Assessing Winterkill In Alfalfa

This winter was one for the record books, but spring has finally sprung.  It is finally time to get out into your alfalfa fields and scout for winter injury.  Symptoms of winterkill will persist throughout the spring. With alfalfa being one of the most important crops in Minnesota it is imperative to see if your stands survived the winter. 

When assessing alfalfa stands for injury there are 2 areas to evaluate, roots and regrowth.  These 2 areas will help determine future yield potential for your alfalfa stand.  First, a stem count should be conducted to help determine the future yield potential. Stems counts are based on density per square foot. 

  • Greater than 55: good stand will not be limiting to production
  • Between 40 -55: reduction occurred, but will reach adequate production
  • Less than 40: poor stand and termination should be considered. 
Secondly, assessment of root and crown health is key to determine status of stand.  Roots are imperative part of the plant as that is how nutrients are taken up, so it is important to have healthy roots.  Roots that suffered winterkill will be gray in color and water can be easily squeezed out. The below picture from the University of Minnesota shows un-healthy to healthy roots (left to right).
  1. Dead plants, little to no roots will not survive
  2. Asymmetrical growth probably will not survive
  3. Winter injury, but there are new spring buds.  This plant has a good chance of making it, but will be delayed.
  4. Healthy plant, lots of growth and a solid root system. 

Assessing crown health for crown rot is important.  Visual signs of crown rot could be regrowth is delayed or yellow.  At that point the plant should be dug up and crown evaluated.  The crown could be brown or look dead in areas.  The brown color could extend down through the cortex of the root.  At this point the vigor of the plant will start to decline. 

After evaluating regrowth, root and crown health you have a decision to make.  Do you keep the current alfalfa stand, reseed within the current stand, or terminate the stand and plant a different crop?  Work with your Centra Sota Crop Advisor to help assist in those decisions. 

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