Bordeaux mixture is an effective fungus treatment authorized for use in organic farming.
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.
Basic Bordeaux mixture facts
Purpose and use – fungicide, algicide
Content – water, copper sulfate and lime
Most relevant plants – grape vine, fruit trees, potato, tomato
What is Bordeaux mixture?
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.
When to use Bordeaux mixture
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.
- Indeed, moisture and warmth are the two conditions that trigger fungus growth.
Bordeaux mixture is also used in fall after leaves have fallen off trees.
- Spraying at this moment helps avoid that any given disease overwinters in the garden.
- It is important to destroy any sick leaves that have already fallen to the ground.
- Spray Bordeaux mixture on the entire tree: branches, trunk, and eventually neighboring areas.
Preventive use is effective to defend against fungal diseases (mushrooms).
Most targeted diseases are:
- Apple scab (and other scab diseases)
- Peach leaf curl
- Knot or canker
- Rotting fruit, European brown rot
- Black spot disease (maple tar, for instance)
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.
Diseases and Bordeaux mixture
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.
- Begin with picking up dead leaves and burning them before spraying Bordeaux mixture.
- The best time for this is the end of winter or the very beginning of spring, just before the first buds appear.
- In both cases, it is highly advisable to renew this step 2 to 3 times at a two-week interval.
- Read also: How to treat rotting fruit, European brown rot
Potato, tomato and strawberry plants
Starting in May, 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.
- Stop treating a few weeks before harvest.
- Read also: growing and caring for potato, tomato, strawberry plants.
- Grape vines are very vulnerable to mildew. You ought to treat them every year in spring and in fall.
That is where the mixture’s name comes from: “Bordeaux”.
- Start treating in April, continue until end of July, spraying Bordeaux mixture every two weeks and after every heavy rain.
- Read also: growing and caring for grapevines, and pruning grapevines.
Read also on diseases and parasites
- Fighting aphids
- Fighting caterpillars
- How to treat downy mildew
- Treating apple scab
- How to treat peach leaf curl
- How to treat canker
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.
Smart tip about Bordeaux mix
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.