Assess alfalfa stands for winterkill

If you haven’t done so already, get out and look closely at alfalfa fields. Even if plants are not dead, they may be injured and in need of attention. Look for slow or no green up and uneven, asymmetrical growth. Dig up some plants and inspect the crown and root. Split the crown and root open lengthwise.

Healthy roots are firm and white inside with little evidence of root rot. Winter-injured roots are gray and water-soaked or brown due to root rots. If the crown/root is soft and water-soaked, it is most likely dead. If over half of the root is damaged, the plant will likely die this year. If less than half of the root is injured, the plant will likely survive for another year.

A minimum of 3 to 4 alfalfa plants per square foot must be present for a stand to still have good production potential. However, stem density is a better determinant of yield potential since plants that are injured can still survive, but will have significantly reduced stem number and thus lower yield potential. Use the following guidelines (Cosgrove and Undersander, 2003) to aid in making a decision about keeping a winter-injured stand:

Alfalfa stem density per square foot

Action

> 55

Stem density not limiting yield

40 – 55

Stem density limiting yield potential

< 40

Stem density severely limiting yield potential, consider replacing the stand


Stands can be slow to recover when injured. So don’t be in too much of a hurry to tear it up until you’ve looked at some roots to determine health. If surviving plants are injured but have adequate stem density to maintain the stand, its probably best to plan to push the stand with annual forages (eg. Italian ryegrass or oats) to get the most out of it this year, then plan to terminate after this growing season. If most surviving plants look reasonably healthy (eg. losses were localized and/or ice-sheeting related) you might consider inter-seeding perennials to stretch the stand beyond this year.

Some options:

  • If the winter-injured alfalfa field was seeded less than one year ago (spring or late summer 2005), alfalfa can be re-seeded safely without autotoxicity concerns. Thin stands or bad spots can be inter-seeded with alfalfa. Italian or annual ryegrass, oats, and/or red clover can be added to thin alfalfa stands to increase short-term yields. Orchardgrass is a good perennial grass option for inter-seeding if you intend to try to keep the stand beyond this growing season. If dead areas are essentially bare, a conventional drill can probably do the job while the ground is still somewhat soft. If the damage is widespread, the stand should probably be torn up and is safe to re-seed to alfalfa this spring.
  • If the field was seeded more than one year ago (2004 or earlier), plant a different crop for a season before planting alfalfa again to avoid autotoxicity problems. If damage is spotty, inter-seed Italian ryegrass, a small grain, and/or red clover. Attempting to inter-seed alfalfa into older alfalfa stands is risky, and unlikely to be successful because of autotoxicity. If most of the stand is dead, corn for grain or silage may be best bet, but small grains and forage grasses can make good use of the N left behind by the alfalfa.
  • Thin and/or dead spots may be a good place to try Italian ryegrass. Seeded soon at 15-25 lb/ac, it would be on schedule to contribute significantly to the 2nd and later alfalfa cuttings with quality similar to alfalfa. Italian ryegrass can be challenging to cure to hay moisture, so plan to chop, make baleage, or graze. If seeding after complete alfalfa winterkill and/or stand termination, use 25-30 lb/ac of Italian ryegrass.
  • Plant new alfalfa stands in different fields. Make sure herbicides used last year are not a problem for seeding alfalfa and that soil pH is OK. Planting a small grain (<1.5 bu/ac) or Italian ryegrass (<5 lb/ac) nurse crop will provide some quicker tonnage in these fields. The nurse crop stubble may also help with snow catch and/or alfalfa crown insulation from cold temperatures.
  • Plant only alfalfa varieties with proven winter hardiness (WSI < 2.5), unless you’re planning for short-term stands (3 years or less). Consult the MN variety trial results (www.maes.umn.edu). Consider seeding a low-alkaloid reed canarygrass variety with new alfalfa seedings. As our winter snow cover continues to become less consistent, a sod-forming grass in mixture with alfalfa may provide some insulation and reduced heaving potential.
  • Plant a short-season forage crop to get some near-term forage with a goal of re-seeding alfalfa in early August. This might include oats or another small grain harvested for forage at the boot stage, mixed with peas and harvested at heading, or Italian ryegrass for silage or grazing. If the pH needs to be improved for an early August planting target, work lime into the soil now. On heavier soils, its safest to wait a full year before attempting to re-seed alfalfa; but on lighter soils, if moisture is adequate, August re-seeding should be safe.
  • For dry cows and young stock, sudangrass, sorghum-sudan, or pearl millet are good, multi-cut/graze options if planting gets delayed into early June. These crops can be seeded following a final spring harvest and termination of a winter-injured alfalfa stand. Foxtail millets can provide some moderate-quality forage in one cutting within 60 days after seeding, and can germinate in cooler soils than the sorghums or pearl millet. But if maximum total-season DM and energy yield are needed, corn silage is probably the best bet, even if planting as late as July 1.
  • Make maximum use of pasture. Good fertilization and rotational grazing management will increase pasture productivity. Look into cost-sharing opportunities to help increase your use and management of this low-cost feed source on your farm.
  • Add 40-50 lb N/ac/cutting or manure to boost yields of grass and legume-grass hay fields where the legumes are thin.
  • Do some shopping and see whether you can buy hay and/or other feeds to build a ration at a cost that still provides an acceptable return. Discuss ideas/experiences with others. Experiment with new ideas on a small scale where possible

Commonly Asked Questions About Alfalfa Winterkill

Can the low, dead spots be reseeded in an otherwise good stand?

Yes, but the success will depend upon the amount of winterkill in the area to be reseeded. Areas with 100 percent kill will reseed best. These areas can be no-tilled or lightly cultivated and seeded conventionally. It's sometimes a good idea to seed a little red clover with the alfalfa to insure forage establishment for the remaining life of the stand. If possible, avoid cutting these areas when the first crop harvest is made.

Can I interseed alfalfa into a thin stand of alfalfa?

No. It rarely is successful. To thicken a stand some producers have had good luck using red clover or a fast growing, cool season grass like perennial ryegrass. Sorghum-sudan grass has also been tried after a first crop harvest but the success of this practice depends largely upon adequate moisture conditions in June for germination and early growth.

How soon can I reseed this old, winterkilled stand back into alfalfa?

The research is pretty conclusive that waiting one year offers the least risk and greatest yield potential for the new stand. However, producers can seed a short season small grain or small grain/pea mixture this spring, harvest it for forage in late-June or early July, and reseed alfalfa around the first of August. This will result in the near equivalent of an established stand the following year. Quackgrass will need to controlled before reseeding in August.

Source: University of Minnesota Extension Service,Paul Peterson, Dan Martens, Dave Nicolai, and Krishhona Martinson