STUDIES UPON THE COPPER FUNGICIDES: THE FUNGICIDAL VALUE OF THE COPPER OXIDES1

Abstract

SUMMARYIt is suggested that the field performance of protective fungicides is dependent upon (1) factors determining the quantity (retention and tenacity) of material present throughout the period of protection, and (2) factors which determine the relative fungicidal value of this residue.The fungicidal values of various samples of cuprous and of cupric oxide have been examined by a laboratory method employing spores of Macrosporium sarcinaeforme and of Cladosporium carpophilum and the following conclusions reached: Within each series of cuprous or cupric oxides, fungicidal value is dependent upon method of manufacture and upon particle size. When allowance for the effects of these two factors is made cuprous oxide is shown to inhibit spore germination to a greater degree than cupric oxide of equivalent copper content. If inhibition of spore germination by these copper oxides is due to the formation of soluble copper derivatives, the superior fungicidal value of cuprous over cupric oxide may be explained both (a) by the more ready solubility in certain solvents of cuprous oxide (i.e. greater availability), and (b) by the greater potency of the active fungicide produced from cuprous oxide (i.e. greater inherent toxicity). Evidence is given bearing on these two hypotheses.