INFLUENCE OF BROAD-LEAVED WEED HERBICIDES ON THE ACTIVITY OF FENOXAPROP-P-ETHYL

The activity of fenoxaprop-P-ethyl applied alone or in tank-mixture wi th different formulations of mecoprop or sulfonylurea herbicides was c ompared in a series of pot experiments using Avena fatua L. (wild oat) as a test plant. A logistic model was fitted to the results and dose- response curves of fenoxaprop-P-ethyl applied alone and in mixture wit h the broad-leaved weed herbicides were estimated using non-linear reg ressions. Tank-mixtures of fenoxaprop-P-ethyl and mecoprop or metsulfu ron-methyl were antagonistic. In general, the activity of fenoxaprop-P -ethyl decreased with increasing doses of the broad-leaved herbicides. In mixture with 1200 g a.i. ha(-1) mecoprop, doses of fenoxaprop-P-et hyl had to be increased by 60% to 130% (dependent on formulation) to o btain the same effect as when fenoxaprop-P-ethyl was applied alone. Bo th the active and the inactive isomers of mecoprop were involved in th e antagonism, and the ester formulation of mecoprop-P was less antagon istic than the amine formulation. In mixture with the recommended dose of 8 g a.i. ha(-1) of metsulfuron-methyl, doses of fenoxaprop-P-ethyl had to be increased by 20% to 110% to obtain the same effect as with fenoxaprop-P-ethyl applied alone. Fenoxaprop-P-ethyl did not lose acti vity when applied in mixture with recommended doses of chlorsulfuron, tribenuron and amidosulfuron. Antagonism of the sulfonylurea herbicide s seemed to be related to the susceptibility of A. fatua to these herb icides.