Effect of subsurface and foliar applications of bispyribac-sodium on water hyacinth, water lettuce, and giant salvinia

摘要

Bispyribac-sodium [2,6-bis(4,6-dimethoxypyrimidin-2-yloxy)benzoic acid] recen tly received a USEPA Section 3 aquatic registration for control of hydrilla and other nuisance aquatic plants. Similar to the herbicides penoxsulam [2-(2,2-difluoroethoxy)-N-(5,8-dimethoxy [1,2,4] triazolo[l,5-c]pyrimidin-2-yl)-6 (trifluoromethyl) benzenesulfonamide] and imazamox [2-[4,5-dihydro-4-methyl-4-(l-methylethyl)-5-oxo-lH-imidazol-2-yl]-5-(methoxymethyl)-3-pyridinecar-boxylic acid], bispyribac-sodium inhibits the production of branched-chain amino acids by binding to the acetolactate synthase (ALS) enzyme (Tranel and Wright 2002). Without these essential amino acids, protein synthesis and growth are inhibited, ultimately resulting in plant death (WSSA 2007). Whilethe ALS inhibitors target the same plant enzyme, the large number of ALS inhibitors registered for terrestrial use attests to significant differences in plant selectivity between these compounds; therefore, evaluation of two or three different ALS inhibitors on a suite of plant species may yield very different outcomes. For example, Koschnick et al. (2007) reported EC_(50)values for penoxsulam, bispyribac-sodium and imazamox on duck potato shoot biomass (Sagittaria lancifolia L.) to be 9, 105, 96 mug (9, 105, and 96 ppb) active ingredient (ai) L~(-1), respectively. If the management goal was to control hydrilla without damaging stands of duck potato, then the use of penoxsulam may not be the product of choice since herbicide concentrations of 5 to 20mug L~(-1) are required.