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Rain will be the deciding factor on tar spot’s impact

A field crops pathologist says while tar spot was found earlier than normal this year, the rest of the season will determine its impact as it spreads in states surrounding Lake Michigan and westward.

Marty Chilvers with Michigan State University tells Brownfield corn tar spot thrives in wet conditions and wide-sweeping rains at the end of June brought along ideal conditions through Great Lakes states.

“Fungicides are probably going to be best between R1 through about R3 growth stages typically, we sort of want to catch the disease at the start,” he explains.

Continued rainfall events, leaf wetness, and heavy dew will drive its spread moving forward.

“If we get a lot of very frequent rain events, that’s when we’re going to be quite concerned about tar spot,” he says.  “And the other thing as we get toward the end of the season, we’re going to be looking for is if any fields have been heavily affected with tar spot, they’re very likely to be at risk of lodging.”

Chilvers recommends farmers check out the Crop Protection Network for resources on the disease or the Corn IPM PIPE website for mapping tools tracking its spread.