What Is A DIY Bordeaux Fungicide?

What is a DIY Bordeaux fungicide? For starters, there are three kinds of fungicide out there.

  • Chemical fungicides are fast-acting but can harm beneficial plants and insects, with the risk of some plants building up a tolerance if one recipe is used too often.
  • Organic fungicides, such as neem oil, take longer to work and are less reliable, but they’re generally safe to use and rarely result in a tolerance buildup.
  • The third type, homemade fungicides, fits somewhere in the middle. A homemade fungicide uses a mix of chemical components and (as the name implies) can be made in your kitchen.
Bordeaux mixture - copper sulphatePin

Homemade types tend to use natural chemicals ad/or organic components to create a fungicide that’s highly effective and relatively fast-acting.

They pose a minor risk to plants and animals but are usually safe when used properly, and they won’t result in a tolerance buildup because they use natural ingredients.

One such homemade remedy is Bordeaux fungicide, a simple recipe that can bear excellent results.

What Is Bordeaux Fungicide?

1761 saw the first use of copper sulfate to treat wheat seeds against disease.

Fast-forward to 1882, Millardetof Bordeaux University noticed that copper sulfate was affecting downy mildew-infected grapes.

Upon further experimentation, it was found that mixing the sulfate powder with a lime suspension effectively killed the infection.

This mixture was named Bouillie Bordelaise (AKA “Bordeaux mixture”) and is the basis for modern-day Bordeaux fungicide

Advantages Of Bordeaux Fungicide

Bordeaux fungicide lasts longer and is more effective than fixed copper sprays.

It can be stored in stock and dry forms, but its effectiveness decreases over time once mixed with water.

Freshly-made Bordeaux sticks better to trees and won’t wash away as easily.

The mixture works against many fungal infections, from the common downy mildew and powdery mildew to the more serious black spot, and is even an effective treatment of the dreaded fire blight.

Other issues the fungicide will help treat include:

  • Apple scab
  • Cankers
  • European brown rot
  • Leaf curl
  • Peacock spot
  • Walnut blight

Disadvantages Of Bordeaux Fungicide

Unlike fixed copper sprays, Bordeaux fungicide can leave behind stains on surfaces such as countertops.

This staining can also occur on plants, so it’s usually best to use it on deciduous plants while they’re dormant and away from painted surfaces.

The lime content means the fungicide has a high pH level and will leave behind mineral salts, making it more phytotoxic *, i.e., Harmful to sensitive plants).

The mix is also more corrosive, so you need to use caution when preparing, including the need for safety gear.

Bordeaux is a preventative fungicide, meaning it’s generally ineffective once the fungal infection has set in but can be very effective at preventing infection from forming in the first place.

How To Make Bordeaux Fungicide?

There are a couple of things to consider when preparing Bordeaux fungicide.

For example, you can prepare it as a dry mix, stock, or ready-made spray.

Additionally, you’ll need to consider ratios when preparing the mix.

Different Mixes For Different Jobs

Bordeaux fungicide is a mix of copper sulfate and lime in water, but some variations in these ingredients should be noted.

You’ll want only to use powdered copper sulfate when making Bordeaux, as this ground substance dissolves easily and has great shelf stability.

Using the sulfate in chunk form (or getting it wet, which will cause it to cake) makes it far more difficult to dissolve.

Likewise, using a fixed copper fungicide will ruin the final product.

You can use wither dry hydrated lime or slaked lime as the secondary ingredient.

Hydrated lime has a short shelf life when air exposure but is quite easy to get hold of since it’s a common ingredient for plaster-making.

Slake lime is created by adding quick lime to water, which will cause the water to boil.

You must add only small amounts at once using a wooden stick to stir and wearing proper eye protection.

You’ll need a total of 1 pound of quick lime per gallon of water, and the entire process can take anywhere from ½ hour to 2 hours.

While slaking lime can be dangerous and requires more time and effort than straight dry hydrated lime, it provides a superior suspension and is used when making stock solutions.

Storing Bordeaux Fungicide Components

Once mixed with water, Bordeaux has a short shelf life, so it needs to be stored either in dry form or stock form.

Drey form is exactly how it sounds. Store your copper sulfate and hydrated lime in airtight containers.

You’ll need to discard any unused lime annually, so only purchase what you know you’ll need.

Stock mixtures store a little differently.

Dissolve 1 pound of copper sulfate in a gallon of water and store it in a stoppered glass bottle until needed.

You can also store slaked lime in a stoppered container, which will have a much longer shelf life than dry hydrated lime.

Make sure to label both containers clearly.

How To Calculate Mixing Ratios?

Although variations exist, the general consensus is that a 10-10-100 ratio works best.

This ratio indicates how many parts of copper sulfate, lime, and water are added.

So 10-10-100 means 10 pounds of copper sulfate, 10 pounds of lime, and 100 gallons of water.

But that’s a little much if you just want to retreat one or two plants.

Thankfully, it’s easy to calculate smaller amounts.

For 1 gallon of water, a 1-1-100 ratio would equate to 1tsp of copper sulfate and 1tsp of lime.

Thus, a 10-10-100 ratio would equate to 10tsp copper sulfate, 10tsp lime, and 1 gallon of water.

Pro Tip: 3 teaspoons equals 1 tablespoon, making measuring much faster.

While 10-10-100 can be used as a stop-all ratio, you can also use more precise ratios to prevent specific diseases.

For example, 8-8-100 is generally used on cherry trees to prevent dead bus, while 12-12-100 is often used to prevent peach Coryneum blight.

Applying Bordeaux Fungicide

Always apply Bordeaux when the plant is dormant, as it can not only stain but can also easily damage foliage.

If you are using dry ingredients and have an agitator, this is the process:

  • Gather the correct ratio amounts for your ingredients based on the gallon capacity of the spray tank.
  • Fill the tank ⅓ full with water.
  • Activate the agitator and wash the copper sulfate using a screen and wooden paddle to slush the powder around as water from the supply hose dissolves it into the tank.
  • Stop when the tank is ⅔ full, and the sulfate has been added.
  • Mix the dry hydrated lime and some remaining water in a plastic bucket.
  • Add the suspension to the tank.
  • Top off the tank while the agitator continues running.
  • Use before the end of the day.

For adding stock to a sprayer, you’ll need to adjust your ratios a bit.

To fill a 2 ½ gallon container:

  • Add 2 gallons of water to a plastic bucket.
  • Vigorously shake the container of calcium sulfate solution to mix, then add 1 quart to the bucket.
  • Use a wooden stirrer to keep mixing as you add ingredients, or seak the container and shake while preparing the lime.
  • Vigorously shake the slake lime solution and add 1 quart to the sprayer.
  • Continue stirring or shaking the bucket.
  • After several minutes, add the mixture to a sprayer.
  • Continue shaking the sprayer as you work to prevent clogs.
  • Use immediately

Note that you can also use stock in early spring, but you should only add 1 pint of each ingredient per 2 gallons of water.

This weaker mixture will also be somewhat safer to use on sensitive parts of the plant.