To date, there have been no reports of this disease in Ontario field cucurbit crops but it is still very early. Downy mildew has been reported in a several commercial cucurbit fields in Florida during April and the beginning of May 2010.

The disease has been spreading around the southern US state and has recently been found in commercial cucurbit fields in Georgia, Texas and North Carolina. The pathogen does not over-winter outside in Ontario; however, it can over-winter inside Ontario cucumber greenhouses. Historically the disease is carried by weather fronts moving from the southern U.S. into Ontario. During warm wet conditions, the disease can spread rapidly resulting in complete defoliation of entire fields within one week.

In recent years, the disease has arrived in Ontario in early June. In 2006, the early arrival of this disease caused significant losses to the Ontario cucumber industry. Subsequently, several fungicides have been registered through the Minor Use Program for the control of downy mildew in cucumbers. 

It is imperative that growers keep up to date on the downy mildew situation in Ontario and when the disease shows up in field cucumbers, growers act accordingly by applying a recommended registered fungicide to protect their crop from this disease. Since the disease has been found in a few greenhouse cucumber crops in Essex County, it is recommended that field cucumber growers apply a targeted fungicide to protect the young crop. By spraying early and preventatively before the disease shows up in the field crop will significantly reduce the impact of this disease on yield.

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