The fungi Taphrina cerasi and Taphrina weisneri cause witches' broom of cherry.Witches' brooms can be a symptom of fungal or viral infection.Phytoplasma diseases may also be responsible for witches' brooming in lilac, dogwood, willow, apple, black locust, honeylocust, papaya, peach, and sassafras.Witches' brooming, chlorosis, and general decline are symptoms of these diseases. Diseases caused by phytoplasmas are elm yellows, ash yellows, and bunch diseases of walnut.Phytoplasma diseases appear to colonize in the sap conducting tissue (phloem) and damage the tissue by interrupting the sap flow.Phytoplasmas are related to bacteria, lack a rigid cell wall, and have an amoeba-like shape.When witches' brooms are caused by mutation, horticulturists sometimes propagate them for the breeding of dwarf plants.The growth around the witches' broom may become less vigorous, indicating that the witches' broom may divert nutrients from other parts of the plant.In most cases, the causal agent kills a growing point and results in the prolific growth of side shoots.Eriophyid mites, mistletoe, environmental damage, or a mutation in vegetative cells may also cause witches' brooming. Witches' brooms may be caused by fungal, viral, or phytoplasmas. The shoots are usually shorter, stockier, and have an upright but more compact growth habit than normal.
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