Hybrid bermudagrass (Cynodon dactylon × C. transvaalensis Burtt-Davy) is widely used in the warm, humid climatic regions for golf course putting greens. Traditional bermudagrass putting green cultivars such as ‘Tifdwarf’ and ‘Tifgreen’ can only tolerate long-term mowing heights 4.8 mm or greater, which produce inferior playing surfaces compared with creeping bentgrass (Agrostis stolonifera L.) greens (Beard, 1973; Foy, 1991). Dwarf-type bermudagrass cultivars are improved selections that tolerate long-term mowing heights of 3.2 mm or less and create fine textured golf greens comparable to creeping bentgrass (Hanna and Elsner, 1999; McCarty and Miller, 2002). Finer leaf textures and lower growth habits of dwarf-type cultivars are accredited to genetic and morphologic differences from ‘Tifdwarf’ and ‘Tifgreen’ bermudagrass cultivars (Burton, 1991; Capo-chichi et al., 2005; Hannah and Elsner, 1999).
Dwarf-type bermudagrass cultivars require intensive management as a result of poor shade tolerances, heavy thatch/mat accumulation, and disease susceptibility (Bunnell et al., 2005; White, 1998; White et al., 2004). These cultivars are also sensitive to herbicides and plant growth regulators used for managing higher-mowed bermudagrass cultivars such as ‘Tifway’ bermudagrass and creeping bentgrass golf greens (McCullough et al., 2006; Webster et al., 2003). Although dwarf-type bermudagrass cultivars tolerate close mowing, continuous golf green mowing heights of 3.2 mm may further exacerbate root growth of these low-growing grasses (White, 1998). Practices potentially injurious to dwarf-type bermudagrass roots such as preemergence herbicide applications may reduce turf vigor, inhibit recuperation from stress, and increase susceptibility to root pathogens (Beard, 1973; Engel and Ilnicki, 1969).
Preemergence herbicides are applied in the spring before soil temperatures become favorable for summer annual weed establishment (McCarty and Murphy, 1994). There is also potential for these herbicides to inhibit turfgrass root growth. Warm season grasses such as bermudagrass are vulnerable to root growth inhibition during spring root growth regeneration, which coincides with spring preemergence herbicide applications (Engel and Ilnicki, 1969).
Preemergence herbicides present in soil may reduce bermudagrass root growth from initial and residual herbicide activity. Root tip swelling from preemergence herbicides is characteristic of dinitroanilines (DNA), carbamates, and pyridines commonly used to control summer annual weeds (Vaughn and Lehnen, 1991). DNA herbicides, like pendimethalin, and pyridimine herbicides such as dithiopyr prevent spindle formation during mitosis by binding to tubuilin proteins necessary for polymerization into microtubules (Ross and Lembi, 1999). Pendimethalin effectively controls summer annual weeds but has shown to cause root growth abnormalities, including enlarged epidermal and cortical cells in ‘Tifgreen’ bermudagrass (Dernoeden et al., 1984; Finney, 1991). Dithiopyr applied 30 d after sod installation at 0.84 and 2.5 kg·ha−1 (a.i.) reduced ‘Tifway II’ bermudagrass rooting by 59% and 70% 60 d after treatment (Ferrell et al., 2003). Fall applications of dithiopyr at 0.56 kg·ha−1 (a.i.) inhibited ‘Tifway’ bermudagrass establishment up to 25% compared with the nontreated bermudagrass (Fagerness et al., 2002). Spring applications of dithiopyr have also shown to reduce root mass of ‘Penncross’ and ‘L-93’ creeping bentgrass putting greens (Dernoeden et al., 1993; Hart et al., 2004).
Bensulide is a thiocarbamate herbicide that disrupts root cell division, which effectively prevents establishment of annual bluegrass (Poa annua L.) and crabgrass species (Digitaria spp.) in higher-mowed bermudagrass cultivars (Johnson, 1976a; PBI Gordon Corp., 2004; Ross and Lembi, 1999). Bensulide applied at 14 and 28 kg·ha−1 (a.i.) on dormant ‘Tifgreen’ bermudagrass caused minimal to no foliar injury during spring transition and summer growth (Callahan, 1976). However, Bingham (1967) reported bensulide at 8.4 and 16.8 kg·ha−1 (a.i.) reduced root mass of ‘Tifgreen’ bermudagrass in greenhouse and field experiments. Bensulide also inhibited root growth of ‘Belair’ zoysiagrass (Fry et al., 1986), ‘Merion’ Kentucky bluegrass (Poa pratensis) (Engel and Callahan, 1967), and ‘L-93’ creeping bentgrass (Hart et al., 2004).
Oxadiazon is commonly applied for preemergence control of summer annual weeds in bermudagrass tees, fairways, and roughs (Bayer Environmental Sciences, 1998). Oxadiazon has residual activity of 8 to 15 weeks and inhibits the enzyme protoporphyrinogen oxidase causing loss of chlorophyll and eventually membrane leakage (Rao, 2000). On ‘Tifgreen’ bermudagrass, oxadiazon gave 100% control of Digitaria sanguinalis (L.) in 3 consecutive years (Callahan and High, 1990). Single and sequential applications of oxadiazon effectively control Kyllinga squamulata, annual bluegrass, and goosegrass (Eleusine indica L.) in higher-mowed bermudagrass turf (Johnson, 1976a; Bunnell et al., 2001; Toler et al., 2003). Oxadiazon is also used in combination with bensulide for preemergence weed control in bermudagrass turf. Dernoeden et al. (1984) noted oxadiazon at 1.7 kg·ha−1 (a.i.) with bensulide at 6.7 kg·ha−1 (a.i.) effectively controlled goosegrass and crabgrass (Digitaria spp.). Johnson (1980) noted the registered rate of oxadiazon, 4.5 kg·ha−1 (a.i.), did not reduce rooting of ‘Tifgreen’, ‘Tifdwarf’, or ‘Tifway’ bermudagrass in field experiments.
