BROOKINGS – As fall approaches and temperatures decrease, it’s important to give some serious thought to whether that last late cutting is really worth the damage it might cause your alfalfa crop.

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 usually means late September - early October (check https://www.weather.gov/unr/aff for frost dates in your area).

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. It’s important to weigh the odds of an additional cutting against potential stand losses.

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:

1) For those looking to 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 sees during the growing season (ie: drought, insect pressure, disease, etc.), 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.

2) Another consideration is harvesting after the winterization period; technically, it should be safe to take a cutting after winterization. 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; however, dry years like this one may have created forage shortages and require producers to make tough decisions. For more information on alfalfa see the forage page on our website (extension.sdstate.edu).

Fall cover crop management

Cover crops can provide many benefits to growers including erosion control, nutrient cycling, increased water infiltration, weed control, additional forage, compaction relief, crop rotation diversification, etc. Regardless of the purpose of your cover crop, there is great benefit in allowing it to winterkill or over-winter on its own. 

Tilling up cover crops in the fall defeats many benefits of a cover crop as it opens the soil for erosion all winter long, provides no soil cover for weed control in the spring, and speeds up vegetation breakdown rather than allowing nutrient capture to slowly breakdown in standing plants to potentially be available for the next cash crop.

Although it may be tempting to terminate cover crops manually this fall, allowing them to winter kill or (depending on the specie) over-winter and be terminated in the spring provides great benefits to the health of the soil and gives your investment more power in the long run. Although we cannot always put a direct dollar amount on the benefits of cover crops to our soils, many research projects have shown yield bumps to cash crops as a result of cover crops.

In addition, for future cover crop related decisions, visit the Midwest Cover Crop Council website at https://mccc.msu.edu/ and click on the South Dakota cover crop selector tool. This online tool can assist you in choosing the cover crop specie or mixture that is right for your operation. Many other useful cover crop resources can be found at bit.ly/SDCoverCrops as well.