Tank mix involving desiccants plus residual herbicides have been used by farmers in no- till system. Nevertheless, it has been commented that the residual herbicides can stay retained in the straw when used in pre-emergence in this system. The objective of this trial, was to study the reaction of the residual herbicides atrazine and acetochlor in tank mix with desiccants herbicides for corn crop in no-till system. The experiment was settled in Londrina, State of Paraná, using a randomized complete block design in a split plot arrangement. Nine treatments were located at the main plots: 1) acetochlor + glyphosate; 2) acetochlor + glyphosate + 2,4D; 3) acetochlor + paraquat; 4) acetochlor + paraquat + 2,4D; 5) atrazine + glyphosate; 6) atrazine + glyphosate + 2,4D; 7) atrazine + paraquat; 8) atrazine + vegetal oil; 9) check without herbicides. Two modalities of herbicides application of herbicides were tested in split plots: 1) application on a "non rolled" cover crops; 2) application on a "rolled"cover crops. The winter cover crops were a mixture of plants formed by Avena strigosa Schreb plus Vicia sativa L. The best control of Brachiaria plantaginea, Euphorbia heterophylla and Bidens pilosa was obtained with atrazine treatments. In general terms, the treatments "non rolled" were better than the "rolled" ones for weed control. The chromatografic analysis of the soil sampled from the plots before and after 41 mm of a rainfall that occured 24 h after application of the herbicides, showed that less than 6% of the acetochlor applied was detected in soil in both modalities of application. In respect to atrazine however, more than 78% of the total applied was detected in soil after the rain in the "rolled" modality in any treatment. In this case, the highest values were obtained with atrazine + vegetal oil (91%) and atrazine + glyphosate + 2,4D (90%). In the same manner, in "non rolled"modality, the highest values were obtained with atrazine + vegetal oil (77%) and atrazine + glyphosate + 2,4D (70%).
corn; chromatography; mulch