Estratégias de manejo das plantas daninhas na cultura da mandioca em diferentes sistemas de cultivo e texturas de solo

Abstract

Herbicide selectivity and weed control efficiency can vary according to the cropping system and soil texture. The aim was therefore to assess the selectivity and effectiveness of herbicide management strategies in controlling weeds under different cropping systems and soil textures. Four experiments were set up in a randomized block design with four replications with 'BRS CS01' cassava, using conventional and no-till systems in sandy and clay soils. The treatments and their respective doses (g ha-1) consisted of: [clomazone + amethrin (800+1200)]/S-metolachlor + clethodim + mineral oil (1920+250); [clomazone + amethrin + vegetable oil (800+1200)]/S-metolachlor + clethodim + vegetable oil (1920+250); [pyroxasulfone + flumioxazin (200+200)]/clomazone + clethodim + mineral oil (1250+250); [pyroxasulfone + flumioxazin + vegetable oil (200+200)]/clomazone + clethodim + vegetable oil (1250+250); the dose recommendation of 0.5% of the spray volume was standardized for mineral and vegetable oil. A control with coexistence and one without coexistence were added. In the experiments on sandy soil, damage was only noticed after the second sequential application, with phytointoxication averaging 60 and 78% in plants treated with clomazone (1250 g ha-1) 4 days after the first application in the conventional system and 3 days after the second application in the no-till system. As for the treatments containing S-metolachlor (1920 g ha-1), the plants showed symptoms below 35%, regardless of the cropping system used, which regressed over time. On the other hand, the first sequential application of the [pyroxasulfone + flumioxazin] mixture showed a residual control effect up to 59 days after the first application, regardless of the presence of vegetable oil in the mixture, while the [clomazone + ametrine] mixture showed 28% more persistence in the soil when associated with vegetable oil. In general, the strategies containing [pyroxasulfone + flumioxazin + vegetable oil (200+200)]/clomazone + clethodim + vegetable oil (1250+250) and [pyroxasulfone + flumioxazin (200+200)]/clomazone + clethodim + mineral oil (1250+250) maintained weed control above 90% until the end of the evaluations, regardless of the cropping system. Similarly, there was similar control efficiency following applications of [clomazone + amethrin + vegetable oil (800+1200)]/S-metolachlor + clethodim + vegetable oil (1920+250) and [clomazone + amethrin (800+1200)]/S-metolachlor + clethodim + mineral oil (1920+250) in the conventional system. However, in the no-till experiment, these herbicides showed control below 70% at 81 days after the first application. In the experiments on clay soil, phytointoxication was noted in both cropping systems after the second sequential application, reaching symptoms of up to 60% at 5 days after the second application. At 21 days after the second application, the plants in both cropping systems already showed a reduction in damage (<30%), demonstrating the recovery of symptoms. The addition of vegetable oil in a mixture with [pyroxasulfone + flumioxazin] in the 1st sequential application did not increase the residual effect in the soil, regardless of the cropping system evaluated. The same scenario was observed with the [clomazone + ametrin] mixture in a no-till system, but when evaluating this mixture in a conventional system, an increase of 13 days more residual effect was observed when associated with vegetable oil. In theory, all the management strategies showed weed community control of over 88% up to 66 days after the first application, which is in line with the tendency to reduce weed biomass collected at 100 days after the first application in both cropping systems. The treatments proved to be selective for the 'BRS CS01' cultivar grown in clay soil, regardless of the cultivation system used, as well as showing higher average yields and starch accumulation in the plants grown in the no-till system compared to conventional planting. Thus, it can be concluded that the management strategies containing the [pyroxasulfone+flumioxazin] mixture applied in the first sequential application were efficient in controlling weeds in the experiments on sandy and clay soil, regardless of the cropping system used, while the strategies containing the [clomazone+amethrin] mixture showed inadequate control only on sandy soil in the no-till system. It was found that the herbicides included in the management strategies were selective for the cultivar 'BRS CS01', regardless of soil texture and cropping system.