The Best Fungicide for Peach Leaf Curl

Copper Products

• The most effective products on the consumer market are fixed copper fungicides containing copper ammonium complex products and copper soaps containing copper octanoate. These products are made more effective by adding 1 percent horticultural oil. The Fair Oaks Horticulture Center, a project of the University of California Cooperative Extension, found in their trials that copper soap with horticultural oil controlled 80 percent of the infection, while copper ammonium complex with horticultural oil controlled 70 percent of the infection.

Bordeaux Mixture

• The ingredients for Bordeaux mixture may be difficult to find, but this home-mixed fungicide is effective when mixed from dry minerals just before application. It contains powdered copper sulfate, hydrated or slaked lime, and water. The spray is corrosive and permanently stains clothing, so protective clothing and goggles are required when mixing and applying to the peach tree. Bordeaux mixture is not as effective as fixed copper fungicides, but it better withstands winter rains.

When to Spray

• Fixed copper fungicides and Bordeaux mixture damage healthy foliage, so only treat peach leaf curl after all leaves have fallen. A single application in the fall or early winter may be sufficient. However, with severe infection, two applications, one after leaf drop and a second in early spring before buds open, provide better control. In areas with frequent winter rains, a fall application of Bordeaux mixture followed by fixed copper fungicide in spring works well.

Resistant Varieties

• Several peach varieties, such as Frost, Indian Free and Muir, are known to be resistant to peach leaf curl. However, they still require treatment in the first three years of growth. Also, they are carriers of the fungus even when they do not show symptoms of the disease. If nonresistant varieties are planted nearby, it may be necessary to treat the resistant varieties so they do not spread or harbor the fungus.