Discovered at the end of the 19th century, Bordeaux mixture is used to fight against cryptogamic diseases affecting vegetable plants. If this fungicide , traditionally prepared with copper sulphate, can still claim to be among the organic products and to remain approved for use in organic farming , the fact remains that Bordeaux mixture remains a chemical product, to be used with moderation, in particular because it leads to a concentration of copper in the soil .
If we can do without it, it is therefore better! Horsetail decoction , baking soda and milk , discover 3 organic alternatives to Bordeaux mixture .
Copper toxicity
The fungicidal properties of copper have been known for a long time. The ancients had taken the habit of piercing the bottom of the stems of tomatoes with a copper wire. Myth or reality, according to them, the rising sap was loaded with copper and distributed it systemically to all the organs of the plant, which gave it resistance to the infamous tomato downy mildew. .
The action of Bordeaux mixture is comparable, with the difference that the product is sprayed on the surface of the foliage and thus does not affect the sap circulation system. Nevertheless, copper is a heavy metal. It is not only toxic to fungi that grow on the leaves. Leached by repeated rains, it tends to accumulate in the soil where its fungicidal action continues (In certain vineyards treated each year with Bordeaux mixture, studies had shown that each kilo of soil contained 200 mg of this heavy metal !). Copper is also toxicfor the microfauna, the bacteria, and the fungi which make the life of the soil and, consequently, affect its fertility.
How to prepare a decoction of horsetail?
Whether field horsetail (Equisetum arvense) or marsh horsetail (Equisetum palustre) is used, maceration of horsetail can be used to fight against cryptogamic diseases of fruit trees and vegetables: peach leaf curl, downy mildew, monilia, powdery mildew , rust… Rich in silica, this natural decoction is used from March to October in regular sprays on the foliage and helps prevent the installation of fungi responsible for diseases.
Harvest and chop 1kg of horsetail stalks. Soak them for 24 hours in 10 liters of rainwater, at room temperature. After this time, bring to a boil in a pot and boil for 30 minutes. Filter after allowing to cool. Applied as a spray, this decoction of horsetail must be diluted to 20% (200 ml of horsetail for 800 ml of rainwater)
Baking soda: an excellent antifungal
It is an old product, classically associated with grandmother’s recipes and endowed with a subjective element of mystery, even magic. Sodium bicarbonate ( or soda ) is used for almost everything! It is widely used in the field of DIY to get rid of difficult stains, or even to revive the colors of an old carpet… In the garden, spraying a solution of baking soda on the leaves as a preventive measure helps to significantly the pH, interfering with the germination of fungal spores such as powdery mildew.
Respect a dosage identical to the Bordeaux mixture . Renew the treatment approximately every 2 to 3 weeks, sooner if the product is washed away by heavy stormy rains. As with all treatments, make the last spray at least 2 weeks before harvest begins.
How to use milk in the garden?
This is probably the most harmless organic alternative to Bordeaux mixture for humans. With a downside all the same! If milk is effective in fighting against powdery mildew , the fungus that covers the leaves of cucumbers, zucchini and squash with a white veil, it remains ineffective against other fungi such as scab or mildew.
It does not matter whether it is skimmed, semi-skimmed, whole or even whether we prefer whey, which is less expensive, it is the proteins contained in the milk that act. Under the effect of light, these are transformed into oxidizing agents and destroy the mycelium of fungi .
Dilute one volume of milk (100ml) in 9 volumes of rainwater (900ml). Shake and spray preferably early in the morning for greater effectiveness. Renew after a few days and regularly, in prevention, like the Bordeaux mixture .