Amine Salts of Growth Regulator Herbicides Antagonize Paraquat

Amine formulations of 2,4-D [(2,4-dichlorophenoxy) acetic acid] and MCPA {[(4-chloro-o-tolyl)oxy] acetic acid} caused a reduction in paraquat (1,1-dimethyl-4,4′-bipyridinium ion) phytotoxicity to barley (Hordeum vulgareL. 'Summit′), wheat (Triticum aestivumL. ‘Neepawa′), and wild oats (Avena fatuaL.). Dicamba (3,6-dichloro-o-anisic acid) reduced paraquat activity in barley only. Paraquat phytotoxicity was antagonized more by 2,4-D amine at high than at low rates. Higher rates of paraquat relative to a fixed rate of 2,4-D amine overcame the antagonism. Paraquat phytotoxicity was not antagonized by 2,4-D or MCPA amine applied as a separate treatment. The technical components of the 2,4-D- or MCPA-amine formulations were solely responsible for the antagonism. Ester formulations did not affect paraquat phytotoxicity.