Revista Brasileira De Herbicidas 2020; 19(3): 1-9
EFFECT OF EXPOSURE TIME TO DIQUAT FOR CONTROL OF SUBMERSED AQUATIC PLANTS AND DEVELOPMENT OF A NEW EFFECTIVE EVALUATION TABLE
The objective of this study was to evaluate the time of exposure to diquat in the control of Egeria najas, E. densa (Planchon) and Hydrilla verticillate (L.F.) Royle, and use of a new evaluation table to analyze the effectiveness of submerged aquatic plants. For this, concentrations were used 0.2; 0.8 and 1.6 mg L-1 of diquat and a control (without herbicide application). The 10 cm plants remained exposed for 5, 15, 30, 60, 240, 480, 720 e 1440 minutos. They were then transferred to plastic containers with 1,0 L of water and 200g of sand for 56 days. Efficacy was assessed by signs of toxicity at 7, 15, 21, 28, 35, 42, 49, and 56 days post application (AAD) in new assessment table for submerged aquatic plants. The E. densa showed greater sensitivity to diquat with 100% control in the three concentrations, being in 0.2 mg L-1 from 240 minutes and in 0.8 and 1.6 mg L-1 at all times exposure. For H. verticillata 100% control occurred at the three concentrations, at 0.2 mg L-1 at 720 and 1440 minutes at 49 and 56 AAD respectively. In 0.8 mg L-1, 100% control occurred after 240 minutes and in 1.6 mg L-1 after 30 minutes. For E. najas, 100% control was achieved in 0.8 mg L-1 and 240 minutes and in 1.6 mg L-1 in 15 minutes, 8 and 24 hours in 56 AAD. The exposure time of 240 minutes and the concentration of 0.8 mg L-1 of diquat showed excellent control of the three submerged aquatic plants. The table of signs of toxicity developed for control evaluation was essential for the standardization of the results obtained.
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