Alfalfa winter injury tends to come in question this time of year. Of course, we cannot predict with any certainty whether stands will show signs of injury, but there are a few factors that come into play when determining the likelihood of experiencing issues.

Although plant stress from drought conditions may weaken plant vigor, dry conditions can also have a positive effect on alfalfa winter hardiness. Alfalfa grown in well-drained areas tends to be less prone to winter injury, and low fall moisture levels can actually make winter kill less likely to occur. Dehydration of the plant is one of the primary factors required for alfalfa to tolerate winter temperatures. Stands that go into the winter months with lower soil moisture have less difficulty losing remaining plant moisture and are actually less likely to winter kill. In some areas, extreme drought may have caused more plant stress, but dry soils can also be helpful for plant dehydration.

Another important factor in alfalfa winter-kill is snow cover. A blanket of snow insulates soils; however, many parts of the state have had little to no snow cover for much of the winter. Temperature fluctuations in the soil tend to be minimized under snow cover. In fact, a 4-inch blanket of snow can result in a 10°F difference in soil temperatures. With no snow cover, soil temperatures are more susceptible to fluctuate faster and become more extreme. Leaving high stubble (~6 inches) after the last fall cut can help to catch snow, but also provide more insulation as well. Winterkill usually occurs if soil temperatures (2-4 inches deep) reach 12-13°F or lower.

Other factors that can effect winterkill include:

• Stand age — the older a stand gets, the more susceptible it is to winter injury.
• Soil fertility — stands with high fertility, especially adequate to high potassium levels, are less likely to experience winter injury than stands with inadequate fertility.
• Cutting schedule — Harvest frequency and the timing of the last fall cutting are important factors in stand winter hardiness. Intense, frequent cutting schedules tend to experience higher levels of winter stress. In addition, if a cutting was taken between Sept. 1 and mid-October, the stand is at higher risk for winter injury as plants may not have had enough time to replenish root carbohydrate reserves before a the first hard frost.
• Variety — varieties with excellent winter-hardiness ratings and high disease resistance markers tend to experience less winter injury.
• Soil pH — A soil pH of 6.6-7.5 is most ideal for alfalfa stands.
• Ice sheeting — Refroze snow/rain or winter rains can result in ice sheets that prevent air exchange to alfalfa crown roots. A healthy alfalfa stand can tolerate up to ~3 weeks of being covered by ice before dying.
• Heaving — repeating freeze/thaw cycles may result in an alfalfa field pushing a portion of the plant roots out of the ground, causing a heaved appearance. This may cause the crown and root to have exposure above the soil surface. Often, these exposed roots are cut during harvest, resulting in plant death.

When any remaining snow clears and temperatures rise, check for alfalfa winter injury. Should you have concerns, stem or plant counts should be taken across problem areas, and replant options can be considered based upon stem density threshold values. Search the SDSU Extension website for “alfalfa winter kill” for more information on this topic.

While we’re talking forages, another important spring considerations include pasture conditions and turnout timing. Feed reserves, timing, order of grazing, and pasture readiness are all important factors to consider before turning livestock out to graze. Of these things, pasture grazing readiness is often the most challenging decision-making factor to navigate. SDSU Extension has created a tool to help livestock growers understand the earliest date/range of spring turnout dates on their operation.

In order to use the Spring Turnout Map tool effectively, it’s ideal to outline your management principles and understand the species composition of your pastures. The tool allows the user to identify the average spring turnout and the range of possible turnout dates based upon location (over 40 years of growing degree day data) and compares them between two native cool-season grasses (Green Needlegrass and Western Wheatgrass), a native warm season grass (Blue Grama), and an introduced cool season grass (Crested Wheatgrass). You can access this free tool here.

This tool is meant to be used in conjunction with other management objectives and considerations. Historical turnout dates, biomass measurements, and close monitoring all remain important parts of effective range management. This tool simply adds another option for producers to take advantage of.