Written collaboratively by Tracey Erickson, former SDSU Extension Dairy Field Specialist and Sara Bauder, SDSU Extension Agronomy Field Specialist.
With a very challenging growing season and flooding across parts of South Dakota, many growers have struggled to harvest high quality forages in-between rains this summer. As summer winds down and fall approaches, it is time to start shutting down the alfalfa cutting equipment.
Alfalfa requires about 500 uninterrupted growing degree-days to winterize- this translates to roughly six weeks (depending on temperatures). Winterization typically begins about three weeks prior to the average date of the first 32°F frost. In South Dakota, this converts to late September - early October (Figure 1). Currently, our first fall frost outlook points to an average to late date. This is encouraging for many late-planted row crops, but alfalfa plants determine winterization based upon day length and cooling average daily temperatures, hence the first average frost guideline. Plants cut during the winterization period will attempt to put on regrowth; this takes away from their ability to accumulate root proteins and carbohydrates, which may cause poor stand and vigor the following spring.
To avoid winter injury next spring, it is best practice to leave the alfalfa in the field at this point. However, if you are in need of feed there are a few things to consider:
- For those looking to take a risk and cut late in an effort to extend a high quality forage crop, cutting during winterization is a risk to weigh. The more stress an alfalfa stand saw during the growing season, the more apt it is to experience winter-kill after a late cutting. If a field was cut multiple times (4+), it is more likely to have winter-kill issues than those that were cut fewer times. Younger, well-established, winter hardy/disease-resistant varieties may tolerate a late season cutting better than older stands or those that experienced heavy pest pressure over the growing season. Well-drained soils, adequate soil fertility, and insulating snow covers are also helpful in the way of avoiding alfalfa winter-kill. If the need for feed and price of hay outweigh the risk of stand loss next year, a late season cutting may be a risk some producers are willing to take.
- Another consideration is harvesting after the winterization period; technically, it should be safe to take a cutting at this time. This correlates to cutting after a killing freeze (23-24°F for several hours) after the plant is dormant. This is not as stressful to the plants as cutting during winterization, and can be a viable option for those who need feed and do not want to risk next year’s stand. However, remember that you should leave 5-6” of stubble, which leaves some plant tissue and helps to reduce erosion. Leaving soils bare over winter is a recipe for erosion and will likely result in less snow cover with little plant residue on the soil surface.
Alfalfa stands may last several years in various parts of South Dakota. Taking care of stands and skipping late fall cuttings can help prolong plant vigor and overall stand for years to come. For more information on alfalfa see the forage page on our website.