Figure 1. Winter kill in a Central South Dakota wheat field, Spring, 2015.
Photo by Ruth Beck.
Winter Kill Causes
Adverse winter weather can result in damage and even death to winter wheat in South Dakota.
In the fall, winter wheat goes through a hardening process, which allows it to withstand low temperatures during the winter. Periods of extreme cold or rapid fluctuations in temperatures can still result in damage to the winter wheat. Winter wheat plants are killed outright when their crowns die.
Snow cover on fields can insulate the wheat and mitigate cold and fluctuating temperatures. Lack of snow cover on fields increases the incidence of winterkill. Ice from rain could also result in problems, as oxygen supply to dormant plants may be cut off due to water puddling and ice formation. Additionally, in fields with low residue, multiple freeze/thaw cycles can cause soil to heave, which can physically push plants up and out of the ground.
Fields planted late in the fall can be more vulnerable to winterkill, as plants do not have time to develop and harden off sufficiently before winter. The degree of winter hardening changes with time, fluctuating temperatures, day length and other factors.
The key to protecting winter wheat is to keep the crown from dying. Sometimes cold weather will kill leaves, but if the crown survives, plants will recover.
- Look at winter hardiness ratings and yield data when purchasing seed. SDSU Extension’s Winter Wheat Variety Trial Results are an excellent local resource.
- The recommended planting window for winter wheat in South Dakota is September 10 to October 10. It is important that winter wheat is planted early enough to allow for good crown development and growth of 2-3 tillers prior to a hard freeze.
- Plant into protective cover (such as cover crops or upright stubble). Snow trapped by stubble insulates wheat seedlings against cold temperatures and improves winter survival. Residue cover can also mitigate spring temperature fluctuations that may result in winterkill.
2016-17 Winter Wheat Conditions
The fall of 2016 was conducive to timely planting and good fall growth of winter wheat. Snow cover across South Dakota during the winter protected much of the winter wheat crop. Warm temperatures in late February resulted in loss of the snow cover. Green wheat appeared from under the snow indicating that the wheat had suffered very little desiccation from winter winds. This could be a positive indication that much of the winter wheat made it through the winter in good condition. However, as the wheat loses its winter hardiness this spring, it can still be at risk if temperatures fluctuate and become cold for an extended period, especially in fields without upright residue to mitigate the fluctuations.
There may also be areas in fields, such as low areas or south facing slopes that are showing some winterkill. Some areas in central South Dakota received rainfall in December. It may be too early to assess damage, if any, that resulted from the “winter” rain.
The “Bag Test” can help producers evaluate winter wheat condition.
- Choose plants from different parts of the field.
- Brush away dry, loose soil from the row revealing green plant tissue.
- Dig out 4-6 plants with care using a spade, including up to three inches of soil containing plant crown and roots. Green tissue and white crowns are signs of healthy plants.
- Thaw at room temperature and wash off plants with cold water to remove soil.
- Cut leaves about 1.5” above crown and roots just below crown.
- Rinse crowns with cool tap water.
- Place crowns in plastic bag, inflate, secure shut, and place in lit room, but not direct sunlight.
- After 5-7 days, crowns should show ½” or more of new growth.
- Plants not growing after 6 days are assumed dead.
This test can be helpful in providing insight into the survival of your wheat sample. However, it is only a snapshot of what happened within a small sample size at the time of sampling. To truly understand how your field faired over the winter, you must wait until widespread dormancy breaks; this happens at soil temperatures of 39° F or above. If this has already occurred in your fields, it may be most beneficial to wait until the risk of a sustained hard freeze has passed and reassess your options.
Figure 2. Wheat with new growth after following the ‘bag test’ procedures.
Photo by Bob Fanning.
Keeping an eye on your crop from planting to harvest is crucial for success. For more information see the iGrow Wheat: Best Management Practices for Wheat Production or contact Ruth Beck or Sara Berg.