Step 1: Composition.
Bordeaux mixture is a classic protectant fungicide created by combining copper sulphate (blue vitriol) and freshly prepared lime (calcium hydroxide) in water.
Step 2: Typical preparations and use.
Common field formulas include 1:1:100, 4:4:50, or 5:5:50 (copper sulphate : lime : water), adjusted based on crop sensitivity and disease severity.
The lime neutralizes the solution, lowers phytotoxicity, and helps copper remain finely dispersed as copper hydroxide, which adheres to plant surfaces.
Step 3: Why alternative options are incorrect.
Lime combined with calcium sulphate lacks the fungicidal copper ion necessary for action.
Sulphur with lime forms lime sulphur, a different product primarily used against mites and some fungal pathogens, not Bordeaux mixture.
Copper sulphate with sulphur is not the standard Bordeaux formulation and is missing the buffering lime component.
Step 4: Historical context and mode of action.
Discovered in the 1880s for downy mildew control in vineyards, Bordeaux mixture functions as a surface protectant. It releases copper ions that impede spore germination.
Step 5: Conclusion.
Therefore, Bordeaux mixture is composed of copper sulphate and lime.