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    Sulfosulfuron Efficacy Is Affected by Surfactants, pH of Spray Mixture, and Salts

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    Sulfosulfuron {1-(4,6-dimethoxypyrimidin-2-yl)-3-[(2-ethanesulfonyl-imidazo[1,2-a]pyridine-3-yl)]sulfonylurea} must be applied with an adjuvant for effective postemergent weed control. Experiments were conducted to determine sulfosulfuron phytotoxicity to green foxtail (Setaria viridis L.) as influenced by surfactant chemistry, surfactant hydrophilic/lipophilic balance (HLB), spray mixture pH, and common nitrogen fertilizers. Regardless of accompanying surfactant chemistry, surfactant HLB, and nitrogen fertilizers, sulfosulfuron efficacy to green foxtail was greatly enhanced when applied in alkaline spray mixture (pH 7.4–8.2) compared to pH 4.0–5.7 unbuffered spray mixture. Secondary alcohol ethoxylate surfactants increased sulfosulfuron efficacy as HLB of these surfactants increased from 8.3 to 17.4 in unbuffered and buffered spray mixtures. The optimum HLB of various block copolymer surfactants for sulfosulfuron was from 9.0 to 13.0. In unbuffered spray mixture, ammonium nitrate at 0.25% w/v had no effect or antagonized sulfosulfuron phytotoxicity, especially when applied with block copolymer surfactants. However, urea fertilizer at 0.25% w/v enhanced herbicide efficacy, regardless of surfactants. Commercial 28% N liquid fertilizer (urea/ammonium nitrate solution) also increased sulfosulfuron efficacy with most surfactants, especially in unbuffered spray mixtures. In spray mixtures buffered above pH 7, the effects of surfactant HLB and nitrogen fertilizers on sulfosulfuron efficacy were less evident. Spray droplet spread and droplet drying time did not relate to sulfosulfuron efficacy.

    These data demonstrate a potential for optimizing sulfosulfuron efficacy by carefully selecting surfactant chemistry, surfactant HLB, addition of proper nitrogen fertilizer, and by regulating the pH of the spray mixture.


    adjuvant, HLB, ammonium nitrate, urea, 28% N liquid fertilizer, triethanolamine, spray pH, green foxtail

    Author Information:

    Woznica, Z
    Visiting ScientistProfessor, North Dakota State UniversityAgricultural University, FargoPoznan, ND

    Nalewaja, JD
    Professors, North Dakota State University, Fargo, ND

    Messersmith, CG
    Professors, North Dakota State University, Fargo, ND

    Committee/Subcommittee: E35.22

    DOI: 10.1520/STP10714S