The use of strategies such as sequential applications and mixtures may increase the control spectrum and the residual effect of chemical control of weed in the cassava crop. Thus, the objective was to evaluate the selectivity and efficacy of sequential applications and tank mixture of herbicides in the control of weed in the cassava crop cultivar 'Baianinha'. The experimental design was of randomized blocks, with eleven treatments and four replicates. The treatments consisted in: harrowed control, control without harrow, clomazone, mesotrione, S-metolachlor, clomazone+S-metolachlor, mesotrione+S-metolachlor, clomazone+mesotrione, sulfentrazone/clomazone, clomazone/[mesotrione+S-metolachlor], S-metolachlor/[mesotrione+clomazone]. The doses used for clomazone, mesotrione, sulfentrazone and S-metolachlor in the single applications, in sequence and in tank mixture were of 1.25, 0.24; 0.6 and 1.92 kg ha -1 , respectively. The first application of the sequential treatments occurred 50 days after planting (DAP) and the second at 92 DAP. The applications of mesotrione, mesotrione+clomazone and mesotrione+S-metolachlor, were carried late, at 92 DAP. Based on the data obtained, it is concluded that the mixture mesotrione+S-metolachlor and the sequential application of clomazone/ [mesotrione+S-metolachlor] were selective to cassava 'Baianinha' and efficient in the weed control (over 80% up to 148 days after planting).

The development of cassava varieties with more efficient nutrient absorption can prevent losses caused by weed competition. The objective of this study was to evaluate dry matter accumulation and leaf nutrient content in traditional and improved cassava varieties, with and without coexistence with weeds throughout the cycle. A randomized complete block design was used in a 2 x 2 x 11 factorial scheme with four replications. The first factor consisted of two varieties (Baianinha and Clone 56-03); the second factor was composed of the conditions with and without coexistence with weeds, and the third factor was 11 harvest periods. Coexistence with weeds reduced leaf contents of N (20.8% and 24.8%), P (26.7% and 4.6%) and K (27.1% and 12.6%) for 'Baianinha' and 'Clone 56-03', respectively. For coexistence with 'Baianinha', the period up to the maximum daily nutrient accumulation rate (N, P and K) ranged from 82 to 99 days after planting (DAP), while for 'Clone 56-03', coexistence in this period ranged from 80 to 88 DAP. The plants from the variety 'Clone 56-03' presented higher total dry mass and root dry mass accumulation, as well as higher leaf contents of N, P and K than the traditional cassava variety 'Baianinha', especially when in coexistence with weeds during the whole cycle.

The objective of the present study was to evaluate the row hoe model CHOPSTAR®, the mechanical control of weeds in between the rows of soybean implanted in organic direct sowing system, associated with the camera-guided system. Two experiments were carried, being that in the first experiment an experimental design with sub-subdivided plots with four replicates. The plots corresponded to two soybean varieties ('Embrapa BRS 284' and 'Coodetec CD 216'), the subplots corresponded to the sowing densities of 329.2 and 574.6 thousand plants ha -1 ; and the subsubplots corresponded to four managements of weeds: one mechanized hoe (2 days after sowing -DAS), two mechanized hoes (22 and 47 DAS), one control manually hoed and other control without hoeing. In the second experiment a randomized block design in subdivided plots with three replicates was used. The plots corresponded to two soybean varieties ('BRS 284' and 'DF 2353'), Fey et al.; JEAI, 42(2): 25-36, 2020; Article no.JEAI.55215 26 the subplots constituted of different times when the hoes were made, being: one (14 DAS); two (7 and 21 DAS; two (14 and 28 DAS); three (7, 14 and 28 DAS); besides one control manually hoed up to 28 DAS. In the first experiment it was observed that the automatized hoe was efficient in controlling the weeds and it was necessary only one mechanized hoe (22 DAS) for the 'BRS 284' independent of the sowing density, while for the 'CD 216' the number of mechanized hoes depended on the sowing density. In the second experiment, it was necessary only one mechanized hoe (14 DAS) to avoid production losses in the varieties 'BRS 284' and 'DF 2353'. The automatized hoe is an alternative to control weeds in areas of organic soybean in direct sowing system, however, damages to the crop can occur depending on the sowing density, mainly in the late management of the mechanized hoe. Original Research Article

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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 1 st 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 2 nd 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.

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.