June 18, 2010, Guelph, Ont – Downy mildew was confirmed in a field of fresh market cucumbers near Milton, Ont. on June 17, 2010.

The arrival of this disease is very early and the first confirmed report of this disease in field cucumbers in Ontario this season. It is very possible that other fields may have the disease or will soon. The infected cucumbers plants were at about the four to five leaf stage and growing on black plastic mulch. Approximately 10 per cent of the field was infected with 10 per cent of the leaf area affected. No sporulation was found in the field at the time; however, lesions on leaves brought back to a lab at the University of Guelph began to sporulate within 12 hours.

Cucurbit growers should have their fields scouted regularly for this disease. Successful management of this disease is accomplished when fungicides are applied prior to the disease infecting the crop so it is imperative that growers apply a fungicide to prevent the establishment of downy mildew in their crops on five to seven day schedule. If possible, apply a fungicide before a rainfall event, dew or prior to overhead irrigation.

When implementing a fungicide program it is important to avoid the potential of resistance developing to fungicides by rotating between fungicides from different chemical families.

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