Bordeaux Mixture

Bordeaux mixture is a bactericide and fungicide made by mixing copper sulfate and lime (calcium hydroxide) with water. It persists in rainy weather and can provide long-lasting protection against a variety of diseases in vine and tree crops. Additionally, because it contains copper, it has a multi-site mode of action and may be a particularly useful spray in a pesticide resistance management program. 

Bordeaux mixture is used as a preventive or curative spray to manage bacterial or fungal diseases and is usually applied after harvest, before rainy weather starts. Diseases commonly controlled using Bordeaux mixture during the dormant season are peach leaf curl in nectarine and peach; shot hole disease in apricot, nectarine, and peach, and bacterial blast; Phytophthora brown rot and Septoria spot in citrus. 

Springtime applications are used to control fire blight in apple and pear, and walnut blight in walnut. Applying Bordeaux mixture to newly growing leaves, however, can cause injury to the new growth. 

Bordeaux mixture can also be used to control certain invertebrates, such as brown garden snail and Italian pear scale. In these cases, Bordeaux mixture is applied to the trunks to prevent snails from moving into the canopy, or by killing moss and lichen that protect the scale insects from natural enemies.

Fixed copper sprays are also effective against many of the same pathogens as Bordeaux mixture and may be an effective alternative. The main advantage of Bordeaux mixture over fixed copper is that it lasts longer, especially in rainy weather. Fixed copper sprays, however, are easier and safer to prepare, less phytotoxic (and therefore safer to apply to new growth), less corrosive, don’t stain, and may be tank mixed with a wider variety of pesticides including zinc sulfate.  Alternatively, fixed coppers can be mixed with lime to increase persistence.

For Bordeaux mixture, zinc Bordeaux mixture, and fixed copper (with or without lime added), thorough spray coverage is crucial for an application to be effective.

Read the label directions carefully for both copper sulfate and lime. Always wear the personal protective equipment indicated by the strictest label when preparing stock solutions, mixing Bordeaux mixture, and applying it. This includes protective clothing, eye protection, respiratory protection, and chemical-resistant gloves.

The effectiveness of a Bordeaux mixture spray depends on mixing the copper sulfate and lime in the correct order. Once mixed, use the Bordeaux mixture the same day because it begins to lose efficacy quickly. It is also highly corrosive, so rinse equipment immediately after applying it by rinsing the equipment at least three times, adding a small amount of vinegar to the rinse water to neutralize the high pH of the Bordeaux mixture residue.

Bordeaux Formula

Bordeaux mixtures are described as a ratio of three numbers. Each number represents the amount of each material to add: the first number referring to pounds of copper sulfate, the second to pounds of hydrated lime, and the third to gallons of water.

For example, a ratio 10-10-100 would be prepared with:

• 10 pounds copper sulfate
• 10 pounds hydrated lime
• 100 gallons water

If zinc sulfate is added, then the first number is for the zinc sulfate.

Making Bordeaux Mixture Using Dry Ingredients

If the ingredients are in dry form, you must use a tank with a mechanical agitator. Bypass agitator systems usually are not adequate for preparing a tank mix of Bordeaux.

Fill the tank with about one-third of the desired final volume of water. With the mechanical agitator running, wash the copper sulfate through a screen into the tank with water. You can use a wooden paddle to help the copper sulfate dissolve and move through the screen but be careful not to force it through. Give the copper sulfate time to dissolve. By the time you have added two-thirds of the final volume of water, all the copper sulfate should be dissolved.

Then, in a corrosion-resistant container, mix the dry hydrated lime into a portion of the remaining water. Slowly add the lime suspension to the copper sulfate and water solution. Rinse the container into the tank and finish filling the tank to the desired volume (e.g., 100 gal).Continue agitating the mixture while spraying.

Bordeaux mixtures can also contain zinc sulfate, which is commonly used in citrus to increase activity against Septoria spot and to correct zinc deficiency in trees. When adding zinc sulfate to preparare a zinc Bordeaux mixture, always add the zinc sulfate first, followed by the copper sulfate, then the hydrated lime, using dry ingredients.

Making Bordeaux Mixture Using Stock Solutions

Mixing Bordeaux mixture from already prepared stock solutions can be an easier option if you are only making a small amount, or do not have a sprayer with an agitator. The procedure to make Bordeaux mixture with stock solutions is similar to that of preparing it with dry ingredients. When mixing with stock solutions, make sure that all of the stock solutions are well mixed before adding them to the spray water. Continue mixing the spray mix while adding the stock solutions, and for several minutes after. Remember that the stock solutions contain water, which must be factored into the calculation of the mixture (10 gallons of 10-10-100 Bordeaux mixture would be mixed with 8 gallons of water, 1 gallon of copper sulfate stock solution, and 1 gallon of lime stock solution).

