Freeze injury in wheat impacts management options
Since May 11 fields in southwestern North Dakota may have experienced three freeze events which may have damaged wheat growth and development. The most recent freeze occurring on Friday morning, May 25, could very well have severely damaged winter wheat that was in the boot stage to early stages of flowering. NDAWN on that day recorded low temperatures of 29oF at Beach and Mott and 30oF at Bowman and Dickinson. Some producers in low lying areas reported temperatures as low as 20 to 25oF. Tonight and tomorrow night, other areas of the state could experience freezing conditions. Whether freeze injury will cause damage to the wheat crop (winter or spring) depends on several factors including plant growth stage, plant moisture content, freeze type, duration of exposure and lowest temperature reached. Determining if a wheat crop has been injured and how severely it has been injured will help the producer decide if another fungicide or nutrient application is required or if the crop should be hayed or terminated. Freezing normally does not kill the entire plant and the roots may continue to absorb nitrates from the soil. With no grain to use the nitrates, the plant may accumulate nitrate in the forage.
Susceptibility to freezing temperatures steadily increases as maturity progresses through the flowering stage then decreases slightly as seed develops. All cereals are most sensitive to freeze injury during reproductive growth, beginning at jointing and continuing through the boot, heading and pollination stages. A light freeze (28-32oF) can severely injure cereals at these stages and greatly reduce grain yields.
Mechanical disruption of cells by ice crystals that enlarge both within and between cells will injure plants. Cereals grown under good growing conditions and high soil test nitrogen levels are more susceptible to freeze injury. Drought and other stresses tend to harden plants to cold.
The degree of injury is influenced by the duration of low temperatures as well as the lowest temperature reached. Prolonged exposure to a given temperature can cause much more severe damage than brief exposures. Topography can affect the extent of freeze injury. Also, the temperature that is recorded at a particular site may not reflect the actual temperature experienced by the plant in the field. These factors make it difficult to make general statements about the extent of damage caused by a freeze event. Extensive scouting of a field will help in defining severity and area affected by freezing.