Eficiência e seletividade do herbicida terbutilazina aplicado em pré-emergência e pós-emergência no milho

Abstract

Terbuthylazine has a longer persistence in the soil compared to atrazine, therefore it is believed that terbuthylazine has greater weed control than atrazine in corn crops. With this, the objective was to evaluate the efficiency and selectivity of terbuthylazine applied pre-emergence and post emergence in corn crops. Four experiments were carried out under field conditions. The experiments corresponded to the mode of application of herbicides in pre and post-emergence of weeds and corn, with two experiments (pre and post) conducted in the municipality of Ponta Grossa and two experiments (pre and post) conducted in Tibagi, in the state from Paraná, Brazil. The experimental design used was randomized blocks, with four replications. The treatments in each experiment corresponded to: Control not weeded, control weeded, terbuthylazine (500 g ha-1), terbuthylazine (1000 g ha-1), terbuthylazine (1500 g ha-1), terbuthylazine (2000 g ha-1) and atrazine (2000 g ha-1). In the pre-emergence application modality, in the municipality of Ponta Grossa, the terbuthylazine treatment (2000 g ha-1) achieved control of all weeds evaluated by more than 80% up to 28 days after application. While atrazine in the same period achieved control below this percentage for Chenopodium album and Brachiaria plantagina. In the same application modality in Tibagi, terbuthylazine (1500 g ha-1 and 2000 g ha-1) also achieved control greater than 80% on the evaluated weeds, while atrazine achieved control below 80% for Eleusine indica. In the post-emergence application modality, in the municipality of Ponta Grossa, terbuthylazine (2000 g ha-1) was effective for all weeds evaluated, being superior to treatment with atrazine. While in the city of Tibagi, atrazine achieved control of less than 80% of the weeds evaluated and terbuthylazine efficiently controlled the Galinsoga parviflora species. Furthermore, weed control from 35 to 56 days after application was greater with the application of terbuthylazine (dose of 2000 g ha-1) than with atrazine in all experiments, indicating greater residual activity of the herbicide in the ground. Consequently, greater productivity gains were observed for treatments with a higher level of weed control and for the weeded control. However, terbuthylazine was superior to atrazine in controlling weeds regardless of application modality and location.