Bordeaux paste

Bordeaux paste is a freshly prepared mixture of copper sulphate and slaked lime in water, used in Indian orchards as a wound dressing on freshly pruned mango, citrus and other fruit trees. The thicker paste is a sister formulation of the dilute foliar Bordeaux mixture developed in 19th-century Bordeaux vineyards, both first described by Pierre-Marie-Alexis Millardet.

Composition / Active ingredient

Active ingredients: Copper sulphate pentahydrate + slaked lime [Ca(OH)₂]
Paste ratio: 1 : 1 : 10 (CuSO₄ : lime : water) by weight
Spray ratio: 1 : 1 : 100 for the dilute Bordeaux mixture used as foliar fungicide

Mode of action

Bordeaux releases cupric ions (Cu²⁺) that bind to fungal and bacterial enzymes (sulphydryl and carboxyl groups), causing protein denaturation and membrane disruption. It is a multi-site contact protectant (analogous to FRAC group M01, inorganic copper). The lime buffer neutralises free copper, slowing ion release so that the dressing protects the wound surface for weeks without causing phytotoxicity to live cambium.

Target use and dose

In orchard practice, freshly cut twigs and pruning wounds are slant-cut and immediately painted with Bordeaux paste to prevent colonisation by die-back fungi (e.g. Lasiodiplodia) and bacterial canker organisms. Always add slaked lime to the copper sulphate solution, never the reverse, to avoid free-acid burn. Copper oxychloride suspension (see Input Copper Oxychloride) is a substitute when fresh lime is unavailable.

Safety and regulatory status

Bordeaux mixture is approved for use in organic and conventional agriculture in India and worldwide. Copper accumulates in soil over years of repeated use; the wound-paste application limits soil loading because it is localised. Preparation should use earthen, plastic or wooden containers — never galvanised iron.

References

Preparation of Bordeaux mixture. KVK / ICAR extension bulletin.
Bordeaux Paste and Bordeaux Paint as Wound Fungicides. Indian Farmer.