Tar spot has now been established in the midwestern US for almost a decade and is an annual concern in many Midwestern states like Illinois, Indiana, Iowa, Michigan, and Wisconsin. While tar spot was not as yield-limiting in these areas in 2022, it continued to expand its range across the corn belt, as far west as Kansas and South Dakota, and as far east as New York, Maryland, and Pennsylvania. Ontario joined the tar spot group in 2020 and is well established in the southwest and mid-central regions of the province especially along the north shore of Lake Erie (Essex through Haldimand-Norfolk). As with the US, 2022 was much different than 2021 and shows the importance of environmental conditions on tar spot disease development. Remember, this holds true for any disease!
If 2023 goes the way of the past 2 years, tar spot will most likely be confirmed in southwest Ontario during the first 2 weeks of July. Farmers, consultants, agribusiness, and others are encouraged to scout for the disease and be aware of reports of tar spot in the province. As of June 28, tar spot has been detected in Iowa, Missouri and Kansas. The drought conditions in states such as Michigan, Indiana, Illinois and Wisconsin which have potential to impact Ontario’s risk to the disease has been very dry but the most recent rain in these areas will help the crops but likely tar spot as well. The fungus which causes tar spot favours dry and wet environmental cycles like those we have had in the southwest the past few weeks.
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