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Virus diseases of Daphne | AG0175 |
Jane Moran, Knoxfield
March, 1995 |  |
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The genus Daphne includes a number of evergreen and deciduous shrubs with attractive. highly fragrant flowers. D. odora Thunb. is the most common of the numerous species sold in Australian nurseries. More than 10 virus or virus like diseases have been found in D. odora. Relatively little information is available on symptoms caused by infection with individual viruses. In general. plants infected with virus show varying degrees of decline including: small] thin leathery leaves; leaf curling; excessive defoliation during autumn and winter; death of single limbs or whole plants.
Leaf symptoms include pale green streaks and blotches. or occasional scattered orange blotches and frequent yellow streaks and rings, or flecks usually in the centre of light green or orange blotches. Flower size is reduced. with loss of brilliance and uneven colour of flowers. Flowering can be delayed and buds often fail to open completely. Plants grown in the shade rarely display virus symptoms.
The viruses that infect D. odora can be divided into three groups; aphid-borne viruses. nematode-borne viruses and viruses spread by contact.
1. Aphid-borne viruses
Alfalfa mosaic virus, cucumber mosaic virus. daphne virus S and daphne virus Y are all spread from plant to plant by aphids.
2. Nematode-borne viruses
Arabis mosaic virus, tobacco ringspot virus and daphne latent ringspot virus are spread from plant to plant by nematodes. These viruses are not a problem in Australia due to the absence or small distribution of the nematode vectors.
3. Contact spread viruses
Carnation mottle virus, daphne-tobacco mosaic virus and daphne virus X are all spread by sap via cutting implements, cultivation tools, etc.
Control
Once a plant is infected, there is little the grower can do to solve the problem. The only method of controlling virus diseases is through the use of virus tested stock in conjunction with careful management practices.
Figure 1. Daphne plant severely infected by a number of viruses
Recommendations
- Use planting material derived from pathogen tested (P.T.) stock plants.
- Use suitable insecticides for the control of aphids. When using chemicals, always follow the directions on the label carefully.
- Rogue and destroy any plants showing symptoms.
- Educate staff
- Wash hands before working with P.T. stock.
- Keep old infected stock away from P.T. stock.
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For effective pest and disease control, correct diagnosis is essential. A commercial diagnostic service is available at the Institute for Horticultural Development. For further information, contact the Diagnostic Service. ph: (03) 9210-9222 or fax (03) 9800 3521.
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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