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Distinguishing tar spot in corn fields

Farmers across the Midwest are vigorously scouting for the corn disease tar spot.

Iowa State University Extension crops pathologist Dr. Alison Robertson says it appears as small, raised, black spots scattered across the upper and lower leaf surfaces.

“Those little black spots are very, very easy to be confused with insect poop.”

She tells Brownfield there’s a simple way to determine if it’s tar spot.

“See if you can scrape it off with your fingernail, or just put a bit of saliva on your finger and see if you can wipe it off the leaf.”

And Robertson offers an additional method for confirmation.

“The other thing about tar spot, that black spot, you’ll be able to see it on the top surface of the leaf. That’s where you’ll see it first, but if you turn the leaf over and look on the underside, you should see the black spot on the underside as well.”

Tar spot was confirmed in central Iowa earlier this month.