Several producers in North Dakota reported that alfalfa fields have been exposed to temperatures well below freezing in the last week.
Whether these low temperatures will kill alfalfa plants depends on many factors, such as the maturity of the alfalfa, duration of the freezing temperature and soil water level.
Dwain Meyer, North Dakota State University professor emeritus in the Plant Sciences Department, noted that several years ago, he saw alfalfa survive a 14-degree frost with less than 30 percent stem kill and more mature stems killed at 25 degrees.
To check for damage after a frost occurs, wait until the air temperature recovers, which usually is the same afternoon. A hard frost will cause the alfalfa stems to "shepherd hook" or act as a lazy stem. If the stems straighten after a warming period, the stem is uninjured and will resume normal growth.
If the stem does not straighten up following a frost, it has been killed and will start to dry out.
"However, even the reported low temperatures won't hurt the alfalfa," says Marisol Berti, NDSU associate professor in the Plant Sciences Department. "It might set it back, but the recommendation is to do nothing. Even if some of the alfalfa was damaged, regrowth will start again from the axillary buds in the crown."