Summary:In several pot and field experiments additions of 1–10 w/v ammonium sulphate and/or 0.1–2.5 w/v surfactant increased the phytotoxicity toA. repensof sprays containing 0.2–0.5 kg/ha glyphosate. There were similar results with technical glyphosate‐isopropylamine salt and formulated ‘Roundup’. Higher ammonium sulphate concentrations were sometimes antagonistic. Additions of ammonium sulphate without surfactant generally had less effect on phytotoxicity. While several surfactants increased glyphosate activity the order of effectiveness of these products varied according to whether or not ammonium sulphate was also present. When used alone, relatively hydrophilic non‐ionic or cationic products had more effect. In mixtures with ammonium sulphate, however more lipophilic surfactants gave superior results. Ammonium sulphate (5) with a lipophilic cationic surfactant (0.5 Ethomeen C12) enhanced the effects of very low volume controlled‐drop applications as well as conventional medium volume sprays. In a field trial 0.25 kg/ha glyphosate applied with those additives in 20 l/ha of spray had as much effect on bud viability as l kg/ha applied
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