Increasing urban expansion in the southwestern United States will result in higher demands for potable water. Limited annual precipitation causing periodic droughts and scarcity of surface water sets the priority on the allocation of potable water resources, and in turn limits the amount of water that can be used for nonhuman consumption. Turfgrass is considered a nonessential crop, as it does not provide food or nutrition for humans, therefore water that can be allocated for outdoor landscape irrigation is often restricted (City of Albuquerque, NM, 2000; State of California, 2009). Decreasing water supplies and current or impending water use restrictions throughout California and the southwestern United States demand serious and demonstrable efforts to conserve water among end users, especially on outdoor landscapes. These days, it is common for municipalities and water agencies to offer their customers monetary incentives for replacing turf with alternative, drought tolerant landscape plants or xeriscape materials (Metropolitan Water District of Southern California, 2013).
Tall fescue is the most common turfgrass species used on lawns in California and other regions in the southwestern United States because it retains green color throughout the year as long as supplemental irrigation is provided in the summer. Although one of the most drought tolerant (avoidant) cool-season turfgrass species because of deep rooting, tall fescue has a high water use rate (Fry and Huang, 2004). Richie et al. (2002) found that tall fescue required on average 80% crop evapotranspiration (ETcrop)/irrigation uniformity [where ETcrop = reference evapotranspiration (ETo) × crop coefficient (Kc)] to maintain acceptable turf in Riverside, CA. This translates into an annual irrigation requirement for tall fescue (including natural precipitation) of ≈46 and 36 inches in Riverside and Irvine, CA, respectively (Green, 2005).
Converting preexisting cool-season to warm-season turf swards is one strategy that can potentially save up to 20% or more water, based on differences in ET and drought tolerance (Huang and Fry, 1999; Meyer et al., 1985). Evapotranspiration rates reported in the literature for warm-season species range from 3 to 9 mm·d−1, while rates for cool-season turfgrasses typically range between 4 and 13 mm·d−1 (Kenna, 2008). In Texas, tall fescue can use up to 47% more water than zoysiagrass [Zoysia japonica (Kim, 1983)]. Transitioning from cool-season to warm-season turf species has helped golf course superintendents to reduce pest management and irrigation costs (Zuk and Fry, 2006).
Regardless of potential water savings, the conversion of an existing cool-season turf into warm-season turf can be problematic. Removing the existing sod and replacing sod of a warm-season species would be the ideal remedy, but this may be cost prohibitive for many homeowners and facilities. An alternative approach would be to seed or plug the warm-season species directly into the existing sward. In this case, competition among species needs to be either reduced or removed to allow the new turf to establish. Therefore, identification of methods to convert cool-season into warm-season stands would be helpful to those who wish to minimize turf maintenance costs in addition to reducing irrigation water use.
Interseeding a new species into a preexisting one is the simplest approach to replace cool-season species. Interseeding has minimal impact on activity and therefore it will not involve loss of revenue or aesthetics. However, competition for resources, including light, water, and nutrients, may prevent the interseeded species from germination and establishment. A maximum of 2% coverage was achieved in a study conducted in Indiana and Kentucky when zoysiagrass was interseeded into perennial ryegrass (Lolium perenne) without prior herbicide application (Patton et al., 2004). In another study, zoysiagrass cover reached only 9% when the existing perennial ryegrass sward was not treated with either an herbicide or a plant growth regulator (Zuk and Fry, 2005). Similarly, greater bermudagrass cover was reported if herbicides were applied to perennial ryegrass stands before seeding for species transition (Jellicorse et al., 2012; Williams and Burrus, 2004). Jellicorse et al. (2012) concluded that trying to establish bermudagrass on top of a perennial ryegrass sward is not effective unless the cool-season grass is eradicated first with an herbicide.
Several studies showed that applying glyphosate (Roundup Pro; Monsanto, St. Louis, MO), a nonselective herbicide, before seeding is the fastest and most efficient method to convert cool-season to warm-season turf areas (Fry et al., 2007; Jellicorse et al., 2012; Patton et al., 2004; Williams and Burrus, 2004; Zuk and Fry, 2005). Glyphosate applications immediately before seeding had little or no negative effect on germination and establishment (Egley and Williams, 1978; Hurto and Turgeon, 1978; Kaufman, 1978; Kollenkark and Daniel, 1978; Marshall and Naylor, 1984). However, some studies reported a significant loss in turfgrass quality during the transition period from perennial ryegrass to bermudagrass when glyphosate was applied before seeding (Jellicorse et al., 2012; Williams and Burrus, 2004). Similarly, Mittlesteadt et al. (2009) reported that turfgrass quality dropped below acceptable levels when glyphosate was used to remove a kentucky bluegrass (Poa pratensis) and perennial ryegrass mixture before bermudagrass seeding. Moreover, glyphosate application will impact aesthetic turf quality during conversion and could require closure of the treated area with a consequent loss of revenue. The cost of the herbicide and seeds might be prohibitive as well (Fry et al., 2007).
Scalping taller cut cool-season turf such as tall fescue before interseeding can help hasten warm-season turfgrass establishment. Zuk and Fry (2005) demonstrated that seeded zoysiagrass coverage at the end of a 3-year study was similar between scalping and glyphosate treatments. However, the plots had to be scalped three times per week at 0.6 cm for several weeks, until zoysiagrass tillering.
