Wheat Versus Winterkill

February 11, 2014 06:05 PM

The New Year started with a meteorological monstrosity called a "polar vortex" that blasted extreme cold to much of the country. For the upper Midwest and Great Plains, that meant temperatures plummeting well into the -30s, but even southern geographies were affec­ted, with single-digit temperatures as far south as Memphis and wind chill warnings as far south as Baton Rouge, La.

For many crop farmers, the winter weather was a non-factor. But one crop in particular—winter wheat—is in the ground. Should farmers worry? Not necessarily, says Jim Shroyer,
Kansas State University (KSU) crop production specialist.

Dry soils without snow cover are more a cause for concern, he adds. Dry soils cool down much more quickly than moist soils, which accelerates the risk for damage.

"That doesn’t mean the whole field will be wiped out, but some plants will be lost," he says.
Shroyer and colleague Jeff Whitworth, KSU Extension entomologist, shared additional information regarding winter wheat hardiness and factors that affect winterkill in the December 2013 Extension Agronomy eUpdate.

How well has the wheat cold hardened? When temperatures gradually get colder through fall and early winter that helps wheat plants develop good winterhardiness. When temperatures remain unusually warm late into the fall (which can lead to excessive vegetative growth), then suddenly drop into the low teens, plants are less likely to have had time to cold harden properly and will be more susceptible to winterkill. This fall, temperatures generally fell gradually. It did not go from unusually warm with strong plant growth to bitterly cold in a single day. As a result, the wheat should be adequately cold hardened, in most cases.

How well developed is the root system? Good top growth of wheat doesn’t necessarily indicate good root development. Poor root development is a concern where conditions have been dry. When wheat plants have a good crown root system and two or more tillers, they will tolerate the cold better. If plants are poorly developed going into winter, with very few secondary roots and no tillers, they will be more susceptible to winterkill or desiccation, especially when soils remain dry.

Is the crown well protected by soil? If wheat is planted at the correct depth—about 1.5" to 2" deep—and in good contact with the soil, the crown should be well protected by the soil from the effects of cold temperatures.

What are the symptoms of winter survival problems? If plants are killed outright by cold temperatures, they won’t green up next spring. But if they are only damaged, it might take them a while to die. They will green up and then slowly go "backward" and eventually die. There are enough nutrients in the crown to allow the plants to green up, but the winter injury causes vascular damage so that the nutrients that are left cannot move, or root rot diseases move in and kill the plants. This slow death is probably the most common result of winter injury in wheat.

Direct cold injury is not the only source of winter injury. Under dry soil conditions, wheat plants can suffer from desiccation. This can kill or weaken plants and is actually a more common problem than direct cold injury.

You can e-mail Ben Potter at bpotter@farmjournal.com

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