Evaluate alfalfa stands for winter injury It's a good time to evaluate alfalfa stands for winter injury, a South Dakota State University specialist said.
SDSU Extension Forage Crops Specialist Peter Jeranyama said alfalfa stands are at risk for winter injury or winterkill each year in South Dakota and most of the upper Midwest.
"Winter injury or winterkill can occur from extremely low soil temperature, fluctuating air temperature, ice sheets, or heaving of the crowns. Many areas of South Dakota had minimal snow cover this past winter, which can lead to winter injury or winterkill of alfalfa if soil temperature dropped below about 10 degrees Fahrenheit. Therefore, be sure to evaluate your stand for potential winter injury or winterkill early this spring."
Once lawn grasses begin growth in the spring, uninjured alfalfa should begin sending up little green leaves. If the alfalfa does not initiate growth at this time, dig some of the roots to see if they are winterkilled. A plant that has been winterkilled will have a root that appears yellowish, corky, and soft, Jeranyama said. Occasionally, winterkilled plants will actually begin growth, but it dies quickly because the root has been damaged. If a plant is uninjured, the root will be firm and white.
Even if the root is firm and white, the alfalfa plant could have experienced winter injury. One form of winter injury is to kill the young shoots (leaves) that normally overwinter on uninjured plants. If this happens, the plants will be very slow to green up in the spring, but they will initiate new buds on the crown and recover. Be sure to permit stands that have been winter injured to go to the early bloom stage before harvest to allow the plants time to repair some of the damage.
Once winter-injured stands have about 2 to 4 inches of growth, determine the yield potential by counting the number of stems per square foot, multiple by 0.1, and add 0.38. This gives a potential yield estimate.
Jeranyama cautioned that many factors such as soil moisture, nutrient deficiency, diseases, insects, and harvest management affect the actual yield obtained.
"Generally, stem densities greater than 55 per square foot is adequate for near maximum yield, 40 to 54 may have some yield limitation, and less than 40 yields will be severely limited. Producers with such low densities should consider replacing the stand," Jeranyama said.