If you grow peach trees (Prunus persica), you may eventually have to treat them with a fungicide mixture that contains copper sulfate. Hardy in U.S. Department of Agriculture plant hardiness zones 5 through 8, peach trees can develop fungal diseases, including peach leaf curl and shot hole disease, in wet spring weather. Peach leaf curl causes reddish, curled or puckered leaves, and shot hole disease causes purplish black lesions on shoots and leaves. The name “shot hole” refers to the holes that appear in the middle of the lesions. Copper sulfate is an ingredient in Bordeaux mixture, which is an effective fungicide spray for these peach tree diseases.
Bordeaux Mixture Ingredients
Bordeaux mixture contains copper sulfate, lime and water, often in a 10-10-100 ratio. You can buy commercially prepared Bordeaux powder or you can prepare your own stock solutions for future use. Copper sulfate and hydrated lime are available for purchase at garden centers. Stock solutions of 1 pound of copper sulfate in 1 gallon of warm water and 1 pound of dry hydrated lime in 1 gallon of water will keep indefinitely in airtight glass containers, according to the University of California Integrated Pest Management Program. You can use “quick lime” or calcium oxide to make a slaked lime solution, but you must add it to the water slowly to prevent the rapidly heating solution from boiling over. A lime solution must sit for two hours before it is effective.
Preparing Bordeaux Mixture Spray
If you have stock solutions on hand, add 1 quart of copper sulfate solution to 2 1/2 gallons of water while stirring the water, and then add 1 quart of lime solution, as recommended by the University of California Integrated Pest Management Program.
A homemade mixture for one-time immediate use contains 3 1/3 tablespoons of copper sulfate, 10 tablespoons of hydrated lime and 1 gallon of water. Pour 1/3 of the water into a spray tank that has an agitator. Slowly add the copper sulfate and 1/3 gallon of additional water. In a separate container, add the lime to the remaining 1/3 gallon of water, and then add the lime mixture to the copper sulfate mixture. To make Bordeaux spray from commercially prepared powder, add 4 tablespoons of the powder to 1 gallon of water.
Controlling Peach Tree Diseases
To control peach leaf curl with Bordeaux mixture, spray peach trees with the mixture in late fall or early winter when the trees go dormant, and in early spring before the leaf buds swell. An application during spring bloom helps control peach shot hole disease. You should cover the entire surface of the peach tree branches and twigs with the spray. The mixture withstands rain better than fixed copper fungicide sprays such as tribasic copper sulfate, so single applications in the winter and spring are usually sufficient.
Precautions for Using Bordeaux Mixture
Bordeaux ingredients are toxic and corrosive, so you should wear goggles and a respirator when handling these ingredients. Label stock solutions and keep them out of reach of children and pets. People should stay away from treated peach trees until the spray completely dries. Bordeaux mixture can leave a blue stain on plants and structures, so you should not spray the mixture near evergreen plants or fences or other structures. Excessive spraying can injure tender new leaves on peach trees. Bordeaux mixture is not compatible with most pesticides, according to the University of California Integrated Pest Management Program.
- University of Florida IFAS Extension: Prunus Persica -- Peach
- University of California IPM Online: Peach Leaf Curl
- University of California IPM Online: Peach Shot Hole Disease
- University of California IPM Online: Shot Hole Disease (Coryneum Blight) -- Wilsonomyces Carpophilus
- University of California IPM Online: Bordeaux
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