Nighttime temperatures haven't stayed low enough, or daytime temperatures high enough, to cause concern.
A lack of snow cover during December and January hasn’t caused any damage to Wisconsin’s alfalfa crop up to this point, says Dan Undersander, forage specialist with University of Wisconsin-Extension.
The key factor, says Undersander, is that nighttime temperatures haven’t been low enough over a sustained period to affect soil temperatures. “For problems with winterkill or killing the shoots to occur, the soil temperature has to get down to 15 degrees in the 2-4” range. While we’ve had one or two nights where air temperatures have been down in the single digits, it hasn’t happenedover a long-enough period to reduce the soil temperature.”
On the other end of the spectrum, Undersander also points out that daytime highs have not been warm enough to cause concern. “While the temperatures have been warmer than average, we haven’t had those 60-degree days where we’d likely lose some winterhardiness and see some damage to shoot growth.”
A snowfall in parts of the state last week should help. “The major concern has been that we could get some extremely cold temperatures for a prolonged period of time without any snow cover. In that case, we could start to see some damage to the alfalfa. As little as 4” of snow will insulate the soil against up to 16 degrees of temperature. So the recent snow will insulate the soil from cooling sufficiently to damage the alfalfa.”