Bordeaux mixture is a preparation used as a fungicide (to control fungi) on plants. Bordeaux mixture is composed of copper sulphate and calcium hydroxide, and is used as a fungicide. is allowed within organic farming. Another fungicide permitted in organic farming is copper oxychloride.
The use of the copper sulphate in Bordeaux mixture in organic farming is only allowed as a bactericide and fungicide and up to 6 kg of copper per hectare per year.
HOW TO PREPARE BORDELAISE BROTH
To make one litre of Bordeaux stock you will need:
- 10 grams of copper sulphate.
- 10 grams of quicklime (lime oxide). You can find it here.
- pH meter
- We start by making 2 dilutions.
- A solution of 10 grams of copper sulphate in water
- A solution of 10 grams of quicklime in water.
- Let both solutions stand for several hours. Pass the lime solution through a strainer or filter to remove the small undissolved lime particles. You can use a piece of cloth as an improvised filter.
- Pour the copper sulphate over the lime. Do not do it all at once but little by little in order to measure the pH at the same time with a paper indicator or a pocket phmeter. Stir as the two liquids come together with wood or plastic, if you use metal it will rust.
- As copper sulphate is added, the pH decreases (the copper sulphate decreases the alkalinity of the calcium hydroxide formed by dissolving calcium oxide in water). When the pH is close to 7, the Bordeaux stock is ready. If you find that the pH falls below 6.5, you can raise it by adding a little calcium hydroxide.
- Pour the formed liquid, which will have the blue colour of copper sulphate, into the fumigation apparatus to be used.
- Now, with the help of the sprayer, spray the whole plant, applying the liquid to both sides of the leaves. Avoid the hottest hours when spraying.
Sometimes only a dilution of copper sulphate as fungicidewithout making Bordeaux mixture. Copper oxychloride is also commonly used for this purpose.