Tar spot has been ramping up across Ontario ever since the leaf disease was first spotted in the province back in 2020.
Visual signs of the disease — tar-like speckling on the upper surface of corn leaves — typically show up in early to mid July and growers need to be ready to tackle this yield robber. On this episode of RealAgriculture's Corn School, BASF Canada agronomist Ken Currah looks at the potential impact of tar spot on the 2025 crop and shares strategies growers can employ to manage yield loss in infected fields.
Currah says work done by Ontario Ministry of Agriculture and Agribusiness pathologist Albert Tenuta continues to show that fungicide application at the VT/RI green silking stage is the most effective timing. In 2024, growers saw yield protection from fungicides ranging from 20 to 80 bushels per acre, depending on the severity of tar spot infection. Currah notes this spray timing also aligns with fungicide application for gibberella ear rot and other foliar diseases, giving growers a significant opportunity to protect the yield potential of their crop.
Currah also looks at the impact of drought stress and field history when building a tar spot management strategy, and the importance of growers working with their seed company and agronomist to understand how susceptible the hybrids they plant are to tar spot. Growers can still plant high-yielding hybrids that have a weaker genetic tar spot defence, but they must manage them effectively with fungicide application to reduce disease impact and optimize yield.
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