Suscetibilidade de Digitaria insularis a herbicidas inibidores de EPSPs e ACCase e alternativas de controle

Abstract

The frequent use of the herbicide glyphosate in an agricultural production system has selected populations of sourgrass (Digitaria insularis) resistant to this herbicide. The control option of these biotypes has been made, almost exclusively, with ACCase inhibitor herbicides. In order to evaluate the efficiency of the herbicides cletodim and haloxyfop in control of D. insularis biotypes collected in the states of SP, GO, PR and RJ, and to propose control alternatives with pre and post emergent herbicides of soybean, three trials. In the first assay (EI) conducted in a greenhouse, increasing doses (0, 1, 2, 4 and 8 times from the highest leaflet dose) of the herbicides haloxifop (60 g ha-1of a.i.), clethodim (96 g ha-1 of a.i.) and glyphosate (1440 g ha-1 of a.e.) in plants of 9 biotypes of sourgrass with three to four leaves. The control response of the plants to the herbicides, the resistance factor to glyphosate through dose response curves, the evaluation of the chlorophyll parameters in addition to the biometric data of shoot length, root length and total dry biomass were evaluated. The second assay (EII) and the third assay (EIII) were performed under field conditions with 3-4 leaf stages, 3-4 tillers and full flowering stages where doses of 0, ½ and dose were tested maximum of package leaflet. For EII, the herbicides quizalofop (120 g ha- 1 of a.i.), haloxifop (60 g ha-1 of a.i.), clethodim (96 g ha-1 of a.i.) and sethoxydim (184 g ha- 1 of i.a.) and For EIII the herbicides paraquat (600 g ha-1 of a.i.), paraquat + diuron (200 + 100 g ha-1 of i.a.) and glufosinate (600 g ha-1 of i.a.). EII and EIII evaluated the response of plants to herbicides at three stages of development as well as evaluation of chlorophyll a parameters and biometric data. In the first experiment, a variation in susceptibility to glyphosate was observed among the evaluated biotypes. In all evaluated biotypes the resistance factor was lower than 10. The evaluation of chlorophyll fluorescence showed that the biotypes collected in Toledo1/PR and Cascavel/PR, treated with glyphosate, showed a recovery of the photosynthetic parameters evaluated, At 21 DAA, when compared to the control treatment. For all the biotypes the herbicide clethodim offered control superior to the 7 DAA when compared to the haloxifop. However, at 14 DAA the control of the biotypes exerted by the two herbicides was similar. For EII, the action of the systemic emergent powders showed high control efficiency (superior 80%) of the sourgrass. At the 3-4 leaf phenological stage, the control provided by the herbicides tested at 14 DAA, even at the lowest evaluated dose, was superior to 90%. At 21 DAA the control of 100% of the sourgrass plants was obtained. For EIII, the action of the contact herbicides provided severe damage to the aerial part of the sourgrass plants, especially those that were in the 3-4 leaf stage, when at the 7 DAA a 100% control was observed. In the other stages for the herbicides paraquat and the commercial mixture between paraquat + diuron the control above 95% was reached at 14 DAA and only for the herbicide glufosinate the recovery of the sourgrass plants was observed.