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.