Aquatic herbicides are used to ensure navigable waters, to improve human health by limiting mosquito habitat, and to provide an environment that is suitable for wildlife and human uses. There are a limited number of herbicides labeled for aquatic weed control, due in part to high registration costs relative to the limited market size. The recent development of resistance in certain aquatic weeds to herbicides such as fluridone and diquat further limits the choices available for effective weed control in lakes, ponds, and other water bodies (Koschnick et al., 2006; Michel et al., 2004). Thus, the need for additional effective aquatic herbicides is great. The herbicides tested in these experiments—bispyribac-sodium, quinclorac, topramezone, and trifloxysulfuron—are not currently registered for aquatic use. However, the efficacy, selectivity, and potential use rates of these herbicides are being evaluated under experimental use permits (EUPs) to determine whether they may be useful in aquatic systems.
Bispyribac-sodium is labeled for postemergence control of annual bluegrass (Poa annua), rough bluegrass (Poa trivialis), certain broadleaf weeds in certain turfgrasses, and for postemergence weed control in dry-seeded or water-seeded rice (Oryza sativa). Bispyribac-sodium is a pyrimidinylthiobenzoate and acts as an acetolactate synthase (ALS) inhibitor, which interferes with synthesis of the amino acids valine, leucine, and isoleucine (Senseman, 2007).
Quinclorac is currently labeled for postemergence weed control in rice and in grasses including tall fescue (Festuca arundinacea), kentucky bluegrass (Poa pratensis), and others. It is a substituted quinolinecarboxylic acid that acts as an auxin mimic and stimulates induction of 1- aminocyclopropane-1-carboxylic acid (ACC) synthase activity. Increased ACC synthase activity promotes ethylene biosynthesis, which triggers accumulation of abscisic acid (ABA) and causes epinasty, growth inhibition, and senescence in susceptible plants (Grossmann, 1998).
Topramezone is labeled for postemergence weed control in field corn, sweet corn, and popcorn (Zea mays). Topramezone rapidly degrades in plants to [3-(4,5-dihydro-5-hydroxy-isoxazol-3-yl)-4-methanesulfonyl-2-methyl-phenyl]-(5-hydroxy-1-methyl-1H-pyrazol-4-yl)-methanone (M670H02), a metabolite that inhibits the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD) (U.S. Environmental Protection Agency, 2005). This disrupts photosynthesis and carotenoid formation and damages the structural integrity of membranes (Pest Management Regulatory Agency, 2006).
Trifloxysulfuron-sodium is labeled for postemergence control of broadleaf, sedge, and grass weeds in warm season turfgrasses such as bermudagrass (Cynodon dactylon × C. transvaalensis) and zoysiagrass (Zoysia japonica). It is also used to control the shoreline weed torpedograss (Panicum repens) in bermudagrass turf (Stephenson et al., 2006). Trifloxysulfuron-sodium is a sulfonylurea derivative of trifloxysulfuron in the pyrimidinylsulfonylurea class of herbicides (Wood, 2009). Similar to bispyribac-sodium, trifloxysulfuron is an ALS inhibitor and interferes with biosynthesis of the essential amino acids valine, leucine, and isoleucine (Senseman, 2007).
Terrestrial use rates for bispyribac-sodium, topramezone, and trifloxysulfuron are relatively low (e.g., measured in ounces per acre) and aquatic use rates for these herbicides would likely be less than 100 ppb. On the other hand, terrestrial use rates for quinclorac are higher (e.g., up to 0.75 lb/acre a.i.), and this herbicide is being evaluated for aquatic use at concentrations of up to 300 ppb.
The U.S. Environmental Protection Agency (USEPA) regulates the level of herbicide allowable in irrigation water if that water will be applied to food crops (U.S. Environmental Protection Agency, 2003). However, no regulations are in place if this same water is used to irrigate ornamental plants. This is important because many ornamentals are high-value crops and accidental injury of these valuable plants with herbicide-treated irrigation water is highly undesirable. Previous research has reported the effects of other aquatic herbicides on turfgrasses, crops, and ornamental species (Andrew et al., 2003; Gettys and Haller, 2009; Koschnick et al., 2005a, 2005b; Mudge et al., 2007; Mudge and Haller, 2009), but little is known regarding the effects of bispyribac-sodium, quinclorac, topramezone, and trifloxysulfuron on foliage plants. Homeowners living adjacent to canals and lakes often use water from these sources to irrigate turf, bedding plants, foliage species, and other ornamental plants. Therefore, a study of the possible phytotoxicity of these herbicides is important to determine appropriate irrigation restrictions on turf, ornamentals, and foliage plants. The objective of these experiments was to evaluate the effects of these herbicides on selected foliage plants to provide further information for potential irrigation restrictions that will limit damage to foliage plants in landscapes that are irrigated with herbicide-treated water.
Andrew, W., Haller, W.T. & Shilling, D.G. 2003 Response of st. augustinegrass to fluridone in irrigation water J. Aquat. Plant Mgt. 41 61 63
Gettys, L.A. & Haller, W.T. 2009 Tolerance of selected bedding plants to four herbicides in irrigation water HortTechnology 19 546 552
Koschnick, T.J., Haller, W.T. & Fox, A.M. 2005a Turf and ornamental plant tolerances to endothall in irrigation water. II. Turf species HortTechnology 15 324 329
Koschnick, T.J., Haller, W.T. & Glasgow, L. 2006 Documentation of landoltia (Landoltia punctata) resistance to diquat Weed Sci. 54 615 619
Koschnick, T.J., Haller, W.T. & MacDonald, G.E. 2005b Turf and ornamental plant tolerances to endothall in irrigation water. I. Ornamental species HortTechnology 15 318 323
Michel, A., Arias, R.S., Scheffler, B.E., Duke, S.O., Netherland, M. & Dayan, F.E. 2004 Somatic mutation-mediated evolution of herbicide resistance in the nonindigenous invasive plant hydrilla (Hydrilla verticillata) Mol. Ecol. 13 3229 3237
Mudge, C.R. & Haller, W.T. 2009 Ornamental and row crop susceptibility to flumioxazin in overhead irrigation water Weed Technol. 23 89 93
Mudge, C.R., Koschnick, T.J. & Haller, W.T. 2007 Ornamental plant susceptibility to diquat in overhead irrigation water J. Aquat. Plant Mgt. 45 40 43
Pest Management Regulatory Agency 2006 REG2006-09: Topramezone 18 Aug. 2008 <http://www.pmra-arla.gc.ca/english/pdf/reg/reg2006-09-e.pdf>.
Stephenson D.O. Jr, Brecke, B.J. & Unruh, J.B. 2006 Control of torpedograss (Panicum repens) with trifloxysulfuron-sodium in bermudagrass (Cynodon dactylon × Cynodon transvaalensis) turf Weed Technol. 20 351 355
U.S. Environmental Protection Agency 2003 Pesticides: Regulating pesticides – pesticide tolerances 18 Aug. 2008 <http://www.epa.gov/pesticides/regulating/tolerances.htm>.
U.S. Environmental Protection Agency 2005 Pesticide fact sheet: Topramezone 18 Aug. 2008 <http://www.epa.gov/opprd001/factsheets/topramezone.pdf>.
Wood, A. 2009 Compendium of pesticide common names. Trifloxysulfuron-sodium 18 Aug. 2008 <http://www.alanwood.net/pesticides/derivatives/trifloxysulfuron-sodium.html>.