Although many people find some level of snow cover to be appealing for at least part of the winter, particularly during the holiday season, farmers and ranchers are often perfectly happy with little or no snow. One exception is winter wheat (and alfalfa) producers, who like to see at least some snow cover on their crops as it provides insulation against winterkill.

There is currently little or no snow covering winter wheat in much of South Dakota. This could lead to concern as to how the crop is faring. Most winter wheat varieties that are adapted to and grown in South Dakota can withstand temperatures at the crown of 5 – 10 degrees F when dormant. However, there are other factors in addition to temperatures that play a role in a plants ability to overwinter.

Ideal soil moisture for winter wheat survival is between 55% and 85%. When the soil moisture is lower than 55%, the plant tissues undergo excessive wrinkling, which increases their susceptibility to winterkill. Dry soil also cools off quicker, and can get colder than moist soil.

When the soil moisture is higher than 85%, the natural antifreeze characteristics of the plant cell fluids become diluted, also making the plants subject to winterkill.

In looking at the Automatic Weather Station data for the Oacoma station: the soil temperature at the 4” level dipped to 30 degrees F on several dates in early and mid-December, even with little or no snow cover, well above the 5-10 degrees considered critical. Even near Leola, which may be one of the colder locations in South Dakota, when the air temperature dropped to just below zero on December 9, 2011, the soil temperature at the 2” level only dropped to 23 degrees F.

The biggest risk for winterkill in winter wheat is almost certainly the fields or areas of fields that may suffer wind erosion. When the soil is blown away from the crown of the wheat plant, it can die from desiccation, and is much more prone to damage from cold than crowns that are well down in the soil. No-till cropping practices offer multiple benefits for winter survival of winter wheat; not only does the residue cover provide protection against wind erosion, it also provides insulation, minimizing the soil temperature variation as the air temperature rises during the day and drops during the night. Surface residue also keeps the soil more moist around the crowns and increases snow catch, which insulates the plants from low temperatures and provides moisture for spring growth.

As the winter progresses, it would be beneficial to monitor snow cover and soil temperatures, particularly if areas experience low air temperatures with little or no snow cover. The “2011 Winter Wheat Variety Yield Results” contains winter hardiness ratings for each of the winter wheat varieties tested in the 2011 Crop Performance Testing (CPT) plots.

For more information, review the section on Cold Acclimation and Vernalization in the University of Minnesota publication, MI-08421 “Winter Wheat in Minnesota” and  “Application of Physiology in Wheat Breeding” (Chapter 9 – Cold Tolerance).