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Don’t rush to change crop rotation because of tar spot

Crop rotation is not a reliable management strategy against tar spot, according to the recent Tar Spot Summit by AgReliant Genetics.

Damon Smith, an Extension plant pathologist with the University of Wisconsin-Madison, says growers shouldn’t change their cropping or tillage systems.

“We see little, tiny incremental decreases in disease with residue management and crop rotation but they aren’t the end all be all and so I don’t think a farmer needs to go in and change the whole operation just to manage tar spot,” he says. “Don’t give up conservation tillage and no till. If you’re doing it, stick with it. if you’re corn on corn, I think that’s okay. Put some energy into those resistant hybrids.”

Christy Toedebusch, vice president of product management, marketing, and digital agriculture with AgReliant Genetics, says the company’s recent survey confirmed tar spot management challenges.  

“One of the things we have found on the Tar Spot survey is that the top three management strategies that farmers use are crop rotation, scouting, and hybrid selection,” she says. “What we heard (during the Tar Spot Summit) from a lot of the academics is that crop rotation and scouting are really not useful against tar spot.”

Smith says the most effective management strategy against tar spot is hybrid selection.

“With tar spot being such a sneaky disease, having that hybrid resistance there really helps us take some of the sneakiness out and it gets us a long way to being able to manage tar spot and being able to manage it efficiently,” he says.

Fungicide applications can help, but Michigan State University Associate Professor Martin Chilvers tells Brownfield, “(fungicides) are not a complete solution. They’re only going to minimize and suppress tar spot for a period of time. So, we really want to pair that with some hybrid resistance.”

There are a lot of unknowns about Tar Spot as it was first reported in the United States in 2015.