Spore traps monitoring for causal agents of tomato late blight in Chatham-Kent

Joseph Tomecek (Tomecek Agronomic Services/M.Sc. candidate, Dept. of Plant Agriculture, Univ. of Guelph); Amanda Tracey (OMAFRA), Dr. Cheryl Trueman (Ridgetown Campus, Univ. of Guelph)

Late blight, caused by the Oomycete pathogen Phythophthora infestans, is a devastating disease of tomato and potato. Its appearance in Ontario can be sporadic, with symptoms first reported anywhere from late June to late August depending on the year. This has made it difficult for growers to know when to modify fungicide programs to account for increased risk of these diseases.

To better understand if spore trapping is a useful tool to better predict risk of late blight, a spore trapping network has been deployed in Chatham-Kent for a third year. We are comparing the Spornado and rotorod spore traps at eight sites in Kent County, including a comparison of trap height at four of locations (Fig. 1). Two of these locations include unsprayed sentinel plots of tomatoes that are being monitored for first appearance of late blight. The BliteCast forecasting model, first developed in New York State is also being evaluated to indicate late blight risk based on environmental factors. To determine if there is a benefit of spore traps or BliteCast, we are comparing fungicide program modifications based on the current high-risk trigger (late blight reported in the Great Lakes Region) to modifications based on detections in a spore trap, the BliteCast threshold, or both, in field trials at Ridgetown Campus and the Cedar Springs Research Station.

So, what is the risk of late blight so far this year?

• No positive detections of P. infestans spores in Spornado or rotorod traps, which were installed June 6
• The BliteCast forecasting model has hit the threshold (18 DSV) for the first fungicide application at Cedar Springs but not yet at Ridgetown Campus (5 DSV as of June 23).
• There are no reports of late blight on tomato or potato in Ontario or anywhere in the Great Lakes Region.
• Growing conditions are dry.
• Taken together, the above points mean that the environment has not been very conducive for infection by P. infestans, and so far, we have no evidence that there is an active source of inoculum present in the growing region.

If you suspect late blight in your tomato (or potato) crop, please reach out to Amanda Tracey (amanda.tracey@ontario.ca, 519-350-7134) or Cheryl Trueman (ctrueman@uoguelph.ca, 226-971-0654) to confirm the diagnosis.

Project collaborators: Yaima Arocha Rosete and Kristine White (Sporometrics), Hervé van der Heyden (Phytodata), and Genevieve Marchand (AAFC).