Control químico de malezas en maíz en un sistema de siembra directa

in order to evaluate the efficacy and period of weed of two preplanting herbicides, five preemergence herbicides and two selective postemergence herbicides, in a maize, zea mays l., no tillage system, a trial was established at the agronomy faculty of the central universidad of venezuela with the white hybrid (himeca 2000). treatments were arranged in a randomized block desing with four replicates. treatments were: paraquat + diuron, paraquat + diuron + acetochlor + fluorochloridone, paraquat + diuron + metolachlor, paraquat + diuron + pendimethalin + atrazine, paraquat + diuron + nicolsufuron + atrazine, paraquat + diuron + nicolsufuron + bentazone + mcpa, trimesium glyphosate, trimesium glyphosate + acetochlor + fluorochloridone, trimesium glyphosate + metolachlor, trimesium glyphosate + pendimenthalin + atrazine, trimesium glyphosate + nicosulfuron + atrazine, trimesium glyphosate + nicosulfuron + bentazone + mcpa. an equipment of constant pressure with co2 to 200 l ha-1 of herbicide solution was used. weeds species were evaluated by visual control index and dry weight, maize was evaluated by, phytotoxicity, yield and plant dry weigth. results showed that preplant herbicides provided similar and insufficient control of grasses and broad leaves, nevertheless trimesium glyphosate produced better control of cyperus rotundus. it was necessary to apply selective postemergences herbicides to improve weed control. the preemergences herbicides used in mixtures with presowing treatment, did not offter satisfactory weed control. only acetochlor + fluorochloridone caused moderate damage to crop. total dry weight of weeds had a negative correlation with maize yield. the best yields of maize were reached when the two selective postemergence herbicides were used in sequence with any of the preplanting treatments.