The production of new shoots of American pondweed (Potamogeton nodosusPoir.) and sago pondweed (P. pectinatusL.) was reduced significantly when winterbuds and tubers of these species were planted in dwarf spikerush [Eleocharis coloradoensis(Britt.) Gilly] sod. In most instances, the number of shoots produced was several times greater when winterbuds and tubers were planted in bare soil than when planted in spikerush sod. Similar results were obtained when the pondweeds were grown in separate aquaria, each aquarium being exposed to 500 ml of leachate per day from spikerush sod. The differences in reproduction of pondweeds could not be attributed to altered water quality nor to reduced levels of nutrients. No appreciable allelopathic response was elicited by the pondweed plants originating from planted tubers or winterbuds. The principal response appeared to be reduction in numbers of new shoots produced from the original propagules, although the reduction in biomass of the pondweeds exposed to the effects of spikerush was obvious. Of the two pondweeds investigated, sago pondweed was most sensitive to the influence of spikerush.

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.

A mixture of diquat [6,7-dihydrodipyrido(1,2-α: 2′,1′-c) pyrazinediium ion] and copper sulfate pentahydrate was applied to artificial chinook salmon (Onchorhynchus tshawytschaWal.) spawning channels to reduce excessive growths of algae [Cladophora glomerata(L.) Kutz]. Juvenile salmon were not harmed by the applications. A concentration of 100 ppb w/w diquat plus 150 ppb copper-ion was maintained for 3 hr. The alga was controlled satisfactorily for distances up to 0.5 km per treatment. Each treatment consisted of one to three applications, each made on consecutive days. Water temperature was 11.2 C during three winter applications and 15.5 C during a spring application. Diquat was rapidly sorbed out of the treated water to 3.8 ppb at 1.6 km. Copper-ion residues dissipated to 60 ppb at 1.6 km.

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Copper content and growth of excised hydrilla [DioeciousHydrilla verticillata(L.f.) Royle # HYLLI] apical shoot segments were determined following exposure to copper sulfate (CuSO4), copper-triethanolamine (Cu-TEA), and copper-ethylenediamine (Cu-EDA). For all copper formulations, inhibition of growth was related to the amount of copper associated with the excised shoots. At equal copper exposure, the Cu-EDA formulation produced the greatest inhibition of growth and generally the highest copper levels in the plants. The Cu-EDA formulation inhibited dry weight gain by more than 80% 3 weeks after a 2-h exposure to 2.0 or 4.0 ppmw copper. Under similar conditions, CuSO4or Cu-TEA produced 60% inhibition. The presence or absence of light during a 2-h exposure had no effect on the efficacy of uptake of copper from any of the formulations. Formulation-dependent differences in the mechanism of copper uptake is suggested because rinsing of exposed shoots with dilute acid (0.01N HNO3) removed copper from shoots treated with CuSO4or Cu-TEA but not from those treated with Cu-EDA.