An experiment was conducted at the Research Station of the University of Chapingo (Mexico) (2250 m above sea level, average annual rainfall 550 mm( loamy soil, 1,7% O.M.), where different cultural practices were combined in order to design a weed control system for corn. The work was done under rainfed conditions and the variables included were: two population densities (44.400 and 66.600 pl/ha), two plant distributions (normal and equidistant) and seven weed control methods (cyanazine + alachlor (1,2 + 1,92 kg/ha), atrazine + alachlor (1,2 + 1,44 kg/ha), one cultivation, two cultivations, a weeded check, a weeded check + two cultivations and a weedy check). The main weed species were: pigweed (Amaranthus sp.), Lopezia mexicana Jacq., hairy galinsoga (Galin-soga parviflora Cay.), Encelia mexicana Mart., Sporobulus poiretti (Roem. et Sch.) Hich., and large crabgrass (Digitaria sanguinalis (L.) Scop.). The increase in plant population had no effect on the degree of weed control, incidence of diseases and crop growth. The equidistant distribution improved weed control over the normal one, but it also had a nigher incidence of diseases; this, is turn, may have caused the lack of differences in vegetative growth, a lower amount of cobs per ha and the lack of difference in grain yield between the two distributions. Atrazine + alachlor was better than cyanazine + alachlor in terms of weed control, although the difference was statistically observed only for the visual ratings. There were no differences between both chemical treatments in terms of incidence of diseases or their effect on crop growth, but grain yield for cyanazine + alachlor was slightly lower. The chemical methods were better than the mechanical ones regarding weed control, but no differences were detected in terms of in cidence of diseases or crop growth. One additional weeding does not improved weed control significantly, nor does it affect the incidence of diseases or crop growth, thus appearing to be unnecessary. The main effect of cultivations is weed control, and if this can be done in any other way, cultivating does not bring about additional benefits.
weed; corn; control methods; plant population