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Evaluate stands for optimum productivity.

Agronomy Bulletin 21 ─ Alfalfa Winter Injury

Frost injury to alfalfa taproot.

Situation

Each year, alfalfa stands risk being injured or killed by cold temperatures, ice sheets or heaving. Evaluating alfalfa stands for winter injury is crucial to crop rotation decisions.

Factors to Consider

  • Stand age
  • Soil pH
  • Variety
  • Cutting management
  • Soil moisture
  • Snow cover
  • Soil fertility
Winter injury to alfalfa crowns.

Action Plan

  1. Evaluate your alfalfa stand. Alfalfa plants with winter injury may be slow to green up, have asymmetrical shoot growth or root damage. The best way to diagnose winter injury is to dig up and examine 4 to 6 inches of roots. Healthy roots should be firm and white in color with little evidence of root rot. Winter-killed roots will have a gray, water-soaked appearance. If 50 percent or more of the root is blackened from root rot, the plant will likely die during spring greenup or later in the year.
  2. Determine yield potential. Estimate the potential yield of an alfalfa stand by counting the number of stems in a square-foot area. Once stem density is determined, use the following formula to calculate the yield potential of that stand: Yield (tons/acre) = (stems/ft 2 x 0.1) + 0.38.
  3. Use stem density to evalute alfalfa stands. Stem counts can be taken when the plants are 4 to 6 inches tall or taller. Count any stem that would be cut at harvest. The following chart provides guidelines on when to take action if stem density is reduced.
  4. Manage fields moderately affected by winter injury. Provide adequate fertility in order to reduce plant stress. Allow plants to mature longer before cutting and increase cutting height. Control weeds. Allow adequate regrowth to allow the plants to build up food reserves prior to winter, unless you intend to plow down the stand. Contact your Mycogen Seeds customer agronomist or trusted agronomic adviser to discuss cutting dates specific to your region.
  5. Evaluate options for fields severely affected by winter injury. If more than half of your stand was killed, you may want to consider replanting. Select varieties with good fall dormancy and winter hardiness scores.
Use stem density to evaluate alfalfa stands.

Summary

Stand evaluation is based on two factors: stand density and stand health. Accurate assessment of alfalfa stands for winter injury is an important and economically sound management practice to optimize productivity of the crop. For more information, contact your local Mycogen Seeds customer agronomist or trusted agronomic adviser.

Published on Thursday, August 15, 2013