Source
Bordeaux mixture – photo credit bioautop.fr
Copper is the active substance Bordeaux mixture in the form of sulphate. Other preparations based on copper are offered to the gardener, in the form of tetracopper oxychloride, copper hydroxide, cuprous oxide.
Copper is used to fight against a large number of cryptogamous diseases , in particular downy mildew on vines, potatoes, tomatoes… It is also used as a bactericide on fruit trees.
I take this opportunity to make a clarification, Bordeaux mixture is effective on a large number of fungi but has no effect on powdery mildew , another common disease in the garden (roses, cucurbits, etc.)
But copper has some significant side effects.
Copper is found in the air, in water, and in food, but it really does take excessive amounts of copper to harm health; (damage to liver, kidneys, but there is no "yet" evidence that copper is carcinogenic).
On the other hand, the impact on the environment is real. Copper in the soil binds to organic matter It is a metal that is almost not leachable, concentrations in the soil are sometimes very high, copper does not degrade in the environment.
It destroys bacteria and fungi soil, mycorrhizae and it is harmful to earthworms. The transformation of organic matter is reduced.
Copper also has a recognized phytotoxicity , many plants cannot grow in soils polluted with copper.
And it is the sheep that suffer the most from copper, eating grass with a high dose of this blue metal. They can poison themselves even with low doses.
Bordeaux mixture is tolerated in organic farming, but many "organic" farmers no longer use it or use it at lower doses per hectare/year than the maximum authorized by legislation.
Copper replacement can be achieved using horsetail decoction. Tests have been done with baking soda, and even sugar, but I do not have reliable results to give you more details. If your experience is conclusive with substitutes for Bordeaux mixture, leave me your comment, you are at home here.
*and**:source of info in italics:https://fr.wikipedia.org/wiki/Bouillie_bordelaise
To be continued…
