Chemical Composition and 1% Standard Ratio
Bordeaux mixture is traditionally prepared as a 1% formulation (1:1:100 ratio), consisting of 1 kilogram of Copper Sulphate (blue vitriol) and 1 kilogram of Calcium Hydroxide (hydrated lime) dissolved in 100 liters of water.
The chemical reaction between copper sulphate and slaked lime precipitates insoluble copper hydroxide complexes. These gelatinous complexes adhere to foliage, providing residual protection and slow release of fungitoxic cupric (Cu2+) ions upon wetting.
- Standard 1% formula: 1 kg Copper Sulphate + 1 kg Hydrated Lime in 100 liters of water
- Chemical reaction: Produces gelatinous basic copper sulphate and copper hydroxide precipitates
- Fungicide group: FRAC Group M01 (Inorganic multi-site contact protectant)
- Adherence: Gelatinous precipitate exhibits exceptional tenacity and rainfastness on plant bark and foliage
Step-by-Step Preparation Protocol and Acidity Test
Dissolve copper sulphate in 50 liters of water in a wooden, plastic, or earthen container. In a separate non-metallic vessel, slake lime in 50 liters of water. Slowly pour the copper sulphate solution into the lime suspension while stirring continuously.
Never prepare the mixture in iron, galvanized, or metal containers, as copper reacts with metal vessels. Check neutrality using a clean iron knife; if reddish copper deposits form on the blade, add more lime suspension until the knife remains clean.
- Dissolution: Dissolve copper sulphate and lime in separate non-metallic barrels
- Mixing order: Pour copper sulphate into the lime solution with vigorous stirring (never vice versa)
- Container rule: Use only high-density plastic, wooden, or earthen containers
- Knife blade test: Dip a polished iron knife blade for 1 minute; rust-colored deposit indicates excess acid needing lime
Target Diseases and Practical Precautions
Bordeaux mixture must be sprayed fresh on the day of preparation, as the gelatinous copper precipitate crystallizes and loses foliar adherence upon standing.
It is widely used as a prophylactic dormant spray or protective foliar treatment against downy mildew in grapes, foot rot in black pepper, koleroga in arecanut, and citrus canker.
- Grapevine: Downy mildew (*Plasmopara viticola*) and anthracnose
- Arecanut & Black Pepper: Fruit rot / koleroga (*Phytophthora meadii*) and foot rot
- Citrus: Citrus canker (*Xanthomonas axonopodis*) and gummosis
- Freshness: Always spray immediately following preparation; discard unused mixture after 12 hours
Official source
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Central Insecticides Board and Registration Committee (CIBRC) ↗Related on KisanPe
Common questions
Why must Bordeaux mixture be prepared only in plastic or earthen vessels?
Copper sulphate is acidic and reacts corrosively with iron, galvanized steel, or metal containers, which destroys the vessel and destabilizes the spray solution.
How can a farmer verify that Bordeaux mixture is safe to spray on foliage?
Dip a clean iron knife blade into the mixture for one minute; if a reddish copper coating forms, the solution is acidic and requires more lime to prevent foliar scorch.
Can Bordeaux mixture be kept overnight and sprayed the next morning?
No, the gelatinous copper hydroxide precipitate crystallizes and breaks down within hours, drastically reducing foliar adherence and fungicidal efficacy.
General guidance, not personal advice. For your farm, ask your local Krishi Vigyan Kendra or agriculture officer.
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