Peach leaf curl and shot hole disease of peaches are common problems for the backyard gardener. Both are fungal diseases that are treated with copper-based fungicides in late fall after all the leaves have fallen from infected trees. The same copper product can be used to combat both diseases.
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Leaf fall dates change every year depending on weather patterns. During the next couple of weeks, monitor your peach and nectarine trees for complete leaf fall and check the weather reports for predictions of rain. Rains and overhead irrigation can wash off the fungicides.
Peach leaf curl
The most obvious symptom of peach leaf curl occurs in spring during cool, wet weather as the new leaves on peach and nectarine trees turn red instead of green and become thick, curled and distorted. The thicker sections of infected leaves turn yellow and then are covered with a grayish white fuzz of fungal spores. The infected leaves usually fall off and are replaced by a new crop that shows fewer or no symptoms of the disease. Peach and nectarine trees infected with untreated peach leaf curl disease decline in vigor over several years; the fruit is affected, as well.
When choosing trees for your backyard orchard look for resistant varieties. (There aren’t that many resistant varieties available.) If you’ve inherited an unidentified peach tree, plan on spraying for peach leaf curl every fall to minimize chances of infection.
Shot hole disease
Shot hole disease gets its name from the small round holes that are seen in leaves on infected trees. That’s usually the first clue for the home gardener. You’ll also see tan marks or lesions and oozing or gumming on twigs. That’s the second clue. The fungus continues to produce spores through the winter on infected twigs and buds. Those spores are spread by splashing water and rain in spring.
A thorough cleanup of all fallen twigs and leaves helps remove some of the overwintering spores. Pruning out infected twigs before treatment with a fungicide on peach trees infected with shot hole fungus will reduce the number of fungal spores.
Labels on Bordeaux mixtures or liquid copper ammonium complex fungicides list the MCE or metallic copper equivalent. Liquid copper ammonium products are currently the only copper formulations available to home gardeners and they have an 8 percent MCE. Some formulations of copper are approved for use in the organic garden. Bordeaux mixtures are no longer available for sale, but many home gardeners still have the ingredients on their garden shed shelves.
Adding 1 percent horticultural spray oil to the mixture will make it more effective. The oil will also smother some aphids and their eggs, and some scale and mites, as well. Applications of horticultural oils to treat for many species of pest insects are usually made in late spring when the eggs hatch.
Spray the copper mixture to thoroughly drench all surfaces of the tree including bark cracks and crevices. The tree should be dripping wet with fungicide.
Copper levels can build up in the soil eventually making it toxic to microorganisms; copper runoff into gutters or canals can harm some aquatic species. Always read labels carefully, follow instructions for application and disposal of the products and wear protective clothing, goggles and gloves.