Many folks have sick-looking lawns this spring, me included. The lawns are still ailing from winter injury, especially in centipede and St. Augustine turf.
Most people have a few dead patches in the grass. A few unfortunate souls with St. Augustine have lost as much as half of their lawns.
Symptoms of winter kill can mimic disease problems. There will be irregularly shaped, dead, brown areas surrounded by green grass.
The grasses were first injured in December and early January, when we had cold weather for days on end. I remember thinking in December that it would be a welcome relief to just have a day when the temperature would get into the 50s.
Even worse were the frosts on March 27 and 28, after most lawns had greened up. If I remember correctly, I did not notice any dead patches in my yard until after the March 28 frost.
Dr. Gil Landry, a University of Georgia turfgrass specialist, reported that rapid temperature drops below 25 degrees may result in injury. Past research showed the following killing temperatures of plant tissue:
St. Augustine - 23 degrees
Carpet grass - 23 degrees
Bahia grass - 23 degrees
Bermuda grass - 19 degrees
Centipede - 11 degrees
Meyer Zoysia - 6 degrees
Turf grasses with rhizomes have the added insulation of the surrounding soil, and observations suggest there is significant variation among cultivars within some of these species. These numbers are far from absolute. Research also shows that more winter injury tends to occur in late winter as plant hardiness declines.
A number of environmental and management factors influence susceptibility to winter kill. They include:
General health: Weak and poorly rooted plants are more injury prone.
Soil drainage: Poorly drained areas have more injury.
Soil compaction: Compacted or fine-textured soils have more injury.
Mowing height: This is especially true with centipede. It should be mowed no higher than 11/2 inches.
Moisture: Turf stressed because of a lack of water will be more susceptible to winter kill.
Thatch: Excessive thatch increases winter injury.
Fertility: Excessive levels of nitrogen or improper levels of potassium and phosphorus and improper soil pH increase the chance of injury.
Other stresses: Chinch bug damage to St. Augustine, disease problems, grub worm or mole cricket damage play a role in winter kill.
If you have these dead patches in your lawn, you might want to rake as much of the dead foliage out as you can. Then you can either wait for the healthy grass to spread back in if the areas are very small, or you may want to plant new seed, sod or sprigs to hasten the filling in of the grass.
Sid Mullis is director of the University of Georgia Extension Service office for Richmond County. Call him at 821-2349, or send e-mail to firstname.lastname@example.org. The offices that serve Richmond and Columbia counties have a Web page at www.griffin.peachnet.edu/ga/columbia