Trial aims to better detect late blight pathogen before it infects tomatoes

The three-year project will evaluate early detection, management approaches and potential benefits

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A new three-year project is in place at the University of Guelph, Ridgetown Campus, to help detect late blight pathogen presence in the air before it infests tomatoes, allowing for better control management.

There is currently no method to detect the presence of the phytophthora infestans, making it difficult for growers properly manage late blight, which can wipe out an entire tomato crop.

Why it matters: A lack of pathogen detection makes it difficult for growers to create a proper management plan and causes higher costs because of increased use of fungicides.

Cheryl Trueman.
photo: Supplied

“(Currently) if we hear of late blight in Ontario or Ohio, we send an alert to growers so they know the pathogen is in the area, but that’s a bit of a crude method,” says Cheryl Trueman, assistant professor at the Department of Plant Agriculture Vegetable Disease and Insect Management, Ridgetown Campus.

The project is sponsored by Ontario Agri-Food Innovation Alliance, Ontario Tomato Research Institute and the Fresh Vegetables of Ontario and is using two new late blight trap styles, across eight sites in Kent County.

Three of the sites contain sentinel tomatoes, unprotected and susceptible types, to help detect the relationship between the trap findings and the late blight symptoms on the foliage.

One site is a validation trial — with expansion to one more site expected by 2021.

The spornado style trap is a passive trap, mainly controlled by wind to allow air particles to flow through and then through a mesh filter, where particles are captured.

The rotorod style is an active trap. It contains a bar, which is set to spin for 10 minutes on, 10 minutes off consistently from six in the morning to three in the afternoon. The air particles attach to two rods, which are coated with a sticky silicone.

“You know how much air is passing through (the rotorod), it’s a better constant sampling volume, but the disadvantage is that it requires a power source, where the spornados, you just set them up, that’s it,” says Trueman.

Spornado (left) and rotorod (right) spore traps setup at Ridgetown Campus, University of Guelph.
photo: Source: Cheryl Trueman

The traps are sampled twice a week and then the components undergo DNA testing to detect the presence of the phytophthora infestans pathogens.

If the pathogen DNA is found, it doesn’t automatically mean that the disease outbreak will occur. All pieces of the pathogenic triangle must be present; the pathogen, susceptible host and the proper environment conducive to the disease.

“We are taking the information we are learning about the traps throughout the season and simulating management decisions, based on what we are finding,” says Trueman.

The Ridgetown site contains a field trial to help understand the best management practices with a positive detection of late blight in the spore traps.

The trial is set up to compare a standard fungicide program, not focused on late blight; a fungicide program that changes to include late-blight-specific fungicides after the positive detection within the spore traps and today’s standard practice, waiting until late blight symptoms are recorded in the area to change the fungicide program.

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It will take three years before conclusions can be made to allow for the adequate evaluation of the pathogen findings and the effect on management styles.

“I think from this we will be able to say ‘are the traps performing equally in terms of when they find phytophthora infestans’ but also relating that back to ‘if a grower changes their fungicide program based on what is found in a trap, does that actually benefit, is there a benefit in terms of managing that late blight better?’” says Trueman.

Currently, tomato growers apply fungicides regularly to control fungal disease. Some of these help to control late blight, but several do not. When there is a late blight risk, other products need to be added to the program.

Being able to detect when this occurs and how different management styles affect the presence of the disease will benefit farmers.

To date, five sites have contained positive detections. The sequence of July 15-18 contained one positive detection, the following sequence, July 18–22 contained four positive detections.

About the author


Jennifer Glenney

Jennifer is a farm reporter who lives in Cayuga, Ontario.



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