Six assays were carried out under greenhouse conditions to study the efficacy of diquat, glyphosate, sulfosate, imazapyr, 2,4-D, metsulfuron-methyl, sulfentrazone and imazapic in controlling Eichhornia crassipes (Mart.) Solms. The same CO2 pressurized sprayer was used in all assays. Diquat , glyphosate , imazapyr and sulfentrazone were studied in the first assay. Diquat and glyphosate were highly efficient in controlling E. crassipes. The symptoms developed faster in diquat-treated plants. The symptoms promoted by imazapyr and sulfentrazone were progressive all over the experimental period, suggesting that higher control intensity could be achieved obtained during a longer observation time. Waterhyacinth control was studied in the second assay, using diquat, glyphosate, imazapyr, imazapic, 2,4-D, metsulfuron-methyl, and sulphosate. Diquat, glyphosate, imazapyr and 2,4-D showed good control of waterhyacinth The control promoted by diquat and 2,4-D showed quick results. Imazapyr showed slow control action. Under the experimental conditions, imazapic, sulfosate and metsulfuron-methyl did not show good control of this aquatic weed. Waterhyacinth control promoted by imazapyr and glyphosate sprayed at 3, 6, and 9 hours before simulated rain were studied. Glyphosate was more efficient in controlling E. crassipes than imazapyr. For glyphosate, the interval between spraying and rain did not affect the final control (thirty days after spraying), but the development of the symptom was faster at higher doses. In the fourth assay, waterhyacinth control was studied using diquat sprayed during the day or at night. The herbicide was efficient in controlling waterhyacinth at 1,0 L ha-1 or higher. Night spraying showed faster symptoms than day-spraying, but the symptons were similar in the final control. In the fifth assay, diquat's waterhyacinth control efficacy was studied. It was sprayed during the day or night, at intervals of 30, 60 and 120 minutes between spraying and simulated rain. Diquat was very efficient in controlling waterhyacinth, mainly at 2,00 L ha-1. Herbicide action was stronger during night spraying when broader intervals occurred between spraying and the first rain. A last assay was carried out under field conditions, to study waterhyacinth control by imazapyr sprayed on E. crassipes grown in small ponds. All the doses promoted a good waterhyacinth control. The effects were faster at higher doses.
herbicide; aquatic plant; weed
