Seletividade e eficácia de herbicidas aplicados em isolado ou associados para o controle de plantas daninhas em trigo

Abstract

The use of herbicides to control weeds in wheat crops is a common practice among producers, due to its effectiveness, speed and lower cost when compared to other forms of management. Therefore, the objective of this study was to evaluate the selectivity and effectiveness of herbicides applied alone or in combination in the control of weeds in wheat crops. The experiments were conducted in the field, in 2022 and 2023 in a randomized block design, with four replications. The treatments consisted of two controls, one weeded and the other infested, and the following herbicides: terbuthylazine (500 and 750 g ha-1), clodinafop-propargyl (96 g ha-1), carfentrazone-ethyl (80 and 120 g ha-1), saflufenacil (28 g ha-1), 2,4-D amine (670 g ha-1), terbuthylazine + clodinafop-propargyl (500 + 96 and 750 + 96 g ha-1), piraflufen-ethyl + clodinafop-propargyl (3.75 + 96 and 5 + 96 g ha-1). Phytotoxicity and weed control evaluations were carried out at 7, 14, 21, 28, 35 and 42 days after treatment application (DAT). The physiological characteristics, substomatal CO2 concentration (Ci - μmol mol-1), stomatal water vapor conductance (Gs - mol m-1 s-1), photosynthetic rate (A - μmol m-2 s-1), transpiration rate (E - mol H2O m-2 s-1), carboxylation efficiency (EC - mol CO2 m-1 s-1) and water use efficiency (WUE - mol CO2 mol H2O-1) of the crop were evaluated at 21 DAT. At pre-harvest, the number of spikes per area, number of full and sterile grains per spike and spike length were evaluated. At harvest, the hectoliter weight, thousand-grain weight and grain yield were also determined. The best productivity was achieved with the weeded control, terbuthylazine (750 g ha-1) + clodinafop-propargyl (96 g ha-1). The loss in wheat grain yield is considerably higher if no weed control method is adopted. The best physiological performance of wheat plants was obtained by applying terbuthylazine (750 g ha-1), carfentrazone-ethyl (80 g ha-1), 2,4-D and terbuthylazine+clodinafop-propargyl (750+96 g ha-1). The herbicides that caused the greatest phytotoxicities to the wheat cultivar Audaz were terbuthylazine (500 and 750 g ha-1)+Dash, carfentrazone-ethyl (120 g ha-1), saflufenacil and pyraflufen-ethyl (3.75 and 5 g ha-1)+clodinafop-propargyl. The best physiological performance of wheat plants was obtained by applying terbuthylazine (750 g ha-1), carfentrazone (80 g ha-1), 2,4-D amine and terbuthylazine+clodinafop-propargyl (750+96 g ha-1). The herbicides terbuthylazine (500 and 750 g ha-1) and pyraflufen (3.75 and 5 g ha-1) associated with clodinafop-propargyl (96 g ha-1) showed the best turnip and ryegrass controls and the best performance in the grain yield components, especially in relation to the yield of the wheat cultivar TBIO Audaz. If no method of controlling turnip and wheat ryegrass is adopted, there is an average grain loss of 91.04%.