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PEST OF THE MONTH Peach leaf curl By Fuzz Martin What does it look like? Peach leaf curl is a disease caused by the fungus Taphrina deformans. The disease causes defoliation and destroys the fruit of nearly all cultivars of peach and nectarine trees. Affected trees have thick, curled, deformed and discol- ored leaves. Infected leaves may be light green, yellow, red or purple in color. Mature leaves may have a dusty appearance due to the presence of fungal spores. Infected leaves eventually brown, shrivel and fall from the tree. Fruit that has been infect- ed with Taphrina deformans may also become deformed and drop from the tree early in the growing season. In other instances, infected fruit will develop purplish, wart-like extrusions. Photo courtesy of University of Georgia Plant Pathology Archive, University of Georgia, Bugwood.org Photo by William M. Brown Jr., Bugwood.org Prevention tips Photo by Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org Once the symptoms of a peach leaf curl infection are visible, it is too late to prevent the disease from taking hold. The best way to prevent a peach leaf curl infection is by treating peach and nectarine trees with a fungicide contain- ing chlorothalonil or copper compounds in the late fall. Fungicide applications should be applied once 90 percent of the tree's leaves have fallen. Late winter or very early spring fungicide applications may also be effective, so long as the treatment is applied prior to bud swell. Once bud swell has occurred, the dis- ease will have already taken Host material and range Leaf curl affects nearly all cultivars of peach trees around the globe. The first instance of leaf curl was reported in the United States in 1821. The disease has been a common problem ever since. In early spring, winds and rainwater push Taphrina deformans spores into the peach leaf buds. The germinating spores penetrate the growing leaves and dissolve the cell structure, causing the infection. As the leaf matures, the fungus produces spores that are washed or blown down into various crevices of the tree. The spores overwinter in the crevices, and the cycle continues the following spring. Current threat Each year, peach leaf curl accounts for damage to peach and nec- tarine crops, as well as to ornamental peach and nectarine trees. The disease rarely causes permanent damage or die off. However, as the disease often causes defoliation early in the growing season, affected trees will often grow a second crop of leaves and fruit later in the sea- son. The stress caused by the second crop of leaves and fruit can lower the tree's vigor and increase its susceptibility to injury over the winter. www.arborage.com root and a fungicide application will be ineffective. Certain varieties of peach trees have better resistance to leaf curl than others. When planting new crops, consider Redhaven peach and its cultivars, as they are more likely to withstand the effects of Taphrina deformans than Redskin or other peach varieties. Treatment tips Care should be taken to ensure trees that are heavily infected with peach leaf curl retain their vigor. A proper care program may include increased thinning of the tree's fruit crop, regular irrigation during dry conditions and a nitrogen-rich fertilizer application. What can you do? If your trees are already infected with peach leaf curl, ensure the trees' vigor by following the above treatment steps. Also, plan a proper fungicide application prior to the spring bud swell. Remember that once bud swell has occurred, the disease will already have been established, and further fungicide treatments will be ineffective. Fuzz Martin is the senior writer at EPIC Creative, Wis. Article provided by Mauget, a leader in passive microinjection and micro-infusion tree care. To learn more about peach leaf curl, contact Mauget or visit www.Mauget.com. Arbor Age / November/December 2011 3