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The study aimed to determine the interference periods of weeds in cassava 'IAC 90' cultivated in different cycles and cropping systems. An experiment was conducted in the period 2014/15 (1st cycle) and another was conducted from the pruning of cassava plants in the period 2015/16 (2nd cycle). The experimental design was a randomized block design with splitsplit plots and four replicates. The plots represented the cropping systems (conventional and no-tillage) and the split-split plots corresponded to the periods with and without coexistence with weeds (0, 25, 50, 75, 100, 125, 150, 175, 200 and 225 days after planting or pruning - DAP/DAPr). In the 1st cycle, there was no interaction between the cropping systems and the coexistence periods and, therefore, based on the acceptable losses of 5% in the root and starch yield of 'IAC 90' cassava, the PCPI was estimated between 20 and 212 DAP and 14 to 214 DAP, respectively. In the 2nd cycle, the CPPWI ranged from 17 to 176 DAPr and 30 to 216 DAPr based on the root and starch yield obtained in the conventional method, respectively. While in no-tillage, the estimated CPPWI ranged from 18 to 198 DAPr and 9 to 218 DAPr based on root and starch yield, respectively. In general, the data indicate that conventional weed management should be carried out in a more intensified way than in no-tillage. In addition, CPPWI based on starch losses can avoid losses in root production. [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]

The interaction with weeds jeopardizes the nutrients accumulation in the carrots' plants. The mulch can reduce competition effects and provide advantages to the cultivation. This research aimed to assess the black oat (Avena strigosa Schreb.) hay mulch effect on dry matter accumulation of weeds and nutrients (N, P, K, and S) accumulation in the carrots plants cultivar "Alvorada." The experiments were set during the crop seasons 2016/2017 and 2017/2018 in a randomized-block design with a factorial scheme 2 x 5, with five repetitions. The first factor corresponded to soil cover (with or without mulch), and the second factor, to the interaction time with weeds (0, 15, 30, 60, and 120 days after emergence). The interaction with the weed community reduced nutrients absorption and dry matter accumulation in the roots of the carrot's plants. Interference with nutrients absorption was more intense in crops without black oat hay mulch than with mulch. Mulch can reduce weeds' dry mass by 75.6% during the entire culture cycle. Therefore black oak oat mulch reduces the weed interference allowing higher nutrients accumulation and roots biomass in the carrots plants cultivar "Alvorada.". [ABSTRACT FROM AUTHOR]

The selectivity and efficacy of protoporphyrinogen oxidase (PROTOX) inhibitor herbicides in cassava varieties depend on product formulation, dosage, and soil texture. The aim of this study was to assess the selectivity and efficacy of flumioxazin and sulfentrazone in the cassava variety 'IPR B36' and the clone 'VN 117'. Two experiments were carried out: one in a clayey soil and one in a sandy soil. Both experiments were laid in a split-plot randomized block design with three replicates. The two cassava varieties were used as main plots, with subplots consisting in 10 treatments including, flumioxazin at 50, 75, 100, and 125 g ha-1; sulfentrazone at 250, 500, 750, and 1000 g ha-1; one weed-free control, and one unweeded control. Flumioxazin (=75 g ha-1) and sulfentrazone (=250 g ha-1) achieved mean weed control rates > 70 and 90% in both types of soil for up to 90 days after application. Flumioxazin exhibited fewer residual effects on the cassava varieties than sulfentrazone, particularly in clayey soil. Flumioxazin was selective to the different cassava varieties planted in both soil types, whereas sulfentrazone was more selective in clayey soil. PROTOX inhibitors were effective in controlling weed growth in cassava plots, and there were no varietal differences in herbicide selectivity; however, the use of sulfentrazone should be restricted to maximum spray rates of 250 g ha-1 in sandy soils. [ABSTRACT FROM AUTHOR]