Combinations of Diquat and Several Cations for Control of Hydrilla (Hydrilla verticillata)

Abstract

Numerous cations were evaluated as possible substitutes for copper in mixtures with diquat (6,7-dihydrodipyrido[1,2-α:2′,1′-c] pyrazinediium ion) for control of hydrilla [Hydrilla verticillata(L.f.) Royle]. Several cations, including ferrous and ferric iron, when substituted for equal weights of copper in the mixtures, were as effective as copper in enhancing the phytotoxicity of diquat to hydrilla. In most instances, death of the test plants occurred more rapidly when the substitutes were used. Ferric chloride, because of its apparent innocuous behavior in the aquatic environment, is a desirable substitute for the more toxic copper. Bluegill sunfish (Lepomis macrochirusRAf.) were unaffected by week-long exposure to ferric chloride at concentrations as high as 100 ppmw. Since ferric chloride alone exhibited no toxicity to hydrilla in the range of concentrations tested, the greater phytotoxicity of the mixtures probably was due to the increased toxicity of diquat. In evaluations using other species of aquatic weeds, neither the addition of copper nor the addition of other cations increased the phytotoxicity of diquat. In most tests, the mixtures of diquat with other cations reduced the level of activity of diquat on weeds other than hydrilla.