Shading After Application Affects the Efficacy of Post-Emergence Herbicides

Light and shading after application play an important role on herbicide efficacy, however its effect on different mechanisms of action is not well understood. Therefore, this work was developed with the objective of evaluating the effect of shading on the efficacy of post-emergence application of herbicides with different mechanisms of action. Five independent greenhouse experiments were carried out in Machado - MG, using the herbicides atrazine (500 and 1,000 g ha-1), dicamba (240 and 480 g ha-1), diquat (200 and 400 g ha-1), saflufenacil (24.5 and 49.0 g ha-1), and tembotrione (50.4 and 100.8 g ha-1). Ipomoea triloba plants were used as bioindicator at the phenological stage of 5-6 leaves. The effect of shading was evaluated after applications, once plants were subjected to a period of 48 hours of altered light incidence in all treatments with this factor. A (2×3)+1 factorial arrangement was used for each experiment, consisted of two herbicide rates, three shading levels (100% shade screen, 50% shade screen, and no shade screen), and checkplots without application of herbicides. The shading environment consisted of small chambers fully covered with the respective shade screens (50% and 100%). During the trials, herbicide efficacy was evaluated weekly, as well as dry matter at the end of the period. The efficacy of the herbicides was not hindered by shading after applications. The shading had no significant effect on the efficacy of the herbicide dicamba. The efficacy of atrazine was slightly higher when the plants were kept in the shading chamber after application. Shading after application contributed positively for the efficacy of the herbicides diquat and tembotrione. The herbicides dicamba, diquat, and saflufenacil were effective for post-emergence control of I. triloba.