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Winterkilled Alfalfa?

By Nathan Drewitz and Jared Goplen et.al

Some areas of Minnesota have suffered significant alfalfa winterkill and winter injury this year. Current reports indicate some new seedings in central Minnesota and 3rd year and older stands in parts of southwestern and south-central Minnesota may have been hit the hardest. 

alfalfa

Figure 1. A 3-year old alfalfa stand in western MN
with significant winterkill. Photo: Jared Goplen

Much of the state experienced a relatively mild winter with some snow cover, which typically does not result in widespread winterkill, but snow cover and winter temperatures are only part of the equation. The issues that contributed to winterkill are still unknown, but some factors that may have played a role include last year’s drought stress, late fall cuttings, and warm weather in March and April that may have caused the alfalfa to break dormancy before periods of unseasonably cold weather, with air temperatures in the 20s.

Alfalfa producers should take this opportunity to scout existing alfalfa fields to determine if areas of fields have lower-than optimal stands and stem counts. Conducting a stand assessment this spring will help you make decisions related to stand management, cutting schedules, fertilizer applications, or stand replacement. In this article,  we'll review stand assessment principles and management as well as interseeding and replant options.

Evaluating Stands

Figure 2. A 1-year old alfalfa plant with a healthy, turgid crown with appearance similar to a potato.
Figure 2. A 1-year old alfalfa plant with a healthy, turgid crown
with appearance similar to a potato. Photo: Dave Nicolai

When making stand assessments this spring, make sure that the brown areas are actually dead. Some winter-injured plants may take longer to green up, even though they are still alive. It is important to not make decisions too early. 

It is also important to dig up a few plants to assess the crowns. Crown pith should be off-white and turgid, similar to a potato (Figure 2). If slow-growing plants are symmetrical with healthy-looking crowns, they will likely recover. Brown and decaying crowns will not recover. More details on evaluating alfalfa stands, including how many stems per square foot constitutes optimal yield potential, can be found here:

Next steps

Steps to decide whether to keep, terminate, or supplement the stand include:

  • Evaluate forage and animal inventory as well as your crop rotation and replant options. Some fields should be rotated out of alfalfa and into another crop, like corn. Other fields could be supplemented by interseeding additional forages. The correct decision will vary by operation. Resources to assist in crop management decisions can be found here:
  • Seeding into winterkilled areas. If alfalfa stands are thin or patchy and termination of the stand is not an option, there are a number of forage options to seed into winterkilled areas. The best option for your operation may depend on seed and equipment availability as well as how many additional years are desired out of the stand. Several recommended options are listed in Table 1. Supplemental forages are ideally seeded with a no-till drill in the affected areas, but often conventional drills will work if the ground is somewhat soft.
  • Consider seeding new stands this spring. This spring may provide a reasonable opportunity to seed new stands. Ensure herbicides used in the last year or two do not have crop rotational restrictions when seeding alfalfa. Resources related to stand establishment and fertility management can be found here:

Table 1. Several recommended forage options for interseeding into an existing alfalfa stand that has suffered winterkill or winter injury. The ideal option will vary by situation, including field condition, equipment and seed availability, and forage requirements.

Forage speciesIdeal useYield
potential
Forage
quality
Seeding
rate**
Seeding
depth
  T DM/ac lb/acinches
AlfalfaONLY if stand established last year.
NOT recommended for older stands due to
autotoxicity.
3-5ExcellentOpen areas: 12
Thin areas: 6-8
0.25-0.75
Small grains*Spotty or thin stands to be terminated after
this year. Likely best option if early-season
forage is top-priority.
1-3Moderate to
excellent
60-901.5-2
Sorghum-
sudangrass
Spotty or thin stands to be terminated after
this year when forage will be ensiled or if
interseeding delayed until June. Could be
seeded following 1st cutting alfalfa. If dry hay
needed, substitute sudangrass (easier to dry)
2-3Moderate20-301-2
Small grain followed
by sorghum-
sudangrass
Spotty or thin stands to be terminated after
this year when forage will be ensiled. Could
be used for dry hay if harvested at milk stage
Likely produces early and late-season tonnage.
3-5ModerateSee above1-2
Italian/ Annual
ryegrass
Spotty or thin stands with 1-2 years additional
production desired. Best when forage not
baled for dry hay. Good yields achieved by 2nd
or later cuttings.
3-5GoodOpen: 25-30
Thin: 5-10
0.25-0.75
Orchardgrass/
Tall fescue
Spotty or thin stands with 2 or more years
production desired. Excellent fit for dry hay.
Not ideal for emergency forage as most yield
is late-season in seeding year.
3-5Good5-100.25-0.75
Red cloverSpotty or thin stands with 1-2 years additional
production desired. Can be chopped
for haylage or baleage or used as dry hay,
but drying can be difficult. Red clover
will cause slobbers in horses.
3-5GoodOpen: 25-30
Thin: 5-10
0.25-0.75

*Small grains could include a variety grains, including oats, barley, wheat or spring triticale.
**Higher rates should be used if seed is broadcast.
Additional information: Seeding into standing alfalfa - University of Wisconsin

Failed seedings due to last year’s drought

The drought of 2021 caused poor establishment of some fields seeded last spring. Some of these fields have patchy stands with healthy plants. Patchy stands with  less than 55 stems per square foot will have reduced yields. It is possible to interseed these thin areas with alfalfa as long it is early enough, since stands that are 1 year old or less contain less autotoxic compounds. Including some red clover and/or perennial grasses in the mix can help mitigate the risk of autotoxicity.

Managing a winterkilled or injured alfalfa field adds unexpected costs and additional stress to the farming operation. Walking fields, evaluating forage needs, and planning is critical to making the best decision for your farm. The resources provided here should help you make the decision to keep or terminate the stand, seed supplemental forage, purchase additional forage, and/or seed new alfalfa. The right answer for you will depend on your specific field and operation.

Source : umn.edu

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