Tolerance of cassava to postemergence herbicides and determination of residues in the roots

Assessing the tolerance of cassava to herbicides is essential for the development of weed management programs. Nevertheless, this assessment must include analyses of herbicide residues in the food so as to guarantee safety to the final consumer. Thus, this study evaluates the selectivity of cassava to different herbicides and quantifies pesticide residues in cassava roots ( Manihot esculenta Crantz). The experimental design was randomized blocks with four replicates. The treatments were: control; mechanical weeding; bentazon (900 g a.i. ha -1 ); mesotrione (120 g a.i. ha -1 ); and imazethapyr (100 g a.i. ha -1 ), applied in postemergence. We used the herbicides clomazone (1080 g a.i. ha -1 ) and fluazifop (125 g a.i. ha -1 ) in pre-emergence and postemergence, respectively, in all treatments. Throughout the crop cycle, we assessed the following: cassava intoxication at 10, 20, and 30 days after the application (DAA) of postemergence herbicides; and plant height and stem diameter at 30 DAA. At the end of the crop cycle, we assessed the following: number of roots per plant; root length and diameter; root yield (kg/ha); starch content (%); and pesticide residues in cassava roots (multiresidue method). Despite its high phytotoxicity in the early development of cassava, mesotrione shows high selectivity and viability for weed control in this crop since, in general, it did not impair the other yield variables. Moreover, the study identified clomazone and sulfentrazone residues in cassava, indicating root contamination and high persistence of these herbicides in the environment.