Copper sulfate is used as an algicide and root killer. When using it as a fungicide, it is important to neutralize its acidity (3 to 4) with lime or other plant friendly pH raising agent to a pH of 7. Low pH increases absorption by plants to possibly toxic levels. I believe copper sulfate has been replaced with other copper molecules because it is inefficient and leads to excessive copper accumulation in soil, which at high toxic levels is harmful to roots, blocks iron absorption and disrupts photosynthesis. Copper soaps (Cueva) and copper oxide (Nordox) work similarly as a fungicide with less copper and less worries about pH and toxicity.
Thanks, you raise important points.
Copper Oxychloride is used heavily on grapevines around here, the Cu issues are a concern after decades of use.
As Copper Oxychloride washes off with rain, several sprays are required per season. Overhead irrigation will be the same.
If Bordeaux spray persists better, less sprays may be required per season.
That may or may not be less actual Cu Copper applied over time, depending on the chemical formulation and spray formulation.
The same for the other copper products.
I have used Copper Oxide, seemed similar holding to Oxychloride, but that is just a just an observation.
The Bourdeaux mix proportions of Copper and Lime will affect activity of the Copper, probably the persistence on the leaves and ease of spraying through nozzles.
Highly efficient low volume spray nozzles will allow good leaf coverage without using too much spray mix. ( for all Copper sprays ).
To dilute the amount of Copper applied and increase the stick, I used Copper Oxychloride and powdered milk as a painted paste on trunks and wounds.
Somewhere between 30% Copper & 70% milk powder to 50/50 each.
As for Copper toxicity issues, those with a few trees sprayed can collect the fallen leaves and dispose or burn/ compost and spread more widely around than just under the same tree.