Comparative Phytotoxicity of Glyphosate, SC-0224, SC-0545, and HOE-00661

Toxicities of the isopropylamine salt of glyphosate [N-(phosphonomethyl)glycine], SC-0224 (trimethylsulfonium carboxymethylaminomethylphosphonate), and SC-0545 (trimethylsulfoxonium carboxymethylaminomethylphosphonate) were similar to hard red winter wheat (Triticum aestivum L. ‘Centurk 78′) at equal dosages, carrier volumes, carrier water qualities, and sulfuric acid concentrations in the greenhouse and field at Lincoln, NE. Toxicity of HOE-00661 [ammonium (3-amino-3-carboxypropyl)-methylphosphinate] was less than the other herbicides at equal dosages. Rate of development of injury to wheat was similar at 0.4 kg/ha for glyphosate, SC-0224, and SC-0545, but greater for HOE-00661 up to 4 days after application and less thereafter. Reductions in carrier volume from 190 to 96 L/ha resulted in improved phytotoxicities for glyphosate, SC-0224, and SC-0545 at 0.1 kg/ha and HOE-00661 at 0.4 kg/ha. Addition of 0.25% (v/v) concentrated sulfuric acid to 190 L/ha of well water carrier resulted in improved phytotoxicities for glyphosate, SC-0224, and SC-0545 at 0.1 kg/ha and HOE-00661 at 0.4 kg/ha. Carrier water with reduced levels of polyvalent cations resulted in increased phytotoxicities of glyphosate, SC-0224, and SC-0545 at 0.1 kg/ha in 190 L/ha. Phytotoxicity of HOE-00661 was not affected by carrier water quality. Glyphosate, SC-0224, and SC-0545 at equal rates and HOE-00661 at a 4 X rate showed similar toxicity to wheat.