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Symptom Characteristics, Causes, and Control Methods of Oleander Witches' Broom

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The oleander witches' broom pathogen mainly attacks oleander branches. The disease initially occurs mostly on individual branches, showing mass sprouting of axillary buds and adventitious buds, with many slender weak branchlets growing in clusters, stagnation of main shoot growth, shortened internodes of branchlets, and smaller leaves with indistinct mosaic patterns. Infected branchlets can produce further branchlets, and the bases of newly sprouted branchlets are swollen, pale red, and often clustered in groups. The branchlets become increasingly slender and weak, and the leaves become increasingly smaller, resembling a bird's nest in appearance, forming the typical witches' broom symptom. Most affected branchlets stand upright, and the branches have tumor-like growths. The cortex rots and peels off in strips, forming cankers,

The oleander witches' broom pathogen mainly attacks oleander branches. The disease initially occurs mostly on individual branches, showing mass sprouting of axillary buds and adventitious buds, with many slender weak branchlets growing in clusters, stagnation of main shoot growth, shortened internodes of branchlets, and smaller leaves with indistinct mosaic patterns. Infected branchlets can produce further branchlets, and the bases of newly sprouted branchlets are swollen, pale red, and often clustered in groups. The branchlets become increasingly slender and weak, and the leaves become increasingly smaller, resembling a bird's nest in appearance, forming the typical witches' broom symptom. Most affected branchlets stand upright, and the branches have tumor-like growths. The cortex rots and peels off in strips, forming cankers, and eventually the entire plant dies.

Oleander witches' broom is caused by infection with mycoplasma-like organisms. These mycoplasma-like organisms are pleomorphic, round or oval, approximately 53-700 nanometers in diameter, and infect and spread the disease.

The mycoplasma-like organisms of oleander witches' broom exist in the phloem parenchyma cells of oleander. Cuttings and grafts from diseased branches can transmit the disease. This disease mostly occurs in large trees over five years old; young trees 1-5 years old generally do not develop the disease or are only slightly affected. In some parks and street trees, the incidence rate reaches nearly 100%, with a mortality rate of over 60%. The severity of the disease is related to the flower color of the variety. Red-flowered oleander is most severely affected, white-flowered oleander is less affected, and yellow-flowered oleander is resistant to the disease.

Control Methods

1. When cultivating nursery stock, strictly select disease-free plants as mother trees for collecting cuttings. Before cutting, soak in tetracycline at 1000-2000 PPM (parts per million) for 2-4 hours. It is prohibited to transport diseased cuttings and nursery stock from affected areas to disease-free areas.

2. Slightly diseased branches in the early stage of the disease should be sawed off as early as possible, and severely diseased plants should be dug out and burned in a centralized manner.

3. Do not plant oleander of a single flower color; use mixed planting with multiple flower colors as much as possible to reduce further spread and expansion of the disease.

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