Some herbicides can influence the water use efficiency by the direct negative effect on photosynthesis, transpiration and stomatal conductance, or indirect, by reduction of plant metabolic rate. Therefore, this study aimed to evaluate the influence of fluazifop-p-butil and fomesafen herbicides, alone and in mixture, on the characteristics associated with water use efficiency in cassava cultivars, seeking to select the most tolerant cultivar to these herbicides. The experiment was carried out in a greenhouse in a randomized block design with four repetitions. The factorial scheme 5x7 was adopted: the first factor was five cultivars: Cacau-UFV, Platina, Coqueiro, Coimbra e IAC-12; and the second factor was four doses of the commercial mixture of fomesafen + fluazifop-p-butil (0.5; 0.75; 1.0 and 1.5 L ha-1), in addition to the commercial dose recommended for each active ingredient isolated and a control without herbicide. The characteristics evaluated were: stomatal conductance (gs), transpiration rate (E) and water use efficiency (EUA). In general, E, gs and EUA were negatively affected by the application of the herbicide mixture. Cassava cultivars have different levels of sensitivity to fluazifop-p-butil + fomesafen, being the cultivar Platina more tolerant to application of the mixture. Fluazifop-p-butil showed selectivity to the cropand fomasafen caused negative effects on the physiology of cassava.
transpiration; stomatal conductance; herbicides; Manihot esculenta
