Bordeaux Mixture Preparation Guide

Bordeaux mixture is an effective and economical fungicide and bactericide used to control a wide range of plant diseases caused by fungi and bacteria. It is particularly useful for diseases like downy mildew, blight, anthracnose, and leaf spots on crops such as grapes, potatoes, tomatoes, citrus, coffee, and many fruit trees. Preparing it correctly is crucial for its effectiveness and to avoid crop damage.

Ingredients and Equipment Needed

To prepare Bordeaux mixture, you will need the following:

Copper Sulfate (Neela Thotha): Available as blue crystals.
Quicklime (Chuna): Fresh, unslaked lime is best.
Clean Water: Soft water is preferred.
Non-Metallic Containers: Use plastic buckets or drums. Metal containers react with copper sulfate and should be avoided.
Weighing Scale: To measure ingredients accurately.
Wooden or Plastic Stirrer: For mixing.
Fine Sieve or Muslin Cloth: To strain the mixture before spraying.
Red Litmus Paper or Iron Knife/Blade: For testing the mixture's acidity.
Safety Gear: Gloves, mask, and eye protection.

Common Ratios for Preparation

The strength of Bordeaux mixture is usually expressed as a ratio of copper sulfate:quicklime:water. A common ratio for general use is 1:1:100, meaning 1 kg copper sulfate, 1 kg quicklime, and 100 litres of water. For different crops or disease severity, the ratios may vary:

Ratio (Copper Sulfate:Lime:Water) Use Case Example Crops 1:1:100 (1 kg:1 kg:100 L) General purpose, preventative spray Grapes, Potatoes, Tomatoes, Citrus 0.5:0.5:100 (0.5 kg:0.5 kg:100 L) Sensitive crops, young plants, maintenance Some vegetables, young fruit trees 2:2:200 (2 kg:2 kg:200 L) Higher disease pressure, larger areas Coffee, Rubber, some fruit trees

Step-by-Step Preparation Process

Dissolve Copper Sulfate: Take half of the total water (e.g., 50 litres for a 100-litre batch) in a plastic drum. Tie the measured copper sulfate (e.g., 1 kg) in a muslin cloth and suspend it in the water, just below the surface. Let it dissolve completely overnight or stir until fully dissolved. This creates a blue copper sulfate solution.
Slake Quicklime: In a separate plastic bucket, slowly add a small amount of water to the measured quicklime (e.g., 1 kg) to slake it. Once slaked into a paste, add the remaining half of the water (e.g., 50 litres) and stir well to make a milky lime solution. Strain this lime solution through a fine sieve or muslin cloth to remove impurities.
Mix the Solutions: Slowly pour the copper sulfate solution into the lime solution while continuously stirring with a wooden stick. It is crucial to always pour the copper sulfate into the lime solution, never the other way around. This ensures a stable mixture. The resulting mixture should be sky-blue in colour.
Stir Thoroughly: Continue stirring for several minutes to ensure a uniform mixture.

Testing the Mixture for Safety

Before application, it is essential to test the Bordeaux mixture to ensure it is not acidic, as an acidic mixture can burn plant leaves. There are two common methods:

Iron Knife Test: Dip a clean, polished iron knife or blade into the mixture for about 1-2 minutes. If a reddish-brown deposit (copper) forms on the blade, it indicates that the mixture is acidic and has free copper, which can harm plants. If this happens, add more lime slurry (prepared by mixing a small amount of lime with water) to the mixture, stir well, and retest until no deposit forms on the knife.
Litmus Paper Test: Dip a piece of red litmus paper into the mixture. If the paper turns blue, the mixture is alkaline or neutral, which is safe. If it remains red, the mixture is acidic, and more lime slurry should be added until the red litmus paper turns blue.

Application and Storage Best Practices

Use Immediately: Bordeaux mixture should be used as soon as possible after preparation, ideally within 24 hours. Its effectiveness decreases rapidly upon storage, and it can become phytotoxic (harmful to plants).
Application: Apply the mixture as a fine, uniform spray, ensuring complete coverage of the plant's leaves and stems. Use a sprayer with a fine nozzle.
Safety Precautions: Always wear protective clothing, gloves, and a mask during preparation and application. Avoid inhaling the spray mist. Wash hands and exposed skin thoroughly after handling.
Disposal: Dispose of any leftover mixture and rinse water responsibly, away from water sources and edible crops.

By carefully following these steps, you can prepare an effective Bordeaux mixture to protect your crops from various diseases and ensure healthy yields. Always prioritize safety during preparation and application.