Abstract: A chemotherapeutic composition for the control of plant diseases caused by mycoplasma-like organisms, rickettsia-like organisms, or seed-borne legume viruses. The composition is composed essentially of the tannate complex of picro ammonium formate combined with a minor amount of a surfactant sufficient to prevent formation of ammonium picrate. The preparation and use of the composition are disclosed. Also disclosed is a related chemotherapeutic composition for the control of plant diseases caused by plant pathogenic fungi and bacteria and composed essentially of a tannate complex of picro cupric ammonium formate in aqueous solution combined with a minor amount of a surfactant sufficient to prevent formation of ammonium picrate, along with its method of preparation and manner of use.