Star-of-bethlehem is a perennial weed of managed turfgrass areas throughout the upper transition zone of the United States. Plants grow from bulbs that are 2 to 3 cm long, producing channeled leaves that are 3 to 8 mm in diameter. Leaves are characterized by their pale, whitish-green midrib (Goetz et al., 2003; McCarty et al., 2001). Bulbs produce lateral bulblets containing alkaloids poisonous to grazing animals (Facciola, 1990). In Tennessee, star-of-bethlehem begins to flower in early May and enters dormancy by early June (Main et al., 2004).
Star-of-bethlehem can invade open areas lacking plant competition (Haragan, 1991; Uva et al., 1997). Infestations have been reported on golf course fairways in Tennessee that have been associated with core aerification practices (Main et al., 2004). These star-of-bethlehem infestations negatively affect the aesthetic and functional quality of golf course fairways (Main et al., 2004).
Herbicides increasing the production of reactive oxygen species have shown activity against star-of-bethlehem. Bromoxynil is a member of the nitrile herbicide family that inhibits photosystem II by occupying the QB-binding domain on the D1 protein, inhibiting electron flow from photosystem II to photosystem I (Senseman, 2007). This action prevents the carotenoid system from quenching reactive oxidizing energy (Hess, 2000). Main et al. (2004) reported that applications of bromoxynil at 1.11 lb/acre provided 78% control by 21 d after treatment (DAT) and 80% control at 35 DAT. Applications of imazaquin at 0.50 lb/acre, metsulfuron at 0.031 lb/acre, and halosulfuron at 0.06 lb/acre did not provide effective control (<30%) at 35 DAT when applied alone; however, when applied in combination with bromoxynil at 1.11 lb/acre, each of those treatments provided >80% control at 35 DAT (Main et al., 2004).
Carfentrazone-ethyl inhibits protoporphyrinogen IX oxidase [protox (E.C. 126.96.36.199)] in the chlorophyll biosynthesis pathway, increasing the production of reactive oxygen species in susceptible plants (Senseman, 2007). Askew and Willis (2006) reported that carfentrazone-ethyl at 0.06 lb/acre provided 96% control of star-of-bethlehem 1 month after treatment; however, this exceeds the maximum labeled use rate of 0.031 lb/acre (FMC Professional Products, 2006a). Sequential applications of carfentrazone-ethyl at 0.031 lb/acre in combination with dicamba did not increase control compared with carfentrazone alone at 0.053 lb/acre (Askew and Willis, 2006). No tall fescue (Festuca arundinacea) injury was observed following either treatment.
Sulfentrazone is a protox inhibitor in the same chemical class as carfentrazone-ethyl that can be absorbed by the roots and shoots of treated plants (Senseman, 2007). Like carfentrazone, sulfentrazone is labeled for use on several warm- and cool-season turf species (FMC Professional Products, 2008a); however, its efficacy against star-of-bethlehem is not known.
Hydroxyphenylpyruvate dioxygenase [HPPD (EC 188.8.131.52)]-inhibiting herbicides prevent the carotenoid system from quenching reactive oxidizing energy; thus, carotenoid biosynthesis is disrupted, resulting in chlorophyll destruction, lipid oxidation, and membrane breakdown (Lee et al., 1997). These herbicides act by inhibiting the enzyme p-HPPD responsible for converting hydroxyphenylpyruvate to homogentisate, from which α-tocopherols and plastoquinones are synthesized (Hess, 2000; Lee et al., 1997). Two commonly used HPPD-inhibiting herbicides are mesotrione and topramezone. Mesotrione, a triketone herbicide, is registered for preemergence (PRE) and postemergence (POST) control of broadleaf and grassy weeds in turf (Syngenta Professional Products, 2008b). Topramezone is a pyrazolone herbicide registered for control of broadleaf and grassy weeds in corn [Zea mays (AMVAC, 2006b)]. Mesotrione and topramezone cause foliar bleaching of susceptible species (Mitchell et al., 2001); however, the efficacy of these herbicides against star-of-bethlehem has not been reported.
