With cold snaps hitting most of the state this past week and silage and high moisture corn harvest well underway, there is no doubt fall is approaching. As row crops dry down and growers consider planting winter small grains and cover crops, now is the time to think about wrapping up alfalfa harvest and managing noxious weeds.
Late season alfalfa management
If you live in a part of the state that has received timely rains, you likely had a plentiful alfalfa hay harvest this year. However, producers in dry areas may be looking for just one more cutting to boost production. 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 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-degree frost. In South Dakota, this usually converts to late September or early October.
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. With the potential for an early frost this season, 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 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 sees during the growing season, the more apt it is to experience winter-kill after a late cutting. If a field was cut multiple times (four or more), 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 degrees 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 inches 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 (extension.sdstate.edu).
Fall noxious weed management
Another important thing to note this time of year is fall weed control. Often overlooked by harvest, late season control can be an important part of noxious weed management. Fall can be a great time to control weeds depending up on the previous season’s pest management.
If weeds were sprayed or clipped (set back in some way) previously this summer, and they have significant regrowth on them at this time, now is an excellent time to spray to achieve a good kill. If weeds were controlled earlier in the season, but regrowth is minimal or the plant is beginning to dry up, spraying may or may not be effective. If you spray these areas, be sure to use a chemical with residual effect so the plant will be controlled when it begins actively growing again.
If weeds were not controlled earlier and are now tall and quite mature, herbicide control at this time is likely not worth the time and investment. Since frost has already hit or is likely to occur soon for most of the state, remember that perennial plants have started to send nutrients to the roots to prepare for the winter. This means spraying perennials (musk thistle, leafy spurge, Canada thistle, sow thistle, etc.) very soon is imperative.