CRITICAL PERIOD OF WEED COMPETITION ON IR RIGATED ANNUAL COTTON

A field trial was conducted in Boa Ventura, PB, Brazil, in 1986, to in vestigate the effect of row spacing on critical period of weed competi tion on irrigated annual cotton (Gossypium hirsutum L.r. latifolium Hu tch.). The results showed that, 1) the presence of weeds for a period of 20 days after plant emerging did not consistently affect cotton yie ld; 2) weed-free periods of 40, 60 and 80 days promoted higher cotton yields than the whole-cicle weed-free control; 3) wider row spacing co tton had a long critical period of weed competition (30 days) and the competitive process began earlier(16 days after emergence); and 4) for narrow row-spacing cotton, the critical period was shorter (12 days) and the weed interference took place later (28 days) when the plants w ere more resistent to weed competition.