The light intensity in the cultivation environment and the impact of glyphosate on plants of the Urochloa genus

The variation in light within the environment triggers morphophysiological changes in plants and can lead to distinct responses in sun-exposed or shaded plants to glyphosate. The response of Urochloa genotypes subjected to desiccation with 2160, 1622.4, 1080, 524.4, 273.6, and 0.0 g ha(-1) of glyphosate was evaluated in full sun and shade conditions. Cayana grass, mulato II grass, and sabi & aacute; grass - hybrids recently launched on the market, in addition to palisade grass and congo grass were evaluated. Under full sun, we achieved control of congo grass using 1080 g ha(-1) of glyphosate, while the other grasses required 2160 g ha(-1). In the low-light environment, sabi & aacute; grass was effectively controlled with 524.4 g ha(-1) of glyphosate, but the other grasses needed 273.6 g ha(-1). In shading, compared to full sun, the savings with glyphosate were 75 and 76% for the control of congo grass and sabi & aacute; grass, respectively, and 87% for palisade grass, mulato II grass and cayana grass. Increasing glyphosate doses leads to a decline in the quantum efficiency of photosystem II and in the electron transport rate, especially in the shade. Urochloa genotypes are more sensitive to glyphosate in the shade, which must be considered when determining the herbicide dose.