ANTAGONISM OF HALOXYFOP ACTIVITY IN TALL FESCUE (FESTUCA-ARUNDINACEA) BY DICAMBA AND BENTAZON

Studies were conducted to test if dicamba reduces haloxyfop herbicidal activity and to determine if this interaction by auxin-type herbicides or bentazon was caused by preventing the haloxyfop-induced inhibition of acetyl-CoA carboxylase (ACCase). Addition of dicamba at concentrations of 2.17 or 4.34 mM reduced haloxyfop activity on tall fescue shoots. Haloxyfop at 14 to 20-mu-M inhibited the activity of ACCase in cell-free extracts from tall fescue by nearly 50%. Dicamba did not prevent the inhibitory effect of haloxyfop on ACCase activity in these cell-free enzyme preparations. Dicamba alone at concentrations as high as 3.2 mM had no significant effect on the in vitro activity of the enzyme. Bentazon concentrations up to 10 mM did not prevent haloxyfop inhibition of ACCase activity. Bentazon alone or mixed with haloxyfop significantly inhibited ACCase activity at bentazon concentrations starting at 1 mM with near 40% inhibition at 10 mM. Of the numerous possible explanations for the interference of dicamba or bentazon with haloxyfop action, interaction directly at the enzyme level appears to have been eliminated.