Selectivity and efficiency of herbicides in cassava on the floodplain of the Solimões river

Resumo

Cassava is grown on the floodplains of the Solimões river and guarantees food security and income for farmers. However, negative interference of weeds can result in a significant yield loss in the crop. Therefore, the aim of this study was to evaluate the selectivity of herbicides and efficiency of chemical weed control in the cassava ‘Aipim-manteiga’ cultivar, in the floodplain of the Solimões river, in Iranduba, Amazonas. The experimental design was in randomized blocks with four replications. The herbicides evaluated were clomazone (1080 g ha-1), diuron (1750 and 2500 g ha-1) and oxadiazon (400 and 800 g ha-1), applied alone or with hoeing 90 days after planting (DAP). Two control treatments were included: weeding (hoeing) at 30, 60, 90 and 120 DAP and with no weed control. Clomazone caused mild toxicity in the plants, while with diuron and oxadiazon toxicity was moderate; all three were considered safe for the crop. The plant population of the crop was not affected by the herbicides. Clomazone afforded effective weed control up to 45 DAP only, and weeding was necessary at 90 DAP to eliminate negative interference by the weeds on crop yield. Diuron and oxadiazon were effective in controlling weeds throughout the crop cycle of the cassava. Weed interference during the crop life cicle reduced yield by 83.8%.