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Issue No. 3, Article 7/April 13, 2007

Alfalfa After the Freeze

The following information is adapted from an article by Dr. Stephen Barnhart, Extension forage agronomist at Iowa State University. It can be found on their web site.

Cold temperatures have prompted questions on the degree of injury to alfalfa.

With spring seedings, new plants are very cold tolerant at emergence. At the second trifoliate leaf stage and older, the plant is more susceptible to cold temperatures and may be killed by 4 hours or more at 26°F or colder. If alfalfa was seeded with a companion crop, damage from exposure to cold temperature may be lessened as a result of protection provided by the cover crop, as temperature at the soil surface is warmer than at the top of the canopy. Wait a few days and then check the seedlings for signs of new growth or new tissue.

On established stands, a light frost will cause the top growth to look wilted. If there was only leaf damage and the stem tip is recovering, harvest as normally planned.

If a high percentage of the stem tips are permanently damaged on taller alfalfa, regrowth will occur from axillary buds below the damaged portion of the stem. Regrowth will also arise from crown buds. Waiting on this regrowth will delay the first harvest. However, if the decision is made to harvest the damaged stand now (earlier than normal), this will place an added stress on the plant, and recovery from harvest may be slower than normal.

With colder temperatures (teens to low 20s), buds and crowns of established plants can be seriously injured. In this case, it is best to wait 7 days or so to see if the cold caused any permanent damage. Dig random plants, split the taproot and crown, and observe any new shoot regrowth and the condition of the taproot. Healthy taproots and crowns are creamy white and firm, while freeze-damaged ones will be watery, brown, and soft. Pay particular attention to the condition of the upper 1 to 2 inches of the taproot.

There is no toxin produced in alfalfa as a result of a frost or freeze, but the bloat potential is increased substantially. If alfalfa is being grazed, allow the frosted plants to dry, then implement normal bloat preventative measures.--Jim Morrison

Author:
Jim Morrison

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