Association of quizalofop-P-tefuril to 2,4-D in hairy fleabane (Conyza bonariensis) control: is the antagonism reciprocal to that observed in sourgrass (Digitaria insularis)?

Resumo

The antagonism between auxinic herbicides and graminicides on poaceae weeds is widely known. However, the reciprocal antagonism between these herbicides in the control of eudicots is not known. This study aimed to evaluate the effect of adding quizalofop-P-tefuril and/or adjuvant to 2,4-D in the control of hairy fleabane (Conyza bonariensis). The treatments were organized in factorial (7 x 2 x 2), with seven doses of 2,4-D, presence or absence of quizalofop-P-tefuril, and presence or absence of adjuvant alkyl ester ethoxylate of phosphoric acid. Treatments were applied in hairy fleabane plants at 12-leaf rosette-stage. Weed control was evaluated at 14, 21, 28 and 35 days after the treatment (DAT), in addition to relative shoot dry mass (SDM) determination at 35 DAT. The addition of fluazifop-P-tefuril to 2,4-D results in antagonism in the control of hairy fleabane only when 2,4-D is applied at doses lower than recommended (less than 1,005 g a.e. ha^-1). The addition of adjuvant improves the efficacy of 2,4-D, offsetting the negative effect caused by the addition of quizalofop-P-tefuril. However, at doses of 2,4-D from the recommendation (1,005 g a.e. ha^-1), the addition of adjuvant is not necessary for the control of haity fleabane with up to 12 leaves. Therefore, it is concluded that the antagonism between quizalofop-P-tefuril and 2,4-D is reciprocal, but it depends on the dose of 2,4-D and the absence of adjuvant to the spray solution.