Corn School: Fungicides claim victory in the fight against tar spot


Tar spot was a little late arriving in Ontario cornfields in 2023, but the leaf disease ramped up post tasseling, and with an extended fall, took a late-season bite out of grain yields in southwestern areas of the province.

Growers who sprayed fungicides to defend their crop against disease were rewarded with higher yields, reports Ontario Ministry of Agriculture, Food and Rural Affairs plant pathologist Albert Tenuta. In yield trials, his data reveals some of the strongest performance for fungicides since the disease first touched down in the province in 2020, with yield advantages ranging from 15 to 80 bu/ac for hybrids where fungicide was applied.

On this episode of RealAgriculture Corn School, Tenuta and Rodney, Ont., farmer Mike Miller share tar spot control experiences and observations from 2023. On his farm, Miller says he saw “a huge response” to fungicides with hybrids yielding between 15 to 70 bushels more than areas of fields where no product was applied.

Once again in 2023, application timing played a significant role in fungicide success. Tenuta says research continues to confirm the VT/R1 timing is the best application timing. “It’s been the most consistent, most uniform, not only here but elsewhere in the US as well in the Midwest so it’s hard to go away from,” says Tenuta.

The next management consideration is whether a second application could provide additional protection; should be applied before or after the VT/R1 timing; and whether it delivers an economic return. In 2023, Miller applied a second application 15 days after the first pass and saw a 9 bushel advantage for the two-pass strategy over the single application.

In the video, recorded at the Ontario Agricultural Conference at University of Guelph’s Ridgetown campus, Tenuta also shares product performance results from his trials and notes how several fungicides consistently deliver high levels of yield protection from tar spot.

Tap here for more Corn School videos.

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