Late Blight Update – None Reported in Ontario

Janice LeBoeuf, OMAFRA Vegetable Crop Specialist, Ridgetown

We continue to follow the news on late blight from neighbouring states and to check on fields with suspicious symptoms, but to date, there are no confirmed reports of late blight in Ontario.

It is important to scout your fields regularly and know the symptoms of late blight.  Remember that conventional tomato growers following a regular fungicide spray program (by calendar or TOMcast) for early blight, septoria leaf spot, and anthracnose, are also protecting the crop from late blight infection.

It is most likely that the first symptoms would show up in areas that have incomplete spray coverage (eg. gore rows), in fields where the fungicide interval was too long, or in organic systems where good options for protecting the crop are lacking.  Flooded, waterlogged fields where the plants are wet and under stress could also be more susceptible to infection.  In 2009, most conventional fields survived the late blight outbreak without harm.

If a late blight outbreak occurs in Ontario, OMAFRA will notify the industry and remind growers of the recommendations for controlling late blight.  Is it necessary to cover the crop with a systemic, targeted late blight fungicide at this time?  Since we haven’t found late blight in Ontario to date, the protectant fungicides are very suitable choices (continuing your regular fungicide schedule).  If an outbreak occurs in your region, however, that would be the time to consider adding the systemic products into the fungicide rotation.