Efficiency of Glyphosate to Control Crabgrass in Different Phenological Stages and Soil Water Potentials

Herbicide efficacy on weeds under water deficit conditions may be reduced because water stress decreases cuticle hydration, thereby limiting the penetration of herbicides such as glyphosate. This study evaluated the efficiency of the herbicide glyphosate to control crabgrass (<i>Digitaria nuda</i> Schumach.) in different phenological stages of development and when submitted to distinct soil water potentials. A completely randomized design with four replicates was adopted. The treatments were arranged in a 3 × 3 × 2 factorial scheme, consisting of three soil water conditions (-0.03, -0.07, and -1.5 MPa), three glyphosate doses (0.0, 270.0, and 540.0 g a.e. ha^-1, corresponding to 0, 50, and 100% of the label-recommended dose, respectively), and two phenological stages (4-6 leaves and 1-3 tillers). The following were evaluated: the specific leaf area, stomatal conductance, the difference between environmental and leaf temperature, and shoot and root dry matter. There is a decrease in crabgrass morphophysiological components according to the increase of water restriction, regardless of the phenological stage evaluated. The 4-6 leaves stage of crabgrass plants influences the control provided by the herbicide glyphosate, irrespective of the dose used. The different water deficits studied reduced the efficiency of the herbicide glyphosate in the two development stages of crabgrass plants.