Cucumber Cucurbits Disease Downy Mildew Fungicides Pest Management Research

University of Guelph Cucumber Downy Mildew Results

Cheryl Trueman, Ridgetown Campus, University of Guelph
Rachel Riddle, Simcoe Research Station, Dept. of Plant Agriculture, University of Guelph
Elaine Roddy, OMAFRA

This article is an updated version of ‘2016 University of Guelph Cucumber Downy Mildew Results’ by Elaine Roddy, which first appeared May 1, 2017.

Comparison of fungicide programs
In 2016 and 2017, Cheryl Trueman compared several different cucumber downy mildew control programs in plots at the University of Guelph Ridgetown Campus.

Different product rotations included:

  • 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.

Results indicate that the highest level of control was achieved using a high input three product rotation of Orondis Ultra A+B, Torrent and Zampro when downy mildew pressure was high in 2016. Under these conditions final yields for both the high input and single Orondis Ultra (in rotation) were both significantly higher than the Bravo only programs and yield for the high input program were significantly higher than all other treatments. When pressure was moderate in 2017, the high input and single Orondis Ultra in rotation program were very effective. All fungicide programs except Bravo only increased both fruit number and yield by weight.

2016 2017
Product Rotation Leaf Area Affected at Harvest Defoliation at Harvest Leaf Area Affected at Harvest Defoliation at Harvest
Bravo Only
(6 applications)
45% 23% 12% 5%
High Input 3% 0% 1% 0%
Low Input 40% 20% 7% 1%
Single Orondis Ultra in rotation 28% 8% 0% 0%
Control 80% 80% 55% 42%

Fungicide application intervals using susceptible and tolerant hybrids
In another project, the effect of fungicide application interval and cucumber hybrid are under evaluation at the Ridgetown Campus (Cheryl Trueman) and Simcoe Research Station (Rachel Riddle and John O’Sullivan).

  • Hybrids include the susceptible ‘Vlaspik’ and downy mildew tolerant ‘Citadel’ and ‘Peacemaker’.
  • The fungicide program includes applications of Bravo when disease risk is low, and applications of Orondis Ultra, Torrent and Zampro applied during high risk periods at a seven, 10, or 14-day interval.
  • Early and late seeded trials were completed at Ridgetown and Simcoe in 2017.


  • Ridgetown (early seeded, low disease severity): Fungicide application interval, including the no fungicide control, had no effect on total disease severity for Citadel and Peacemaker, but the 7-day interval did reduce disease severity in Vlaspik compared to applying no fungicide. Fungicide application interval or hybrid did not influence yield.
  • Simcoe (early seeded, moderate disease severity): Application of fungicides at any interval reduced total disease compared to the no fungicide treatments in all cultivars. Applications at a 10-day interval resulted in greater yield by weight than the no fungicide control. Vlaspik produced more cucumber yield by weight than Citadel and Peacemaker, but Peacemaker produced more fruit than Citadel and Vlaspik.
  • Ridgetown (late seeded, high disease severity): Shorter application intervals resulted in lower total disease among all hybrids. Total disease in Vlaspik was higher than Citadel and Peacemaker. Yield by weight was higher using a seven or 10-day interval than no fungicide among all hybrids. Peacemaker had higher yield by weight than Vlaspik.
  • Simcoe (late seeded, high disease severity): A seven-day application interval resulted in less total disease than 10 and 14-day intervals, but all programs had less total disease than the control. Peacemaker had less total disease than Citadel, and Citadel less total disease than Vlaspik. Cucumber yield for Peacemaker was not affected by fungicide program (all treatments equivalent to no fungicide). Conversely, all fungicide programs increased yield to an equivalent level for Vlaspik. Yield by weight for Citadel was higher than the control using a seven and 10-day interval, but not a 14-day interval. Yield for the seven and 10-day interval treatments for Citadel was equivalent.

Future work:

  • Trials will continue in 2018 and data analyzed to determine if fungicide application intervals can be lengthened when using downy mildew tolerant hybrids.

The Pesticide Risk Reduction Program (PRR16-040), Agriculture and Agri-Food Canada is sponsoring this research.

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