Copper Sulphate Pentahydrate 24%: Agricultural Fungicide & Bordeaux Mixture Preparation

Copper is an indispensable trace micronutrient that functions both as an essential plant cofactor and as one of the oldest, most reliable broad-spectrum agricultural fungicides in modern organic and integrated crop management.

1. Dual Role of Copper: Nutrition & Fungal Protection

In crop physiology, copper is a structural constituent of plastocyanin, a copper-protein complex essential for electron transport during photosynthesis. It also catalyzes polyphenol oxidases responsible for synthesizing lignin—the woody polymer that hardens plant cell walls against fungal mycelium penetration. Copper Sulphate Pentahydrate (CuSO4 · 5H2O) contains a guaranteed 24.0% to 25.2% elemental Copper (Cu) in deep azure blue crystalline form.

2. The Chemistry of Neutral Bordeaux Mixture

Bordeaux mixture—first discovered in France in 1885—is prepared by reacting Copper Sulphate with Calcium Hydroxide (hydrated lime) in water. The reaction forms a complex mixture of copper hydroxides and basic copper sulphates:

• •Chemical Equation: CuSO4 + Ca(OH)2 → Cu(OH)2 + CaSO4

• •Mechanism of Action: Insoluble copper precipitates adhere tenaciously to leaves. When rainwater or dew contacts the leaf, tiny concentrations of cupric ions (Cu2+) are released, rupturing fungal spore membranes on contact.

• •Weather Fastness: Unlike synthetic organic fungicides, Bordeaux mixture resists being washed off by heavy monsoon rains.

3. Step-by-Step 1% Bordeaux Mixture Preparation Ratio

For 100 Liters of 1.0% Neutral Bordeaux Spray:

• •Step 1: Dissolve 1.0 kg of Auron Copper Sulphate Crystals in 50 Liters of water in a plastic bucket (Never use iron or galvanized metal drums).

• •Step 2: Slake 1.0 kg of fresh high-grade Quicklime (or 1.3 kg Hydrated Lime) in 50 Liters of water in a separate plastic drum.

• •Step 3: Slowly pour the blue copper solution into the white lime suspension while stirring vigorously. (Never pour lime into copper).

• •Step 4 (Litmus / Iron Knife Test): Dip a clean, bright iron knife blade into the mixture for 1 minute. If the blade turns reddish-copper, the mixture is too acidic and will scorch leaves—add more lime until the blade remains clean.

4. Target Crops & Controlled Pathogens

• •Grape Vineyards: Downy Mildew (*Plasmopara viticola*) and Anthracnose.

• •Apple & Pear Orchards: Apple Scab (*Venturia inaequalis*) and Fire Blight.

• •Citrus Groves: Citrus Canker (*Xanthomonas axonopodis*) and Gummosis.

• •Rubber & Coffee Plantations: Phytophthora leaf rot and Black Pod disease.

5. Frequently Asked Questions (FAQ)

• •Q: Can Bordeaux mixture be stored overnight for the next day's spray?

• •A: No! Bordeaux mixture deteriorates rapidly upon standing as colloidal copper crystals aggregate into coarse particles. Always apply within 8 to 12 hours of preparation.