Back40 sets Robert straight on the use of copper as an “organic” fungicide:
Copper is no more “inorganic” or “unnatural” than nitrate. Yes, they are both minerals but that’s what plants eat and what microorganisms make. However, it is well to remember that it’s the dose that makes the poison. So long as they are not present in high concentrations they are food rather than poison.
Actually, copper is probably the least of organic’s dirty secrets.