Due to the cold temperatures throughout Oklahoma this past December and January, some areas have experienced more winter-kill of bermudagrasses than in most previous years.
Winter-kill is a relative term, meaning that some portion of a plant or portion of a turfgrass stand has died during the winter. In this article we discuss winter-kill, what it is, how it occurs, and how to detect the amount of winter-kill so that planning can begin to effectively help the turfgrass stand recover in spring.
Winter-kill or tissue death during the winter can be from dehydration, true low temperature injury, or a combination of the two. For the purposes of this article, we discuss winter-kill associated with low temperature injury.
Cold temperatures can damage warm-season grasses, such as bermudagrass, through a series of days and nights with sustained below-freezing temperatures or a series of unseasonably warm days followed by a sudden extreme drop in temperature to well below freezing.
The grasses are especially vulnerable if they are types with poor winter tolerance and they are left unprotected by some type of cover, such as snow, straw, or geotextile tarp, and when soil temperatures are also below freezing.
Moderate to severe winter-kill of nonprotected, low-cut bermudagrass golf course putting greens is relatively common in Oklahoma. However, moderate to severe winter-kill of bermudagrass lawns is a fairly rare event. The amount of damage present on any bermudagrass stand varies greatly from year to year due to differences in weather and how a turfgrass stand has been managed.
Cases of winter-kill can be severe, such as when an entire turfgrass stand dies and no plant parts survive to regenerate the stand in spring. However, during most Oklahoma winters, only small portions of the upper aerial shoots system are killed. In the latter case, most crowns (growing points) located in the lower canopy, survive, leading to rapid greenup and turfgrass stand regeneration in the warm days of mid to late spring. It is not too early for homeowners to begin scouting for winter-kill damage.
Areas that are most likely to experience winter-kill are:
Areas with heavy foot or vehicle traffic.
North facing hills and slopes.
Areas with moderate to heavy shade.
Areas with poor drainage.
Areas with low soil fertility.
Areas with excessively high fertility or that received high rates of fertilizer late into the previous growing season.
Areas that are thin or that were planted much later in the growing season and did not completely cover prior to the first frost.
Areas with less cold tolerant bermudagrass cultivars.
Bermudagrasses known to have suffered greater amounts of winter-kill as assessed in multiple past research trials include “Arizona Common,” “NuMex Sahara,” “Sahara,” “Tifway” (also known as “419”). Most common bermudagrasses sold as “U-3” have demonstrated respectable levels of winter tolerance although there can be great variability in cold hardiness of types sold as “U-3.”