Corn School: How weather influenced tar spot in 2022


Tar spot was found in many regions of Ontario again in 2022 but dry weather conditions throughout the growing season reduced the leaf disease’s impact on the corn crop.

On this episode of the RealAgriculture Corn School, we pay a return visit to the provincial tar spot nursery at Rodney, Ont, where Ontario Ministry of Agriculture, Food and Rural Affairs plant pathologist Albert Tenuta has been monitoring the yield robber for three years.

Again this year, Tenuta observed high levels of the disease in the nursery — symptoms include raised, black lesions on leaves and husks — but the rate of disease development was much slower. He adds that the tar spot arrived pretty much on schedule this year with the first leaf lesions being detected in early July, but dry weather conditions prevented the disease from accelerating and spreading at the pace witnessed during the wet summer of 2021.

Tenuta notes the disease has had a significant impact in pockets of growing areas along the shores of Lake Erie, but dryer weather and less disease inoculum travelling north from U.S. corn regions, where tar spot levels were also lower, has reduced overall impact on the Ontario corn crop. (Story continues after the video.)

In the nursery in 2021, Tenuta observed up to a 40 bu/ac impact on tar spot susceptible hybrids that did not receive a fungicide. This year he estimates that yield loss to be five to 10 bushels.

What impact will the disease have in 2023? In the video, Tenuta says he expects the disease to overwinter well in regions along Lake Erie. He believes risk levels will vary from region to region, but the the overall impact will be determined by weather during the growing season and how hard the disease hits U.S. corn growing regions. If it prospers there, Ontario growers can expect to see high levels of disease spores moving north and impacting corn in the province.

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