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 sabiá 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, sabiá 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 sabiá 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.

Light restriction associated with halosulfuron methyl application efficiently reduces the number and mass of tubers of Cyperus rotundus L.

This study evaluated the effect of light availability in the culture environment and the application of a post emergence herbicide, halosulfuron methyl, on the management of Cyperus rotundus. The experiment was arranged in a 2 × 6 factorial design; the first factor was two levels of light availability: photosynthetically active radiation at 1180.4 and 411.6 µmols m-2 s-1, and the second factor was halosulfuron methyl doses from 28.13 to 140.62 g ha-1. Photosynthetic efficiency, biomass allocation, accumulation of starch in tubers, and percentage control of C. rotundus were evaluated from 7 to 28 days after herbicide application. Doses greater than 70.30 g ha-1 of halosulfuron methyl were efficient to control C. rotundus, regardless of light availability. However, C. rotundus was managed faster under full sunlight than under shading. The efficiency of the photosystem, starch accumulation, and biomass formation decreased with increasing doses of halosulfuron methyl. In a shaded environment, a dose of 28.13 g ha-1 was sufficient to reduce 96.74% of the dry mass and 91.33% of the number of C. rotundus tubers. The decrease in light intensity associated with the use of halosulfuron methyl represents a promising practice for the control of C. rotundus.