CRITICAL COMPETITION PERIOD BETWEEN COTTON AND (Gossypium hirsutum L.) HARMFUL WEED COMMUNITIES IN THE GOIÁS STATE

Abstract

In order to study the critical time that weeds compete with the cotton plant, five trial experiments were conducted from 1978-1981. Two of the trials were carried out in a dark red latosoil with 4.70% organic matter and 10.73% clay, at the Rio Verde Agricultural School in the state of Goiás, during the 1978—79 and 1979—80 planting seasons. The other three were carried out in dark red latosoil, with a loam clay texture, moderate acidity and a low proportion of organic matter, at the Experimental station in Goiânia, Goiás during the 1978—79, 1979—80 and 1980—81 planting seasons. The treatments designed were: weeding up to 2, 4, 6, 8 first weeks, and weeding during the whole cycle ,and weeding after the 2, 4, 6, 8 first weeks and no weeding at all during the cycle. The results showed that weed competition , when not controlled, determined a yield loss of 88.75% in Goiânia and 90.65% in Rio Verde. Regarding the group control, which was maintained without weed competition, the best yield was obtained when the cotton was maintained without competition during eight weeks after the emergence in Rio Verde and during 4, 6, 8 weeks in Goiânia. The critical competition period occurred between the fourth and sixth weeks after the emergence in Rio Verde and in the fourth week after the emergence in Goiânia.