Corn School: Inside the tar spot management toolbox


Tar spot is taking a bite out of yields in some Ontario corn fields but there is hope that growers will have effective tools to manage the leaf disease.

Characterized by tar-like speckling on the upper surface of corn leaves, the fungal pathogen has been delivering yield hits ranging from 20 to 60 bushels per acre (in highly infected fields) since it was first identified in Indiana and Illinois in 2015.

Last year, the disease was confirmed in Ontario and Albert Tenuta, Ontario Ministry of Agriculture, Food and Rural Affairs plant pathologist has been working to identify the best defence against the pathogen. On this episode of RealAgriculture’s Corn School, Bernard Tobin visits Tenuta at his disease nursery near Rodney, Ont. for an update on his 2020 research work.

Tenuta says Ontario growers have been reporting tar spot-related losses of up to 40 bu/ac so far during harvest 2021 but he’s optimistic that growers will be able to manage the yield robber based on his trials. He’s testing a wide range of genetics (64 hybrids) as well as fungicides (14 products) to help identify the best control options.

Tenuta notes that there is no true genetic resistance to the disease but there are different levels of tolerance, which allow some hybrids to mount a stronger defence. Fungicide performance is similar — some products offer little benefit in managing tar spot, while others deliver higher levels of control.

After the first year of trials, Tenuta says plenty of work needs to be done to better understand the disease in Ontario. However, early evidence suggests an integrated management strategy, including tolerant genetics and efficacious fungicides, could provide good protection against tar spot.

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