Always add the copper sulfate stock solution before adding the lime stock solution.

Example Mixture

To make 2.5 gallons of a 10-10-100 Bordeaux mixture:

1. Add 2 gallons of water to a strong plastic bucket.
2. Shake the copper sulfate solution vigorously, add 1 quart (0.25 gal) to the water, stir the solution.
3. Shake the lime mixture and add 1 quart (0.25 gal) to the water and copper sulfate solution, continue stirring.
4. Stir the spray mixture for several minutes before pouring it into the sprayer.
5. Constantly agitate the mixture while applying it, to help prevent clogging.

Bordeaux performs best if nothing is added to the prepared mixture, with the exception of adding zinc sulfate. If adding zinc sulfate, start by adding it first, followed by copper sulfate and then hydrated lime.

Making Stock Solutions

These components of Bordeaux mixture, especially the copper sulfate, are very toxic and corrosive. Store them in clearly labeled containers.

Prepare separate stock solutions for the copper sulfate and lime components of the Bordeaux mixture. Prepare each stock solution so that they contain 1 pound of ingredient per gallon of water.

Copper Sulfate Stock Solution

Dissolve 1 pound of copper sulfate per gallon of warm water in a plastic container. Transfer the solution to a sealed glass container for storage.

Lime Stock Solutions

Stock solutions of lime can be made with either hydrated lime or slaked lime. Slaked lime makes a superior stock solution but is more dangerous to prepare and requires more time, effort, and containers than preparing a hydrated lime stock solution.

Preparing a stock mixture of lime eliminates the need to buy fresh lime each time you prepare a Bordeaux mixture.

Hydrated Lime Stock Solution

Mix 1 pound of fresh, hydrated lime per gallon of water. This mixture needs to stand for about 2 hours before use. Store in a sealed container.

Slaked Lime Stock Solution

Slaked lime is prepared by adding quick lime (calcium oxide) to water to produce calcium hydroxide. Quick lime is also called burned lime or hot lime.

Slaking quick lime in water can produce enough heat to boil the mixture, so add quick lime to the water slowly to prevent it from splashing or getting dangerously hot. Use a wooden stick to stir the mixture while adding the lime to the water.

To make a stock solution with slaked lime, add 1 pound of quick lime per gallon of water to get a mixture with the consistency of milk. The slaking reaction takes 0.5 to 2 hours, so make sure to account for this when planning your Bordeaux mixture preparation. Store in a sealed container.

Components

Copper Sulfate

Powdered copper sulfate, also called bluestone, is a blue powder that dissolves in warm water. Do not use lumpy copper sulfate because it is too slow to dissolve. In storage, powdered copper sulfate becomes lumpy and difficult to work with when it gets wet, so store it in a dry place. Lime can be added to fixed copper products to improve adherence to the plant. In the citrus industry, zinc sulfate is often added to Bordeaux mixtures to correct zinc deficiencies in the plant and to increase activity against Septoria spot of citrus.  If adding zinc sulfate in preparation of a zinc Bordeaux mixture, always add the zinc sulfate first, followed by copper sulfate, followed by the hydrated lime.

Lime

Use either fresh, dry hydrated lime or slaked lime to prepare Bordeaux mixture.

If using hydrated lime, use only high-quality, fresh hydrated lime that has not been carbonated from exposure to air. Hydrated lime is a dry product commonly used to make plaster and is readily available under several trade names.

Adding Zinc to Bordeaux Mixture

Zinc may be added to Bordeaux mixture or fixed copper sprays for additional disease control activity and as a foliar-applied micronutrient.

When mixing zinc-containing sprays, add zinc first and allow to dissolve. Then add copper and allow to dissolve. Finally, add lime. Zinc acidifies the water and helps copper dissolve into solution and the lime is basic which bring the pH up. If you add lime first that the pH is alkaline, then the zinc and copper will not dissolve

In citrus, zinc is often added to Bordeaux mixture to help manage Septoria spot and correct zinc deficiency. No phytotoxicity has been observed on citrus trees when using the rates listed in the tables below when it is applied in the late fall (October to November) or early winter (January to February).

For deciduous tree crops, zinc can be added to late fall applications of Bordeaux mixture as a foliar micronutrient application, as long as it is applied before leaf drop. Fall application rates of zinc in deciduous trees tend to be higher than the rates listed in the tables below.