Herbicide application at post emergence stage may cause injuries to maize plants, when these plants are reached randomly by non selective products. Since these herbicides act basically blocking metabolic processes , the question which has been raised is concerned what are the effects that these injuries will result in the grain production. Therefore the objective of this work was to study the phytotoxic effects caused by the application of herbicides at the initial phase and at late post emergency stage of the crop and its effect in the grain production. It was used the hybrid BRS 3123, with 12 treatments in 4 replications. These treatments were performed by the combination of the application of the following herbicides: cyanazine + simazine with or without Assist, applied at growth stages of 4 and 6 corn leaves; paraquat + extravon and ametryn + Assist, applied as directed spray at the growth stage of 12 leaves. In addition, it was included the treatment with and without hoeing and the defoliation of first and third pair of leaves at the 12 leaf stage. It was evaluated: leaf area, dry matter, chlorophyl content in the leaves, plant height, ear height, ear index, weight of ears and grains. The first year (1994/95) the variables of growth were not affected by the treatments, whereas at the following year (1995/96), the best development of plants was obtained by the application of cyanazine + simazine, and the worst treatments were paraquat + extravon, ametryn + assist and the plot without hoeing. The greater production of ears and grains at first year came from the treatment cyanazine + simazine + assist, whereas in the second year, paraquat + extravon and ametryn + Assist resulted in the best yield. Application of herbicides in post emergence at the initial phase of the crop, besides providing a good weed control, did not affect the development of maize plant.
Injury; carbohydrates; recovery; Zea mays