Interação entre herbicidas para manejo de Digitaria insularis e Conyza spp. em áreas de produção de soja

Abstract

One of the major problems of today's agriculture is how to control weeds that are resistant to glyphosate. Not Brazil as species Digitaria insularis (sourgrass) and Conyza spp. (fleabane) has been occurring together and with great aggression in soybean properties. Because it is a monocotyledon and a dicotyledone or mechanism of action of the herbicide used for control should be specific for each species. An application of graminicides, inhibitors of the enzyme ACCase, has been the management option of the sourgrass resistant to glyphosate. Already for fleabane the inhibitory herbicides of ALS and the auxin-mimicking are efficient. However, little is known about the use of the two mechanisms of action in sequential applications or in mixtures for species control. The objective of this study was to evaluate the interaction between synergism and antagonism between ACCase inhibitors, ALS and auxin mimics for control applications of D. insularis and Conyza spp. resistant to glyphosate. The experiments were conducted in pots with soil at the Federal University of Rio de Janeiro, Seropédica / RJ. These were developed in randomized blocks with 4 replicates, divided into 4 cases, case I and II for 3-4 field sourgrass and flowering stage, and case III and IV for construction plants in the 12-15 sheets. The herbicides used were: (A) haloxifop (62,4 g ha-1), (B) chloransulam (40 g ha-1) and (C) 2,4-D dimethylamine salt (1005 g ha- sequential applications were 3, 6 and 12 days. As the applications evaluated when they are planned, there is no proposed phenological stage. Each case consisted of 10 treatments, in case I and III (control, A, C, A + C, sequential A + C and C + A with interval between applications of 3, 6 and 12 days) and the case II and IV (control A, B, A + B, sequential A + B and B + A with interval between applications of 3, 6 and 12 days). At 7 and 35 days and 14 and 35 days after application (DAA) for fleabane and sourgrass respectively, chlorophyll fluorescence and visual symptom analysis were performed and at 35 DAA the plants were collected with dry mass selection of part area and root. The data generated in the experiments were submitted to ANOVA (p <0.005), if a biometric data and visual symptom data were required and submitted to the Tukey test and the chlorophyll fluorescence data to the Ducan test at the 5% probability level. It was possible to observe antagonism between herbicides administered without sourgrass control. The control of 100% of the plants was found in a stadium of 3-4 users of sourgrass, when haloxyfop was applied before chlorosulfan or 2,4-D in a minimum interval of 6 days. At flowering stage of sourgrass major damage as plants were also observed with sequential haloxifop / chloransulam or 2,4-D. On the other hand, the control herbicides without control, without control of construction plants, regardless of the range or order of application of the herbicides haloxifope and cloransulam or 2,4-D, was observed 100% control. Therefore, in areas infested with fleabane and bittergrass the recommendation is to apply the graminicide 6 days before the latifolicide for an effective control of both species.