Posicionamento de herbicidas pré-emergentes na cultura da mandioca: seletividade e eficácia de controle

Abstract

Aiming to stablish greater production levels, in cassava’s crop, the weeds management through pre-emergence herbicides emerges as an option, while its essential to secure its selectivity to the crop, something that its difficulted by the lack of registered herbicides for this crop. Therefore, the purpose of this work was to evaluate the efficacy and selectivity of pre-emergence herbicides with differente mechanisms of action applied in the sow-apply modality in cassava’s crop weed management. The experiment was conducted at the city of Ivinhema-MS with the following geographical coordinates: 22°21’36’’ of latitude south and 53°35’31’’ of longitude west, with an altitude of 327. The predominant weather and sol in the region is Cwa and red-yellow latosol respectively. It was implanted variety IPR Paraguainha maniocs in experimental design of casualized blocks with four repetitions. The experiment was constituted by the following treatments: ametrin (3000g a.i.ha-1); clomazone (1750g a.i.ha-1 ), flumioxazin (125g a.i.ha-1), s-metolachlor (1920g a.i.ha-1), pyroxasulfone (200g a.i.ha-1), isoxaflutol (93,75g a.i.ha-1), metribuzin (1890g a.i.ha-1), diuron (2400g a.i.ha-1), metribuzin + clomazone (373,4 + 1570,32g a.i.ha-1), ametrin + clomazone (1500 + 1570,32g a.i.ha-1), pyroxasulfone + flumioxazin (120 + 80g a.i.ha-1), flumioxazin + s-metolachlor (63 + 1260g a.i.ha-1), sulfentrazone (600g a.i.ha-1), besides two witness with no herbicide application, the first one with weeding and the second onde without it. At 7, 14, 21, 28 and 35 days after the emergence (DAE), it was conducted phytotoxicity evaluations, control, number of plants, crop’s height, stalk diameter and chlorophyll. After 10 months, it was evaluated yield and starch levels through ImageJ® program. All statistical analysis was conducted through R’s software with Deviance analysis and Tukey’s test. All statistical analyses were performed using R software with Deviance Analysis. GAMLSS models with different distributions and link functions were adopted, depending on the variable studied. The effects of Treatment, Period and their interaction were evaluated by the F test, and the results were presented in caterpillar plots to facilitate visual comparison of treatments. At 35 DAE, the treatment sulfentrazone presented the highest levels of phytotoxicity (next to 20%). When evaluated control, it was possible to notice that s-metolachlor when applied alone, provided less efficacy among all treatments with control levels next to 30%. There was no significant difference when evaluated the chlorophyll levels. It’s worth to notice that ametrin, although presented expressive initial phytotoxicity, figured among the highest yields. Therefore, the positioning of ametrin + clomazone, among the registered herbicides, obtained the best control results. For the non-registered herbicides, it’s highlighted the use of metribuzin and flumioxazin + s-metolachlor, which showed control’s efficiency. The positioning of pre-emergence herbicides for cassavas’s crop is a viable modality and essential in weeds management.