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Factors affecting winter wheat survival

By Anne Kirk, Manitoba Agriculture

Significant accumulation of snow throughout the winter will have helped to keep the soil temperature warm enough for winter wheat to overwinter. While good snow cover is important, climate is only one factor contributing to winter survival in winter cereals. There are several management factors that determine how winter hardy the winter wheat crop will be. Consider the following when evaluating the outlook for the winter survival of wheat:

How winter hardy was your crop?

Winter wheat plants acquire cold tolerance through the process of cold acclimation. Seeding date, depth, fall fertility and the weather in the fall all play a role in determining the level of cold hardiness your plants will have acquired and how winter hardy your crop will be.

  • Winter wheat should ideally be seeded from late August to mid-September. Seeding too early allows the crown to get too big prior to freeze up, which makes it more susceptible to freezing injury. Seeding too late can result in poorly established plants. Going into winter, plants should have a well-developed crown and about three leaves.
  • Shallow seeding is important. Deep seeding delays emergence and can result in weak, spindly plants that are at greater risk of winterkill. The crown develops about three-quarters of an inch to one inch below the surface – if seed is placed deeper, the plant must expend extra energy to move the crown up.
  • Seed-placed phosphorus fertilizer is important for root growth, winter survival of the crown and recovery from winter injury. Seed-placed nitrogen fertilizer increases the risk of winter injury.
  • A warm fall with early snow cover can result in poorly hardened plants that are susceptible to cold injury. An open fall with no snow cover until freeze up where soil temperatures slowly decline will result in plants that are better able to withstand cold temperatures.

Was snow cover adequate and uniform across the field?

Stubble should be tall enough to hold at least four inches of snow to keep the soil temperature at crown depth warm enough for the crop to overwinter. Snow cover may be lower on headlands where field traffic flattened stubble, or on hill tops where winds may have reduced snow cover. These are areas where winterkill can be more of an issue.

How did soil temperature fluctuate in your region?

Manitoba Agriculture monitors soil temperatures in stubble at the Crop Diversification Centres in Arborg, Carberry, Melita and Roblin. The data collected is made available to the University of Saskatchewan and Western Ag Professional Agronomy for their Winter Crop Survival Model, available at: wheatworkers.ca/wcsm.php. The model compares the cold tolerance of winter wheat varieties to the daily average soil temperature at crown depth, about one inch. These graphs identify winterkill days based on their model and give an early indication if there is a concern for winter injury or winterkill.

There are articles on both the Manitoba Agriculture and Manitoba Crop Alliance websites on assessing winter wheat survival for people eager to assess their crops. Regardless of how winter wheat survival looks, plant stands should be assessed once dormancy has broken and regrowth has started.

Information provided by Anne Kirk, cereal crops specialist with Manitoba Agriculture.