Will last winter”s unusual weather pattern result in damage to alfalfa? Many farmers are asking this question as spring arrives in Wisconsin.
Last winter, little snow cover existed in many parts of the state, and temperatures were warm in November and December, promoting some late season growth.
“Both of these conditions can be detrimental to winter survival,” said Dan Undersander, UW-Extension forage specialist and UW-Madison professor of agronomy. Mild winters, with little snow cover, is when winterkill frequently occurs because snow insulates the alfalfa against short periods of very cold weather.
This year, however, Undersander expects little winterkill. “We have not had cold periods with exposed alfalfa., ” he explained. In addition, he said, improved alfalfa varieties developed in the last five years are much more winter-hardy than older varieties.
“Most newer varieties can tolerate one freeze, as happened last December,” he said. “We should remember that the same pattern occurred in the 1997-98 winter, and very little winterkill occurred.”
Undersander said most of the alfalfa in Wisconsin appears to be alive and well as of late March. Stand kill, if it occurs, will depend on the weather during the next month. Alfalfa top growth may be killed if it is subjected to temperatures under 25 F. for four hours or more after one or more periods of growth.
“In general, soils are dry this spring, and this increases their insulating ability and reduces the chance of heaving from repeated freezing and thawing,” Undersander added.
How can you tell if alfalfa is alive? Undersander suggests digging a few plants 4 to 6 inches deep. Split the taproot and examine it. If the taproot is turgid and off-white like the inside of a potato, the plant is alive. If the taproot is dehydrated and brownish, the plant is dead or dying. He cautions, however, that healthy, live plants over 2 years old will have some black crown root at the top of the root.
Farmers should also check for winter injury to alfalfa plants. Such damage means reduced yield for the season, even though the plant has survived.
“You can identify winter injury by watching as plants green up in the spring,” he said. “If a few stems come early (from the buds produced last fall) and then, when first growth is 3 to 4 inches tall, more shoots appear on the crown, it means that most of last fall”s buds were killed. As a result, the plant had to produce new growth this spring. The new growth is late and will result in reduced yield.”
Undersander suggests that farmers who see this pattern in their alfalfa stands should consider planting a more winter-hardy variety in the future.