Plantas daninhas em pastagens de várzeas no Estado de Minas Gerais

Weed control can raise production costs in agriculture, causing damages to the environment. This study was carried out to investigate the weed populations occurring in pasture of six counties located along the Sao Francisco River, Minas Gerais, Brazil, from May 1997 to April 1999, in Iguatama, Bom Despacho, Luz, Martinho Campos, Pompeu and Abaete. One hundred samples of 0.50 m x 0.50 m from each site were used to calculate frequency, density, abundance, value of importance of each species and the similarity index among the sites. A total of 110 weed species were identified, from 29 botanical families, with the Asteraceae being the family with the greatest number of species in all the sites. The most important species in each site were Vernonia polyanthes, in Iguatama (IVI = 69.32); Corchorus hirtus, in Bom Despacho (IVI = 54.87); Echinochloa cruz-galli, in Pompeu (IVI = 42.27); Ipomoea grandifolia, in Martinho Campos (IVI = 39.13); Hypenia densiflora, in Abaete (IVI = 33.46); and Sida rhombifolia, in Luz (IVI = 28.41). The similarity Index calculated for the localities was low.