Preparation of Bordeaux mixture

About Bordeaux mixture

In the year 1761, Schulthez first used the copper sulphate for the seed treatment of Wheat diseases. Later on Prevost termed the copper as fungicide. In 1882, Millardet in France (Bordeaux University) accidentally observed the efficacy of the copper sulphate against the downy mildew of grapes caused by Plasmopara viticola. When copper sulphate was mixed with lime suspension, it effectively checked the disease incidence. The mixture of copper sulphate and lime was named as “Bouillie Bordelaise” (Bordeaux Mixture).

The original formula developed by Millardet contains 5 lbs of CuSO₄ + 5lbs of lime + 50 gallons of water. The chemistry of Bordeaux mixture is complex and the suggested reaction is: CuSO ₄ + Ca (OH) ₂ = Cu(OH) ₂ + CaSO ₄

The ultimate mixture contains a gelatinous precipitate of copper hydroxide and calcium sulphate, which is usually sky blue in colour. Cupric hydroxide is the active principle and is toxic to fungal spores.

Bordeaux mixture is generally accepted even in organic cultivation. It is easy to prepare and can be locally prepared by farmers themselves.

Preparation of 1 % Bordeaux Mixture

Materials required

1. Copper sulphate powder - one kg
2. Lime - 1 kg
3. Water - 100 litres

Methodology

One kg of copper sulphate powder is dissolved in 50 litres of water. Similarly, 1 kg of lime is powdered and dissolved in another 50 litres of water. Then copper sulphate solution is slowly added to lime solution with constant stirring or alternatively, both the solutions may be poured simultaneously to a third contained and mixed well.

Preparation of 0.5% Bordeaux mixture is same as above but reducing the copper sulphate and lime half of the amount but keeping water same as 1% mixture preparation.

In general, 1% Bordeaux mixture is applied to hardy plant parts such as roots, stem and 0.5% of mixture is applied on leaf/foliage.

Tests to determine pH of the prepared Bordeaux mixture

The ratio of copper sulphate to lime solution determines the pH of the mixture. The mixture prepared in the above said ratio gives neutral or alkaline mixture. If the quality of the used materials is inferior, the mixture may become acidic. If the mixture is acidic, it contains free copper which is highly phytotoxic resulting in scorching of the plants. Therefore, it is highly essential to test the presence of free copper in the mixture before applied.

There are several methods to test the neutrality of the mixture, which are indicated below:

1. Field Test: Dip a well polished knife or a sickle in the mixture for few minutes. If reddish deposit appears on the knife/sickle, it indicates the acidic nature of the mixture.
2. Litmus paper test: The colour of blue litmus paper must not change when dipped in the mixture.
3. pH paper test : If the paper is dipped in the mixture, it should show neutral pH.
4. Chemical test : Add a few drops of the mixture into a test tube containing 5 ml of 10% potassium ferrocyanide. If red precipitate appears, it indicates the acidic nature of the mixture.

If the prepared mixture is in the acidic range, it can be brought to neutral or near alkaline condition by adding some more lime solution into the mixture.

Precautions

The following precautions are needed during preparation and application of Bordeaux mixture.

• The solution should be prepared in earthen or wooden or plastic vessels. Avoid using metal containers for the preparation, as it is corrosive to metallic vessels.
• Always copper sulphate solution should be added to the lime solution, reverse the addition leads to precipitation of copper and resulted suspension is least toxic.
• Bordeaux mixture should be prepared fresh every time before spraying. In case, the mixture has to be stored for a short time or a day, jaggery can be added at the rate of 100g/100 litres of the mixture.
• Bordeaux mixture is sometimes phytotoxic to apples, peaches, new shoots/leaf.

Advantages of Bordeaux mixture

• Very easy and can prepared by farmers themselves.
• Can act as fungicide, bactericide and algaecide.
• Applicable to tomato, potato, chilli, other vegetables, fruits (orange, lime, lemon), beetel vine, ginger, flower and ornamental plant diseases such as foot rot, stem rot, leaf spot, leaf blight, anthracnose, canker, damping off, black spot, downy mildew, late and early blight etc.
• The chemicals required for this is copper sulphate and lime which is easily available in the market.
• All the diseases controlled by copper based fungicides such as leaf spot, blight diseases can be controlled by this.
• It is less toxic to human as compare to other commercial fungicides.

Disadvantages

• It cannot be keep for long periods (More than 2 days after preparation).
• It cannot be applied during the cold and cloudy weather, as it causes phytotoxicity to plants.
• It cannot be applied to apple, maize and some of the dwarf rice varieties.

Bordeaux paste

Bordeaux Paste consists of same constituents as that of Bordeaux mixture, but it is in the form of a paste as the quantity of water used is too little. It is nothing but 10 per cent Bordeaux mixture and is prepared by mixing 1 kg of copper sulphate and 1 kg of lime in 10 litres of water. The method of mixing solution is similar to that of Bordeaux mixture. It is a wound dresser and used to protect the wounded portions, cut ends of trees etc., against the infection by fungal pathogens.

Bordeaux paint

Bordeaux paint consists of 100g copper sulphate with 200g lime in 300ml water. It is a wound dresser and used to protect the wounded portions, cut ends of trees etc., against the infection by fungal pathogens.

Source : CAU Farm magazine Vol 6. No. 3