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).
This is a re-post from 2016 – Late-July to early-August is the key time for powdery mildew management! With any disease, preventative management provides the best control.
Powdery mildew typically arrives in Southern Ontario in mid-to-late July. Plants are most susceptible to infection during the fruit sizing and development. Poor control results in decreased yield and poor fruit quality at harvest. The threshold for treatment is 1 lesions/50 plants. Optimum powdery mildew control is a combination of variety selection, fungicide timing and fungicide selection.
Powdery Mildew Lesion on the Lower Leaf Surface
Cheryl Trueman, a vegetable pest management researcher at the University of Guelph’s Ridgetown Campus, has been conducting powdery mildew efficacy trials since 2009. In these trials, several products consistently provided good control of powdery mildew. These products are powdery mildew targeted, and have a single site mode of action. To prevent the development of resistance, it is essential to always rotate between different fungicide groups and/or tank mix with a broad spectrum fungicide.
Powdery Mildew Targeted Fungicides Showing Consistent Control in the Ridgetown Field Trials:
Group 13: Quintec (quinoxyfen)
Quintec was the most consistent powdery mildew product tested in Ridgetown. It provided excellent control in 4/5 years and good control in 1/5 years tested.
Group U8: Vivando (metrafenone)
Vivando provided excellent control in 1/3 years and good control in 2/3 years and tested.
Group 7: Fontelis (penthiopyrad), Aprovia (benzovindiflupyr), Sercadis (fluapyroxad) and Pristine (boscalid/pyraclostrobin).
Fontellis was somewhat less consistent. Control with this produce ranged from excellent to poor, depending on the year. It provided excellent control in 1/5 years, good control in 2/5 years and poor control in 2/5 years. Note: Aprovia, Sercadis and Pristine were not tested in the Ridgetown Campus trials.
Group 3: Inspire (difenoconazole), Proline (prothioconazole) and Quadris Top (azoxystrobin/difenoconazole)
Inspire provided a level of control similar to Fontelis; good control in 3/5 years, and poor control in 2/5 years. Proline and Quadris Top were only tested for one year in the Ridgetown trials, in which they both provided good control.
Fungicides containing chlorothalonil(Bravo ZN and Echo) provided a lower level of powdery mildew control, but are still better than the untreated checks. They also control a broad range of other foliar diseases including scab and alternaria.
Research in Ontario and other jurisdictions indicates that the group 11 (QoI) fungicides, Cabrio (pyraclostrobin) and azoxystrobin (a component of Quadris Top) no longer control powdery mildew. However, they may provide control of other cucurbit diseases such as anthracnose and alternaria.
Cheryl Trueman, University of Guelph – Ridgetown Campus
Risk of downy mildew to cucumbers and cantaloupe remains high, with new reports regularly occurring throughout the great lakes region.
Scouting for downy mildew in pickling cucumber fields in Norfolk County began on June 13 and in Kent County on June 19. This is the final cucumber downy mildew scouting report for the 2017 season.
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.
Elaine Roddy, OMAFRA and Cheryl Trueman, University of Guelph – Ridgetown Campus
Cucurbit downy mildew was confirmed on June 28th. Additional reports now include the areas of Norfolk, Oxford and Kent. The risk of downy mildew infections remains high throughout Southern Ontario.
At this time all cucumber growers should use only targeted downy mildew fungicides.
Cantaloupe/muskmelon growers should alternate between broadspectrum fungicides and downy mildew fungicides. In melon crops, broadspectrum fungicides are required to manage other foliar diseases including alternaria, anthracnose and powdery mildew.
Scouting for downy mildew in pickling cucumber fields in Norfolk County began on June 13 and in Kent County on June 19.
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.
Cucurbit downy mildew has been reported on pickling cucumbers and cantaloupe in Essex County. This is the first field report for this disease in 2017.
All Ontario cucumber growers should now switch from a broadspectrum program to a 3-product rotation using targeted downy mildew fungicides.
The following products have shown the most consistent results in fungicides trials at the University of Guelph, Ridgetown and Simcoe campuses. Under high downy mildew pressure, follow a spray interval that is no longer than 7-days.
Orondis Ultra A (mandipropamid) + Orondis Ultra B (oxathiapiprolin) + Bravo (chlorothalonil)
Elaine Roddy, OMAFRA and Cheryl Trueman, University of Guelph – Ridgetown Campus
There have been numerous new reports of cucurbit downy mildew in the Southern US last week. Late June to early-July is typically when downy mildew arrives in the Great Lakes region. The on-going wet weather, and speed at which the tropical storm fronts pass through the region mean that disease conditions can change very quickly.
At this time, use a broadspectrum fungicide such as cholorthalonil or mancozeb. Fungicides are most effective when used preventatively. Band spraying small plants helps to reduce the costs of the fungicide program. For information of band spraying, see Sprayers 101.com.
Scouting for downy mildew in pickling cucumber fields in Norfolk County began on June 13 and in Kent County on June 19.
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.
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
Product Rotation
Leaf Area Infected
Defoliation
Bravo Only
(6 applications)
45%
23%
High Input
3%
0%
Low Input
40%
20%
Single Orondis Ultra in rotation
28%
8%
Control
80%
80%
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.
