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Agronomy Talk: Alfalfa Winterkill

Published on Wednesday, March 27, 2019

The weather we experienced this winter has caused difficulties for everyone, but for farmers, the winter of 2018-2019 has led to uncertainty when in the hopes of a normal spring planting season.

Across a large swath of the Northern Corn Belt, especially those areas where alfalfa is an integral crop, a late, wet Autumn resulted in saturated soils going into the winter months. Compounding this situation were the late December rains (in some locals approaching 2.0 in.), an extremely cold January, persistent low temperatures throughout February and multiple heavy snow events in early March. As of March 13, 2019, when this article was written, Minnesota has experienced our second inch of cold rain.  And though the snow depth has gone from 26 in. to a level of 18 in. in the past 36 hours, the chances of injury to our alfalfa crop is higher than normal this year.

Alfalfa Breaks dormancy as soil temperatures rise in the spring.  

Wisconsin and Minnesota recording stations measured soil temperatures as low as 13°F due to the lack of snow earlier this winter. This defines a critical threshold for alfalfa; temperatures below 15°F can result in severe injury or winter kill of an alfalfa crop. Factors such as the age of the stand, the last crop cut height, and stresses due to disease or nutrient deficiencies tend to be multipliers for winterkill. The snow in late January 2019 provided some insulation to the crop, bringing the soil temperatures up to the mid-twenties. However, the amount of snow we received could lead to ice sheeting.

Because of the recent rains we have received, the significant snowmelt is causing ponding or "ice rinks" in the low areas of some fields. These "ice rinks" are thick (fully covering stubble) and if they persist long enough, the alfalfa underneath is subject to injury. The bigger issue is in areas where an entire field has been subjected to multiple wet snow falls that have settled and remained most of the winter. There is often ice underneath the snow and if the plant can’t adequately respirate, damage can occur. Problems should be reduced where the last cut stubble is able to poke through the icy snow cover.

Pay close attention to low spots in the field where ice may have ponded; these areas are at higher risk for winterkill. 

Dr. Dan Undersander, the Wisconsin Forage Team and the University of Wisconsin-Extension have developed an excellent resource for evaluating and managing alfalfa stands for winter injury. You can click here to read it now. 

For those farmers growing alfalfa who are looking to take their management to the next level, I encourage you to reference Alfalfa Management Guide from the American Society of Agronomy – it is the “A to Z” for alfalfa production.

Although it’s too early to evaluate or even observe alfalfa stands today, farmers need to be prepared, especially if your planned alfalfa production acres will need to be replanted. Fall seeded Beck’s Elite Alfalfa comes standard with our Escalate® yield enhancement system and is eligible for replant in the first spring after planting. If you have questions about assessing the health of your alfalfa stand, contact your local Beck’s representative.

Winterkilled alfalfa plants will be brown and have water soaked tissue. You can evaluate a plant by splitting the stalk and checking to see whether the stem is white or yellow and healthy or brown and discolored. If the growing point is dead, that plant will not recover.

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Mike Blaine

Mike Blaine

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