Alfalfa Winterkill

Every year in some of our northern geography there are concerns about alfalfa winterkill. Sometimes, it is widespread and well anticipated, and other times it is a surprise. Many people talk about and try to predict the severity of winterkill, but waiting for spring to walk the field is the only way to know what your alfalfa stands look like and if any winterkill or winter injury is present, if at all.

Main Weather Conditions that Affect Alfalfa Survival

• Soil Conditions-ponded water and saturated soils make alfalfa go into anaerobic respiration which can build up lactic acid which can injure and kill plants
• Snow cover provides insulation from freeze-thaw cycles, or warm-ups followed by harsh cold, absence of snow cover and exposure to very cold temperatures allows soil temperatures to go below the survival limit of alfalfa

Management can also play a role

• Poor fertility – particularly low potassium puts alfalfa at risk as the roots cannot make enough “anti-freeze” that keeps cells from bursting
• Keep pH between 6.5 and 7 for optimum nutrient uptake
• Young stands are at less risk than old stands, especially young stands with more than adequate plant counts
• Alfalfa harvest in September is not recommended, cutting before September 1^st or after alfalfa goes dormant in October is recommended
• Alfalfa benefits from proper dormancy onset-consistent weather, not cutting during preparation period of September and having adequate fertility to prepare
• Plant a variety with a good winter survival and disease index score

Things to Look for When Evaluating Stands

1. Stands slow to green-up: If the entire field is not greening up, give it more time – even if the neighbor’s field is greening up. It likely needs more heat and time to come out of dormancy. Field variation and soil type affects green up or winterkill.
2. Check plant and root health: If green-up is spotty, check individual plants within spotty patches to see if they have signs of life.
   • Are there any buds developing, or any stems starting to grow?
   • Dig up a plant and look at the roots after splitting them open.
     • Healthy roots should be firm and white in color with little evidence of root rot.
     • Winter-killed roots will have a tan/brown color and the tissue will be stringy or pithy.
   • Did the roots break due to frost heaving?Live root on left and two dead on right.
     From: Assessing Alfalfa Stand Conditions in the Spring*
3. Evaluate the stand: Assess the percentage of the field that has dead patches and decide if planting another forage crop in those spots is better than rotating out of alfalfa. It is not recommended to reseed or overseed alfalfa into these areas as autotoxicity may prevent successful thickening of the alfalfa stand unless the alfalfa stand is less than one year old.
4. Assess forage needs: The tables below (from Forage Options Following Alfalfa Winterkill **) compare a few cropping options if forage is needed, and the field is rotated out of alfalfa.

April-May planting

May-June planting

Summary

There are many weather and environmental factors that affect winterkill. Where reasonable, implement known management practices that reduce the risk of winterkill. Once alfalfa is dormant, there is no real way to manage winterkill. For more information, contact your Legend Seeds team.