To verify the behavior of the c. IAC -17, as well as, the control of weeds and competitive aspects of the infesting floristic complexes over the cotton culture under the presence of the herbicides, diuron and sethoxydium, atrial was contucted in Viçosa, Minas Gerais. The soil at the experimental site, Podzolic Red-yellow, had a clay texture wi th 1,38% of organic carbon an low natural fertility. Diuron was applied at pre -emergence time at the rates of 0, 0; 0, 8; 1,6 and 2,4 kg a.i. /ha and sethoxyd im at post-emergence at the rates of 0, 150, 300, 450 and 600 g a.i./ha. The trial was setup in a randomized blocks design with 2 1 treament sunder a factorial scheme (x 5 + 1) . Out of them, 20 composed all the combinations with different dosis of the two herbicides under study plus a relative control weeded with the aind of a mattock. Several traits concerning growth and plant development were evaluated, such as leaf area, leaf area in dex, seed -cotton yield, plant height, stem diameter. By means of syn ecological methods, th e population density, hydrated epigeous phytomase of dominant weed species, and the total of all species were evaluated. Diuron exerted a high control overlati foliates such as Galinsoga parviflora Cav . and Bidens pilosa L., at the rates of 1, 6 an d 2,4 kg a. i. /ha, seth oxydim, even using the lowvest tested rate (150 g. a. i. /h a) fully controled Brachiaria plantaginea (Link.) Hitch. None of th e herbicides was able to control Emilia sonchifolia DC. Th is species although being considered an important weed did not affect the normal crop development because of its low competition ability. The weeds showing highes trates of competition were G. parviflora (due to high population density) an d B. plantaginea, because of its greater aggresivity.
Upland-type cotton; weeds; diuron; sethoxydim; competition