Experts’ Insights: Winter Injury

Winter injury becomes apparent in the spring when turfgrass comes out of winter dormancy. (Photo courtesy of John Kaminski)

Winter injury in turfgrass actually is a catchall term for several different causes, according to Karl Danneberger, Ph.D., professor of turfgrass at The Ohio State University. These causes can include freeze injury, winter desiccation, winter diseases and low-temperature kill.

It’s fairly easy to diagnose turf with winter injury as grasses come out of dormancy.

“You see them in the spring when everything else is greening up, and the turf is just whitish brown in color,” he says. “There’s not a whole lot you can do. Especially with warm-season grasses, you can try to cover it, warm it up and get it to grow.”

Danneberger says you can take a sample of turf that’s suspected to have winter injury, put it in a warm place and watch for symptoms as it grows out. Another way to diagnose winter injury is to check the viability of the crown.

“The crown is always hard to find, but if you squeeze it, and it’s still hard and white, that plant will come back even if the leaves are dead,” he says. “If it’s mushy or dark colored, that plant is probably dead.”

The best defense against winter injury is to have healthy warm-season turf.

“Adequate potassium levels — applied in fall — can help with reducing the likelihood of winter injury or helping bermudagrass get through the winter,” Danneberger says.

Covering also is an option for ultradwarf bermudagrass, especially in areas like Kentucky and Tennessee.

“If you cover bermudagrass in the fall and have it covered for a prolonged period of time, that plant is not going to harden off,” he says. “Keep that in mind when you uncover.”

Eric Reasor (Photo: PBI-Gordon)

PBI-Gordon Corp.

Eric Reasor
Southeast research scientist

Winter injury is the result of exposure to low temperatures, soil moisture, humidity, wind, shade and disease pressure. Symptoms can include thin and chlorotic turfgrass in irregular patches. On warm-season turfgrasses, symptoms will not appear until spring when noninjured turfgrass resumes growth and damaged areas do not. For preventive winter injury management, raise the mowing height, limit nitrogen fertilization in fall, promote soil drainage, limit compaction and ensure proper irrigation. On putting greens, a light sand topdressing can help reduce desiccation by protecting the crown and the turfgrass plant. Wetting agents and soil surfactants have been shown to help with winter injury. Warm-season turfgrasses are less tolerant to winter injury. Lower-mowing-height areas are more susceptible to winter injury. Covers can be effective, especially for warm-season putting greens grown in the Transition Zone.

Lane Tredway (Photo: Syngenta)

Syngenta

Lane Tredway
Technical services manager

There are a number of fungal diseases that could be considered forms of winter injury. Symptoms range from distinct patches or rings caused by take-all or spring dead spot to irregular areas of thin, weak turf. On bermudagrass putting greens, diseases like take-all root rot, spring dead spot, leaf spot and Pythium begin in late summer and may continue through the fall and winter. All warm-season grasses become more susceptible to disease from fall through spring. Ultradwarf bermudagrasses are at particularly high risk. Fewer diseases have been observed on zoysiagrass greens. Covers are an important tool in helping protect warm-season greens from cold-temperature injury. However, fungal diseases can become active under covers, especially if they are left on during the day and canopy temperatures underneath get to 50-60 degrees F.

Rick Fletcher (Photo: Nufarm)

Nufarm

Rick Fletcher
Technical services manager, turf and ornamentals

Winter injury can include cold-temperature fungal diseases, crown dehydration or desiccation, ice encasement damage and direct low-temperature kill. For cold-temperature and ice damage, the turf when moist often displays a flat, gray, water-soaked appearance that later dries into a compressed mat on the soil surface. For injury related to disease, consider a timed application of preventive fungicides. For desiccation-related injury, make changes in fall cultural practices and use protective covers and heavy sand topdressing. Fungal damage often recovers after spring green-up, whereas crown desiccation and anoxia may require overseeding, aeration or more vigorous measures. The three grasses commonly associated with winter injury are bentgrass, Poa annua and warm-season grasses grown in the upper end of the Transition Zone. Desiccation can be more pronounced on open areas lacking snow cover or elevated areas exposed to dry winds. Historically, the use of wind breaks, topdressing or turf covers can reduce this exposure.

Ian Rodriguez (Photo: Quali-Pro)

Quali-Pro

Ian Rodriguez
Technical services manager Control Solutions Inc.

Common signs of winter injury may include leaves or crowns that appear water-soaked or whitish, progressing to dark brown. Damaged turf can become matted and may produce a rotten smell. Preventive practices include fall fertility to ensure ample potassium is available and avoiding high rates of nitrogen. Raising mow heights in late summer and early fall helps the turf produce and store more carbohydrates, which increase cold tolerance. Avoid excessive thatch buildup, which leaves crowns exposed. Addressing drainage issues to prevent pooling or waterlogged soil after a thaw will help avoid crown hydration. If enough turf survives to avoid the need for replacement, provide good growing conditions once you’re confident the last of the cold has passed. Cold damage may be more severe on north-facing slopes and shaded areas. Compacted, poorly drained areas and green edges with a lip preventing good surface drainage also are more prone to cold injury. Covers can be helpful by providing an insulating airspace and preventing desiccation by wind.