Bordeaux mixture is a traditional copper-based protective plant fungicide prepared mainly from copper(II) sulfate, calcium hydroxide (slaked lime), and water. It is used to help control a range of fungal and oomycete plant diseases. The mixture was developed in the Bordeaux region of France during the nineteenth century and has since been widely used in plant disease management.
Composition of Bordeaux Mixture
Bordeaux mixture is prepared using three principal components:
- Copper(II) sulfate: CuSO4·5H2O
- Slaked lime: Ca(OH)2
- Water: H2O
A traditional formulation is commonly expressed as 1:1:100, meaning approximately 1 kg of copper sulfate and 1 kg of slaked lime dispersed in 100 L of water. However, formulation strength and application rates can vary according to the crop, disease, product formulation, and local agricultural recommendations.
Preparation of Bordeaux Mixture
The components are normally prepared separately before being combined:
- Dissolve the required amount of copper(II) sulfate in water in a suitable non-reactive container.
- Prepare a separate suspension of slaked lime in water.
- Slowly add the copper sulfate solution to the lime suspension while stirring continuously.
- Mix thoroughly to obtain a uniform blue suspension.
- The preparation is generally used soon after mixing rather than being stored for long periods.
Chemical Changes in Bordeaux Mixture
The interaction between copper(II) sulfate and calcium hydroxide can be represented by the following simplified, idealized equation:
When hydrated copper sulfate is used, the water of crystallization also becomes part of the aqueous system. The equation above is therefore best regarded as a simplified representation of the chemical interaction rather than a complete description of the composition of the final preparation.
Bordeaux mixture is not a single pure chemical compound. It is a complex copper-containing suspension. The nature and availability of copper-containing particles depend on factors such as the proportions of the ingredients, pH, water quality, mixing procedure, and storage conditions.
Why Is Lime Added?
Slaked lime plays an important role in Bordeaux mixture. It reacts with copper sulfate and helps reduce the concentration of readily soluble copper species. This can decrease the risk of copper-related phytotoxicity while allowing copper-containing material to remain available on the plant surface.
- It helps reduce the immediate solubility of copper.
- It helps lower the risk of plant injury caused by excessive soluble copper.
- It contributes to the formation of a copper-containing deposit on plant surfaces.
- It helps maintain conditions suitable for the protective action of the preparation.
Properties of Bordeaux Mixture
- It is generally a blue or bluish suspension.
- It is a copper-based plant-protection preparation.
- It mainly acts as a protective contact treatment rather than a systemic fungicide.
- It can form a copper-containing deposit on treated plant surfaces.
- Its effectiveness depends on concentration, coverage, timing, weather, and the target pathogen.
- Excessive copper application can cause phytotoxicity in susceptible crops.
- Repeated copper applications can contribute to copper accumulation in agricultural soils.
Fungicidal Action of Bordeaux Mixture
Bordeaux mixture primarily provides protection on the surface of treated plant tissues. Copper-containing material deposited on the plant surface can release copper ions gradually under suitable conditions.
These copper ions can interact with essential cellular components of susceptible fungal and oomycete pathogens. Their effects can include disruption of enzyme activity, interaction with proteins and other cellular components, and interference with essential biochemical processes.
Because Bordeaux mixture acts mainly on exposed pathogen structures, it is generally most effective when applied before or during the early stages of infection, depending on the crop and disease.
Uses of Bordeaux Mixture
Bordeaux mixture has traditionally been used to help control various plant diseases caused by fungi and oomycetes.
- Protection of plants against certain fungal diseases.
- Management of some downy mildew diseases caused by oomycete pathogens.
- Protection of fruit crops against selected diseases.
- Use in vineyards for certain disease-management programs.
- Use on vegetables and orchard crops where copper-based treatments are appropriate.
Examples of crops in which copper-based disease-management treatments may be used include grapes, apples, pears, citrus, and various vegetable crops. The suitability of Bordeaux mixture depends on the crop, target disease, formulation, growth stage, and local recommendations.
Advantages of Bordeaux Mixture
- It has a long history of use in plant disease management.
- It provides protective surface activity against a broad range of susceptible pathogens.
- It can provide relatively persistent protection, although the duration varies with crop, formulation, weather, and application conditions.
- It can be economical where its ingredients are available and permitted for use.
- Its multiple-site copper activity can make it useful in disease-management programs.
Limitations of Bordeaux Mixture
- Excessive copper can cause phytotoxicity in sensitive crops.
- The correct concentration depends on the crop and disease.
- Repeated applications can increase copper levels in soil.
- Rainfall and weather conditions can affect the persistence of the protective deposit.
- The freshly prepared mixture may be preferred because its physical and chemical properties can change during storage.
- Compatibility with other agricultural products must be considered before mixing.
- Application should follow the product label and applicable local agricultural regulations.
Bordeaux Mixture vs Copper Sulfate
| Feature | Bordeaux Mixture | Copper Sulfate |
|---|---|---|
| Nature | Copper-containing suspension prepared from copper sulfate, lime, and water | Inorganic copper salt |
| Main formula | Not represented by a single fixed chemical formula | CuSO4·5H2O is the common hydrated form |
| Role of lime | Helps reduce the availability of readily soluble copper and contributes to the protective deposit | Absent |
| Plant protection | Mainly used as a protective contact treatment | Applications vary; concentrated copper sulfate can be phytotoxic |
| Physical form | Blue or bluish suspension | Usually blue crystalline solid in the pentahydrate form |
Important Exam Points
- Bordeaux mixture is a traditional copper-based protective plant fungicide.
- Its main ingredients are copper(II) sulfate, slaked lime, and water.
- The traditional formulation is commonly expressed as 1:1:100.
- Its preparation involves combining copper sulfate solution with a lime suspension.
- The equation involving CuSO4 and Ca(OH)2 is an idealized representation of the chemical interaction.
- It is not a single pure compound but a complex copper-containing suspension.
- It mainly provides protective contact activity on plant surfaces.
- Copper ions can interfere with essential biochemical processes in susceptible pathogens.
- Excessive or repeated copper use can cause phytotoxicity and copper accumulation in soil.
Conclusion
Bordeaux mixture is a traditional and important copper-based plant-protection preparation made from copper(II) sulfate, slaked lime, and water. Its protective action is associated with copper-containing deposits formed on plant surfaces. Copper released from these deposits can interfere with essential biochemical processes in susceptible fungal and oomycete pathogens. Although it has a long history of agricultural use, correct formulation and application are important because excessive copper can cause phytotoxicity and contribute to copper accumulation in soil.
Pronunciation: Bordeaux is approximately pronounced “bor-DOH” in English. The final x is silent. It is not pronounced as “bor-dox.”