Early frost nips Upper Midwest crops

The freezing temperatures likely will cut into soybean yield and corn quality in some parts of North Dakota.

Prolonged frost ends the growing season for most crops. (Pixabay photo)

Widespread frost in the region likely ended the growing season in some fields, which for many places puts 2020 among the earliest ends of the growing season on record.

For instance, the Alamo station of the North Dakota Agricultural Weather Network registered 18 degrees early in the morning on Tuesday, Sept. 8.

“I could not find a colder reading (in the record books) in North Dakota on Sept. 8,” said Daryl Ritchison, NDAWN director.

It will take a few days to see the damage in crops, but those freezing temperatures likely will cut into soybean yields in some places, as well as reduce test weight and quality in corn, he said.

Overall, Ritchison believed the Sept. 8 and Sept. 9 freezes, which were widespread across most of North Dakota as well as into the surrounding states, were in the top 10 earliest ends of the growing season in the state’s history.


Ritchison said temperatures at 32 or below early on Sept. 8 were widespread west of Highway 281, which runs through Cando, Carrington and Jamestown, about two-thirds of the way from the Montana line to the Minnesota line. But even to the east of 281, where official temperatures were mainly 32 and higher, Ritchison believes there will be freeze damage.

Freezing temperatures were even more widespread in North Dakota on Sept. 9, with most of the state falling lower than 32. Even places that didn’t officially register freezing temperatures only showed readings in the mid-30s.

Parts of South Dakota, Montana and Minnesota also experienced frost on Sept. 8 or 9.

Laura Edwards, South Dakota State Climatologist and climate field specialist for South Dakota State University Extension, said the freezing temperatures in her state mostly were in the Black Hills, in the west, and in the north-central portions of the state.

In looking at more than 100 years of records for Aberdeen, Pierre and Lemmon — all on or west of Highway 281 — Edwards said the Sept. 8 freeze was extreme.

“They have had frost (in the past) in early September, but this would be in the top three or five earliest,” she said.

That’s especially striking because recent years have trended toward longer and longer growing seasons. That means some farmers have moved toward longer-maturing varieties of corn and soybeans.

Some earlier-maturing soybeans already may be drying up and dropping leaves, but the later-maturing varieties likely have still been green. Ritchison said some longer-maturing varieties are meant for late September freezes, so the top layer of soybeans likely hasn’t filled yet. Those top beans are often the bonus on yields.


“This caused some damage. It caused some yield loss. That’s a guarantee. It’s just a matter of how much,” Ritchison said.

In corn, the yield might not be affected, but Ritchison expects that the test weights might be.

Edwards doesn’t anticipate a lot of damage in South Dakota, where she said a hot summer already had pushed crops ahead. But she agreed that later-maturing varieties could see some loss in yield or quality.

And Ritchison warns that even if an official freezing temperature wasn’t reached, the temperature may have dipped enough in certain spots to damage crops. He recalls official low temperatures in the mid-30s on Aug. 20, 2004. The records show that as the year with one of the area’s longest growing seasons, but some crops suffered frost damage when the temperature hit 34, he said.

“That’s always the problem when you do this,” Ritchison said. “32 isn’t necessarily magic.”

The amount of time the temperature stays below 32 also affects the amount of damage, as does having two consecutive days with temperatures dipping below freezing, Ritchison said.

Ritchison said the 2020 growing season has included a “beautiful” summer, with consistent heat, and after the two days with frost, he expected a long stretch before any more freezing temperatures.

In South Dakota, Edwards said the colder temperatures were accompanied by moisture, which was very welcome in many places. More than a quarter of the state was listed in moderate or severe drought in the Sept. 9 U.S. Drought Monitor. Edwards said much of the state received more than half an inch of moisture on Sept. 8, which should help provide moisture for new plantings of winter wheat and help set up pastures and forages for next spring.

Jenny Schlecht is the director of ag content for Agweek and serves as editor of Agweek, Sugarbeet Grower and BeanGrower. She lives on a farm and ranch near Medina, North Dakota, with her husband and two daughters. You can reach her at or 701-595-0425.
What To Read Next
Get Local