RESPOSTA DE BIÓTIPOS DE CAPIM PÉ-DE-GALINHA (Eleusine indica) AOS HERBICIDAS GLIFOSATO, CLETODIM E HALOXIFOPE-P-METÍLICO

Abstract

Goosegrass (Eleusine indica) is currently one of the most troublesome weed species in the Brazilian cropping system, due to its wide dispersion and the several cases of resistance already confirmed, cases that besides hamper the management of this species, also increase production costs for producers. Thus, the present work aimed to evaluate the response of goosegrass biotypes to glyphosate, clethodim, and haloxyfop-p-methyl aiming for the possible diagnosis of biotypes resistant to these herbicides. For such, seventeen goosegrass biotypes (B1 to B17) were collected in production areas in the region of Primavera do Leste, Mato Grosso State, and screened in a greenhouse in a completely randomized design with four replications. The seeds were sown in pots of 5 dm-3, and when the plants reached the stage of one to three tillers (4 plants per pot), the herbicides were applied in their respective recommended rates, glyphosate (960 g a.e. ha-1), haloxyfop-p-methyl (60 g a.e. ha-1), and clethodim (96 g a.i. ha-1). Control efficacy assessment (0 to 100%) was performed at 28DAT to select which biotypes showed the lowest control level to each herbicide and conduct the dose-response trials. From the seventeen biotypes, B1 and B4 were chosen for the graminicides clethodim and haloxyfop-p-methyl; B11, B14, and B15 for the herbicides clethodim, haloxyfop-p-methyl and glyphosate; and B16 only for haloxyfop-p-methyl and glyphosate, in addition to the selected biotypes, a susceptible one to the herbicides was added as a comparison. The dose-response trials followed the same methodology of the screening; however, it was adopted a dose range of 0 to 16 times the recommended rate of each herbicide (0D, D/16, D/8, D/4, D/2, D, 2D, 4D, 8D, 16D, where D is equal to the recommended rate). At 28DAT, an efficacy assessment was performed. Also, the biomass of uncontrolled plants was collected for drying in an oven at 65°C until constant weight to establish the dry biomass of goosegrass per pot. The efficacy and dry biomass data were used to construct the dose-response curves using the non-linear log-logistic model and determine the values of C50/C80 and GR50/GR80 for each herbicide. Despite having the same mechanism of action, it was possible to observe variations in resistance to haloxyfop-p-methyl and clethodim, with a greater number of resistant biotypes and greater resistance factors for the FOP compared to the DIM. Among the four biotypes selected and treated with glyphosate, three presented poor control (<80%) at the recommended rate. Out of these three biotypes B11 and B15 stood out because, in addition to being characterized as resistant to glyphosate, they were also not satisfactorily controlled by clethodim and haloxyfop-p-methyl, being a suspicion of multiple resistance to these three herbicides. F1 generation seeds of these biotypes were collected and will be subjected to a new dose-response curve trial if confirmed; these may be one of the first cases of goosegrass multiple resistance in Brazil involving clethodim, haloxyfop-p-methyl, and glyphosate.