Mixtures of HPPD and photosystem II-inhibiting herbicides, like atrazine and bromoxynil, have been reported to provide increased weed control in various cropping systems. Armel et al. (2003, 2005) found that mixtures of mesotrione at 0.09 lb/acre and atrazine at 0.250 lb/acre provided an improved level of horsenettle (Solanum carolinense) and canada thistle (Cirsium arvense) control over mesotrione alone at 0.09 lb/acre. Johnson et al. (2002) reported improved ivy-leaf morningglory (Ipomoea hederacea) and yellow nutsedge (Cyperus esculentus) control with mixtures of mesotrione at 0.062 lb/acre and atrazine at 0.226 lb/acre. Abendroth et al. (2006) reported a synergistic effect in sunflower (Helianthus annuus) control when mixing mesotrione at 0.008, 0.016, and 0.031 lb/acre with atrazine at 0.250 lb/acre and bromoxynil at 0.06 lb/acre. Synergistic responses in the control of velvetleaf (Abutilon theophrasti) and palmer amaranth (Amaranthus palmeri) have been reported for mixtures of mesotrione with atrazine or bromoxynil (Abendroth et al., 2006) as well. In turfgrass, Willis et al. (2007) reported that mixtures of mesotrione with bromoxynil and atrazine provided an improved level of white clover (Trifolium repens) control compared with these materials applied alone. The efficacy of mixtures containing topramezone, another HPPD-inhibiting herbicide, with photosystem II-inhibiting herbicides like atrazine and bromoxynil has not been reported.
The objectives of this research were to determine if mesotrione and sulfentrazone provided greater control of star-of-bethlehem than the current commercial standards of carfentrazone-ethyl and bromoxynil, and to evaluate the efficacy of mesotrione and topramezone applied alone and in mixtures with photosystem II-inhibiting herbicides for control of star-of-bethlehem.
Abendroth, J.A., Martin, A.R. & Roeth, F.W. 2006 Plant response to combinations of mesotrione and photosystem II inhibitors Weed Technol. 20 267 274
Armel, G.R., Hall, G.J., Wilson, H.P. & Cullen, N. 2005 Mesotrione plus atrazine mixtures for control of canada thistle (Cirsium arvense) Weed Sci. 53 202 211
Armel, G.R., Wilson, H.P., Richardson, R.J. & Hines, T.E. 2003 Mestrione combinations for postemergence control of horsenettle (Solanum carolinense) in corn (Zea mays) Weed Technol. 17 65 72
Askew, S.D. & Willis, J.B. 2006 Carfentrazone for selective star-of-bethlehem control Proc. Northeastern Weed Sci. Soc. 60 95 (Abstr.).
Brosnan, J.T. & Breeden, G.K. 2009 Weed control programs during the spring and summer establishment of tall fescue and Kentucky bluegrass in the transition zone. 2009 Univ. Tennessee Turfgrass Weed Sci. Annu. Res. Rpt 84 98
Goetz, R.J., Jordan, T.N., McCain, J.W. & Su, N.Y. 2003 Indiana plants poisonous to livestock and pets: Star-of-bethlehem 18 May 2009 <http://www.vet.purdue.edu/depts/addl/toxic/plant39.htm>.
Johnson, B.C., Young, B.G. & Matthews, J.L. 2002 Effect of postemergence application rate and timing of mesotrione on corn (Zea mays) response and weed control Weed Technol. 16 414 420
Lee, D.L., Prisbylla, M.P., Cromartie, T.H., Dagarin, D.R., Howard, S.W., Provan, W.M., Ellis, M.K., Fraser, T. & Mutter, L.C. 1997 The discovery and structural requirements of inhibitors of p-hydroxyphenylpyruvate dioxygenase Weed Sci. 45 601 609
Main, C.L., Robinson, D.K., Teuton, T.C. & Mueller, T.C. 2004 Star-of-bethlehem (Ornithogalum umbellatum) control with postemergence herbicides in dormant bermudagrass (Cynodon dactylon) turf Weed Technol. 18 1117 1119
Mitchell, G., Bartlett, D.W., Fraser, T.E., Hawkins, T.R., Holt, D.C., Townson, J.K. & Wichert, R.A. 2001 Mesotrione: A new selective herbicide for use in maize Pest Manag. Sci. 57 120 128
Willis, J.B., Askew, S.D. & McElroy, J.S. 2007 Improved white clover control with mesotrione by mixing bromoxynil, carfentrazone, and simazine Weed Technol. 21 739 743
Yelverton, F.H., Hoyle, J.A., Gannon, T.W. & Warren, L.S. 2009 Plant counts, digital image analysis, and visual ratings for estimating weed control in turf: Are they correlated? Proc. Southern Weed Sci. Soc. (Abstr.) (In press).