Efeito da redução de luz na seletividade a herbicidas e rendimento de grãos do trigo

The solar radiation reduction incident on the terrestrial surface can changes the vegetal behavior and the herbicide selectivity. The aim of this work was to evaluate the herbicide selectivity bentazon, iodosulfuron-methyl-sodium and grain yield of wheat under conditions of reduction of luminosity in different phenological stages of the crop. Two experiments were conducted, the first (I) under controlled conditions and the second (II) in field. In both experiments, wheat was evaluated according to the herbicide application (bentazone, 900 g ha-1 a.i., iodosulfuron-methyl sodium, 5 g ha-1 a.i., and control, without herbicide application) and the variation of the light rate (control; light reduction during the entire cycle; reduction in the initial stage, from emergence to three expanded leaves; reduction in the vegetative stage, three expanded leaves to complete emergence of the inflorescence; and reduction in the reproductive phase, from inflorescence to harvest. The results show that light reduction alters morphophysiological characteristics of wheat, increases plant height, reduces transpiration and stomatal conductance rate, but does not interfere with cereal photosynthesis. However, grain yield is negatively affected by the reduction of light during the vegetative stage, ontogenetic period that coincides with the formation of the main composites of crop yield. The evaluated herbicides are selective to wheat, with or without reduction of luminosity.