Lessons learned about 2023 tar spot cases

A plant pathologist with University of Missouri Extension says tar spot was an earlier-than-usual issue with the drought this year.

Mandy Bish says the disease was confirmed in June and became more widespread after August rains in portions of Missouri. 

“By the end of the growing season, I had about a 90% success rate in stopping at a field and finding corn leaves with tar spot lesions on them in central Missouri. The inoculum is present here now.”

Bish says because the disease spreads faster with moisture farmers might want to consider how to address tar spot in irrigated corn.

“Do I kill the fungus or all the fungus to grow under irrigation? There are some not easy decisions farmers will have to make.”

Bish says fungicide applications can still make a difference in managing the disease.

“One well-timed tassel to R3 fungicide application is going to be sufficient. You won’t get a benefit out of additional fungicide applications,” she says. “However, there are those years where we have occasional early outbreaks. That might be the situation where farmers might see a yield benefit in two passes.”

She says the Tarspotter App, developed at the University of Wisconsin, can also be a helpful tool for growers battling with tar spot. Brownfield interviewed Bish at the MU Crop Management Conference.

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