Golf course superintendents constantly battle annual bluegrass infestations in golf course putting greens, fairways, and roughs. The weapons used against annual bluegrass have included herbicides, growth regulators, management practices, and natural biologic controls (Dernoeden, 2000). Annual bluegrass is a severe and troublesome weed in established turfgrass stands because it reduces aesthetic appearance by producing unsightly seedheads at mowing heights as low as 6 mm, affects ball roll as a result of its upright growth habit that produces an uneven surface, and dies out quickly as a result of summer heat stress, leaving unsightly dead and bare patches (Bingham et al., 1969; Hall and Carey, 1992).
Many biotypes of annual bluegrass are true winter annuals that germinate in early fall, remain in a vegetative state throughout the winter, flower and become a prolific seed producer in the spring, and then succumb to heat stress as summer temperatures rise (Vargas and Turgeon, 2004). These biotypes typically have an upright growth habit and can predominate on golf courses in areas where moist, compact conditions are present (McCarty, 2005). A dormancy period followed by chilling is usually required to maximize germination of upright annual bluegrass seed (Lush, 1989; Wu et al., 1987). Beard et al. (1978) reported consistently high annual bluegrass germination rates (>80%) across a wide temperature range (7 to 29 °C), but determined that alternating day/night temperatures were necessary to achieve highest germination. Bogart (1972) found that annual bluegrass seedhead production occurred only after soil temperatures surpassed 15 °C. When seedheads are produced, a contaminated fairway can appear white in color with seeds easily tracked onto putting greens. The profuse seed production of annual bluegrass contributes to the soil seedbank in which dormant seed can remain viable for 6 years or longer (Roberts and Feast, 1973), ensuring its survival and proliferation.
A major concern is that annual bluegrass resistance to commonly used herbicides is increasing. There have been reports of annual bluegrass resistance to the triazine (Barros and Dyer, 1988; Darmency and Gasquez, 1981) and dinitroaniline (Isgrigg et al., 2002; Lowe et al., 2001) herbicide families after years of continued use. Hutto et al. (2004) noted 31 of 71 golf courses tested in Mississippi contained simazine-resistant annual bluegrass. Gressel and Segal (1978) warned that selection pressure exerted by exclusive use of a single herbicide family over time can contribute to resistance development.
Considerable research has focused on selectively controlling or suppressing annual bluegrass in cool-season turfgrasses with herbicides (Dernoeden and Turner, 1988; Johnson et al., 1989; Park et al., 2002) or plant growth regulators (Isgrigg et al., 1998; Johnson and Murphy, 1995; Neylan et al., 1997; Woosley et al., 2003); however, current peer-reviewed research on controlling annual bluegrass in dormant, nonoverseeded bermudagrass is lacking. Bispyribac-sodium is a recently introduced herbicide that targets the acetolactate synthase (ALS) enzyme and has been used to control annual bluegrass in creeping bentgrass fairways (Lycan and Hart, 2006; Park et al., 2002). Most other recently introduced herbicides registered for use on turfgrasses are in the sulfonylurea (SU) family and also inhibit ALS enzyme activity (Tranel and Wright, 2002).
Increases in annual bluegrass resistance to some commonly used herbicides and the recent introduction of several new herbicides that may offer new options for postemergent annual bluegrass control in turfgrasses prompted this investigation. The objectives of the research were to 1) evaluate annual bluegrass control in dormant, nonoverseeded bermudagrass turf using various herbicides and herbicide combinations, 2) examine effects of these herbicides on bermudagrass greenup the next spring, and 3) compare annual bluegrass control when herbicides are applied in December versus February.