Napropamide is an amide herbicide that is registered for use on warm-season grasses, including bermudagrass (Gowan Company, 2004). Napropamide effectively controls summer annual weeds when applied at 2.2 and 4.4 kg·ha−1 (a.i.) (Dernoeden et al., 1984). However, Johnson (1980) noted napropamide at 3.4 and 10.2 kg·ha−1 reduced root mass of ‘Tifgreen’, ‘Tifdwarf’, and ‘Tifway’ bermudagrass.
Previous investigations have documented weed control and tolerance of traditional bermudagrass putting green cultivars to preemergence herbicides. However, dwarf-type bermudagrass is genetically and morphologically distinct from these varieties, which may increase sensitivity to herbicide applications (Burton, 1991; Capo-chichi et al., 2005; Hannah and Elsner, 1999). Because these cultivars are being widely planted for southern golf greens, research is warranted regarding safety to preemergence herbicide applications. The objective of these experiments was to investigate tolerance of dwarf bermudagrass golf greens to preemergence herbicide applications.
Bunnell, B.T., McCarty, L.B., Faust, J.E., Bridges, W.C. & Rajapakse, N.H. 2005 Quantifying a daily light integral requirement of a ‘TifEagle’ bermudagrass golf green Crop Sci. 45 569 574
Bunnell, B.T., McCarty, L.B., Lowe, D.B. & Higingbottom, J.K. 2001 Kyllinga squamulata control in bermudagrass turf Weed Tech. 15 310 314
Callahan, L.M. & High, J.W. 1990 Herbicide effects on bermudagrass lawn recovery and crabgrass control during spring root decline in the north-south transition zone J. Amer. Soc. Hort. Sci. 115 597 601
Capo-chichi, L.J.A., Goatley J.M. Jr, Philley, W., Krans, J., Davis, D., Kato, A. & van Santen, E. 2005 Dinitroaniline-induced genetic changes in bermudagrass Crop Sci. 45 1504 1510
Dernoeden, P.H., Christains, N.E., Krouse, J.M. & Roe, R.G. 1993 Creeping bentgrass rooting as influenced by dithiopyr Agron. J. 85 560 563
Dernoeden, P.H., Watschke, T.L. & Mathias, J.K. 1984 Goosegrass (Eleusine indica) control in turf in the transition zone Weed Sci. 32 4 7
Engel, R.E. & Ilnicki, R.D. 1969 Turf weeds and their control 240 282 Hanson A.A. & Juska F.V. Agronomy Monograph No. 14. Turfgrass American Society of Agronomy Madison, Wis
Fagerness, M.J., Yelverton, F.H. & Cooper, R.J. 2002 Bermudagrass [Cynodon dactylon (L.) Pers]. and zoysiagrass (Zoysia japonica) establishment after preemergence herbicide applications Weed Technol. 16 597 602
Ferrell, J.A., Murphy, T.R. & Vencill, W.K. 2003 Tolerance of winter-installed tall fescue (Festuca arundinacea) and hybrid bermudagrass (Cynodon transvaalensis × C. dactylon) sod to herbicides Weed Technol. 17 521 525
Fry, J.D., Dernoeden, P.H. & Murray, J.J. 1986 Establishment and rooting of zoysiagrass (Zoysia japonica) as affected by preemergence herbicides Weed Sci. 34 413 418
Hart, S.E., Lycan, D.W. & Murphy, J.A. 2004 Response of creeping bentgrass (Agrostis palustris Huds.) to fall applications of bensulide and dithiopyr Weed Technol. 18 1072 1076
Johnson, B.J. & Burns, R.E. 1985 Effect of soil pH, fertility, and herbicides on weed control and quality of bermudagrass (Cynodon dactylon) turf Weed Sci. 33 366 370
McCarty, L.B. & Miller, G.L. 2002 Managing bermudagrass turf: Selection, construction, cultural practices and pest management strategies Sleeping Bear Press Chelsea, Mich
McCarty, L.B. & Murphy, T. 1994 Control of turfgrass weeds 209 248 Turgeon A.J. Turf weeds and their control American Society of Agronomy Madison, Wis
McCullough, P.E., Liu, H., McCarty, L.B., Whitwell, T. & Toler, J.E. 2006 Bermudagrass putting green quality, growth, and nutrient partitioning influenced by nitrogen and trinexapac-ethyl Crop Sci. 46 1515 1525
Toler, J.E., McCarty, L.B. & Higingbottom, J.K. 2003 New options for annual bluegrass control in overseeded bermudagrass putting greens HortScience. 38 1232 1234
U.S. Golf Assoc. Green Section Staff 1993 USGA recommendations for a method of putting green construction. The 1993 revision USGA Green Section Record. 31 1 3
Webster, T.M., Bednarz, C.W. & Hanna, W.H. 2003 Sensitivity of triploid hybrid bermudagrass cultivars and common bermudagrass to postemergence herbicides Weed Technol. 17 509 515
White, R.H. 1998 Performance and management of new dwarf bermudagrasses. 1998 Semi-Annual Research Progress Report Texas Agriculture Experiment Station Texas A & M University 12
White, R.H., Hale, T.C., Chalmers, D.R., Hall, M.H., Thomas, J.C. & Menn, W.G. 2004 Cultural management of selected ultradwarf bermudagrass cultivars Online. Crop Management