Previous studies investigating the efficacy of converting cool-season into warm-season turf stands included only one species at a time, without determining which warm-season species and establishment method might be the most suitable in replacing cool-season turfgrasses. Objectives of this study were to determine the speed and efficacy of five different warm-season turfgrasses established either from seeds or vegetatively from plugs in replacing a cool-season tall fescue sward using three different conversion methods (scalping, glyphosate, planting into existing turf) in inland and coastal climates of southern California.
BuseyP.2003St. augustinegrass Stenotaphrum secundatum (Walt.) Kuntze p. 309–330. In: M.D. Casler and R.R. Duncan (eds.). Biology breeding and genetics of turfgrasses. Wiley Hoboken NJ
City of Albuquerque NM2000Water budgets and planting restrictions. § 6-1-1-8. In: Code of ordinances. City of Albuquerque NM
FryJ.HuangB.2004Applied turfgrass science and physiology. Wiley Hoboken NJ
FryJ.TaylorR.WolfB.StunzD.ZukA.2007Development of a strip seeder for converting cool-season turf to seeded bermudagrassHortTechnology17363367
GreenR.L.2005Trends in golf course water use and regulation in California. In: Reports on topical issues. 1 May 2013. <http://agops.ucr.edu/turf/>
HurtoK.A.TurgeonA.J.1978Impact of thatch on residual activity of herbicides used in turfgrass renovation. 1977 Mtg. Weed Sci. Soc. Amer. p. 50. (Abstr.)
JellicorseW.R.RichardsonM.D.McCallaJ.H.KarcherD.E.PattonA.J.BoydJ.W.2012Seeded bermudagrass establishment in an overseeded perennial ryegrass stand as affected by transition herbicide and seeding dateAppl. Turfgrass Sci.doi:10.1094/ATS-2012-0721-01-RS
KaufmanJ.E.1978Turfgrass renovation with glyphosate. 1977 Mtg. Weed Sci. Soc. Amer. p. 50. (Abstr.)
KennaM.P.2008Turfgrass and the environment p. 65–90. In: J.B. Beard and M.P. Kenna (eds.). Water quality and quantity issues for turfgrasses in urban landscapes. Council Agr. Sci. Technol. Ames IA
KimK.S.1983Comparative evapotranspiration rates of thirteen turfgrasses grown under both non-limiting soil moisture and progressive water stress conditions. Texas A&M Univ. College Station MS Thesis
KollenkarkJ.DanielW.H.1978Glyphosate and its effect on seed germination. 1977 Mtg. Weed Sci. Soc. Amer. p. 6. (Abstr.)
Metropolitan Water District of Southern California2013Residential turf removal program. 1 May 2013. <http://socalwatersmart.com/index.php/qualifyingproducts/turfremoval>
MeyerJ.L.GibeaultV.A.YoungnerV.B.1985Irrigation of turfgrass below replacement of evapotranspiration as a means of water conservation: Determining crop coefficient of turfgrasses p. 357–364. In: F. Lemaire (ed.). Proc. 5th Intl. Turfgrass Res. Conf. Avignon France July 1985. INRA Publ. Versailles France
MittlesteadtT.L.GoatleyJ.M.AskewS.D.HenslerK.L.AskewW.L.2009Low-impact conversion of cool-season turf to ‘Patriot’ bermudagrassIntl. Turfgrass Soc. Res. J.1112051212
MorrisK.N.2002National Turfgrass Evaluation Program. 1997 National Bermudagrass Test. NTEP No. 02–7. U.S. Dept. Agr. Beltsville MD
MunshawG.C.WilliamsD.W.PowellA.J.JrDoughertyC.T.1998Growth and development of seeded versus vegetative bermudagrass varieties. Annu. Mtg. Abstr. Amer. Soc. Agron. Crop Sci. Soc. Amer. Soil Sci. Sci. Amer. p.136. (Abstr.)
PattonA.J.RichardsonM.D.KarcherD.E.BoydJ.W.ReicherZ.J.FryJ.D.McElroyJ.S.MunshawG.C.2008A guide to establishing seeded bermudagrass in the transition zoneAppl. Turfgrass Sci.doi:10.1094/ATS-2008-0122-01-MD
PattonA.J.RichardsonM.D.KarcherD.E.TrappeJ.20092007 NTEP seashore paspalum trial–Year 1 and 2 results. Arkansas Turfgrass Rpt. Arkansas Agr. Expt. Sta. Res. Serv. 568:60–63
RichieW.E.GreenR.L.KleinG.J.HartinJ.S.2002Tall fescue performance influenced by irrigation scheduling, cultivar, and mowing heightCrop Sci.4220112017
RimiF.MacolinoS.LeinauerB.ZiliottoU.2011Green up of seeded bermudagrass cultivars as influenced by spring scalpingHortTechnology21230235
SchiavonM.LeinauerB.SerenaM.SallenaveR.MaierB.2012Bermudagrass and seashore paspalum establishment from seed using differing irrigation methods and water qualitiesAgron. J.104706714
ShaverB.R.RichardsonM.D.McCallaJ.H.KarcherD.E.BergerP.J.2006Dormant seeding bermudagrass cultivars in a transition-zone environmentCrop Sci.4617871792
State of California2009Updated model water efficient landscape ordinance AB 1881. 1 May 2013. <http://www.water.ca.gov/wateruseefficiency/landscapeordinance>
WilliamsD.W.BurrusP.B.2004Conversion of perennial ryegrass to bermudagrass using seeded cultivars, herbicides, and plant growth regulatorsHortScience39398402
ZukA.FryJ.D.2006Inhibition of ‘Zenith’ zoysiagrass seedling emergence and growth of perennial ryegrass leaves and rootsHortScience41818821