EFFECTS OF HERBICIDES ON AQUATIC MACROPHYTES

The effects of the herbicides atrazine, 2,4-D, glyphosate (direct and rodeo) and trifluralin were determined on the growth and death of fron ds of the aquatic macrophytes Spirodela punctata (G.F.W. Meyer) Thomps on and Salvinia minima Baker, through three series of concentrations o f each herbicide in climatic chamber (3000 lux, 12/12 hours photoperio d, temperature 23 +/- 1 degrees C). After seven days, the concentratio ns of series 1 (0.025, 0.125, 0.625 and 3.125 mg.L-1) inhibited the gr owth of Salvinia minima. In Spirodela punctata, only the herbicides ro deo and trifluralin caused growth inhibition. These concentrations did not caused death of fronds in the species. The concentrations of seri es 2 (40, 60, 80 and 100 mg.L-1) of the herbicides 2,4-D, direct e tri fluralin decreased growth of Salvinia minima; death of fronds was caus ed by 2,4-D and thifluralin to Salvinia minima, and by direct and trif luralin to Spirodela punctata. For the series 3 (200, 400, 600, 800 an d 1000 mg.L-1), the herbicide 2,4-D caused growth decrease of both spe cies. The herbicides rodeo and trifluralin showed to be the most letha l for both species. The herbicide atrazine caused death of fronds in S pirodela punctata.