Identifying Winter Kill in Alfalfa

If you think you may have some winter damage to your alfalfa fields because of excess water or icing of the fields, there are some guidelines you can follow to determine if you should renovate the field.

1. Dig up some plants from three or four locations in the field or the suspected area and inspect the root damage. Make sure you include the top six inches of the root.
2. Slice the root lengthwise and check for rot or discolouration inside the root.
3. If there is significant discolouration with 50% or more of the stems, then this stand will have poor winter survival for next year.
4.  If there are a number of dead plants, to determine if there is an economic stand left, count the viable stems in a square foot. If there are more than 40, it should provide a reasonable yield, if below 30 stems per square foot, consider replacing the stand. Another option is to count the number of plants per square foot. An ideal number is ten or more; if less than three, consider renovation. If there is winter injury, the alfalfa crop will be slow to recover, so leave that first harvest until mid-bloom to allow the damaged crown to recover and build reserves. An alfalfa plant can usually withstand 10-20 days of ice covering before toxic compounds build up and kill the plant. Before you start to tear up a field, do a complete survey.

Reference: Dan Undersander, University of Wisconsin Extension Service.