Hint: It was discovered by a French botanist and mycologist from the University of Bordeaux. He is famously known for his work in plant pests. Bordeaux mixture was the first fungicide to be discovered in the world. The botanist accidently discovered the fungicide in vineyards with the help of winemakers. Bordeaux mixture is the oldest fungicide that is still used today. It is used in fruit gardens and vineyards to prevent infections of downy mildew, Blights and other fungal pathogens.
Complete answer: Bordeaux mixture is a blue coloured fungicide which consists of a mixture of copper sulphate and calcium oxide (quick lime). It gets its name from the Bordeaux region of France where it was discovered and used initially in vineyards against pests such as downy mildew and great French wine blights. The discovery of Bordeaux mixture was accidental. Millardet was studying the vine diseases in Bordeaux region where he noticed vines closest to the roads were unaffected by the pests. He found that the winemakers sprayed their vines with a mixture of copper sulphate and quick lime to prevent thieves from stealing the grapes by making it taste bitter. Millardet then proceeded to perform trials in the vineyards with copper sulphate and quick lime treatment. He was successful in his trials and found Bordeaux mixture to combat down mildew. Bordeaux mixture of \[1\% \] is most commonly used in which copper sulphate and quick lime is used in \[1:1\] ratio. It is a widely used fungicide to control several fungal and bacterial spots, blights, downy mildew and anthracnoses. It works by affecting the enzymes in the fungal spores thus preventing its germination. In this mixture copper sulphate is the ingredient that is toxic to pathogens. Quick lime is used to make the fungicide safer.
Hence Bordeaux mixture was discovered by Pierre-Marie-Alexis Millardet.
Note: The Bordeaux mixture is intensively used in organic farming. It is blue in colour due the presence of copper sulphate. The treatment is usually given to the plants at the end of winter and spring. Over use of Bordeaux mixture creates toxic effects to earthworms and livestock.