continued on page 8 ONTARIO GRAIN FARMER COVER STORY 7 Snow mould and stripe (yellow) rust are caused by different fungal pathogens, but they share several characteristics, and chief among them is the ability to seriously impact winter wheat yields. Marty Vermey, senior agronomist with Grain Farmers of Ontario, says that with both diseases, understanding the effect of preceding conditions and active scouting are very important. And so is the best variety selection for key diseases for your area. STRIPE RUST CAN BE DEVASTATING Stripe rust can devastate wheat production when infection is severe. Stripe rust symptoms first appear as small chlorotic lesions on leaves, followed by yellow to light orange pustules that each contain thousands of spores. The pustules occur in a random pattern and they can be confused with those that cause other rust diseases such as leaf rust. Stripe rust thrives in cooler conditions, between 10 and 18 C, and likes intermittent rain or dew events. Growth slows at about 15 C, but there is now evidence that at least one population in the U.S. has adapted to warmer temperatures. In terms of its severity in Ontario this year, the crystal ball is still a bit cloudy. But Ontario Ministry of Agriculture, Food and Agribusiness (OMAFA) Cereals Specialist Joanna Follings has her antennae up. “We are monitoring throughout this winter the reports of stripe rust appearing in the southern U.S. and we’re tracking weather systems that may carry spores north,” she says. Stripe rust does not typically overwinter in Ontario, but it can do so under specific conditions: high levels of disease pressure in the previous year, good fall with lush growth, mild-to-moderate winter temperatures and early and persistent snow cover – like the kind we had in fall 2025 and fall 2024. Many areas of Ontario received significant snowfall prior to the ground freezing. “This may be conducive to overwintering of stripe rust in some areas, particularly in fields where disease pressure was high in 2025,” Follings says. “These fields should be scouted beginning in early spring once the crop has greened up, particularly if fungicide use is not a standard practice.” Vermey adds that volunteer wheat is a risk factor, and snow cover protects stripe rust that infects volunteer wheat in the “This is why we had stripe rust in the Mitchell area last year,” he says, “and then it spread.” Stripe rust Follings, Vermey and OMAFA Extension Plant Pathologist Albert Tenuta concur that the best defense against stripe rust is a combination of variety selection, scouting, and timely fungicide applications. “Keep in mind that if you see it, you may have to take immediate action as it can explode very quickly,” Tenuta says. “You may need to apply an earlier fungicide application than normal, earlier than T3.” VARIETIES DIFFER Large differences in susceptibility to both stripe rust and snow mould exist in Ontario winter wheat varieties, so check the Ontario Cereal Crops Committee performance trials for specific variety ratings (GoCrops.ca). But only look at the 2025 trials. Follings says if a variety has a rating of six or higher, the variety is susceptible and will benefit from a fungicide application if disease is present. If a variety is rated three to five, then it’s classified as moderately resistant and should be scouted regularly during the growing season. If stripe or leaf rust are present and on the upper leaves of the canopy, consider a fungicide application, particularly if the wheat is before or just at flag leaf. Varieties with a rating less than two are resistant against stripe and leaf rust, but should continue to be monitored. “As we saw in previous stripe rust years, some growers got caught with a severe disease infestation 10 days before the T3 fungicide application timing and had significant yield losses as a result,” Follings says. “So, if a field is more than seven Photo: Marty Vermey
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