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Ontario Grain Farmer Magazine is the flagship publication of Grain Farmers of Ontario and a source of information for our province’s grain farmers. 

Tar spot

AGRONOMIC INFORMATION FROM ONTARIO'S CROP SPECIALISTS

Albert Tenuta, Field Crop Plant Pathologist, Ontario Ministry of Agriculture and Food and Ministry of Rural Affairs

A NETWORK OF Ontario crop specialists and U.S. extension specialists monitored the real-time movement of tar spot in 2021. In September, the disease spread significantly east and north from the original infections confirmed in southwestern Ontario’s lower five counties in 2020.

TAR SPOT DISTRIBUTION – SEPTEMBER 29, 2021.

Tar spot appears as small, raised, black tar-like spots scattered across the upper and lower leaf surfaces. These spots are stroma (fungal fruiting structures). If viewed under the microscope, hundreds of sausage-shaped asci (spore cases) filled with spores are visible. When severe, stroma can even appear on husks and leaf sheaths. Tan to brown lesions with dark borders surrounding stroma can also develop. These are known as “fisheye” lesions.

EARLY INFECTED FIELD, SEPTEMBER 13, 2021.
2020 FUNGICIDE TRIAL TOLERANT VERSUS SUSCEPTIBLE HYBRID (RODNEY, ONTARIO).

Based on what we have seen and observed in corn hybrid trials, there is some degree of tolerance or partial resistance. A 64 hybrid OMAFRA trial in Rodney, Ontario does show some good candidate hybrids.

You can see where the latest confirmations of tar spot have been reported through the Corn ipmPIPE initiative (https://corn.ipmpipe.org/tarspot/). •

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