To find more resources for your business, home, or family, visit the College of Agricultural, Consumer and Environmental Sciences on the World Wide Web at aces.nmsu.edu Assessing Alfalfa Stands After Winter Injury, Freeze Damage, or Any Time Renovation Is Considered in New Mexico Circular 644 Leonard M. Lauriault, Francisco E. Contreras-Govea, and Mark A. Marsalis 1 Cooperative฀Extension฀Service฀฀•฀฀College฀of฀Agricultural,฀Consumer฀and฀Environmental฀Sciences฀฀ This publication is scheduled to be updated and reissued 8/14. Alfalfa growers often become concerned over winterkill, when in fact the injury they are observ- ing is the result of freeze damage from which the alfalfa can recover. This publication addresses the reality that winterkill of alfalfa should be rare in New Mexico, how to prevent winterkill, how to as- sess stands for replacement, and recommendations for stand replacement. What is winter hardiness? Alfalfa’s winter hardiness is determined by its ability to survive cold temperatures. In the past, winter hardiness was estimated by the fall dormancy (FD) rating, which indicates the variety’s tendency to stop growing in the fall (Figure 1); the lower the rating, the more dormant the variety. Some varieties are more capable of withstanding lower temperatures than their FD category indicates. The North American Alfalfa Improvement Conference (NAAIC; http://www.naaic.org) has developed a classification specifically for winter survival that is being included in the alfalfa leaflet published by the National Alfalfa and Forage Alliance (http://www. alfalfa.org/pdf/0809varietyLeaflet.pdf). For this sys- tem, varieties are rated from 1 to 6, where a rating of 1 indicates little or no winter damage and 6 indi- cates plant death. See Figure 2 for typical symptoms of freeze damage on alfalfa. Ratings are made after the first winter for spring seedings. At least two loca- tion years are required for the standard test. Because these tests are conducted in areas that have colder winters than most of New Mexico, few varieties in FD 7 or higher have been rated for winter survival, but that is changing. When using the winter sur- vival data, producers should keep in mind that these tests usually are conducted in the northern states for spring seedings—varieties that will not survive more severe winters up north might survive in New Mex- ico. Conversely, alfalfa sown in late summer to early autumn, which is recommended for New Mexico, may not survive if not sufficiently established before the onset of an early winter. Figure 1. The effect of alfalfa fall dormancy (FD) category six weeks after harvest in early November at Tucumcari, NM. The density of green leaves indicates the level of dormancy, with more dormant varieties having less green throughout the winter. FD 6 & 7 FD 4 & 5 FD 2 & 3 FD 8 & 9 Figure 2. Typical symptoms of freeze damage on alfalfa: Stems die, but regrowth occurs as temperatures permit. 1 Respectively, College Professor, Agricultural Science Center at Tucumcari; Assistant Professor, Agricultural Science Center at Artesia; and Extension Agronomy Specialist, Department of Extension Plant Sciences, all of New Mexico State University.