Bispyribac-sodium (Regiment) is a new herbicide, which is highly effective against Echinochloa spp. However, combinations with other herbicides are needed to broaden the spectrum of control to include other grasses such as sprangletop (Leptochloa fascicularis) and to delay the development of resistance to this herbicide. Bioassays have shown high levels of tolerance to this herbicide by certain watergrass (Echinochloa oryzoides and E. phyllopogon) biotypes in California. In field experiments, the mixture of thiobencarb (Abolish) at 2240 g ai/ha with bispyribac-sodium at 15 g ai/ha applied to rice at the 5- to 6-leaf stage resulted in 88% control of a mixed population of both watergrass species, as opposed to only 18% when each herbicide was applied alone (no surfactant was used with bispyribac-sodium). Similarly, in 2001, the mixture of 2240 g ai/ha thiobencarb with 10 g ai/ha bispyribac-sodium resulted in 93% control of watergrass, while the same rates of thiobencarb and bispyribac-sodium, applied individually, only controlled watergrass by 6 and 5%, respectively. Since the activity of bispyribac-sodium on watergrass is highly dependent on the use of a surfactant, this synergistic effect of the mixture was initially attributed to enhanced bispyribac-sodium absorption facilitated by the surfactants already present in the thiobencarb formulation. However, when the mixture of thiobencarb (2240 g ai/ha) and bispyribac-sodium (10 g ai/ha) was compared with the same rates of the herbicides applied individually, but with a silicon-based surfactant added to bispyribac-sodium, a synergistic effect was also observed. The mixture controlled watergrass 93%, thiobencarb alone 6%, and bispyribac + silicone surfactant 70%. The herbicide rates in these mixtures are about 50% lower than the recommended rates for the herbicides when applied alone. Analysis of the data using Colby’s method suggested synergism on watergrass control in these mixtures. This was further corroborated in dose-response experiments in the greenhouse. The mixtures were safe on rice and also provided excellent control of sprangletop. The effects on sprangletop and other weeds in the field also suggested synergistic effects.
Bispyribac-Sodium and Thiobencarb: Synergism?
VIDOTTO, Francesco
2002-01-01
Abstract
Bispyribac-sodium (Regiment) is a new herbicide, which is highly effective against Echinochloa spp. However, combinations with other herbicides are needed to broaden the spectrum of control to include other grasses such as sprangletop (Leptochloa fascicularis) and to delay the development of resistance to this herbicide. Bioassays have shown high levels of tolerance to this herbicide by certain watergrass (Echinochloa oryzoides and E. phyllopogon) biotypes in California. In field experiments, the mixture of thiobencarb (Abolish) at 2240 g ai/ha with bispyribac-sodium at 15 g ai/ha applied to rice at the 5- to 6-leaf stage resulted in 88% control of a mixed population of both watergrass species, as opposed to only 18% when each herbicide was applied alone (no surfactant was used with bispyribac-sodium). Similarly, in 2001, the mixture of 2240 g ai/ha thiobencarb with 10 g ai/ha bispyribac-sodium resulted in 93% control of watergrass, while the same rates of thiobencarb and bispyribac-sodium, applied individually, only controlled watergrass by 6 and 5%, respectively. Since the activity of bispyribac-sodium on watergrass is highly dependent on the use of a surfactant, this synergistic effect of the mixture was initially attributed to enhanced bispyribac-sodium absorption facilitated by the surfactants already present in the thiobencarb formulation. However, when the mixture of thiobencarb (2240 g ai/ha) and bispyribac-sodium (10 g ai/ha) was compared with the same rates of the herbicides applied individually, but with a silicon-based surfactant added to bispyribac-sodium, a synergistic effect was also observed. The mixture controlled watergrass 93%, thiobencarb alone 6%, and bispyribac + silicone surfactant 70%. The herbicide rates in these mixtures are about 50% lower than the recommended rates for the herbicides when applied alone. Analysis of the data using Colby’s method suggested synergism on watergrass control in these mixtures. This was further corroborated in dose-response experiments in the greenhouse. The mixtures were safe on rice and also provided excellent control of sprangletop. The effects on sprangletop and other weeds in the field also suggested synergistic effects.
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