foliar symptoms of downy mildew on a cucumber leaf
Crop Protection Cucumber Cucurbits Disease Downy Mildew Fungicides

Cucumber Downy Mildew has now been Confirmed in Kent County, Ontario

July 6th, 2020 - Downy Mildew was identified today in a commercial cucumber field in Kent County, Ontario. Risk remains high now that the disease has been confirmed in Ontario despite hot, dry weather. Continue Reading Cucumber Downy Mildew has now been Confirmed in Kent County, Ontario

July 6th, 2020 – Downy Mildew was identified today in a commercial cucumber field in Kent County, Ontario. The disease had previously been identified in the Great Lakes area, in Michigan on June 22nd. Growers were advised to use a downy mildew specific fungicide program once the disease was found in the Great Lakes area. Risk remains high now that the disease has been confirmed in Ontario despite hot, dry weather.

As noted in our previous post, trials in Michigan and Ontario have shown that the three most consistently effective downy mildew fungicides are Orondis Ultra, Torrent and Zampro.  Where possible, it is important for resistance management for these products to tank mix each application with chlorothalonil or mancozeb.  In addition to tank mixing to delay resistance development, never make back-to-back applications of products from the same chemical family.  Follow a 5 to 7-day application interval, and rotation of the three products can be repeated as necessary. 

Cucumbers are most at risk, but cantaloupe growers should be aware that downy mildew that infects cucumbers is also a risk.  See crop labels for listed cucurbit crops registered on the products below.

If you suspect downy mildew in your field, send for confirmation immediately.  Contact either OMAFRA specialist listed below if you have any questions about detection or management. 

Common name
(FRAC group)	Trade Names	Rate per hectare
(Rate per Acre)	PHI (days)	Re-entry interval	Max applications
mancozeb (M03)	Dithane Rainsheild,
Penncozeb 75DF Raincoat
Manzate Pro-Stick	1.1-3.25 kg
(0.4-1.3 kg)	14	24 hours	-
chlorothalonil (M05)	Bravo ZN
Echo	4.8 L
(1.9 L)	2	12 hours	2
Common name (FRAC group)	Trade Name	Rate per hectare (Rate per Acre)	PHI (days)	Re-entry interval	Max applications
cyazofamid (21)	Torrent 400SC	150-200 ml (61-81 ml) + NIS or organosilicone surfactant	1	12 hours	6
amectotradin (45) + dimethomorph (40)*	Zampro	0.8-1 L
(0.3-0.4 L)	1	1 day for hand harvesting, pruning or thinning , 12 hours for other activities	3
oxathiapiprolin (49) + mandipropamid (40)*	Orondis Ultra	0.4-0.6 L
(162-243 ml)	0	12 hours	4

*resistance is known to the group 40 fungicides, mandipropamid and dimethomorph. Only the premix partners oxathiapiprolin and amectortradin in Orondis Ultra and Zampro, respectively, are effective on downy mildew.

Katie Goldenhar, Pathologist—Horticulture, katie.goldenhar@ontario.ca, 519-835-5792

Andrew C. Wylie, Vegetable Crop Specialist (A), andrew.c.wylie@ontario.ca, 519-401-5890

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