Effects of herbicide underdoses on the vegetative development of Panicum maximum cultivars

The advance of intercropping has generated the need for studies that evaluate methods of suppression of forage grasses in order to not harm the development of the commercial culture. The aim of this study is to evaluate the sensitivity of forage grasses to post-emergence herbicide application. To this end, an experiment was carried out in a greenhouse using a randomized complete block design in a 4 x 9 factorial scheme with four replicates. The first factor consisted of the forage grasses Urochloa ruziziensis, Panicum maximum cv. BRS Tamani, P. maximum cv. BRS Quenia, and P. maximum cv. BRS Zuri. The second factor consisted of the combination of eight herbicide treatments applied at post-emergence in association with atrazine (1200 g a.i. ha -1 ), besides a control treatment, without application. P. maximum cv. BRS Kenya was the least sensitive to post-emergence herbicide application. Tembotrione (42 and 84 g a.i. ha -1 ) and mesotrione (48 and 96 g a.i. ha -1 ) have potential for suppression of U. ruziziensis . Tembotrione (84 g a.i. ha -1 ), glyphosate (200 g a.i. ha -1 ), and nicosulfuron (7.8 g a.i. ha -1 ) have potential for suppression of the cv. BRS Kenya, and tembotrione (42 g a.i. ha -1 ) and mesotrione (96 g a.i. ha -1 ) have potential for the suppression of BRS Tamani. The P. maximum cv. BRS Zuri presented a higher plant height, shoot dry matter, and root dry matter than the other forages evaluated. For this forage, the use of nicosulfuron herbicides at post-emergence, regardless of the dose, reduced the shoot dry matter by 70%.