Herbicide/copper combinations for improved control of Hydrilla verticillata.

Greenhouse aquariums were used to evaluate the efficacy of the dipotassium salt of endothall in combination with other products against hydrilla ( Hydrilla verticillata (L.f.) Royle). Copper, diquat, or the mono(N,N-dimethylalkalamine) salt of endothall were combined with the dipotassium salt of endothall to determine if equal or improved hydrilla control could be obtained by combining products and using them in low concentrations. Treatments included 1, 2, and 3 mg dipotassium salt of endothall L -1 used alone and in combination with 0.5 mg Cu L -1 , 0.5 mg diquat L -1 , or 0.2 mg endothall (mono(N,N-dimethylalkylamine salt)) L -1 . A 24hour dissipation half-life was simulated and shoot biomass was harvested 3 and 6 weeks after treatment (WAT). Endothall (dipotassium salt) applied singularly at 2 and 3 mg L -1 resulted in significant reductions in biomass 6 WAT compared to the untreated reference, or >95% control. All combinations significantly decreased the above ground biomass 6 WAT compared to the untreated reference. The dipotassium salt of endothall combined with copper or diquat provided >99% control even at the lowest rate of endothall (1 mg L -1 ). Possible benefits of such applications include reduced herbicide quantity, improved selectivity and control of target plants, and reduced contact times.