Late blight alert

Janice LeBoeuf, OMAFRA Vegetable Crop Specialist, Ridgetown

From Eugenia Banks, OMAFRA Potato Specialist, Guelph:  Yesterday late blight was found in a potato field near Simcoe. The field was senescing so late blight was not aggressive.  The field was topkilled immediately.

A standard tomato fungicide program for early blight, septoria, and anthracnose should provide protection against late blight infection when pressure is low, so there is no need to panic.  Continue to scout your fields carefully and review the symptoms of late blight and other problems that can cause similar symptoms.

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.

Late Blight Look-Alikes

Janice LeBoeuf, OMAFRA Vegetable Crop Specialist, Ridgetown

Please continue to contact OMAFRA or your nearest plant pathologist if you suspect you may have late blight symptoms.  It is important to confirm if it is indeed late blight, so that the rest of the industry can be alerted (not with names or specific locations, of course) and so that you can take appropriate control measures.

There are some other tomato issues that can cause symptoms that resemble late blight.  I’ve included some photos and descriptions so that you can compare the symptoms. Continue reading Late Blight Look-Alikes

Online presentations about late blight

Janice LeBoeuf, OMAFRA Vegetable Crop Specialist, Ridgetown

There are a couple of recently recorded presentations about late blight available online.

Dr. Willie Kirk, Michigan State University Plant Pathologist, has a presentation online at http://bit.ly/csDtUG.  Bayer has a segment at the beginning on some of their US fungicide registrations, but that ends at about 5:00 on the progress bar at the bottom left of the window.  Dr. Kirk gets rolling at about the 6:25 mark (you can slide the indicator on the progress bar back and forth to jump to a different part of the presentation or hear something again).  This presentation is about 1 hour long.

Dr. Sally Miller from Ohio State University and Dr. Meg McGrath from Cornell University delivered an online seminar on “Late Blight Management on Organic Farms” on July 1.  The recording of the webinar is not online yet as I write this update, but some of the resources have been posted at http://www.extension.org/article/28346.  The recorded seminar should be available sometime in the next week.  It runs about 1 hour and 15 minutes.

Of course, keep in mind that some fungicides that they mention are not registered for the same uses in Canada.  However, there is a lot of useful information on late blight biology and management in both of these presentations.

Late blight update

There have been no confirmed cases of late blight to date in Ontario.

The late blight infected potato field detected in Michigan on June 21 was burned and disked very quickly.  No late blight symptoms were found in surrounding fields.  As previously reported, late blight has also been found in east-central Ohio and northwestern Pennsylvania, as well as in several states further south.

Weekly updates about late blight in New York and the contiguous states and Canadian provinces can be found at http://nysipm.cornell.edu/scouting/late_blight/default.asp.

A model predicting favourable weather conditions for late blight infection in North America can be found at: http://uspest.org/risk/tom_pot_map.  This only indicates favourable weather conditions, and not the presence of the pathogen.  Without late blight inoculum, the disease will not develop even in highly favourable conditions.

You can click on a “pin” on the map to get more details and customize the information.  The environmental conditions within an individual field may differ from the macro level conditions reported here.

Information for commercial vegetable production in Ontario