Peach Leaf Curl, a common fungus disease of peaches and nectarines, comes and goes in Eastern Washington, it's severity strongly tied to weather conditions in late winter and spring. This disease is a yearly problem on the wet, mild-wintered West Side of Washington and Oregon, and makes the home garden production of peaches and nectarines very difficult. Due to our cold winters, and generally dry early Springs, we East-siders usually escape this disease. When Eastern Washington winters are unusually mild, and the late winters unusually wet, you can see the disease more commonly.
Peaches and nectarines are rarely killed out-
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right by this disease, but they can be so weakened by repeated attack that they die from Winter cold, or attack by another disease or insect.
The Disease Symptoms:
This is a disease with very distinctive symptoms. As the leaves emerge in the spring, the develop a puckered, rumpled texture, and become yellow with reddish highlights. As the leaves grow, they thicken and become quite twisted and brittle. A white powder grows on the surface of affected leaves. Leaves drop as the Summer progresses. Click Here for another picture.
The Fungus & Its Strange Life Cycle:
Starting with the newly curled leaf: The Fungus, named Taphrina deformans (Burk.) Tulasne, by scientists, form spore production bodies called asci on the upper surface of the affected leaves. These asci develop eight spores each, which shoot out and, if the fungus is lucky, land on a suitable host. These ascospores germinate and develop yeast-like conidia which replicate rapidly by division. These conidia reproduce on the shoot tips and keep the current season shoots covered with spores. These Summer conidia spores do not attack the growing tree tissue, just live on the surface of the tree.The affected tree can be quite contaminated by the conidia by Fall. The conidia overwinter on the tree. As the tree buds swell in the late Winter, the conidia may be washed into the bud cracks, where they germinate and attack the undeveloped leaf tissue. At this point, the yeast like conidia form develops into a more thread-like (mycelium) form, and reverts to it's fungus phase. As the buds break, and leaves begin to form, the fungus develops rapidly inside the leaves, once again causing the malformation, develops asci, ascospores, and the life cycle is completed.
Control:
The simple timing for a moderate control effort- which is effective most seasons in Eastern Washington- is in the late fall. Apply a label rate of a copper-based fungicide, with a sticker, appled when the leaves are mostly off of the tree. (Apply earlier than this if your primary concern is Coryneum Blight.) This copper fungicide should last throughout the Winter, and help control the disease when the buds crack in Late Winter. In severe infection conditions (on previous season affected trees, or very mild Winter years) you might have to break out the sprayer before the buds swell in the Late Winter. Apply another copper fungicide spray.
If you have just a few curled leaves on the tree, you can pick them off in the spring. It is almost impossible to pick all of the affected leaves from severly diseased trees.
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