Downy mildew of brassicas (Hyaloperonospora parasitica syn. Peronospora parasitica) is a fungal-like oomycete that can be devastating in cooler, wet weather. While the ideal temperature for downy mildew development is 8-16˚C it can infect in temperatures outside that range. Prolonged leaf wetness due to fog, dew, or evening irrigation can create ideal conditions for the pathogen to develop.
Downy mildew is most devastating on Continue reading Downy mildew of brassica vegetables
This information is updated from an earlier article by Janice LeBoeuf.
We have had multiple reports of late blight in conventionally managed tomato fields this week. Typically, this disease is well managed in tomatoes with a broadspectrum fungicide program including chlorothalonil. However, high disease pressure due to environmental conditions, combined with a dense leaf canopy and rapid growth may have resulted in poor spray coverage and reduced efficacy.
Commercial growers should scout often and ensure they are using fungicides with good late blight activity in their fungicide program. When late blight is in the area, spray intervals should be shortened.
Under continued high disease pressure, growers should consider adding a targeted late blight fungicide to the spray program. If late blight has been identified in a field, use a fungicide with curative and antisporulent activity, see the table below for late blight fungicides and their properties. Continue reading Late blight alert – July 27th, 2017
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.
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.
Additional reading: http://www.omafra.gov.on.ca/IPM/english/cucurbits/diseases-and-disorders/powdery-mildew.html#advanced
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.
You can track sightings of downy mildew in North America on the IPMpipe Cucurbit Downy Mildew website.
More information:
2017 Downy Mildew Control Strategy for Cucumber Crops
2016 Fungicide efficacy and fungicide program results
Cucurbit Downy Mildew Report for the Week of July 4th, 2017
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 Pest Management Regulatory Agency (PMRA) recently announced the approval of URMULE registrations for Confine Extra fungicide (mono and di-potassium salts of phosphorus acid 53%) for the suppression of bacterial leaf spot (Xanthomonas campestris p.v. vitians) on leaf lettuce in Canada. Continue reading Confine Extra fungicide label expanded via minor use program for suppression of bacterial spot of leaf lettuce
| Weather Station Location | Onion Maggot | Seedcorn Maggot | Cabbage Maggot | Carrot Weevil | Carrot Rust Fly | Aster Leafhopper |
| (base 4°C) | (base 4°C) | (base 6°C) | (base 7°C) | (base 3°C) | (base 9°C) | |
| Harrow | 1265 | 1265 | 1044 | 938 | 1380 | 746 |
| Ridgetown | 1153 | 1153 | 937 | 838 | 1268 | 660 |
| Delhi | 1125 | 1125 | 910 | 813 | 1237 | 636 |
| Goderich | 973 | 973 | 775 | 684 | 1076 | 533 |
| Guelph | 928 | 928 | 735 | 646 | 1034 | 492 |
| Bradford* | 987 | 987 | 795 | 708 | 1086 | 547 |
| Kemptville | 969 | 969 | 786 | 700 | 1069 | 544 |
| Sudbury | 754 | 754 | 597 | 525 | 845 | 394 |
*Bradford weather, degree day data and information courtesy of the University of Guelph – Muck Crops Research Station
Cabbage, onion and seedcorn maggot fly activity should be beginning to increase from Norfolk across to Lambton and south. Most of the province is in-between generations currently but should start seeing the next generation emerge in the next few weeks depending on weather.
For carrot weevil we are now well past the degree day threshold for 90% oviposition across the province. This year we will be monitoring for the presence of a possible 2nd generation of carrot weevils. If you think you are having late season carrot weevil issues, please contact Dennis (dennis.vandyk@ontario.ca).
We have reached the DD threshold for carrot rust fly in Harrow only. The rest of the province should be between generations currently.
Aster leafhoppers adults are now present across the province.
Onion Downy Mildew (DOWNCAST disease forecasting model):
In Bradford, conditions have not been conducive to sporulation so risk of downy mildew is low to moderate.
In Lambton county, sporulation infection periods (SIP) have been accumulated from July 2-5 and then again on July 12 meaning conditions and risk is high in transplant onions and moderate to high in seeded onions.
Late Blight:
Late blight DSVs are accumulating quickly in most areas of the province.
Late blight on potatoes has been confirmed in the Simcoe/Durham county region but the risk remains high across the province. Growers should be applying late blight specific fungicides along with a broad-spectrum fungicide like chlorothalonil (Bravo, Echo), metiram (Polyram) or mancozeb (Manzate, Penncozeb, Dithane).
Check OnPotatoes for up to date late blight risk information and USAblight for currently reported late blight incidence in the Great Lakes region.
Onions: Earliest direct seeded onions have six true leaves while the majority are at the four to five leaf stage. Stemphylium leaf blight, purple blotch, onion smut and Botrytis leaf blight has been detected in Ontario. See the Stemphylium leaf blight article in a previous OnVegetables post for more information.
Garlic: Leaf dieback has been seen in multiple areas with Fusarium basal rot and bulb and stem nematode. Carefully inspect the basal plate and look for fungal growth or rot on the stem. For confirmation, send suspect cloves to a certified pest diagnostic clinic for bulb and stem nematode extraction. Leek moth has been identified in pockets of Southwestern Ontario.
Brassica: Cabbage maggot is active and severely infested plants may wilt in hot weather. Wilt can also be caused by clubroot, a soil-borne pathogen infecting the roots and causing club-like symptoms. A clubroot survey is underway; please contact travis.cranmer@ontario.ca for more information if you find clubroot in your field. Swede midge has also been reported throughout Southwestern Ontario and is affecting the meristems later seeding dates of multiple brassica crops. Continue to scout for flea beetles, diamondback moth, cabbageworm, aphids, thrips and tarnished plant bugs.
Celery: Tarnished plant bugs have been detected in Thedford and the Holland Marsh. Scout for damage from carrot weevils laying eggs.
Below are the various insect DD thresholds for reference.
Use these thresholds as a guide, always confirm insect activity with actual field scouting and trap counts.
| Degree Days | |||
| 1st generation | 2nd generation | 3rd generation | |
| Onion Maggot | 210 | 1025 | 1772 |
| Seedcorn Maggot | 200 | 600 | 1000 |
| Cabbage Maggot | 314-398 | 847-960 | 1446-1604 |
| Carrot Rust Fly | 329 – 395 | 1399-1711 | n/a |
| Carrot Weevil | 138 – 156 | Egg laying (oviposition) begins | |
| 455 | 90% of the egg-laying (oviposition) is complete | ||
| Aster Leafhopper | 128 | Overwintering eggs hatch | |
| 390 | Local adult emergence | ||
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.
You can track sightings of downy mildew in North America on the IPMpipe Cucurbit Downy Mildew website.
More information:
2017 Downy Mildew Control Strategy for Cucumber Crops
2016 Fungicide efficacy and fungicide program results
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.
