Bordeaux Mixture in Autumn: How to Make It and When to Spray

Bordeaux mixture is a copper fungicide made from two ingredients: copper sulphate and slaked lime. It has worked for more than a hundred years and is still one of the simplest ways to stop scab, monilia and leaf spot in the garden. In autumn, after the leaves have fallen, it is sprayed on fruit trees and berry bushes, while fungal spores are overwintering on the bark and on the ground under the canopy.

Why lime goes into the mixture

Copper kills fungal spores, but pure copper sulphate scorches green leaves. Lime softens the effect of the copper, so Bordeaux mixture can be used on plants in leaf, whereas pure copper sulphate is only for bare branches in late autumn or early spring. A side effect is a bluish film on the bark and foliage: it stays put and protects until the next heavy rain.

What it helps against

• Apple and pear scab – spores overwinter in fallen leaves and on the bark
• Monilia (fruit rot, blossom and shoot blight) on stone fruit and apple
• Leaf spot on currants, raspberries and other berry bushes
• Leaf curl on fruit trees
• Late blight of potato and tomato – on the foliage during the season, following the instructions on the pack

The mixture does not help against pests (aphids, codling moths): it is a fungicide, and insects need other products.

When to spray in Estonia

• In autumn – after the leaves have fallen. Here that is usually the second half of October to early November. Choose a dry, windless day with a temperature above zero
• In spring – before bud break: on fruit trees when the buds have swollen and turned silvery, on berry bushes when the buds are only just turning green
• Do not spray trees and bushes while they are in flower
• If you missed the autumn window this year, a spring treatment on bare branches gives the same result

Before spraying, rake up the fallen leaves from under apple and pear trees: scab overwinters on them, and if you leave them under the canopy, the mixture will be fighting the effect, not the cause.

How to make a 1% solution

The proportions below come from the manufacturer’s instructions for the ready-made garden kit Bordoo 200 g: 100 g of copper sulphate and 100 g of slaked lime per 10 l of finished solution. If you buy the kit, follow the instructions on its pack.

1. In a non-metal container (a plastic or enamel bucket without chips), dissolve 100 g of copper sulphate in 1 l of warm water.
2. In another non-metal container, stir 100 g of slaked lime into 1 l of warm water – this gives you milk of lime.
3. In a thin stream, pour the copper sulphate solution into the milk of lime, stirring constantly. The order matters: never the other way round.
4. Top up with 8 l of water – you now have 10 l of finished solution.
5. Spray straight away: the solution does not keep, so it is made right before the job.

Important: you need genuine slaked lime (calcium hydroxide). The garden limestone sold in bags for de-acidifying soil, and lawn lime, are not suitable: they are a different substance and will not make the mixture.

How to spray

• Wet the branches until the drops begin to run off, and treat the trunks and the ground under the canopy
• A guide to quantities for the spring treatment, per the kit’s instructions: 2–5 l per tree, up to 1 l per berry bush
• During the season, treat infected plants on the underside of the leaves too
• You can repeat after 7–15 days, but no more than three times per season, and the last time no later than 15 days before harvest

Safety

• Work in gloves, goggles and a mask and cover your skin – the solution is dangerous on the skin and in the eyes
• Do not spray in wind or close to a well, pond or stream: copper is toxic to aquatic life
• Do not pour leftover solution into a pond or drain – dilute it with water and pour it on the ground under the trees you treated
• Store copper sulphate and lime away from food and animal feed and out of reach of children and animals

Copper does not break down: it stays in the soil and builds up, and earthworms are sensitive to it. That is why its use in EU agriculture is limited – to 28 kg of copper per hectare over seven years. For a home garden that figure is out of reach, but the principle is a useful one: spray when it is needed, not “just in case” every month.

What not to do

• Do not make the solution in a metal bucket or tank: copper reacts with iron, the container suffers and the solution loses its strength
• Do not mix Bordeaux mixture with other products in the same tank
• Do not pour lime into copper sulphate – only copper sulphate into lime
• Do not spray fruit and berries shortly before picking: observe the waiting period stated on the pack
• Do not leave the finished solution “until tomorrow”
• Do not spray in rain, in heat or during frosts

Frequently asked questions

Autumn or spring – which is better?

A pair works best: in autumn on bare trees, to kill spores on the bark and the ground, and in spring before bud break, to close the season. If you have to choose one treatment, take the spring one: it is closer to the start of growth.

Can I replace slaked lime with garden lime from a bag?

No. Limestone (calcium carbonate) for de-acidifying soil is a different substance, and it will not make the right mixture. You need genuine slaked lime (calcium hydroxide); it comes in ready-made Bordoo kits or is sold in building supply shops.

How long does the finished mixture keep?

It is made right before treatment and used up the same day. Leftovers are not stored.

How does Bordeaux mixture differ from pure copper sulphate?

Pure copper sulphate is harsher: it scorches leaves, so it is used only on bare branches. In Bordeaux mixture the lime softens the copper, and the mixture can be used on leaves too. For doses of pure copper sulphate, follow the instructions on the pack.

How long does the protection last?

The film stays on the bark and leaves and protects until the next heavy rain. After heavy downpours, or by spring, the treatment is repeated.

What to pick from the catalogue

Our catalogue has copper sulphate in a 100 g pack (just right for one 10 l batch) and 1 kg for a large garden. Slaked lime (in Estonian kustutatud lubi or hüdraatlubi) is sold in building supply shops. We bring in ready-made Bordoo kits with copper sulphate and lime from time to time – keep an eye on the “Disease control (fungicides)” section. For whitewash and trunk protection, see the “Tree protection” section.