A weed infestation survey was carried out in the two main cultivation regions of autumn corn crops in the State of São Paulo. In the Médio Vale do Paranapanema 85 plantations were visited and in the Região Norte 29 plantations. In this region four crops were sowed directly and 25 after soil preparation with a single harrowing, all without herbicides. In Região do Paranapanema the direct seeding was done in 68 crops, in 11 a single harrowing was done and, in six, a double harrowing, with post-emergence herbicides being used in some areas. The weed species ocurring in Região Norte, according to their frequency, were: Glycine max> Amaranthus retroflexus> Bidens pilosa = Acanthospermum hispidum = Alternanthera tenella > Cenchrus echinatus > Euphorbia heterophylla > Ipomoea spp. > Commelina benghalensis > Sida spp. = Eleusine indica; and, in the Region of Médio Vale do Paranapanema: Euphorbia heterophylla = Glycine max = Commelina benghalensis > Bidens pilosa = Raphanus sativus > Cenchrus echinatus = Acanthospermum hispidum > Brachiaria plantaginea > Sida spp. = Coronopus didymus > Eleusine indica > Digitaria horizontalis > Amaranthus retroflexus. The rates of high weed infestation were as follows: direct seeding > single harrowing > doble harrowing. Commelina benghalensis, Digitaria horizontalis, Sida spp., Eleusine indica and Amaranthus hybridus, occured only with direct seeding in the Region of Paranapanema. In the North Region Ipomoea spp. and Euphorbia heterophylla ocurred only with single harrowing.
Zea mays; soil preparation; weed infestation; direct seeding; herbicides