Disease Featured Late Blight Tomatoes

Current late blight risk in Ontario field tomatoes: August 28, 2019

Late blight symptoms on potato leaf

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

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 by Spornado traps at 1 of 8 sites for the August 22-26 sampling period (Table 1).
Rotorod traps detected spores of P. infestans at 7 of 8 sites for the August 19-22 sampling period and 0 of 8 sites for the August 22-26 sampling period (Table 1).

Aug 28.2019 LB Spore Trap results table
Table 1. Number of sites out of eight (8) in Kent County, with a positive detection for Phythophthora 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 few 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, but there are no reports of symptoms on any crops in 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 (Amanda.tracey@ontario.ca, 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 20, July 10, July 20, August 7, August 14, August 21.

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