The period of herbicide permanence in water can be influenced by the water flow in the reservoirs and the adsorption of clay particles in suspension, as well as by luminous degradation and microorganisms. Thus, the objective of this work was to evaluate the effect of different exposure periods to diquat concentrations on the control of Egeria densa, Egeria najas and Ceratophyllum demersum. The experimental design used was completely randomized, with four replicates, in a factorial scheme 6 x 5, plus a control. Six periods of plant exposure were tested (30, 60, 120, 240, 480 and 960 minutes) in relation to five diquat concentrations (0.075; 0.15; 0.3; 0.6 and 1.2 ppm - commercial product Reward 240 g L-1). Visual evaluations of the immersed weeds were carried out and at the end of the experiment, shoot dry matter was evaluated to determine biomass percentage reduction. Based on the results obtained, it was concluded that exposure of only 30 minutes of the immersed species E. densa and C. demersum to 0.075 ppm concentration was sufficient to reduce shoot dry matter in both species. For E. najas control after 7 DAA, an exposure period longer than 120 minutes was necessary, considering the same herbicide concentration. These results indicate the potential use of diquat to control immersed aquatic weeds in places presenting fast water renewal.
aquatic weeds; immersed plants; herbicide
