Peach leaf curl is a fungal disease that affects the flowers, leaves, shoots and fruit of peach trees and some of their closest relatives. According to the University of California Integrated Pest Management Program, this condition is one of the most common problems experienced by home peach growers. While it's best to plant disease-resistant varieties to control this problem, you can also manage it by applying anti-fungal sprays in the autumn.
Fruit tree sprays containing copper are among the most readily-available fungicides for home gardeners. These are usually sold as fixed copper products, with their copper content listed as a “metallic copper equivalent,” or MCE. Higher MCE percentages indicate a more effective product. This substance is active only when wet, but it should not be applied shortly before heavy rains, as they can wash the copper off of the tree's leaves. Sprays containing copper ammonium complex, one of the most common fixed copper formulations, are most effective when combined with 1 percent horticultural spray oil.
This pesticide has been used to control fungal infections in French vineyards since the beginning of the 20th century. It adheres to peach tree leaves more effectively than fixed copper sprays, but you have to mix up the fungicide just before application, since it is not very stable. The basic ingredients are slaked or hydrated lime and copper sulfate, mixed with water. This substance should be applied to trees only during the cool season, since it can cause damage to new leaves.
Chlorothalonil is the only non-copper fungicide spray currently available to manage peach leaf curl in home growing situations. This protectant fungicide does not work after symptoms of peach leaf curl appear in the spring, making it important to apply it during the winter. Chlorothalonil is not approved for use on organic crops and may be carcinogenic in humans, making it a last resort for many gardeners.
Some gardeners use alternative methods to control peach leaf curl, due to concern about copper's effects on the environment and the potential health risks of other sprays. These methods include applying row cover fabric to individual branches before expected rain and spraying the trees with seaweed or kelp extract. According to the University of California, these treatments are less effective than spray techniques, providing under 60 percent disease control. Kelp sprays have been shown to worsen infection in some cases.
- University of California Integrated Pest Management: Peach Leaf Curl
- University of California Integrated Pest Management: Peach Leaf Curl Quick Tips
- US Government Printing Office: Synthetic Substances Allowed for Use in Organic Crop Production
- University of California Integrated Pest Management: Chlorothalonil
- University of California: 2012 Peach Leaf Curl Trial
- University of California Integrated Pest Management: Bordeaux Mixture
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