If you worry about alfalfa winterkill, Dan Undersander says to choose varieties with university-generated winterhardiness scores.
“I feel very strongly about that,” says Undersander, University of Wisconsin extension forage agronomist.
Seed company-generated winterhardiness ratings aren't always accurate, and varieties that haven't been tested for winter survival are suspect for that trait, he says.
The Universities of Minnesota and Wisconsin jointly conduct the only independent winter survival test of alfalfa varieties. At two locations in each state, plants are cut several times during the seeding year to weaken them going into winter. Then they're evaluated and scored at green-up the following spring. Scores from all sites are combined for one winter survival rating.
Companies each pay a fee to have their varieties tested. Some include those scores in information sent to the Alfalfa Variety Review Board, and use the scores when promoting their varieties. Other companies do their own winter survival testing, too, using the same standardized test that the universities use. However, they don't always come up with the same scores.
“They tend to get numbers that indicate more winterhardiness than we would indicate,” says Undersander. “The issue is in the 2 to 3 winterhardiness range. A lot of varieties we're saying are 3, they're saying are 2.”
A 2 score reflects significantly more hardiness than a 3, he points out.
Some varieties aren't entered in the university tests and aren't tested by the marketer, either. They're sold without winterhardiness scores. Beware of those varieties if alfalfa winter damage is a possibility on your farm, Undersander advises.
“They must not be as winterhardy,” he says. “If the companies had confidence in them, they would have had them tested.”
Fall dormancy ratings are not a substitute for winterhardiness scores, says Undersander. Fall dormancy is a measure of a variety's recovery rate. Over the full range of dormancy ratings (1 to 11), varieties with high scores (fast recovery) are much less winterhardy than those with low scores (slow recovery).
“But in the narrow range of 2 to 4, which is what we're working with in the northern half of the U.S., it doesn't relate,” says Undersander.
Not every alfalfa grower needs to be concerned about winterhardiness. Growers in areas that usually get good snow cover don't gain much from additional winterhardiness. Last year was an exception because of the cold, open winter.
If your alfalfa stands are thin after a normal winter, or if fields green up slowly and unevenly in spring, consider choosing varieties with lower winter survival scores from the Minnesota-Wisconsin tests.
Keep in mind that, in general, yield potential drops as winterhardiness increases.
“The tradeoff is between risk and yield,” says Undersander. “Do you want higher yields or greater insurance? Farmers should select the highest-yielding varieties within the winterhardiness category they need, and then may want to plant some fields to less winterhardy, higher-yielding varieties.”
Some of the winterhardiness scores for varieties listed in Hay & Forage Grower's 2004 Alfalfa Variety Guide (November 2003 issue) are from the university tests. But others are company-generated. Only university-generated scores will be published in next November's 2005 guide.