Tar spot was first confirmed in Ontario at Ridgetown in the southwest corner of the province in 2020. Since then, the corn leaf disease has spread across Ontario, pushing east past Toronto and into Quebec.
Many Ontario farmers experienced the yield robber in their fields for the first time in 2024 and the disease is likely to establish a footprint in more farm fields in 2025. On this episode of RealAgriculture Corn School, Ontario Ministry of Agriculture, Food and Agribusiness (OMAFA) plant pathologist Albert Tenuta looks at tar spot management strategies for the upcoming growing season, based on what he and pathologists from across North America have learned since the the disease first appeared on the continent in 2015.
Tenuta says there are plenty of things to consider when managing the disease, which tends to thrive in high moisture and relative humidity, and when leaf wetness lasts for six to seven hours. In 2024, Tenuta tested 96 hybrids at OMAFA’s Rodney, Ont., disease nursery, finding some tolerant hybrids but no fully resistant genetics. He says the best approach for growers is to know field histories, watch the weather and throw a one-two management punch that includes tolerant hybrids and fungicides to protect the crop.
In 2024, growers saw yield protection from fungicides range from 20 to 80 bushels per acre, depending on the severity of tar spot infection. In the video, Tenuta shares accumulated fungicide trial data from across North America. He also notes that growers can still plant high-yielding hybrids that have a weaker tar spot defence, but they must manage them effectively with fungicide application to reduce disease impact and optimize yield.
Subscribe: Apple Podcasts | Spotify | RSS | All Podcasts
