ONTARIO GRAIN FARMER AGRONOMY 12 Tenuta also touched on red crown rot, a pathogen identifiable by reddish discolouration on lower stems just above the soil, and one that can sometimes produce symptoms very similar to a variety of other common soybean diseases. Red crown rot has not yet been confirmed in Ontario, but it is spreading from the Midwest into states bordering the Great Lakes. Like SCN, red crown rot spreads primarily through the movement of soil on equipment. For this reason, he says anyone “buying equipment from Iowa or Illinois” should “make sure it’s clean.” A novelty for 2026 was highlighted as well: the first trials outside of the United States of a soybean with Bt-based SCN resistance. A Bt soybean is something Tenuta says he “was promised 35 years ago” at the start of his career and will be another source of SCN resistance growers can layer into their cropping plans. “We have nothing that is totally resistant to SCN. It’s a numbers game,” Tenuta says. TAR SPOT —SEASON SIX In Tenuta’s corn research plots, the attending crowd wove between rows of hybrids with varying degrees of tar spot damage. With the arrival of tar spot in southern Ontario in 2020, Tenuta decided it would be useful to test for the pathogen at West Elgin in 2021. This turned out to be a prudent move. “Damn, 2021 was a good tar spot year,” says Tenuta, again spurring many chuckles. Since then, a lot has been learned about tar spot management, including the susceptibility of different corn hybrids and in-season control. Regarding the latter, it was discovered that fungicide application timing for tar spot fit well with pre-existing timing strategies for controlling Gibberella and DON. “We’ve had an 80- to 90-bushel yield response with some experimental tools,” says Tenuta. “There are new things coming down the pipe, new fungicides and formulations.” “We do a lot of experimental work before things are registered.” Now well into the sixth season of researching tar spot, Tenuta and his team walk and assess its development in their corn research plots every one to two weeks. His advice for growers is to choose hybrids by balancing yield and other agronomic needs with tar spot resistance ratings, and to “always ask the seed companies for their tar spot rating and where they do their testing.” If those ratings come from West Elgin research data, they can expect as-advertised performance. • continued from page 11 “When we put crops in a field with good, even disease pressure, we get good results. - Albert Tenuta Field Crop Pathologist, OMAFA Tenuta advises growers to choose hybrids by balancing yield and other agronomic needs with tar spot resistance ratings.
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