Copper Sulfate Spray Mixture for Peaches
Copper sulfate spray for peaches is a combination of copper sulfate, lime and water that is commonly referred to as Bordeaux mixture. It is an effective fungicide and bactericide for controlling diseases in peach trees and other fruit trees, nut trees and ornamental plants. The natural minerals within this mixture are measured in just the right order and amounts to provide peach trees long-lasting protection against diseases.
Bordeaux mixture requires combining copper sulfate and hydrated or slaked lime with warm water. Copper sulfate in powder form is sometimes referred to as bluestone. It is a finely ground material that dissolves rapidly in warm water. Fixed copper fungicides should never be used to prepare Bordeaux mixture. It is necessary to use fresh lime, not lime that has been stored from the previous season. Hydrated lime, or calcium hydroxide, is commonly used to make plaster. If you choose to use slaked lime, be aware that it can produce enough heat to boil water. It should be added to the mixture in small amounts so it does not splash. Slaked lime is made by adding hot or burned lime to water to make calcium hydroxide. Gloves, goggles and a dust-filtering respirator mask should be worn when working with slaked lime.
Bordeaux mixture is generally prepared at a ratio of 10-10-100. This mixture controls most disease-causing pathogens in peach trees. These numbers represent the amount of each component to add. The first number refers to the pounds of copper sulfate, the second number to pounds of dry hydrated lime, and the last number refers to the total gallons of water. To make smaller amounts, such as a 1-gallon mixture, mix 1/10 pound each of copper sulfate and lime in 1 gallon of water. Copper sulfate and hydrated lime are available at most garden centers.
Bordeaux mixture is applied primarily in the fall and winter months to control fire blight, leaf curl and shot hole fungus. It should be applied the same day it is prepared and used as a dormant spray on peach trees in late fall or early spring, when the buds on our tree begin to swell. Bordeaux mixture adheres well to plants in rainy weather, making it an ideal fungicide for winter treatment. However, do not apply this mixture to a peach tree after it breaks dormancy because it can injure leaves. Once the mixture is used up, the equipment used to apply and mix it should be cleaned thoroughly, because the mixture is highly corrosive to metal tanks and parts. Neutralize residue by adding a small amount of vinegar to your rinse water.
Advantages and Disadvantages
Bordeaux mixture can be stored in solution or dry form and it is highly effective and long-lasting. It stains surfaces with a blue tint, so take care when using around siding, fences and other exterior surfaces. Bordeaux mixture has a high pH, so it can leave a salty deposit in the soil, and it is not compatible with most pesticides. It is not recommended that growers prepare Bordeaux solution themselves. Preparation is usually left to professionals because it is highly corrosive. It is commercially available in premixed packages, but often freshly prepared mixtures stick to peach trees better and are more effective.
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