Bordeaux Mixture (Copper sulfate and lime mixture)
Type: Fungicidal spray / plant protectant
Composition: A mixture of copper(II) sulfate (CuSO₄·5H₂O) and slaked lime (Ca(OH)₂) in water. Typically prepared as a 1–4% copper sulfate solution mixed with an equal or slightly greater amount of lime to neutralize acidity.
Description: Bordeaux mixture is a classic inorganic fungicide used in horticulture and agriculture to prevent fungal diseases on plants. It appears as a blue, opaque suspension when mixed with water. The copper ions act as the active antifungal agent, while lime stabilizes the solution and reduces phytotoxicity.
Uses in Gardening & Agriculture:
- Protects against fungal diseases such as downy mildew, powdery mildew, black spot, and blight.
- Commonly applied to fruit trees (apples, pears, grapes), vegetables (tomatoes, potatoes), and ornamentals.
- Also used on vineyards and in citrus orchards as part of integrated pest management.
Application Notes:
- Applied as a foliar spray; coverage should be thorough, especially on the undersides of leaves.
- Reapplication is required during wet periods or heavy fungal pressure.
- Care should be taken to avoid over-application, as excessive copper can cause leaf burn or soil toxicity.
- Mixture should be prepared fresh and used promptly; prolonged storage reduces efficacy.
Botanical Significance:
Bordeaux mixture remains an important tool in organic and traditional horticulture for controlling fungal pathogens. Copper ions interfere with fungal enzyme activity and spore germination, protecting plants from disease while allowing normal growth. It is most effective as a preventative treatment rather than a cure.