ABSTRACT
The rotation of herbicides is the main method used in the prevention and management of herbicide-resistant weeds. However, in addition to being efficient, herbicides should also be crop selective. The objective of this study was to evaluate the selectivity of herbicides with potential use in the control of hairy fleabane, to white oats, common oats, common ryegrass and tetraploid ryegrass. The experiments were arranged in a randomised-block design, in a bi-factorial scheme, with factor A comprising the herbicides, and factor B the herbicide doses X and 2X, where X is the recommended dose of the active ingredient (a.i.). The treatments to be evaluated were: 2,4-D amine (806 and 1,612 g a.i. ha-1); metsulfuron-methyl (2.4 and 4.8 g a.i. ha-1); chlorimuron-ethyl (20 and 40 g a.i. ha-1); imazethapyr (350 and 700 g a.i. ha-1); diclosulam (16.8 and 33.6 g a.i. ha-1); saflufenacil (35 and 70 g a.i. ha-1) and flumioxazin (50 and 100 g a.i. ha-1), as well as the control (no herbicide). Except for the herbicide imazethapyr, the other herbicides were selective to white oats, regardless of the dose. The herbicides 2,4-D, diclosulam, saflufenacil and flumioxazin were selective to common oats when applied at the lowest dose tested, being alternatives in the management of hairy fleabane during the winter. The herbicide metsulfuron-methyl had a toxic effect on common ryegrass, reducing shoot dry matter weight (SDW). Except for imazethapyr and the highest dose of flumioxazin, the remaining treatments were selective to tetraploid ryegrass. Although some treatments produced symptoms of phytotoxicity, this did not reflect negatively on the production of SDW, demonstrating the resilience of the plants.
Key words:
Conyza bonariensis
; Resistance of weeds; Winter pasture;
Lolium multiflorum
; Avena spp