Agriculture & Natural Resources
Assessing winter damage in alfalfa Source: Dr. Mark Sulc, OSU Forage Specialist; and Rory Lewandowski, Wayne Co. (OH) ANR Agent The winter of 2019 has seen a lot of variability, including large temperature swings, snow cover, no snow cover, rain, sleet and ice. One constant for most areas of the state is that soils have remained wet and/or saturated throughout the fall and winter period. Add all of this together and there is the potential for some significant winter injury. Forage growers should plan to spend time assessing winter damage and evaluating the health of their forage stands, particularly alfalfa stands. Assessment and stand health evaluation can begin once plants start to green up and produce two to four inches of growth. One of the primary concerns is the possibility of heaving damage. Tap rooted crops such as alfalfa and red clover are particularly susceptible to heaving damage. Conditions that increase the likelihood of heaving are wet, saturated clay soils with high shrink/swell potential, exposed to rapid freeze/thaw cycles. During these conditions, plants can be physically lifted (heaved) out of the soil exposing the crown of the plant to possible low temperature damage and/or physical injury from harvest operations. In severe cases, the plant can be heaved several inches or more out of the soil, breaking the taproot and killing the plant. Forage stand health evaluation includes stem counts and digging plant roots. Select random sites throughout the field and evaluate the plants in a one-foot square area. Check at least one site for every five to 10 acres. Increasing the number of random samples provides a more accurate assessment. Begin your stand health evaluation by counting the number of stems per crown. Do this evaluation in at least four to five random locations for every 20-25 acres. Stem density counts provide an indication of the yield potential of the stand. While you are counting stems, take note of where growth is taking place. Healthy plants have symmetrical, even growth on both sides of the crown. Damaged plants often have more stems on one side of the plant than the other. While plant and stem counts are useful, to get a true determination of stand health, crown and root tissue should be evaluated to provide an indication of how the plant will hold up to stresses in the coming growing season. This involves digging up plants and splitting the crowns/roots. Dig up five to six plants in those four to five random locations per 20-25 acres. Split the plant open. A healthy root will have a creamy white color and no to very little discoloration in the crown and taproot. These are the plants that have numerous shoots and the shoots are evenly distributed across the crown of the plant.