Posted January 3, 2014
MANHATTAN, Kan. Conditions have been unusually cold throughout Kansas during most of the start of winter. During the first blast of cold weather, there was little or no snow cover. This means in places soil temperatures have been colder than normal, leaving some producers wondering if these conditions will leave wheat fields susceptible to winter die-off?
According to a recent update from K-States agronomy department, there are several factors to consider when evaluating the outlook for winter survival of wheat:
How well has the wheat cold hardened?
Wheat plants are able to develop good winterhardiness when temperatures through fall and early winter gradually get colder. That was the case this fall meaning the wheat should be adequately cold hardened in most cases. Had temperatures remained unusually warm late into the fall then suddenly dropped into the low teens, plants would be less likely to properly cold harden and will have been more susceptible to winterkill.
How well developed is the root system?
Where wheat plants have a good crown root system and two or more tillers, they will tolerate 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. Poor development of secondary roots may not be readily apparent unless the plants are pulled up and examined.
How cold is the soil at the crown level?
Winterkill is possible if soil temperatures at the crown level fall into the single digits. If there is at least an inch of snow on the ground, the wheat will be protected and soil temperatures will usually remain above the critical level. Also, if the soil has good moisture, its possible that soil temperatures at the crown level may not reach the critical level even in the absence of snow cover. But if the soil is dry and there is no snow cover, there may be the potential for winterkill, especially on exposed slopes or terrace tops, depending on the condition of the plants.
Is the crown well protected by soil?
If wheat is planted at the correct depth, about 1.5 to 2 inches deep, and in good contact with the soil, the crown should be well protected by the soil from the effects of cold temperatures. If the wheat seed was planted too shallow, then the crown will have developed too close to the soil surface and will be more susceptible to winterkill.
Is there any insect or disease damage to the plants?
Plants may die during the winter not from winterkill, but from the direct effects of a fall infestation of Hessian fly. Many people are familiar with the lodging that Hessian fly can cause to wheat in the spring, but fewer recognize the damage that can be caused by fall infestations of Hessian fly. Wheat infested in the fall often remains green until the winter when the infested tillers gradually die.
Damage from winter grain mites, brown wheat mites, aphids, and crown and root rot diseases can also weaken wheat plants and make them somewhat more susceptible to injury from cold weather stress or desiccation.
Symptoms of winter survival problems
If plants are killed outright by cold temperatures, they wont green up next spring. But if they are only damaged, it might take them a while to die. There are enough nutrients in the crown to allow the plants to green up, but the winter injury causes vascular damage so nutrients that are left cannot move, or root rot diseases kill the plants. This slow death is probably the most common result of winter injury on wheat.
Direct cold injury is not the only source of winter injury. Under dry soil conditions, wheat plants may suffer from desiccation. This can kill or weaken plants, and is actually a more common problem than direct cold injury.
This weeks wheat scoop comes from a recent K-State Agronomy Department E-Update. To see the full version, including additional information on diagnosing winter-time problems in wheat, click here: https://webapp.agron.ksu.edu/agr_social/eu_article.throck?article_id=116