The alfalfa variety tables in your November issue (“Grade A Alfalfas,” page 11) included helpful information for growers. But some of the winterhardiness scores supplied to you by seed marketers were incorrect. We recommend that growers check independent winter survival ratings before choosing varieties for their farms.
During the late 1980s, we had significant alfalfa winterkill across the northern U.S. That was because some new varieties weren't as winterhardy as older varieties.
In response, universities and alfalfa breeding companies worked together to develop a standard test for winter survival. This test is used by some alfalfa seed marketers to evaluate the winter survival of their varieties. Varieties with low winter survival scores (good survival — see photos) will be more winterhardy no matter where they're planted.
The universities of Minnesota and Wisconsin jointly operate the only independent winter survival test of alfalfa varieties. We plant tests at four sites (two in each state) and then combine scores across sites for one winter survival rating. Examples of winter survival scores for commercially available varieties are shown in the table on page 17.
When do growers need more winterhardiness? Certainly when stands die from winterkill. But more common than complete stand kill are fields injured by winter stress. They green up unevenly in spring. A few stems emerge from crown buds that survived the winter, then stems appear from new crown buds. The uneven growth caused by winterkill to crown buds can result in significant yield loss.
|Variety||Winter Survival Score||Fall Dormancy|
|Varieties in blue are checks.|
|Vernal is the standard for good winter survival in northern regions.|
If you see uneven green-up in spring, you should be planting more winterhardy varieties. Results of university winterhardiness trials are available on the Web at www.uwex.edu/ces/forage.
Extension Forage Agronomist
University of Wisconsin
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