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Winter Wheat Needs Winter to Survive
USAgNet - 11/15/2016

Unlike its cousin spring wheat, winter wheat depends upon cold, winter weather for survival.

"For most of us wheat is wheat; however there is a distinct difference between spring and winter wheat, even though the vegetative characteristics of these two wheat types are very similar," said David Karki, SDSU Extension Agronomy Field Specialist.

Karki explained that unlike spring wheat, winter wheat can withstand freezing temperatures for extended periods of time during the early vegetative stage and actually requires exposure to freezing or near freezing temperatures to trigger reproductive stage.

"In other words, if winter wheat does not go through a period of cold temperatures, then it will not produce seed," Karki said.

In early fall, newly emerged winter wheat seedlings are no different than spring wheat seedlings. However, in order to survive cold winters with subfreezing temperatures, winter wheat has to be exposed to a series of cooler temperatures early in the growth stage.

Scientists refer to this weather condition as "cold acclimation" or simply "hardening."

"The acclimation is possible due to gradual decreases in daily temperatures in the fall after the wheat has emerged," Karki said.

Winter wheat plants adapt to rapidly decreasing temperatures in late fall or winter by lowering moisture content of the crown which is the growing point at the base of the shoot. This process decreases 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," Karki said.

Cold acclimation generally starts when the temperature starts to fall below 50 degrees Fahrenheit.

Vernalization is the other factor winter wheat depends upon to maximize yields.

"Once cold acclimation is achieved, winter wheat requires an extended period of temperatures below 40 degrees Fahrenheit to trigger its reproductive phase the following spring," Karki said.

He explained that 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 negative 15 degrees Fahrenheit.

Better winter survival is achieved when winter wheat is no-till seeded into crop stubble and plants in the fall are 3 to 4 tiller stage before going into winter.

"Crop stubble helps catch snow throughout the winter and form an insulating blanket, increasing significantly the chances of winter survival," Karki said.

Snow also plays a major role in providing the moisture needed the following spring.

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