Current Late Blight Risk In Ontario Field Tomatoes

Current Late Blight Risk In Ontario Field Tomatoes

on September 20 | in Ag News | by | with Comments Off on Current Late Blight Risk In Ontario Field Tomatoes

By: Amanda Tracey, Vegetable Crops Specialist, OMAFRA, Ridgetown and Cheryl Trueman, Department of Plant Agriculture, Ridgetown Campus – University of Guelph

With tomato harvest in full swing, it is time to wrap up the late blight spore trapping for this growing season.

As mentioned in a previous post, this is Year 1 of a three-year research project to assess the value of different spore traps and forecasting models to predict late blight risk for field tomatoes. We are comparing the Spornado and rotorod spore traps at eight sites in Kent County (Fig. 1), along with the BliteCast forecasting model.
DNA of Phytophthora infestans, the organism that causes late blight, was detected bySpornado traps at 3 of 8 sites for the August 26-29 sampling period (Table 1).
Rotorod traps detected spores of P. infestans at 0 of 8 sites for the August 26-29 sampling period (Table 1).

Sept.4.2019 LB Spore Trap results table

Table 1. Number of sites out of eight (8) in Kent County, with a positive detection forPhythophthora infestans, the organism that causes late blight.
* first sampling period with a positive detection for late blight.
– data currently unavailable

Late blight symptoms have been confirmed on a potato plants in Norfolk County.

Late blight caused by the US-23 genotype has been observed in Wisconsin on potato and in New York and Pennsylvania on tomato and potato. Pennsylvania on tomato, but there are no reports of symptoms on any crops in Ontario or Michigan.

A summary of fungicides for late blight management is available here.

If you suspect late blight in your tomato crop, please reach out to Amanda Tracey (, 519-350-7134) to confirm the diagnosis. Cheryl is away on parental leave and will not be available for the remainder of the growing season.

Project collaborators: Tomecek Agronomic Services, Sporometrics, Phytodata, and Genevieve Marchand (AAFC).

Funding acknowledgement: Ontario Tomato Research Institute, Fresh Vegetable Growers of Ontario, and the Ontario Agri-Food Innovation Alliance.

Links to previous late blight posts from the 2019 season: June 20July 10July 20August 7August 14August 21August 28.

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