8 OMAFRA and Agriculture and Agri-Food Canada’s corn breeding program led by Dr. Aida Kebede. “Private companies are also testing their lines against tar spot,” says Tenuta, “and some have some preliminary results showing some lines with tolerance, but we need to know if that’s a purely genetic response or geneticenvironmental interaction. Overall, I think it’s safe to say that with tar spot being a new pathogen to the U.S. and Canada, having a choice of hybrids that are verified tolerant is a few years away. And, of course, growers need to select hybrids according to the total trait package they need on their farms. It is important that farmers evaluate an assortment of hybrids on their farm each year and select hybrids based on individual field needs.” FUNGICIDE CONTROL Tenuta reports that the results of the 2021 fungicide trials done for tar spot in Ontario match that of U.S. research and have contributed Ontario findings to the North American pool of data. He and his colleagues have also engaged with two U.S.-based groups, the Tar Spot Working Group and the Corn Disease Working Group. “So, we’re really well ahead in terms of this being a new disease,” he notes. In general, it’s been found that fungicide application should be done at V.T. stage to silking, which is the same window that applies to DON and other fungal diseases. “So, spraying for tar spot fits into a grower’s existing spraying schedule, which is great news,” says Tenuta. “However, scouting is still critical. We may have favourable environmental conditions, so you may need to apply earlier if disease develops rapidly.” It’s also good news that several multimode fungicides tank mix combinations or preformulated that work well for tar spot also works for DON, northern leaf blight continued from page 6 and other fungal pathogens, but only certain active ingredients will control either DON or tar spot. Vermey notes that weather conditions could lead to multiple infections, and you may need a second spray. “We do not want to create resistance with any disease, so using a good disease management plan and multiple modes of action with alternative prevention methods (hybrid selection) is the best plan,” he says, “with recommended rates and application practices.” Vermey also advises spraying on the first sight of disease presence to reduce spread to the rest of the plant. “If disease is found near the bottom of the plant, this indicates the disease spores came from the field and will continue to spread within the canopy,” he says. “If the disease is found on the top of the canopy, this indicates the disease blew in and is developing from the top down.” l TAR SPOT ON CORN LEAF. PHOTO COURTESY OF ALBERT TENUTA.
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