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Tar Spot making a home in the Midwest

A pathologist says areas around Lake Michigan have been the epicenter for corn tar spot, but outbreaks are spreading. 

Michigan State University’s Marty Chilvers tells Brownfield corn tar spot was first discovered in 2015 in northern Illinois and Indiana before spreading to Michigan and Wisconsin and each year is making it further into the corn belt.

“We’ve got reports now in Missouri, it’s into Ohio as well so it’s continuing to spread.  And the other really amazing thing in 2019 it went all the way across Iowa.”

Chilvers says once the disease is confirmed in counties, it’s likely to stay in crop residue but is also mobile.

“If you are corn on corn, continuous corn, and no-till, you might be at slightly higher risk because you’ve got debris right there harboring the disease, but even if you do all the right things you may very well get a heavy disease onset just from spores blowing in.”

Researchers are still trying to narrow fungicide application windows that protect crops the most which Chilvers says is likely R1 to R3 or later.

“If the fungicide application is made at the right time, we’ve seen 15-20-bushel protection.”

Yield losses have varied from 20 to more than 50-bushels per acre.