WINNEGAGO, Ill. — More challenges are ahead for farmers who already have experienced significant difficulty planting their corn and soybean crops for the 2019 growing season.

“As I’ve traveled in northern Illinois, I’ve see corn just starting to emerge all the way to V7,” said Russ Higgins, University of Illinois Extension commercial agriculture educator.

“And with the weather patterns we’ve been experiencing we are really setting ourselves up for a substantial tar spot year,” Higgins said during a presentation at the Illinois Forage Expo, organized by the Illinois Forage and Grassland Council.

This is especially true if tar spot was a problem in a field during 2018.

“Tar spot showed up in 2015 and then late in the year 2016 and the same thing in 2017,” Higgins said. “2018 was a game-changer because tar spot showed up at the first of July.”

For a plant disease to become a problem, Higgins said, it requires the disease triangle.

“You need the organism, a susceptible crop and the right weather for the disease to take place,” he said.

“Different varieties of corn have shown varying levels of resistance to tar spot, but we don’t have any corn varieties that have full resistance,” he said.

“Tar spot likes it cool and wet with temperatures of 60 to 72 degrees,” he said. “It likes the leaves to be wet for at least seven hours for the infection to take place.”

At this point, Higgins said, the question is what effect the winter had on tar spot.

“We’re suggesting about 10% of the inoculants survived the winter,” he said.

“We had a lot of tar spot last year, so even if only 10% survives, that should be plenty to start the infection cycle this year,” he said. “Once infection takes place, symptoms show up 14 days later.”

Regardless if the corn is at V1 or V7, Higgins encourages farmers to begin scouting now for tar spot in their fields.

“We don’t have set recommendations for fungicide application because this disease is so new,” he said.

“But we recommend if there are symptoms showing up on the corn leaves, you might consider an early season fungicide application before the traditional fungicide application at R1,” he said.

Since tar spot showed so late in the season during 2016 and 2017, Higgins said, the disease did not seem to have an impact on yield. However, tar spot last year was found in cornfields in July and a lot of cornfields were tasseling during the first 10 days of July.

With the later planted corn this year, if tar spot gets established, it will have the opportunity to cycle throughout the growing season, Higgins said.

“I’m concerned if the disease gets established this year it’s going to be even more harmful than last year, although that’s dependent on the weather for the rest of the year,” he said.

“If you don’t know what tar spot is please get in touch with your agronomist or seedsman,” he said.

For more information about the Illinois Forage and Grassland Council, go to:

Martha Blum can be reached at 815-223-2558, ext. 117, or Follow her on Twitter at: @AgNews_Blum.


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