The year 2006 was a memorable one for cucurbit growers, and not for good reasons. Cucurbit crops across the province were devastated by downy mildew. While the losses were highest for cucumber growers; producers of the other vine crops were also impacted.

In preparation for 2007, there are several key initiatives to help reduce the risk of another outbreak. Both the fresh market (FVGO) and the processing (OPVG) grower organizations have allocated funds to support an early warning scouting program here in Ontario. OMAFRA staff will also be working with researchers in North Carolina and across the United States to identify and track the progression of this disease northwards.

The good news is that Downy Mildew does not overwinter in the field in Ontario. It requires living tissue on which to survive. All of last year's innoculum was killed off with the first frosts, so our field growers are starting with a clean slate.

OMAFRA staff are currently working with the PMRA to get registrations for several key downy mildew fungicides. To date 5 minor use submissions have been made to PMRA. We plan to have at least two new products in place at the start of the 2007 growing season. University of Guelph researchers at both Ridgetown and Simcoe will be conducting additional research trials to support further registrations.

Preventative Measures

The primary management strategy for downy mildew is prevention. All downy mildew fungicides are preventative. Once established in a field, it is almost impossible to control this disease. Similar to late blight in potatoes, downy mildew is a community disease. It can move rapidly in weather patterns, with spores surviving for up to 4 days in the open environment.

All vine crop growers are encouraged to follow a basic preventative fungicide program using chlorothalonil or mancozeb on 7-14 day intervals. Banded applications over the row while the plants are small will reduce spray usages and costs. The spray interval can be lengthened under hot, dry conditions. Targeted downy mildew fungicides should be used only when the weather conditions or crop reports indicate a risk of infection.

Growers who use transplants are encouraged to communicate regularly with the transplant grower to ensure that only healthy transplants are set into the field. Purchase transplants only from greenhouses set up to produce transplants exclusively. Transplant growers should follow a greenhouse good sanitation program, including a winter shut-down to destroy any living tissue that may harbour this pest.

Where tunnels or row covers are being used, consider applying a preventative fungicide after planting and before covering. The warm, humid conditions under the tunnel may prove ideal for disease growth.

During the growing season, OMAFRA staff will be producing regular crop updates outlining fungicide recommendations, scouting results and reporting on the progress of this disease as it moves northwards. Growers wishing to receive the Vegetable Crop Updates or a copy of the Downy Mildew Information Sheet can call 519 674-1616 or email elaine.roddy@ontario.ca.