A warm weather pattern in late February caused soil temperatures across most of Iowa to rise above 40 degrees Fahrenheit (F). This warm period was likely long enough for alfalfa and some forage grasses (most ryegrass varieties and less winter-hardy orchardgrass and tall fescue varieties) to break dormancy. When low temperatures resume, alfalfa plants can reharden to a degree, but only to the extent that it still has stored carbohydrates available. Winter injury occurs either when frequent warm-cold cycles deplete carbohydrates, or if the temperature drops so rapidly that the plant does not have time to sufficiently reharden
Iowa State University
Lang, Brian, "Plan to Scout Alfalfa Stands for Winter Survival" (2017). Integrated Crop Management News. 2433.
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