase of product bearing the newly amended label however, will need to be used in accordance with the new label.”
Moving forward, cucurbit growers are reminded that Torrent 400SC is now the registered formulation of cyazofamid for the control of downy mildew in this crop.
While downy mildew has still not been confirmed in Ontario, recent report from Michigan indicate that levels are starting to increase in the Saginaw Bay area. At this time growers should maintain preventative downy mildew fungicide programs, especially for the late harvested crop.
Phytophthora has been identified in a pumpkin field in Norfolk county. This disease thrives under wet soil conditions. For more information, see: Phytophthora Blight of Cucurbits – August 7th, 2014.
Angular leaf spot, a bacterial disease, is present in many pumpkin fields at this time. While this is a sporadic disease of cucurbits in Ontario, under the appropriate weather conditions, it could spread a cause premature defoliation of the crop. Infections may also predispose the fruit to bacterial soft rot at harvest or in storage. Copper fungicides, such as Copper 53W and Copper Spray, will help to control the spread of this disease.
Information for commercial vegetable production in Ontario