Bordeaux mixture, an effective treatment

Bordeaux mix fungicide

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 it 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.

When to use Bordeaux mixture

Main ingredient of Bordeaux mix, aside from water of course, are copper sulfate crystalsThe 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:

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

Fruit trees

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.

Grapevine

  • 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

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.

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.

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Picture related to Bordeaux mix overlaid with the

Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Bordeaux mix on leaves (also on social media) by Pg1945 under © CC BY-SA 3.0
Crystals by Leiem under © CC BY-SA 4.0