Responses of Monoecious and Dioecious Hydrilla (Hydrilla verticillata) to Various Concentrations and Exposures of Diquat

Control of monoecious and dioecious hydrilla [Hydrilla verticillata(L.f.) Royle # HYLLI] biotypes required a minimum 2 days of exposure to diquat (6,7-dihydrodipyrido [1,2-α:2′,1′-c] pyrazinediium ion) at a concentration of 0.25 mg/L under laboratory conditions. When treatment concentration was increased to 2.0 mg/L diquat, the minimum required contact time was reduced to 6 or 12 h depending on plant growth stage. Early growth emerging from sprouting tubers appeared to be more susceptible to diquat treatments. Herbicide uptake was linear during a 4-day exposure to14C-diquat up to 1.0 mg/L, and the amounts of radioactivity in plant tissue varied proportionally with ambient levels of14C-diquat in water. The lethal concentration of diquat in hydrilla tissue was estimated to be 81 μg/g plant dry weight when hydrilla was exposed to diquat at 0.25 mg/L for 2 days.