The present work aimed to evaluate the behavior of glyphosate herbicide in aquatic environment, considering some water quality parameters, in reservoir conditions without flow and without replacement of evapotranspired water. Twenty reservoirs (polyethylene water tanks) with a storage capacity of 1000 liters were used. The recommended herbicide dose according to the manufacturer was 7.0 L or 3360 grams of acid equivalent per hectare. For application in the reservoirs, a precision equipment was used to carbon dioxide (CO2), providing a flow of 200 L·ha-1. Freezing macrophyte death was achieved by storing the plants in a freezer at -18°C for a period of 48 hours. The analyses of control efficiency were performed at 7, 14, 21, 28, 35 and 42 days after application (DAA). Water samples for analysis of quality indicators, pH and dissolved oxygen were collected weekly for nine weeks. The obtained result allows concluding that the herbicide glyphosate presented excellent control efficiency of water hyacinth and did not significantly alter the water quality parameters pH and dissolved oxygen, indicating its use in the management of this macrophyte.
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