As spring arrives each year, it is important to pay attention to your alfalfa fields as they begin to green up and grow. It is time to look for signs of “winterkill.” Winterkill is the generic term used to describe death of an alfalfa stand from fall through spring. However, the name is misleading because most stand death happens during the spring. There are many reasons why alfalfa dies out over the winter and in the early spring. Each of our agronomists sounded the same message around the importance of checking stands for winterkill each spring.

Minnesota update from Jeffrey Sorenson, Sales Agronomist: Last fall was a roller coaster ride for alfalfa stands. We were wet in early fall, but by the time we froze out in mid-December most soils were normal moisture and the alfalfa was in pretty good condition for winter survival. Most of the winter we had pretty good snow pack to insulate and protect the alfalfa during our January and February cold snaps; however, in between those cold snaps we also had some very warm temperatures which melted a lot of snow and, in some cases, the top inch or two of soil also melted. This may have caused some frost heaving of the crown. In this situation, we might think there is a good, healthy stand when it breaks dormancy. However, as the summer progresses the stand quality will continue to diminish. So, even if we think there is a good stand I would encourage everyone to dig a few plants up and examine the crown for any damage based on the winter and spring conditions we experienced.

Rotate or Leave it?

The decision to rotate a field can be hard to make with the irregular patterns of dead areas.The rule of thumb is rotate if the field falls below the average of 40 stems/square foot. We recommend using a larger size hoop than the simple 1-foot squares that are often available and used. A larger circle will give you a better representation. Be sure to sample several areas of the field until you feel comfortable with the numbers you are collecting.

Be sure to keep an eye on the stand quality throughout the summer as well. Additional mechanical damage from haying equipment to damaged crowns and taproots can cause additional loss throughout the summer, so keep that in mind.

If you have questions or would like help in this decision-making process, please contact your local Legend Seeds representative for guidance.

Examples of Winterkill Situations

Example of winterkill with crowns & taproot
Concerns: A few of the agronomists mentioned the crowns heaving or pushing out of the ground. See an example of this condition at right. When there is more than a half-inch of exposed root below the crown, then there is a very high probability that the taproot has been severed and the alfalfa plant will die shortly after greening up in the spring. Sometimes, the taproot gets severed deep enough that the plants will yield close to normal initially, but when cut for the first time the stand will never green up again.

Examples of winterkill from ponded water:

Example of winterkill from cold soil temperatures: