Interaction of dicamba or 2,4-D with acetyl-CoA carboxylase inhibiting herbicides to control fleabane and sourgrass

The presence of monocotyledonous and dicotyledonous weeds resistant to glyphosate in the same area makes tank mixtures of herbicides necessary. However, mixtures containing latifolicides and graminicides may result in less effectiveness. This study aimed to evaluate the interactions of auxin-mimic herbicides with acetyl-CoA carboxylase (ACCase) inhibitors. Experiments were conducted in two consecutive years in an area with a high infestation of fleabane and sourgrass, with history of resistance to glyphosate. The average heights of fleabane and sourgrass plants were, respectively: 30 and 70 cm in the first year; 80 and 120 cm in the second year. Herbicides dicamba, 2,4-D, clethodim, quizalofop and glyphosate were applied alone or in combinations with each other, in a completely randomized design, with thirty treatments and four replications. The results obtained in the control evaluation at 35 days after application were analyzed by Colby’s method. For fleabane control, in the two years evaluated, there were no problems of antagonism of auxin mimics with ACCase inhibitors. However, mixtures of ACCase inhibitors with 2,4-D were more antagonistic than mixtures with dicamba in sourgrass control, since for double mixtures between auxin mimics and ACCase inhibitors, interactions with 2,4-D were antagonistic in 62.5% cases, while for dicamba was 12.5%. In addition, antagonism effects were more pronounced in larger plants of sourgrass, and in mixtures with quizalofop, compared with clethodim. Tank mixtures of glyphosate and clethodim or quizalofop were synergistic for the control of sourgrass.