EFFECTS OF BROADLEAF HERBICIDES ON IMAZAMETHABENZ-METHYL PERFORMANCE ON WILD OAT (AVENA-FATUA L)

The influence of broadleaf herbicides on imazamethabenz-methyl perform ance on wild oat (Avena fatua L.) plants grown outdoors in pots was ex amined. The foliar activity of imazamethabenz-methyl was reduced when applied in mixture with salt formulations of MCPA and mecoprop, salt a nd ester formulations of bromoxynil and bentazone. In contrast, chlors ulfuron had no influence and ester formulations of MCPA and mecoprop e ither had no effect or promoted imazamethabenz-methyl performance. A c omparison of the activity of imazamethabenz-methyl in mixture with the ester formulation of MCPA and the corresponding formulation blank rev ealed that the antagonistic effect of MCPA active ingredient in the sa lt and ester formulations were similar. However, because of an enhanci ng effect of the formulation constituents in the ester formulation ant agonism was masked in mixture with the latter. Similarly, addition of a mineral oil adjuvant only masked but did not eliminate the antagonis tic interaction between the two herbicides. Volume rate did not affect imazamethabenz-methyl activity nor the antagonistic effect of the sal t formulation of MCPA. The ester formulation of MCPA, however, promote d imazamethabenz-methyl performance significantly more at the low than at the high volume rate. Sequential application reduced antagonism of the salt formulation of MCPA on imazamethabenz-methyl. Selective plac ement of droplets revealed that antagonism occurred only if imazametha benz-methyl and the salt formulation of MCPA were applied in the same droplet but not as separate droplets. Neither foliar- nor root-applied MCPA reduced the performance of root-applied imazamethabenz-methyl. T he results indicate that antagonism of MCPA was caused by a reduced up take. The implications of the results of the present study in relation to the performance of tank mixtures of imazamethabenz-methyl and broa dleaf herbicides under field conditions are discussed.