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Surfactants are used in pesticide and spray adjuvant formulations. Unfortunately, some surfactants are phytotoxic and can inhibit pesticide efficacy. Experiments were conducted in the greenhouse and laboratory to determine the phytotoxicity of surfactants that differed in lipophilic chemistry and/or hydrophilic:lipophilic balance (HLB). Barley (Hordeum vulgare L.) was the bioassay species. Foliar injury generally was greater with low than high HLB surfactants when surfactants were applied based on weight/volume but not when applied based on molar concentration. Lipophilic chemistry, HLB, and concentration influenced the surfactant effect on droplet spread, plant transpiration, and proton extrusion from barley calli. Surfactants reduced or had no affect on transpiration 1 h after application. Transpiration recovered to original levels 24 h after application, if no foliar injury occurred. Most surfactants at 0.01 mM reduced proton extrusion from barley calli. Simple relationships were not observed between foliar injury and droplet spread; foliar injury and transpiration; droplet spread and transpiration; or foliar injury and proton extrusion.
Adjuvant, droplet spread, HLB values, proton extrusion, surfactant chemistry, surfactant concentration, transpiration
Assistant Professor, North Dakota State University, Fargo, ND
Research Geneticist, Northern Crop Science Laboratory, USDA/ARS, Fargo, ND