Every winter alfalfa producers are concerned about the weather. The extremes we have seen in recent years with too much snow, not enough snow, too wet, too dry, and now too warm can give farmers heartburn when they think about their perennial forage crops. Kim Cassida, MSU forage specialist, has reported, “The record warm temperatures we are having pose a risk that alfalfa will break dormancy much earlier than usual, although we have not confirmed it yet.”
Michigan State University Extension personnel remind growers to consider several things for the 2017 alfalfa crop. First, when plants break dormancy very early in the year, there is significant risk of frost or freeze damage to the developing buds and shoots. Whenever freezing temperatures kill buds or small shoots, the plant carbohydrate reserves are depleted because new buds and shoots need to be formed. New alfalfa growth can be killed when temperatures fall below 25-27 degrees Fahrenheit for several hours. If the cold period is long and cold enough to damage all leaves on a shoot, the shoot will not recover. In 2012, many areas of Michigan experienced a late freeze that destroyed shoots, resulting in inconsistent yields and quality for first cutting.
Secondly, alfalfa tolerance to ice sheeting is partially dependent on whether plants are dormant. Alfalfa plants that have bud break will be more susceptible to suffocation in the event excess water and ice form in the field if cold temperatures return following excessive rain or snow melt. According to Cassida, “alfalfa plants that have not broken dormancy will be slightly more tolerant to ice sheeting.”
During the winter months when alfalfa is dormant, the living plants will continue to respire. Plants die under ice sheets because respiration continues in the roots, using up available oxygen that cannot be replaced under the ice. If plants are actively growing, root respiration will be increased using more oxygen and the chance of suffocation increases.
The third potential problem is the possibility of increased alfalfa weevil damage. The warmer temperatures will stimulate the overwintering adult weevils to lay eggs earlier resulting in the first larvae hatch possibly being out of sync with available bio-controls. (The normal growing degree accumulation starts March 1 every year with a base of 48 degrees Fahrenheit.) To monitor the accumulation of growing degree units for alfalfa weevil development, go to the MSU Enviro-weather Alfalfa Weevil Development model.
While the mild winter poses significant risks, there are some common sense things that producers can do to mitigate some challenges. The first line of defense is to always scout your fields for possible problems. Before growers can address a problem, they need to know what they are facing.
The second defense is to keep fertility levels up to sufficient levels, particularly potassium. This is critical for winter hardiness. While there is no advantage to fertilizing early this spring to prevent problems, fields that had adequate fertility last fall are likely to show less winter injury to alfalfa. Therefore, growers are encouraged to have adequate levels of nutrients by fertilizing in late summer or early fall.
Lastly, growers should consider letting stressed or winter-damaged alfalfa reach 1/10th bloom at least once during the growing season to allow complete recharging of root carbohydrate levels.