Despite a mild winter with above average temperatures, winter 2019-2020 also saw several cold snaps. Due to the warm weather, there was also less snow ground cover than normal. Snow cover is an excellent insulator, which can help regulate temperature fluctuations and helps forages like alfalfa survive the winter. Older stands are more likely to winterkill, and so are stands with higher soil moisture in the fall. Cutting management also plays a role in winter hardiness of crops like alfalfa – shorter intervals between cuttings increase the risk of winter injury. Stands that are cut later in the fall are at a greater risk of winterkill, because they may not have the time to replenish their stored nutrients before the winter fully sets in. As the weather warms this March and April, it is a good idea to get out in the field and evaluate your forage stands for winter injury.
Uneven growth patterns and slow green up often indicate winter injury. To diagnose damage, you can examine the roots of the plants. To do this, walk diagonally across a field at regular intervals (every 4-5 paces), and dig up several plants 4-6 inches deep with a shovel. Examine the roots. The roots should be firm and the interior color should be white or cream colored. If the roots are soft and the interior yellow to brownish in color, it most likely was winter killed. For alfalfa, the majority of crown buds should be white or pink and firm throughout the bud. It is important to try to inspect as many plants as possible to determine the percentage of your field that was injured.
If your stands are moderately damaged, you can improve stand health and yields by allowing plants to mature longer before the first cutting. This will help them restore needed carbohydrates and continue to produce after the first cutting. If alfalfa was lost in a predominately grass stand, it could be managed for grass. If the alfalfa stand was only partially injured (25 to 50 %) interseeding with a quick germinating forage, such as orchardgrass or perennial ryegrass, could provide additional production. Remember that perennial ryegrass should be considered a short term option since it does not overwinter well in our climate. When dealing with winter injured stands, it is particularly important to adequately fertilize and to control for weed competition.
If your stand is over 50% killed, you might want to consider reseeding. A small grain/field pea mixture will be the best choice if the forage is needed in early/mid-summer. Corn silage will be the best choice for optimizing full season forage production, but at later dates (mid-June to early July), you may want to consider planting a summer annual. A few options include sorghum-sudangrass hybrids, sorghum sudangrass hybrids enhanced with the Brown Mid Rib gene, forage sorghum, or sudangrass. It is important to note that these crops need high temperatures to yield well and may not be the best choice if we are experiencing average to cool temperatures.
More information on managing winter injury in forages can be found in the factsheet: “Evaluating and Managing Forage Stands for Winter Injury” by NWCS, UVM Extension. https://www.uvm.edu/sites/default/files/media/managing-forage-winter-injury.pdf