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Leaf curl, caused by the fungus Taphrina deformans, is mainly a disease of peaches and nectarines, although it may also affect almonds and apricots. The disease occurs wherever peaches and nectarines are grown, and if not controlled can seriously weaken trees.
Symptoms
In spring infected new leaves are thickened, curled and distorted. They are pale-green at first, but soon show red or purple colours and become conspicuous. Often the entire leaf is affected, but sometimes, especially with late infections, only small patches of the leaf are affected. Infected fruit show raised, irregular patches that are often red in colour. Such fruit often falls prematurely. Later the colour fades as the fungus begins to produce masses of powdery grey spores on the upper surface of the leaf. The diseased tissue dies and leaves may fall soon after the spores are produced. However, the tree usually produces new leaves that remain healthy as the season advances. If cool, wet weather persists during spring, infections may continue to appear on new leaves for several months. Infected shoots are thickened, distorted and yellow-green in colour. Heavily infected shoots may be killed.
Economic importance
If uncontrolled, leaf curl is most destructive. It may destroy the new leaves in spring, cause shoot dieback and loss of crop. If unchecked over several years, the disease may gradually weaken the tree until it dies.
Disease cycle
Cool, wet conditions during leaf emergence in spring favour the development of leaf curl. The disease is stopped by high summer temperatures and the fungus survives summer as ascospores. These germinate in autumn rains and form yeast-like spores that can overwinter in bud-scales and on twigs. These spores then infect the newly developing leaves that are produced from such buds in spring.
Control
Leaf curl can usually be controlled satisfactorily by one spray of a suitable registered fungicide at any stage of dormancy. Most effective control is achieved by spraying when the buds are swelling but before they have opened. It is not possible to control the fungus once it has entered the leaf. Poor disease control is usually a result of spraying too late; that is, after budswell. In a planting containing peach and nectarine cultivars, sprays must be timed for that cultivar which shows the earliest movement of buds.
Where the disease has been difficult to control in previous seasons, a program of three sprays is recommended. The first spray should be applied in autumn, at leaf fall. The second spray should be applied immediately before budswell at the late dormant stage, and the third spray about one week later at budswell.
For effective pest and disease control, correct diagnosis is essential. A commercial diagnostic service is available at the DPI PIRVic Knoxfield Centre. For further information, contact the Diagnostic Service. ph: (03) 9210-9222 or fax (03) 9800 3521.
The previous version of this note was published in December 1999.
The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.
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