A January cold spell in the snowless Upper Midwest has forage agronomists fearing the worst for alfalfa fields in much of that region.
“I suspect that we'll see a lot of winter damage, but I also suspect that we'll see some total winterkill,” says Paul Peterson, University of Minnesota extension forage agronomist.
“I don't think we'll lose everything, but I think it's going to be quite a bit,” agrees Dan Undersander, University of Wisconsin extension forage specialist.
At greatest risk are older stands on poorly drained soils or any soils with low fertility, varieties with only moderate winterhardiness, and fields where a late harvest removed the insulating benefit of fall regrowth.
“Growers who took a late fall cutting will probably lose quite a bit of that acreage,” Undersander predicts.
Young stands are tough to kill. So fields seeded in 2002 may be okay, even if the fall regrowth was removed, he adds.
He says alfalfa winter damage begins when the soil temperature in the plants' crown area — the top 4" — drops below 15°. At Madison, WI, the 4"-deep soil temperature hit 8° during the January deep freeze.
That was under a bare soil surface. Under a similar surface in St. Paul, MN, the temperature dropped below 5° on three consecutive nights, Peterson reports. But under an adjacent grass sod it stayed well above 15°.
“The insulation effect of that sod was tremendous,” says Peterson. “But fall residue of alfalfa is not like a grass sod. My fear is that it might be closer to the bare soil.”
“The area we're most concerned about is northern Illinois, northeastern Iowa and all of Minnesota and Wisconsin,” Undersander says.
Some damage seems likely in South Dakota, too, says Vance Owens, forage research agronomist at South Dakota State University.
“I don't have any soil temperature data, but we've had a fairly open winter,” says Owens. “So I'm guessing we'll be facing some of the same situations in this state.”
In parts of North Dakota, soil temperatures dropped below the danger level in January, then again the last week of February, says agronomist Dwain Meyer at North Dakota State University.
“I expect significant winterkill in the Langdon and Minot areas, with the possibility around Fargo, Carrington, Williston and Hettinger, depending on age of stand and other factors,” he says.
Southern Michigan growers should watch for signs of winter injury at spring greenup, suggests Rich Leep, Michigan State University extension agronomist.
The northern part of that state had snow cover during the January cold spell, but fields were mostly bare in the south.
“The key is to look at plants right away in the spring when they start to get some growth,” says Leep. “You should be able to tell if you've got some areas in the field where alfalfa isn't emerging like it should. Then you can cut into some crowns and tell whether or not they've got good tissue.”
If you need to know sooner, dig 6" deep into the frozen ground and remove a plant, Undersander suggests. Plant it in potted soil indoors. If it starts to send out shoots in 7-10 days, it's healthy. If regrowth is sparse, it's probably damaged.
Or, dig up a few plants and examine their roots. The roots of plants that died in January will be dehydrated. They'll be ropey, with brownish tissue inside. The insides of healthy roots are fleshy, like a potato.
For information on emergency crops to replace winterkilled alfalfa, see the story on pages 12 and 13.