Hint: Bordeaux mixture is primarily used as a fungicide in farms, fruit gardens, vineyards and farms of ornamental plants. It mainly prevents the fruits or plants from downy mildew and other such fungi thus preventing fungal diseases in them. Its first time usage was accidental, in 1885 by French botanist, Pierre Marie Alexis Millardet against powdery mildew. Since then it has been used all around the world to prevent fungal diseases in plants.
Complete answer: A mixture of copper sulphate and slaked lime is known as the Bordeaux mixture. Slaked lime is commonly known as calcium hydroxide. The method of preparation of Bordeaux mixture is as follows: -Copper sulphate is dissolved in water. -Lime is dissolved in water separately. -The above two preparations are then mixed. Bordeaux mixture was banned in the UK due to the excessive usage of copper being harmful to the soil. It was harmful to the worms present in the soil. If the copper in the mixture from the soil reaches groundwater, it would contaminate the river and other nearby water bodies and would be harmful for aquatic plant and animal life. Excess of copper can accumulate in the soil and may be harmful for the plants. Moreover, it is also moderately toxic to humans.
Note: Bordeaux mixture is a non systemic fungicide. Copper acts as a fungicide by denaturing the enzymes required for major metabolic processes of the pathogenic fungal cell. Copper is slowly released from the mixture so that there is no harm to the plant due to accumulation.