Agronomist: Too soon to worry about wheat winterkill
If you thought last weekend's temperature change was abrupt, imagine how your wheat crop feels. High temperatures throughout Kansas topped 60 degrees on December 13 and combined with a strong south wind to feel downright balmy. The next day, however, ambient temperature plummeted to 2 degrees with a major winter storm predicted by meteorologists.
Such dramatic variations in temperature have some farmers fearful of winterkill in their wheat. Jim Shroyer, agronomist with Kansas State University Research and Extension, said the majority of the Kansas wheat crop should be fairly well insulated from the bitter cold. Some isolated areas, however, could suffer, based on three factors that influence winterkill in wheat: Lack of soil moisture; the wheat plant's ability to adjust to temperature change, or "hardening"; and soil temperature at one-inch deep.
Shroyer said the 2009 winter wheat crop has likely hardened by now, enabling it to withstand extreme cold temperatures. Some areas of southwest Kansas -- specifically, Morton, Stevens and Hamilton counties, however -- are unusually dry and more prone to damage. The rest of the state should have enough soil moisture to protect the crop from frigid cold and wind. East of Hays, in fact, several inches of snow that fell December 15-16 provide a nice blanket of insulation from extreme cold temperatures, Shroyer says.
"As long as the soil is moist, it takes more energy to decrease the soil temperature," adds Brian Olson, northwest area agronomist with K-State Research and Extension. "Even if cold winds blow, I don't believe we are in any danger of winterkill in most of the state."
Soil temperatures one-inch deep -- commonly called the crown level -- most likely are still above the danger level.
"Where wheat plants have a good crown root system and two or more tillers, they will have better winter-hardiness. 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," Shroyer says. "A plant with one tiller is more vulnerable because it doesn't have the root development and ability to store carbohydrates."
Poor development of secondary roots may not be readily apparent unless the plants are pulled up and examined. Farmers can test for winterkill damage by digging up a few plants, transplanting them into pots and bringing them indoors to warm up. If the plants do not respond to the warmer conditions, they may have suffered winterkill injury.
"If plants are killed outright, they won't green up. But if they are only damaged, it might take them a while to die. They will green up and then slowly go 'backwards' and eventually die," Shroyer says.
There are enough nutrients in the crown to allow the plants to green up, but the winter injury causes vascular damage so that leftover nutrients cannot move, or root rot diseases move in and kill the plants. This slow death is probably the most common result of winter injury on wheat, he adds.