Resumo. This work aimed to evaluate the efficiency of herbicide in reduction of growth stress effects on the incidence of splits and warps on boards originated from Ecalyptus grandis trees. For this, 40 trees were randomly selected, subdivided into four chemical treatments with application of herbicide (“Imazapyr” active principle) and one treatment without herbicide application, with eight repetitions each. After the action of herbicide, the trees were harvested and the first log of each tree was cut. The logs were sawn to perform the analyzes before and after air drying operation. The results indicated higher efficiency of herbicide in treatments 4 and 5 on the effect of growth stresses in the form of splits in the boards. For the crook, the treatments 2 and 4 showed the lowest levels of defects. The bow had influence of air drying operation, while the cup was not observed significantly in the pieces of sawn timber from five treatments.