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The objective of this study was to evaluate the selectivity of cassava cultivar 'Santa Helena' and the efficiency of weed control using herbicides applied alone or tank mixed with and without sequential applications. Two experiments were carried out, both in a randomized block design with four replications. The treatments for the 1st experiment were: Hand hoeing (weed-free control); No hand hoeing (non-weeded control); sulfentrazone (500 g ha-1); sulfentrazone/[clomazone + clethodim] (500/[1125 + 120] g ha-1); sulfentrazone/mesotrione (500/240 g ha-1); S-metolachlor (1920 g ha-1); S-metolachlor/[clomazone + clethodim] (1920/[1125 + 120] g ha-1); S-metolachlor/mesotrione](1920/240 g ha-1); [sulfentrazone + S-metolachlor]/[clomazone + clethodim] ([500 + 1920]/[1125 + 120] g ha-1); [sulfentrazone + S-metolachlor]/mesotrione ([500 + 1920]/240 g ha-1). The treatments of the 2nd experiment were: Hand hoeing (weed-free control); No hand hoeing (non-weeded control); glyphosate (360 g ha-1) + hand hoeing; glyphosate + sulfentrazone (360 + 500 g ha-1); glyphosate + flumioxazin (360 + 50 g ha-1); glyphosate + clomazone (360 + 1125 g ha-1); glyphosate + S-metolachlor (360 + 1920 g ha-1); glyphosate + sulfentrazone + clomazone (360 + 400 + 900 g ha-1); glyphosate + sulfentrazone + Smetolachlor (360 + 400 + 1440 g ha-1); glyphosate + flumioxazin + clomazone (360 + 40 + 900 g ha-1); glyphosate + flumioxazin + S-metolachlor (360 + 40 + 1440 g ha-1). In the first experiment, only the treatments S-metolachlor, Smetolachlor/[ clomazone + clethodim] and S-metolachlor/mesotrione did not present efficient weed control, causing reduction in yields; the other treatments were crop selective and efficient. In the second experiment, all treatments showed excellent levels of weed control up to 65 DAA and were crop selective. It is concluded that applications of tank mixtures, sequential mixtures and the use of glyphosate mixed with pre-emergent herbicides constitute excellent alternatives of weed management strategies in 'Santa Helena' cassava. [ABSTRACT FROM AUTHOR]

The competition caused by weeds in the cassava culture significantly reduces their productive potential and consequently the profitability for the producer. Thus, the objective was to determine the period prior to interference (PPI) and the period prior to damage to economic yield (PPDEY) of weeds in cassava varieties. The design used was randomized blocks in factorial 2 × 2 × 12, with four replications. The first factor was constituted by two varieties ('Baianinha' and 'Clone 56-03'), the second factor was constituted by the conditions of coexistence (with and without) of the crop with the weeds and the third factor corresponded to 12 periods (0, 20, 40, 60, 80, 100, 120, 140, 160, 180, 200, and 220 days after planting - DAP). 'Baianinha' was less tolerant of weed competition compared to 'Clone 56-03'. Considering the use of arbitrary and economic criteria of acceptable losses in the root productivities, the PPI and PPDEY of 11 and 65 DAP were determined for 'Baianinha' and 44 and 138 DAP for 'Clone 56-03', respectively. Likewise, considering the starch productivity data, the PPI and PPDEY of 8 and 21 DAP were determined for 'Baianinha' and 38 and 84 DAP for 'Clone 56-03', respectively. [ABSTRACT FROM AUTHOR]