January 2007

Nebraska wheat fields coated in ice during recent storms have had little chance to recover with the recent cold front. While wheat is dormant in winter, its roots and crown continue to respire slowly, using oxygen and producing potentially toxic gases like carbon dioxide, ethylene and methanol.

When a solid layer of ice prevents the exchange of gases between the soil and the air above it, oxygen can't enter the soil and toxic gases can't escape, causing wheat to suffocate and die. Predicting when and how much damage ice sheets will cause is difficult. Generally, it takes three to four weeks of continuous ice cover to kill wheat. Any fractures in the ice coating, such as those due to thawing and refreezing, will allow respiration to begin again. Most damage would be expected to be confined to lower areas of a field which are more likely to have had saturated soils or been flooded.

A UNL NebGuide, Estimating Winter Wheat Grain Yields (G1429), discusses how to estimate winter survival as well as three methods for estimating potential yield in the spring. It provides the following method for determining if dormant wheat plants are alive and likely to resume active growth in the spring: 

1. Remove the top three inches of soil containing the plant crown (typically located 1 to 2 inches below the soil surface).
2. Thaw the samples and warm to room temperature.
3. Remove soil from the roots and wash with cool water to remove attached soil.
4. Cut off fall growth to within 1 inch above the crown and roots below the crown.
5. Rinse the crowns with cool water.
6. Place 10 wet crowns in a labeled plastic bag, inflate the bag and tie shut.
7. Place the bags in a lighted room, but not in direct sunlight.
8. Check the crowns in two days, rinse with cool water and re-inflate the bag.
9. After four days, the crown should show about two inches of new growth.
10. Plants that are not growing after six days should be considered dead when estimating survival.
11. Some plants may grow poorly and develop molds which live on dead or injured plants.

Remember, winterkill can be a localized event, so select sample areas carefully and don't try to extrapolate results too widely. Also, while some wheat plans may survive these icy conditions, their condition may be weakened. Further assessment in the spring may be helpful. If winterkill is a problem, visit with the appropriate agencies before destroying your wheat crop and carefully plan your alternatives.

Robert Klein
Extension Cropping Systems Specialist