Bordeaux mixture

Bordeaux mixture is a copper-based contact fungicide born in French vineyards, where it was devised to fight downy mildew on grapes. It is prepared by stirring copper sulfate into slaked (hydrated) lime suspended in water; the lime tames the copper’s acidity, leaving a persistent, sparingly soluble copper deposit on foliage that releases fungicidal ions with each wetting. Growers apply it to vines, orchards, and vegetable crops as a protectant spray. Food-safety management focuses on residues: copper is subject to maximum residue limits on harvested produce, and repeated use can accumulate copper in vineyard soils, so modern programmes dose it carefully within integrated disease control.