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Finding ways to overcome tar spot

Photo courtesy of Channel Seed

Midwest farmers are presented with various agronomic challenges each growing season.

Such yield-robbing threats continue to grow as time goes on.

A southeast Iowa agronomist speaks to increasing disease pressure.

Tar spot, a fungal disease, started its spread across North America in 2016. The disease, which has been confirmed in 75-percent of Iowa counties, proves challenging from an agronomic standpoint. Karl Buttenhoff, technical agronomist for Channel Seed in southeast Iowa, speaks to the disease’s rapid spread.

“It was first identified, in the United States, in 2015. It blew up from Mexico and Central America. In 2016, we saw it expand from the epicenter. It had successfully overwintered. Since then, it’s expanded its geography north and west. Unfortunately, we have seen it expand more rapidly than anticipated,” Buttenhoff said.

Tar spot’s impact depends on how early infection occurs and how severe the infection, according to Channel Seed. Buttenhoff reports instances of farmers experiencing 30 to 60 bushel yield losses, following early on-sets of tar spot.

Channel Seed further reports, “No corn products grown in the U.S. Corn Belt are known to have high levels of resistance to tar spot.” However, research indicates genetic differences in susceptibility.

“We’ve worked with our technology development organization, breeding organization and pathology groups to target fields where we saw high levels of tar spot. We planted corn plots in those fields, in an attempt to get disease characterize ratings on our genetics. What we’ve seen so far: There’s genetic differences in the susceptibility to tar spot,” Buttenhoff said. 

Channel Seed also looked to its fungicide portfolio for another effective control method. The company reports good results stemming from its Delaro fungicide, which is labelled for tar spot control.

“We’re still working on timing of the application for tar spot control. We’ve seen fields that would benefit from an early application, as well as a later application. With any fungicide, you’re looking at a 21-day residual. If tar spot starts coming in later like it did this year, there may be an opportunity to see an ROI on that second fungicide application with tar spot,” Buttenhoff said.