Low Temperatures, Drying Winds and Wet Soils in Winter Damage Bermudagrass and Zoysiagrass Turfs
Tom Samples, John Sorochan, Jim Brosnan, Frank Hale, Brandon Horvath and Alan Windham
Many bermudagrass and zoysiagrass turfs throughout Tennessee have suffered damage as a result of low temperatures, strong winds and wet soils during winter. The injury, generally referred to as “winterkill”, may be visible in turfs maintained at high, medium or low mowing heights and fertility levels. Damage is often much greater on north-facing slopes and in swales that collect surface water than on south-facing slopes and in deep, well-drained soils. Newly established turfs, turfs growing in shade and compacted soil, closely mowed turfs and turfs with more than a ½-inch thatch layer may have also suffered severe damage this winter.
FREEZE DAMAGE
When considering direct low temperature or freeze damage of warm-season turfgrasses such as bermudagrass and zoysiagrass, the soil temperature is much more critical than that of the air. In sunken areas or soil surface depressions, entire plants may be killed as large ice crystals rapidly form in plant tissues when the “critical” low temperature is reached. Wet soils lead to hydrated tissue which is especially prone to freezing. On drier sites, only portions of individual plants may freeze, resulting in death of the particular tissue affected and thin, weak turf following winter dormancy.
DESICCATION
Many bermudagrass and zoysiagrass turfs have suffered winter desiccation injury. Damage is most severe in turfs exposed to strong, drying winds and prone to soil drought during winter dormancy. Turfs located at the crest of a slope may also be prone to winter desiccation injury.
SPRING RECOVERY
Spring recovery of damaged turfgrasses depends on the health of the crown and nodes on lateral stems. Healthy crowns and nodes produce roots, leaves and lateral stems. They are vitally important for plant survival. Although leaves, tillers and stolons (segmented, above-ground lateral stems) may have been killed this winter, plants may recover as nodes on viable rhizomes (subterranean stems) well below the soil surface produce new roots and leaves. Although they are not green, healthy rhizomes contain stored energy, are fleshy and firm, and usually snap when torn in two.Since much more energy is required to raise the temperature of water than that of dry soil, the temperature of wet soils in spring may be much lower than that of well-drained soils. Bermudagrass and zoysiagrass plants growing in wet soils and in soils facing north may be slow to recover from winter dormancy in spring.
DISEASES
Symptoms of spring dead spot and large patch, which also appear in spring, may resemble winterkill. Although the fungus (Ophiosphaerella sp.) associated with spring dead spot of bermudagrass is active in early fall, symptoms only appear the following spring. Bleached patches of dead turfgrasses from about 6 inches to 3 feet in diameter appear at greenup. Although bermudagrass plants generally grow slowly over the damaged spots during summer, the infected spots usually remain lower than surrounding plants, and weeds may invade. The fungus (Rhizoctonia sp.), causing large patch of bermudagrass and zoysiagrass, injure plants in both fall and spring. As the name suggests, large and circular or irregularly shaped patches develop as fungi infect plants. As the disease progresses, leaves of injured plants often easily detach from the crown. The disease may first develop in areas in which air flow is limited and leaves dry slowly after a rain or irrigation.
INSECTS
Several insects can injure bermudagrass and zoysiagrass from spring to fall. Some are much easier to detect than others. Young, legless larvae of hunting billbug (Sphenophorus venatua vestitus) feed internally in the crowns, rhizomes and stolons. Stolons that have been fed upon can be found in pieces with chewing damage evident at each end. Older and larger larvae feed on the entire root system so that sod will break apart when lifted. When tugged on, stems of turfgrasses under attack usually break near the crown, and frass (excrement) is visible inside. Patches of injured turf first turn yellow, then brown as plants die. Fall armyworms are the larval form of moths that migrate to Tennessee from Florida and the Gulf Coast in mid-summer. When populations are high, the larvae may devour plants down to the soil surface. Their feeding most often causes circular, bare areas of turf. Turfgrasses injured in the fall may not recover from winter dormancy the following spring.
WEEDS
Seeds of broadleaf weeds and weedy grasses occur naturally in soils and, depending on species and soil depth, may persist for 30 or more years. Summer annual weedy grasses including crabgrasses, goosegrass and foxtails often establish in weak turfs. Several summer annual broadleaf weed species can also become problematic. For example, prostrate spurge, prostrate knotweed and purslane establish from seed each spring and often produce seeds before dying in the fall. Preemergence herbicides are applied to control many of these weeds before seeds germinate and before bermudagrass and zoysiagrass resume growth in the spring. It may be necessary to delay inter-seeding, sprigging or sodding areas previously treated with a preemergence or postemergence herbicide. If freeze damage or winter desiccation is suspected, the use of preemergence or postemergence herbicides with soil residual activity is not recommended.
PREEMERGENCE HERBICIDE PERSISTENCE
The persistence of a particular preemergence herbicide in soils following application varies among products. For example, seeding should be delayed for at least 3 months and sprigging, for at least 5 months after applying Pendulum® 2G Granule Herbicide (pendimethalin). According to the Dimension® Ultra 40WP (dithiopyr) label, reseeding, overseeding or sprigging of treated areas within 3 months after a single application, or 4 months after a split-application program totaling more than 0.46 ounce product per 1,000 square feet, may inhibit the establishment of turfgrasses. Depending on application rate, the recommended time interval from the application of Barricade® 4FL (prodiamine) to overseeding/reseeding ranges from 4 to 7 months in Tennessee. Although bermudagrass and zoysiagrass sprigs may be planted immediately before or after applying Ronstar® G (oxadiazon), seeding bermudagrass and zoysiagrass should be delayed until 4 months after herbicide treatment. Ronstar® G is not registered for use on home lawns.
