OMAFRA says farmers across the province should be aware of tar spot, which occurs during frequent rains and prolonged wetness.

Tar spot was first detected in Illinois and Indiana in 2015 and has slowly spread out, with field crop pathologist Albert Tenuta noting “Last year it would have been the spores coming in from the United States”.

2019 saw yield losses in some Ontario fields reach 40-to-50 bushels, while cases have also been reported over the last week in Michigan, Indiana and Iowa.

Tar Spot appears as tiny, raised, spore-filled black spots scattered across the upper and lower leaf surface but can appear on the husk and leaf sheaths under severe incidents.

Tar Spot was on Ontario’s radar during the annual corn disease survey with Agriculture and Agri-Food Canada, funded by the Grain Farmers of Ontario (GFO) and Canadian Agricultural Partnership (CAP), due to wind patterns and proximity of infected areas in Michigan.

Tenuta says new fungicides are set to become available in Canada that have proven effective against Tar Spot, and Northern Corn leaf blight.