Barros, M.D.C. & Dyer, T.A. 1988 Atrazine resistance in the grass Poa annua is due to a single base change in the chloroplast gene for D1 protein of photosystem II Theor. Appl. Genet. 75 610 616
Beard, J.B., Rieke, P.E., Turgeon, A.J. & Vargas J.M. Jr 1978 Annual bluegrass (Poa annua L.): Description, adaptation, culture, and control Agr. Expt. Sta. Res. Rpt. Mich. State Univ East Lansing
Bingham, S.W., Schmidt, R.E. & Curry, C.K. 1969 Annual bluegrass control in overseeded bermudagrass putting green turf Agron. J. 61 908 911
Bogart, J.E. 1972 Factors influencing competition of annual bluegrass (Poa annua L.) within established turfgrass communities Mich. State Univ East Lansing MS Thesis
Camacho, R.F. & Moshier, L.J. 1991 Absorption, translocation, and activity of CGA-136872, DPX-V9360, and glyphosate in rhizome johnsongrass (Sorghum halapense) Weed Sci. 39 354 357
Darmency, H. & Gasquez, J. 1981 Inheritance of triazine resistance in Poa annua: Consequences for population dynamics New Phytol. 89 487 493
Dernoeden, P.H. & Turner, T.R. 1988 Annual bluegrass control and tolerance of Kentucky bluegrass and perennial ryegrass to ethofumesate HortScience 23 565 567
Gressel, J. & Segal, L.A. 1978 The paucity of plants evolving genetic resistance to herbicides: Possible reasons and implications J. Theor. Biol. 75 349 371
Hall, J.C. & Carey, C.K. 1992 Control of annual bluegrass (Poa annua) in Kentucky bluegrass (Poa pretensis) turf with linuron Weed Technol. 6 852 857
Hutto, K.C., Coats, G.E. & Taylor, J.M. 2004 Annual bluegrass (Poa annua) resistance to simazine in Mississippi Weed Technol. 18 846 849
Isgrigg J. III, Yelverton, F.H., Brownie, C. & Warren L.S. Jr 2002 Dinitroaniline resistant annual bluegrass in North Carolina Weed Sci. 50 86 90
Isgrigg J. III, Yelverton, F.H. & Coble, H.D. 1998 The effect of paclobutrazol on the relative growth of annual bluegrass and creeping bentgrass Proc. South. Weed Sci. Soc. 51 248
Johnson, B.J. 1983 Response to ethofumesate of annual bluegrass (Poa annua) and overseeded bermudagrass (Cynodon dactylon) Weed Sci. 31 385 390
Johnson, B.J., Landry G.W. Jr & Karnok, K.J. 1989 Tolerance of bentgrass to amount, frequency and timing of ethofumesate applications HortScience 24 102 104
Johnson, B.J. & Murphy, T.R. 1995 Effect of paclobutrazol and flurprimidol on suppression of Poa annua spp. reptans in creeping bentgrass (Agrostis stolonifera) greens Weed Technol. 9 182 186
Lowe, D.B., Swire-Clark, G.A., McCarty, L.B., Whitwell, T. & Baird, W.V. 2001 Biology and molecular analysis of dinitroaniline-resistant Poa annua L. Intl Turfgrass Soc. Res. J. 9 1019 1025
Neylan, J., Dickson, D., Robinson, M. & Manning, P. 1997 Control of Poa annua in creeping bent (Agrostis stolonifera) greens Intl. Turf. Soc. Res. J. 8 1398 1406
Park, N., Suto, Y., Miura, Y., Nakatani, N., Iori, S. & Ogasawara, M. 2002 Annual bluegrass control (Poa annua L.) control in bentgrass (Agrostis palustris Huds.) green with sequential application of bispyribac-sodium combined with dinitroanalines Weed Biol. Manage. 2 159 162
Roberts, H.A. & Feast, P.A. 1973 Emergence and longevity of seeds of annual weeds in cultivated and undisturbed soil J. Appl. Ecol. 10 133 143
Woosley, P.B., Williams, D.W. & Powell A.J. Jr 2003 Postemergence control of annual bluegrass (Poa annua spp. reptans) in creeping bentgrass (Agrostis stolonifera) turf Weed Technol. 17 770 776
Wu, L., Till-Bottraud, I. & Torres, A. 1987 Genetic differentiation in temperature-enforced seed dormancy among golf course populations of Poa annua L New Phytol. 107 623 631