POSTEMERGENCE HERBICIDE PERSISTENCE
Several herbicides can be applied before spring greenup to control emerged weeds in bermudagrass and zoysiagrass. Again, persistence in soils following treatment varies among these herbicides. For example, Roundup Pro® (glyphosate) can be applied to dormant bermudagrass turf at the rate of 16 fluid ounces of product per acre to control or suppress many winter annual weeds. Turfgrasses can be planted as early as 7 days after applying the herbicide. Seed can be planted 3 to 4 weeks after applying Trimec® Southern (2,4-D + MCPP + dicamba) at recommended rates. Similarly, seed should be planted no sooner than 3 to 4 weeks after applying Momentum® FX2 (2,4-D + triclopyr + fluroxypyr). The application of Drive® 75DF (quinclorac) for postemergent weed control of crabgrasses and many other weed species before or after seeding bermudagrass or zoysiagrass will not significantly interfere with seed germination.
ENHANCING TURFGRASS RECOVERY
A thorough site evaluation is beneficial when developing a turfgrass recovery plan. Several questions require answers. For example:
- How severe and what is the extent of the turfgrass injury?2) Is most of the damage in shaded and sunken areas, and on soils sloping toward the north?3) Is the soil fertile and well drained?4) What was the cutting height and thatch layer thickness before winter dormancy?5) Will it be necessary to plant seed, sprigs, plugs or sod?
Fertilization and Liming
Bermudagrass and zoysiagrass most often require more nitrogen (N) than the soils in Tennessee can supply. Depending on the amount available for uptake from soils, bermudagrass and zoysiagrass may also respond favorably to supplemental phosphorus (P) and potassium (K) applications. Nitrogen is a basic component of chlorophyll, the compound that allows turfgrasses to use sunlight energy to produce sugars. Many amino acids also contain N. Phosphorus, applied as phosphate (P2O5), is a part of ATP and NADP in plants. Turfgrasses require ATP and NADP to change energy from one form to another. Although K does not become a part of any chemical in plants, it activates many enzymes that regulate growth. Potassium regulates the opening and closing of stomates and as a result, regulates the uptake of carbon dioxide from the atmosphere and the transpiration of water by turfgrasses. Potassium is also essential for protein and starch production. If granular fertilizers formulated for turfgrasses contain K, the K source is most likely potassium sulfate (K2SO4) or potassium chloride (KCl).
Bermudagrass and zoysiagrass generally require more N than P or K, and more K than P. For this reason, granular fertilizers with a 3-1-2, 4-1-3 or 2-1-1 N-P2O5-K2O ratio are often marketed for use in established bermudagrass and zoysiagrass turfs. Fertilizing and liming based on soil test results and recommendations help insure availability and the most efficient use of these essential nutrients.
Soil Drainage
The installation of perforated drainage pipe may help divert water and prevent turf damage in the future. In addition to trenching, the process often involves the installation of a geotextile fabric liner, followed by the addition of a coarse gravel layer on which the drainage pipe is elevated. The trench is then filled with an appropriate and porous aggregate such as pea gravel. If turf must be maintained at the surface of the trench, 6 or more inches of coarse sand is often used to “cap” the pea gravel and serve as the turfgrass rootzone.
Soil Aeration
Core aerification (coring) may be helpful if the soil is compacted and water is slow to move from the surface of the damaged turf through the thatch into the soil below. In addition to improving water infiltration, coring can improve the transfer of oxygen from the atmosphere into the turfgrass rootzone, and carbon dioxide from the soil to the atmosphere. In addition to ‘venting’ the soil, coring may raise the temperature of the soil surface.
Thatch / Organic Debris Removal
Debris and excess thatch can be lifted from damaged turfs using a mechanical dethatcher. Dethatching after coring will also break and scatter aeration cores. Thatch removal, like coring, may raise the temperature of the soil surface.
If it is necessary to plant seed, sprigs, plugs or sod, consider the variety’s low-temperature hardiness in addition to its color, texture and density. Researchers at Oklahoma State University investigating the freeze tolerance of 27 seeded bermudagrass varieties noted that freeze tolerance (in a freeze chamber) ranged from 22.5 oF to 16.3 oF and that ‘Riviera’, ‘Transcontinental’ and two experimental (SWI-1014 and CIS-CD6) varieties were significantly more cold hardy than ‘Arizona Common’. Previous research determined that the variety ‘Yukon’ also has significantly greater freeze tolerance than Arizona Common. Two recently released and vegetatively established bermudagrass varieties ‘Latitude 36’ and ‘Northbridge’ have excellent winter hardiness and are intended for use on golf course fairways, tee boxes and greens surrounds, and on intensively managed lawns and sports fields maintained at a cutting height of ~3/8 to 1¼ inches.
Winter hardiness of zoysiagrass varies among species. For example, Zoysia japonica varieties are generally more tolerant of sustained, low temperature extremes than Z. matrella varieties. ‘El Toro’,‘Meyer’ and ‘Palisades’ are vegetatively established varieties of Z. japonica, while ‘Cavalier’, ‘Diamond’, ‘Royal’, ‘Zeon’ and ‘Zorro’ are vegetatively established varieties of Z. matrella. ‘Compadre’ and ‘Zenith’ are Z. japonica varieties that can be established from seed.
REFERENCES
Anderson, J., C. Taliaferro, D. Martin, Y. Wu and M. Anderson. 2008. Research you can use. Bermudagrass Freeze Tolerance. Green Section Record. U.S.G.A. Pp. 6-9.
Anderson, J. A., C. M. Taliaferro, and D. L. Martin. 2002. Freeze tolerance of bermudagrasses: vegetatively propagated cultivars intended for fairway and putting green use, and seed-propagated cultivars. Crop Sci. 42:975-977.