A blue-tinged spray of copper sulfate and lime, brushed onto trunks or misted over leaves, Bordeaux mixture is the organic gardener’s standby against downy mildew, scab, peach leaf curl and brown rot. Everything hinges on timing: applied before symptoms show, it protects; sprayed once the fungus has appeared, it is almost useless.
It is widely used in the garden to treat plants, vegetables and fruit trees.
Following recommended doses and uses for this product is nonetheless necessary to avoid contaminating nature.
| Purpose and use | Fungicide, algicide |
|---|---|
| Content | Water, copper sulfate and lime |
| Most relevant plants | Grape vine, fruit trees, potato, tomato |
It is a blue-colored fungicide. Its main ingredients are copper and lime.
Spraying is the most common type of use, but sometimes people lather Bordeaux mix on trunks with a wide paintbrush. It helps fight most types of fungal diseases. Fungal diseases are due to mushrooms and fungus. Bordeaux mixture is often used against downy mildew, scab, fruit leaf curl, canker or European brown rot.
Recommended dosage is maximum ⅓ to ⅔ oz. (10 to 20 g) for 1 quart (1 liter) water. However, this depends on the concentration of the initial powder or liquid: be sure to read the label of the product you’re using.
The first Bordeaux mixture treatment should be applied at the end of winter. Doing this during the winter deep cleaning is a good time to eliminate mushrooms that may have overwintered among plants.
It is often used in spring when diseases develop.
Bordeaux mixture is also used in fall after leaves have fallen off trees.
Preventive use is effective to defend against fungal diseases (mushrooms).
Most targeted diseases are:
It is almost useless to spray Bordeaux mix when the fungus has already appeared, because its main purpose is preventive.
But it can be argued that spraying when the disease has appeared can nonetheless contain its spread.
Treat fruit trees preventively in fall when the leaves fall.
Repeat the treatment at the end of winter after pruning to protect fresh wounds from contamination by fungus.
Starting in late spring, spray once every two weeks.
This treatment is a necessity because these vegetables are the most vulnerable to downy mildew, and contamination would compromise the harvest.
The spraying calendar is not the same for an orchard, a vegetable patch and a vine. The table below sums up when to start, how often to repeat, and what each treatment is aimed at.
| Plants | When to treat | How often | Main target |
|---|---|---|---|
| Fruit trees | In fall at leaf fall, then end of winter after pruning | Renew 2 to 3 times at a two-week interval | Scab, peach leaf curl, canker, European brown rot |
| Potato, tomato and strawberry plants | From late spring onwards | Once every two weeks, stopping a few weeks before harvest | Downy mildew (blight) |
| Grapevine | From mid-spring until midsummer, in spring and fall | Every two weeks and after every heavy rain | Mildew |
In every case, pick up and destroy fallen sick leaves before spraying, since the fungus overwinters on them.
Even though using Bordeaux mix is possible in organic agriculture, a strong recommendation is to not increase the doses on product labels.
Also avoid using Bordeaux mixture too often, or in itself it will lead to contamination. Another alternative is to make your own fungicide from weeds, here are the best ones for that.
Studies actually show that halving doses results in almost the same effectiveness. Since this product, in the long run, is toxic, it’s a good idea to reduce doses in order to keep copper from leaching into the soil.
Where can one purchase Bordeaux mixtures to treat fungal problems on my pear trees? I only have three trees, are Kieffer and two Asian varieties.
Hi Fred, in garden stores they usually have ready-to-use mix or just-add-water liquids or powder. Sometimes the name differs but the content and ingredients include “copper sulfide”. There are also options to purchase online.
Copper sulphate not copper sulphide.