Effect of glyphosate in Johnsongrass submitted to different soil water potentials.

This work aimed to study the efficiency of herbicide glyphosate to control Johnsongrass plants ( Sorghum halepense ) in different phenological stages of development and when submitted to different types of soil water potentials. The study was conducted in a completely randomized design, with four repetitions. The treatments were arranged in a triple factor scheme 3 × 3 × 2, being: three soil water conditions [no water deficit (-0.03 MPa), intermediate water deficit (-0.07 MPa), and high water deficit (-1.5 MPa)], associated with three doses of glyphosate (0.0, 270.0, and 540.0 g a.e. ha-1 ) applied in two phenological stages (4-6 leaves and 1-3 tillers). Visual control evaluations were conducted at 7, 14, 21, and 35 days after the herbicide application. Biometric and morphophysiological parameters were also analyzed. With the increase of water restriction, there was a decrease in Johnsongrass morphophysiological components, such as specific leaf area, stomatal conductance, and the difference between environment and leaf temperature, as well as the accumulation of aerial part and roots dry matter, independently of the phenological stage evaluated. The development stage of Johnsongrass influenced the control provided by glyphosate, independently of the dose used. The different water deficits studied reduced the control of glyphosate in the two Johnsongrass development stages evaluated. Severe water deficits reduced the control of glyphosate in Johnsongrass using the recommended dose. In conditions of moderate water deficit, the control was not affected. Thus, the control with lower doses can be the most affected by water deficit.