Copper is an effective way to fight the fungal disease mildiou. However, spraying too much copper in the vineyard is not good for the soil and the water and this has been known a long time. Now researchers have discovered another problem with copper.
Spraying copper can affect the bacterial flora and the yeast population present on the grapes.
Guilherme Martin, a doctorate student at the University of Bordeaux, has investigated several different vineyards around Libourne and he has identified 44 different types of bacteria.
Some of these bacteria have the ability to protect against rot so it is a good thing to have these on the grapes. By spraying copper on the grapes you risk both to reduce the amount of bacteria and their beneficial properties. Using copper as copper sulphate apparently affects the bacteria more than using copper oxide.
Copper is permitted in organic vineyards but not more than 6 kg per hectare and year. For the sake of the environment, less should be used but certain years this is very difficult, like 2012 for instance. Read more on this on La Vigne.
