Eficácia e atividade residual de aplicações isoladas ou associadas de diuron oxyfluorfen e prometryne para o controle de Euphorbia heterophylla

Abstract

Pre-emergence herbicide application in cotton is a usual practice by growers. Herbicides diuron, oxyfluorfen and prometryne are registered options for use in cotton, but limited information is available in relation to the efficiency of such molecules to promote effective control of Euphorbia heterophylla. Due to the significant increasing of poor control of wild poinsettia in cotton areas, this work was aimed to understand the biological response of wild poinsettia in relation the application of these herbicides alone or in combinations. Experiments were carried out in greenhouse. Initially, dose-response curves were elaborated in relation to visual percentage of control at 14 and 28 days after application (DAA) and to relative biomass production (28 DAA). Later, to evaluate residual activity, herbicides or mixtures were applied at 30, 20, 10 or zero days before the weed sowing. Visual efficiency of treatments was evaluated at 28 DAA. Diuron, oxyfluorfen and prometryne applied isolated were considered efficient within the range of doses evaluated. For diuron, doses of 1.1 kg a.i. ha-1 provided residual activity for periods up to 30 days, with reasonable control of wild poinsettia (71-85%). Rates of 0.9 kg a.i. ha-1 provided similar control for 10 days. Control > 85% was found with oxyfluorfen at 0.336 kg a.i. ha-1 for periods up to 10 days and control> 72% for up to 20 days. A control > 83% de with prometryne at 2.050 kg a.i. ha-1 for up to 20 days and control > 71% for up to 30 days was found. Mixtures of diuron+prometryne promoted control > 85% for periods of up to 30 days for doses of 1.0+2.0 kg a.i. ha-1 and of up to 20 days when applied at 2.0+1.0 kg a.i. ha-1. To obtain similar levels of control fo a period of 30 days, a minimum of 1.0+0.228 kg a.i. ha-1 of the mixture diuron+oxyfluorfen was needed. In relation to prometryne+oxyfluorfen, a minimum of 80% of control was found for periods of 10 days when using a minimum of 1.0+0.192 kg a.i. ha-1. Mixtures containing oxyfluorfen were in general considered as additive or antagonistic; the misture of diuron+prometryne was considered as additive or sinergistic combination.