Question

Which is major component of Bordeaux mixture?

• A. Copper sulphate
• B. Sodium chloride
• C. Calcium chloride
• D. Magnesium sulphate

Hint:

Bordeaux Mixture = Blue Stone (Copper Sulphate) + Lime.
It is a "Contact" fungicide; it must cover the surface of the plant to prevent spore germination.
Always prepare it fresh, as the mixture loses its effectiveness if stored for long.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the primary active ingredient in the "Bordeaux mixture," one of the oldest and most effective fungicides used in agriculture.

Step 2: Detailed Explanation:

• Composition of Bordeaux Mixture:
Bordeaux mixture was discovered by Millardet in France in $1882$ to control downy mildew in grapes.
It is a combination of Copper Sulphate ($CuSO_4$), Hydrated Lime ($Ca(OH)_2$), and Water.
A standard ratio is often $1:1:100$ ($1$ kg Copper Sulphate, $1$ kg Lime, $100$ liters Water).

• Role of Copper Sulphate:
Copper sulphate is the active fungicidal component. The copper ions ($Cu^{2+}$) are toxic to fungal spores as they disrupt enzyme activity and denature proteins.
However, pure copper sulphate is "phytotoxic" (harmful to the plant itself) and highly acidic.

• Role of Lime:
Lime is added to neutralize the acidity of the copper sulphate and to make the mixture more adhesive so it stays on the leaves during rain.
The reaction produces a complex precipitate of copper hydroxides and sulphates that releases copper ions slowly over time.

• Applications:
It is used to control various diseases like blights, mildews, and leaf spots in orchards, vineyards, and vegetable crops.

Step 3: Final Answer:
The major and active component of Bordeaux mixture is Copper sulphate.