The Q&A Archives: Fruit Trees

Question: My nectarine tree looks like it has peach curl on the leaves. What can I do for that?

Answer: Peach leaf curl is caused by the fungus Taphrina deformans. The fungus survives the winter as spores (conidia) on bark and buds. Infection occurs very early in the growing season. During cool, wet spring weather the conidia infect new leaves as they emerge from the buds. Host plant tissues are susceptible for only a short period. As the tissues mature they become resistant. The fungus produces another type of spore (ascospore) on the upper surface of the diseased leaves. During wet weather, ascospores produce additional conidia by budding. These conidia are carried to other parts of the tree by rain and wind, where they will overwinter until the next spring. Environment can limit leaf curl infection. This partially explains why the disease does not occur every year. Leaf curl is worse when the weather is cool and wet. Low temperatures are thought to retard maturation of leaf tissue, thus prolonging the time infection may occur. The fungus can penetrate young peach leaves readily at temperatures between 50 and 70 degrees F, but only weakly below 45 degrees F. Rain is necessary for infection. Leaf curl can be controlled with one well-timed fungicide application, either in the autumn after 90% of the leaves have fallen, or in the spring before bud swell. If leaf curl is severe, it is important to maintain tree vigor by thinning more fruit than normal, reducing drought stress with irrigation, and applying extra nitrogen fertilizer.

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