Studies Upon the Copper Fungicides

Evidence is presented for the presence, on apple and dwarf bean leaves, of substances which can dissolve copper from dried Bordeaux deposit. The solution of copper is not associated with the bacterial breakdown of these substances. Copper was dissolved by the action of apparently uninjured as well as injured leaves and it is concluded that copper‐dissolving substances are liberated from intact leaf surfaces. The capacity of leaves to dissolve copper from dried Bordeaux deposit was not lost by repeated washing of the leaf. This further evidence of the sustained activity of the host plant in bringing copper into solution emphasizes the importance of host action in relation to the fungicidal and phytotoxic action of Bordeaux mixture under field conditions.