One of the greatest challenges in agricultural production is protecting plants from disease. For generations, copper sulfate (known in Turkey as göztaşı, or bluestone) and the Bordeaux mixture made from it have been indispensable to farmers and gardeners, and they remain among the most effective, time-tested ways of protecting a wide range of crops, from fruit trees to vineyards.
So what exactly are copper sulfate and Bordeaux mixture, where are they used and how do they benefit plants? Here is everything you need to know to protect your harvest.
What is copper sulfate (bluestone)?
Commonly known as bluestone, copper sulfate is a blue, crystalline chemical compound. Although it can be used on its own in agriculture, its most common role is as the main ingredient of Bordeaux mixture.
- Fungus and algae control: Effective in clearing unwanted algae and fungi from greenhouses, irrigation ponds and tree trunks.
- Soil supplementation: Applied in controlled amounts to copper-deficient soils to meet the nutritional needs of plants.
- Preparing Bordeaux mixture: Its most important use is being combined with lime to make Bordeaux mixture.
What is Bordeaux mixture?
Bordeaux mixture is a broad-spectrum crop protection product made by mixing copper sulfate and hydrated lime with water in specific proportions. It was first developed in the Bordeaux region of France to combat downy mildew in vineyards, which is how it got its name.
Benefits of Bordeaux mixture
Applied in winter while trees are dormant, Bordeaux mixture provides excellent protection for the following season. It acts as a protective shield against both fungal and bacterial diseases.
- Prevents fungal diseases: Stops destructive fungal diseases such as scab on apples and pears, leaf curl on peaches, downy mildew in vineyards and peacock spot on olives from taking hold.
- Protects against bacterial infections: One of the most effective preventive measures against diseases such as bacterial canker and blight in trees.
- Protects wounds: Prevents wounds caused by pruning, hail damage or frost cracks from becoming infected and helps them heal faster.
- Improves cold hardiness: By helping shoots harden off, it makes trees more resistant to winter cold and spring frosts.
When should Bordeaux mixture be applied?
Bordeaux mixture is a preventive rather than a curative treatment, so it is vital to apply it before diseases appear. It is generally applied at two key times:
- Autumn application: Made after 75-80% of the leaves have fallen (usually at a 2% rate), it eliminates pathogens that could overwinter on the tree.
- Spring application: Made just before bud break (usually at a 1% or 1.5% rate), it protects the plant against diseases that become active in spring.