Corn School: A tar spot management plan for 2022


After a methodical march north from the Corn Belt, tar spot has now gained a foothold in Ontario. Last year, the yield-robbing leaf disease was confirmed in five counties in the southwestern, stretching from Essex to Simcoe.

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.

What impact could tar spot have on Ontario corn acres in 2022? What tools can growers utilize to defend their corn acres against the disease? On this episode of RealAgriculture’s Corn School, Ontario Ministry of Agriculture, Food and Rural Affairs plant pathologist Albert Tenuta looks inside the tar management toolbox and shares strategies and tips for growers.

Tenuta says a number of factors will determine the impact tar spot has in 2022. Weather fronts will continue to carry disease spores north from the U.S; the pathogen also has the ability to overwinter; and another year of wet, moist conditions will favour the further establishment and spread.

But hybrid choice, diligent scouting and fungicides do offer growers a solid defence. In the video, Tenuta discusses tar spot hybrid trials he conducted last year at Ridgetown, Ont. The research revealed a high degree of variability of tolerance across hybrids. Some were highly susceptible while others offered strong tolerance. (Story continues after the video).

Fungicide efficacy was also tested last year in trials at Rodney, Ont. Here the research revealed that highly efficacious products can provide a 25 to 30 bu/ac advantage over the untreated check.

Tenuta notes that the best strategy for growers is to combine a more tolerant hybrid with an effective fungicide. In the trials, this tag team delivered up to an 80 bu/ac yield advantage.

Tenuta advises all growers to get out and scout their fields in early July and look for tar spot lesions on the lower leaves. He also advises growers to take advantage of disease tracking and identification tools, including the Tarspotter app. He adds that tasseling (VT to R1) is the most effective timing for applying a fungicide to control the disease.

Click here for more Corn School videos.

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Corn School (view all)Season 11 (2022) Episode 27

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