AMMONIUM-SULFATE EFFECTS ON THE ACTIVITY OF HERBICIDES FOR SELECTIVE GRASS CONTROL

Greenhouse and field experiments were conducted from 1987 to 1990 at t he Lacombe Research Station to determine the influence of ammonium sul fate (AS) on various grass control herbicides. In field studies, AS ha d slight or no effects on the phytotoxicity of aryloxyphenoxypropanoat e (APP) herbicides (fenoxaprop, fluazifop, haloxyfop, and quizalofop). The largest AS-mediated increase in APP herbicide phytotoxicity was 1 9% (based on fresh weight reduction) for wild oat with haloxyfop at 50 g/ha. AS consistently mediated increases in cyclohexanedione (CHD) he rbicide phytotoxicity. With added AS, barley fresh weight was reduced 75% (1988) with BAS 517 at 50 g/ha, and 100% (1990) with clethodim at 25 g/ha. Greenhouse studies confirmed field studies, but differences w ere less substantial and consistent. It is suggested that APP herbicid es are either less susceptible to UV degradation than CHD herbicides, and/or that APP herbicides may penetrate plant cuticles quickly enough to nullify any protection from UV degradation that AS might provide v ia rapid absorption. Nomenclature: BAS 517, -(2H-tetrahydrothiopyran-3 -yl)-2-cyclohexen-1-one; clethodim, ropyl]-5-[2-(ethylthio)-propyl]-3- hydroxy-2-cyclo- hexen-1-one; fenoxaprop, [4-[(6-chloro-2-benzoxazolyl )oxy]phenoxy]propanoic acid; fluazifop, -[4-[[5-(trifluoromethyl)-2-py ridinyl]oxy]phenoxy] propanoic acid; haloxyfop, trifluoromethyl)-2-pyr idinyl]oxy]phenoxy]propanoic acid; quizalofop, [4-[(6-chloro-2-quinoxa linyl)oxy]phenoxy]propanoic acid; wild oat, Avena fatua L. #(3) AVEFA; barley, Hordeum vulgare L.