Winter Survival of Alfalfa

 

• Choose varieties with fall dormancy ratings of 1–3 for better winter survival.
• The better fall dormancy rating a variety has, the earlier the variety goes dormant in the fall, limiting total productivity
• Higher dormancy ratings (4) offer more productivity but require careful management.
• Refer to the Manitoba Seed Guide for fall dormancy and winter hardiness ratings.
• Select varieties with strong disease resistance (bacterial wilt, verticillium wilt, phytophthora root rot).

• Older stands (3+ years) face higher winter kill risk due to:
• Increased disease pressure
• Reduced fertility
• Excessive past cuttings

• Wheel traffic damage - Research shows traffic five days after cutting significantly reduces subsequent yields compared to two days.\Young stands generally survive better due to higher density and plant health.
• Avoid late-season cutting without adequate regrowth before freeze-up.
• Provide sufficient recovery time to replenish root reserves.

3. Fertility – Key Nutrients for Alfalfa

• Critical for root development, disease resistance, maturity, and nitrogen fixation.
• Supports overall plant health and stand persistence.

• Essential for growth and winter hardiness.
• Acts as a natural antifreeze, accumulating in plant cells during fall to protect against freezing.
• High-yielding alfalfa removes up to 45 lb of K per tonne of forage.
• Manitoba soils are generally high in K, but sandy soils and side slopes often require supplementation.

• Soil Testing: Regular testing ensures adequate nutrient levels for alfalfa’s high demands.
• Potassium Application: Apply in fall on low-K soils, especially before establishing new stands.
• Phosphorus Application: Maintain sufficient levels for strong root systems and disease resistance.
• Avoid nitrogen fertilization—alfalfa fixes its own nitrogen.

• Prevents winter kill and injury.
• Maximizes annual yields and stand longevity.
• Reduces weed pressure.
• Improves overall plant health and resilience.

• After cutting, alfalfa relies on root reserves for regrowth.
• Reserves are lowest 2–3 weeks post-cut; replenishment begins once sufficient leaf area develops.
• Recommended interval: 4–5 weeks between cuts, allowing root reserves to recover (typically at ~10% bloom).
• Cutting too early or too frequently depletes reserves, reducing stand longevity.

• Alfalfa needs 450–500 growing degree days between the last cut and freeze-up to restore root reserves.
• In Manitoba, this period spans roughly six weeks before the first killing frost:
• Northwestern Manitoba: Aug 15
• Red River Valley: begins Aug. 17–19
• South-central Manitoba: begins Aug. 23
• Avoid cutting during this period unless harvesting after a killing frost. Alfalfa is a perennial and constantly respiring and using stored energy even during the winter months. 

• Root Reserve Dynamics
• After cutting, plants use root reserves for regrowth.
• Reserves are lowest at 6–8 inches of regrowth and fully replenished at full bloom.
• If frost occurs before reserves recover, winter injury is likely.

• Cutting too late without regrowth risks severe winter kill.
• If taking a final cut:
• Wait until a killing frost (approx. -5°C) for minimal impact.
• Consider baled silage for faster dry-down.
• Allowing one cut to reach 50% bloom, especially the last cut, improves winter survival by maximizing root reserves.
• Leave strips of uncut alfalfa every 40-50 feet to trap snow and insulate crowns

• Use PEAQ (Predictive Equation for Alfalfa Quality) to optimize harvest timing.
• Balance economics with stand longevity—one poorly timed cut can reduce next year’s yield.
• Avoid wheel traffic immediately after cutting; research shows traffic five days post-cut significantly reduces yield compared to two days.

• Ideal snow cover: At least 4 inches to insulate soil and protect roots.
• Leave 6–10 inches of stubble after the last cut to trap snow.
• Alternating cut and uncut rows can help trap snow but may expose cut rows to injury.

• Begins approximately six weeks before the first killing frost (450 Growing Degree Days) (varies by region).
• Avoid cutting during this period to allow plants to:
• Accumulate root reserves.
• Enter dormancy gradually.
• Cutting too late depletes reserves, increasing winter kill risk.

• Alfalfa can survive soil temperatures down to -12°C if fully dormant.
• Warm spells (10°C for 3–4 days) can break dormancy, causing plants to use stored energy.
• Snow cover helps buffer temperature fluctuations and prevent dormancy breaks.

• Excess soil moisture can lead to ice sheets or frost heaving, exposing crowns and breaking roots.
• Clay soils are most susceptible.
• Avoid early wheel traffic on weakened or frost-heaved plants to prevent further damage.

1. Field Inspection
• Do not assume a greening field is healthy.
• Pull or dig several plants for closer examination.
2. Plant Examination
• Healthy plants: firm, white roots and crowns.
• Injured plants: roots appear gray, yellow, or brown, stringy rather than firm.
• Severely damaged plants often break off just below the soil surface when tugged.

• Year 1: ~25 plants per square foot.
• Year 2: Natural thinning to ~12 plants per square foot.
• Year 3+: Count stems, not plants.
• Optimal: 40–45 productive stems per square foot.
• Critical: Fewer than 30–35 stems indicates reduced yield potential and signals stand replacement.

• Protect stands from winter injury by:
• Maintaining balanced fertility.
• Allowing adequate regrowth between cuttings.
• Avoiding late-season harvest during the critical fall period.
• Healthy, pest-free stands with proper rest before freeze-up have the best chance of survival.