Copper is the key to elasticity in the plant. It is an important constituent of many proteins like ascorbic acid oxidase, cytochrome oxidase, diamine oxidase, and polyphenol oxidase. Copper is an important nutrient for many microbes, such as Aspergillis niger. It controls molds and often alleviates perceived zinc deficiencies. Copper interacts with iron and manganese.
Bordeaux mixture is a famous spray used to control fungus in vineyards. Developed in their eponymous provinces of France, Bordeaux mix is copper sulfate, mason's lime (calcium hydroxide), and water.
In agriculture use, applied as Bordeaux Mixture before the fungus spores settle on the leaves, the Copper Sulphate gradually releases small amounts of soluble copper which kills the germinating spores.
As a part of Bordeaux mixture in grape arbors, it functions as a nutrient and not as an insecticide as is often believed. The copper in the mixture is stimulating the plant's immune system.