What Is Winter (Low Temperature) Kill?

Low temperature or cold weather damage to plants is a collective term used to describe several forms of injury.  Death by cold is the consequence of damage to cell membranes and the breakdown of metabolism, primarily that involving nucleic acids, proteins, and energy to the cell. The major types of low-temperature injury are caused by:
 
Crown Hydration. When turfgrass plants remain in or under constant moisture following a thaw, crowns of the plant can absorb (imbibe) high levels of water. If temperatures then decrease below freezing, ice crystals form within the plant cell walls (or intracellularly), rupturing them and, thereby, killing tissues. Intracellular freezing injury is common in spring when plants become de-acclimated, especially in low, poorly drained areas. Ice crystals can also form “extracellularly,” or in intercellular spaces between protoplasts and the cell wall. As ice crystals form, the vapor pressure becomes lower than in the protoplasts; thus, water is drawn from within the cells. The protoplasts then shrink in size and the concentration of dissolved substances, such as salt ions and organic acids, increase and become toxic via osmotic (or moisture stress) damage.


Direct Low-Temperature Exposure. When turfgrass plants are exposed directly to a rapid decrease in temperature below 23°F (5°C), the injury can be lethal, resulting in significant stand loss. Turfgrass leaves initially appear water soaked, turn whitish-brown in color, and then turn dark brown. Low-temperature exposure causes plants to lose control of membrane function, resulting in solute leakage and, eventually, a water-soaked appearance. Damaged turfgrass tends to mat over the soil surface and emit a distinct putrid (rotten) odor.