By David Karki
South Dakota is unique for growing both types of wheat, spring and winter, in almost equal proportion. According to the U.S. Department of Agriculture National Agricultural Statistics Service (USDA NASS), 630,000 acres were planted to winter wheat in 2020 and 770,000 were planted to spring wheat. Although vegetative characteristics of these two wheat types are very similar, there are distinct differences between the two in terms of withstanding freezing temperatures and the requirement of colder temperatures to produce seeds.
Early fall winter wheat growth in in Codington County, South Dakota. Courtesy: David Karki
Winter Wheat Planting Time
As we move into the fall season, winter wheat growers always ask that one question: What is the best time to plant winter wheat? Winter wheat, if planted too early, can have disease and insect problems, which can persist to next season; if planted too late, it can get winter killed, which can result in uneven stands and severe yield impact. A multi-year study conducted in South Dakota showed that the optimum window to plant winter wheat ranged from Sept. 10 to Oct. 10, moving from south to north. Depending on the fall weather conditions, planting into October may not provide the plants for ideal fall growth (i.e. two-to-three tiller stage) before winter dormancy.
Seeding Rate and Variety Selection
Like with any crop, the best management decision starts with selecting the best available variety. While selecting a variety, it is critical to assess, not only the yield, but the regional adaptability within the state. Winter hardiness, lodging score and disease tolerance are some of the other important characteristics to consider while selecting a winter wheat variety. The South Dakota State University (SDSU) Crop Performance Testing program publishes yields and other important agronomic characteristics of wheat (and all major crops). The 2021 winter wheat data can be accessed on our Winter Wheat Variety Trial Results page.
The recommended seeding rate of winter wheat is 1.2 million pure live seeds (PLS), or about 28 live plants, per square foot.
Cold Acclimation
Newly emerged winter wheat seedlings in early fall are no different than spring wheat seedlings. In order to survive through cold winters with subfreezing temperatures, winter wheat has to be exposed to a series of cooler temperatures early in the growth stage, which is called ‘cold acclimation,’ or simply ‘hardening.’ The acclimation is possible due to the gradual decrease in daily temperatures in the fall after the wheat has emerged. Winter wheat plants adapt to rapidly decreasing temperatures in late fall or winter by lowering moisture content of the ‘crown’ (the growing point at the base of the shoot), decreasing the accumulation of carbohydrates and slowing down the overall growth process. This greatly helps with frost resistance and other winter conditions that a winter wheat plant has to go through during its life cycle. Cold acclimation generally starts when the temperature starts to fall below 50 degrees Fahrenheit.
Vernalization
Once cold acclimation is achieved, winter wheat requires to go through an extended period of below 40 degrees Fahrenheit temperatures to trigger its reproductive phase the next spring. The amount of time and range of temperatures required varies among varieties. Winter wheat varieties that are adapted to northern climates are usually more tolerant to extended subfreezing temperatures than those adapted to southern environments. The most winter-hardy varieties can withstand crown temperatures as low as -15 degrees Fahrenheit. Better winter survival is achieved when winter wheat is seeded into crop stubble (or no-till) and plants in the fall are at the three-to-four tiller stage before dormancy. Crop stubble helps hold snow throughout the winter and forms an insulating blanket, preventing plants from suffering by extremely low temperatures. Further, snow also plays a major role in providing the moisture needed the following spring.
Source : sdstate.edu