In the early morning hours of September 19 and 20, some parts of Michigan recorded temperatures of 32 degrees or less. However, the frost was more widespread than what those temperatures suggest because of radiational cooling, said Pioneer agronomist Gary Brinkman.
“Radiational cooling takes place on those really calm, clear, cold nights, and they can cause frost to occur on our windshields and our lawns even when temperatures are not 32 degrees or less,” he said. “Plants are constantly giving off heat during the night, and when the heat is lost very rapidly from a plant, it can actually get colder than the air around it—it can get so cold that it starts to freeze the tissue.”
Brinkman says a lot of Michigan’s corn was at half to three-quarter milk line. But what impact did the frost play?
“If I’m at half milk line, I’m going to see around a 10 to 15 percent yield reduction from frost,” he said. “If I’m at three quarter milk line, it’s closer to 5 to 6 percent yield reduction—that’s significant.”
When temperatures are close to freezing or below, it’s enough to cause leaf tissue to die within an hour and the effects worsen as time goes on.
“When temperatures are below 32 degrees for several hours, that can kill the leaves and stop ear development,” said Brinkman.
One other impact of the frost was a loss of leaf surface.
“The plants are having to cannibalize energy from the stalk, and we’re already starting to see some stalk issues from the frost,” said Brinkman “We had some very hot, dry conditions in August, and that’s why I think we’re going to have a good crop, not a great crop.”
That frost event was the earliest in more than 20 years, but Brinkman says there is a positive to this situation.
“Thank goodness guys reacted to 2019 and planted ultra-early for the most part,” he said. “We had a lot of corn go in April and the first week of May, so that means much of our crop was well along in maturity.”