Bordeaux mixture is one of the substances you can turn to in order to prevent blight from attacking your tomatoes. Bear in mind, however, that it only works as a preventative, meaning it is effective before blight reaches the leaves. Once the disease has taken hold in the plant, you will need to use other treatments.
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Contents
What is Bordeaux mixture?
How to prepare Bordeaux mixture
How to spray tomatoes with Bordeaux mixture
What is Bordeaux mixture?
Bordeaux mixture is a treatment used on tomatoes, potatoes, grapevines and fruit trees, with both fungicidal and algicidal action. It is made from copper sulphate mixed with hydrated or slaked lime, and it is applied to both the plant and the soil.
How to prepare Bordeaux mixture
During the growing season, from the first leaves through to harvest, Bordeaux mixture is applied to the plant at a concentration of 0.5–1%.
1. Prepare the ingredients and suitable containers
To make Bordeaux mixture, you need copper sulphate, slaked lime, water and two containers.
For 10 litres of solution, for example, you will need:
- 10 litres of water
- 50 g of hydrated or slaked lime
- 50 g of copper sulphate
- 2 plastic containers (buckets or canisters), one of at least 5 litres and one of at least 10 litres
2. Prepare the slaked lime solution
In the larger bucket, add 50 g of slaked or hydrated lime and 5 litres of water at room temperature. Stir well until fully combined.
3. Prepare the copper sulphate solution
In the smaller bucket, add the copper sulphate (crushed finely so it dissolves easily) along with the water. Stir well using a stick or a plastic utensil. Avoid metal, as the solution is corrosive.
4. Combine the two solutions
Pour the copper sulphate solution into the lime solution and stir well until fully combined. It should take on a lovely deep blue colour, like the sky.
5. Pour the mixture into your sprayer
The simplest and safest option is to spray with a knapsack sprayer, whether a small 2-litre model or a larger one of 10 litres or more. The quantity above is enough to treat roughly 100 sq m of tomato crop.
Make sure the sprayer is clean. Bordeaux mixture must not be combined with insecticides or other treatments.
How to spray tomatoes with Bordeaux mixture
Tomatoes are most often sprayed after rainfall, when the plants are at greater risk of developing blight. Spray the leaves generously to keep blight fungi at bay.
Avoid spraying on windy days. You will lose much of the solution, and it may blow back onto you.