A January cold spell in the mostly snowless Upper Midwest has forage agronomists worried about the winter survival of alfalfa fields in much of that region.

The ½”-deep soil temperature in St. Paul, MN, dropped to -13 degrees on Jan. 19 and -1 degree the following night, reports Paul Peterson, University of Minnesota Extension forage agronomist. Agronomists used to think alfalfa began to suffer winter damage when soil temperatures in its crown region – the top 4” – dropped under 15 degrees above zero. Peterson thinks newer varieties can handle temperatures lower than that, but the ones recorded last month may be too low.

He suspects that some alfalfa stands were damaged, but probably weren’t killed. Winterkill usually results from a combination of stress factors, and typically happens during alternate freezing and thawing in spring.

“But there’s potential for this cold-temperature exposure to increase susceptibility to that later on,” says Peterson.

In Fargo, ND, the nighttime temperature dropped to -19 degrees on Jan. 20, and soil-surface readings hit 8 degrees in Marisol Berti’s research plots. But the North Dakota State University forage agronomist says the biggest problem may have been an early January warm-up, when temperatures were in the 40s and 50s and alfalfa may have started to break dormancy.

“If they did break dormancy, then we got the cold spell, it’s not going to be very good news in the spring,” Berti says.

Most of Wisconsin got several inches of snow the week before the cold spell, so damage was minimal in that state.

“But we’re losing our snow cover again, and we could have colder weather,” says Dan Undersander, University of Wisconsin Extension forage agronomist. “We just have to keep praying for snow and wait and see what happens toward spring.”

Watch for more on alfalfa winterkill prospects in the February issue of Hay & Forage Grower.