ABSTRACT
Susceptibility of four gramineous crops (Neepawa red spring wheat [Triticum aestivum L.], Wakooma amber durum wheat [T. turgidum L. var. durum], Bonanza 6-row barley [Hordeum vulgare L.], and Norbert 2-row barley) and two grass weeds (wild oat [Avena fatua L,] and green foxtail [Setaria viridus (L.) Beauv.]) to 0.025 to 0.4 kg/ha fenoxaprop- ethyl —- ethyl ester of (±)-2(4-[{6-chloro-2-benzoxazolyl}oxy]phenoxy) propanoic acid — was considerably different in greenhouse studies. Neepawa wheat was the most tolerant and green foxtail the least. With the exception of green foxtail, tolerance was modified in all species by adding any of four growth regulator herbicides (bromoxynil, MCPA, bromoxynil + MCPA, and 2,4-D). Enhanced tolerance was most noted with MCPA at 0.28 kg/ha in Neepawa wheat and also with MCPA at 0.56 kg/ha in Bonanza barley. MCPA at these rates did not reduce control of wild oat or green foxtail. In the field, Katepwa spring wheat was also tolerant of the fenoxaprop (0.18 kg/ha), whereas Bonanza barley was susceptibile to the herbicide even at 0.1 kg/ha. However, addition of three growth regulator herbicides (bromoxynil + MCPA, MCPA, and 2,4-D) at 0.56 kg/ha to fenoxaprop did not change wheat tolerance, but substantially increased tolerance of barley. In the laboratory, absorption and translocation of [l4C]-fenoxaprop-ethyl by wild oat, wheat, and barley were not altered by adding MCPA, suggesting that the antidote interaction occurs at the apical meristem.
