TurfMD: Focusing on the moisture component of winter injury
As winter arrives for most of the northern U.S., turfgrass survival becomes a concern for parts of the country where injury has occurred in the past. Frigid temperatures play a role, but in most instances, the presence or lack of water is instrumental in winter damage to the turfgrass plant.
The freeze tolerance of a turfgrass plant, in large part, is governed by the water in the plant, specifically in and around the cells. When temperatures fall below freezing, cellular water begins to flow out of the cell into the intercellular spaces, causing a decrease in water potential outside the cell. Unfrozen water moves down the gradient created and out of the cell. The colder the temperatures, the more water travels down the gradient. Thus, the degree of cell dehydration is a function of freeze tolerance.
The type of freeze injury associated with water around the plant cells occurs on golf courses in the U.S. at relatively high freezing temperatures — 25 to 28 degrees F — during late winter/early spring. This type of freeze injury is technically described as “expansion-induced lysis” because it occurs during freeze/thaw cycles — ice that rapidly forms or collapses ruptures cell membranes.
Excessive water around the crown of the plant during these freeze/thaw cycles in late winter increases the severity of the damage. Removing water from around the plant is the primary method of reducing the likelihood of freeze injury.
Conversely, the lack or unavailability of water can cause winter injury primarily through desiccation. Winter desiccation is the death of turfgrass leaves or plants from winter drying. Desiccation most often occurs on open semi-dormant turf exposed to windy, low atmospheric humidity conditions. The two different types of winter desiccation are termed atmospheric and soil drought.
Atmospheric drought is normally associated with leaf tissue death. Favorable conditions for this type of desiccation are periods of sunny, windy conditions combined with low atmospheric humidity. The soil may have adequate soil moisture but is frozen or cold enough to increase the viscosity of the soil water to the point where uptake is severely restricted. Plants with restricted or shallow root systems like Poa annua are also sensitive to atmospheric drought. Desiccation symptoms appear similar to drought in that the leaves are brittle, dry and have a burned look.
Through the Midwest and eastern U.S., atmospheric drought is common. Although atmospheric desiccation can cause leaf death, it is not normally associated with crown or plant death. However, juvenile or succulent growing turf is especially susceptible to desiccation, and death may occur. Generally, the injury sustained with atmospheric desiccation recovers once the plant begins growth in early spring.
The second type of desiccation occurs under low atmospheric humidity and progressively droughty soil due to a lack of rain or snow. Desiccation resulting from soil drought conditions can cause plant death.
It’s fascinating how golf course superintendents in the western U.S. and northern Great Plains manage putting greens in the region. Applying enough water to greens to reduce the severity of desiccation without applying too much water, especially in later winter when the potential for excess water resulting in freeze injury is an important concern, is a tight balance that’s important for superintendents to master.
Temperature is an important factor in winter injury. Preparing or initiating practice to minimize winter injury must focus on the moisture (water) component as a means of reducing the potential for winter injury.
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