![]() The brooming symptoms on true firs caused by M. As a result, the rust may be found in areas where one of the hosts is not present. This fungus is systemic and perennial on both aecial and telial hosts. It is also important to remove all chickweed plants in the vicinity of these trees. On a more serious note, pruning the witches' brooms on high-value ornamental trees can stop the disease from spreading and eliminate its effects. The witches' broom deformity caused by the disease has fuelled a number of stories about woods being haunted by wicked witches. The disease may sometimes be present on a lot of balsam fir in some wood lots. Although the infected needles are shed each year, the disease persists in the woody tissues of the witches' broom hence, the new shoots become infected year after year. The following spring, the third type of spores ends up infecting some balsam fir, thus spreading the disease. During the summer, three new types of spores will be produced on this alternate host. These spores become windborne and spread the infection to chickweed hosts. ![]() In the middle of summer, a second type of spores is produced on the lower surface of the needles. The spores form on fruiting bodies that look like small, round orange-yellow blisters. Infected needles are stunted and yellowish-green in colour. A first type of spores is produced in spring on the two faces of needles contained in the broom. The fungus lives on two hosts: the primary host is balsam fir and the secondary host is chickweed. Fir broom rust is rarely fatal, but it can result in growth reduction. This article originally appeared in the issue.The fungus causes witches' brooms, that is, an excessive proliferation of twigs from a single point on a branch. Witches' broom, cause unknown, on willow. The cause of the witches' broom on the willow sample sent to the Plant Disease Clinic was not identified with certainty. Analyzing the plant tissue for infectious agents such as phytoplasmas requires specialized testing that can be costly. Pinpointing the cause of a witches' broom can be difficult, especially if the formation is related to an environmental factor. Unlike brooms caused by living organisms, there is usually just one broom per tree when the cause is a genetic mutation. Some brooms appear to be caused by genetic mutations in the buds of the branches. Environmental stresses that injure the growing points of branches can also trigger the formation of brooms. Organisms such as fungi, phytoplasmas (bacterial-like organisms), mites, aphids, and mistletoe plants can cause abnormal growth when they attack a host tree. ![]() In others, they are small and well-hidden.Ī number of stresses, both biological and environmental, can lead to the formation of brooms. In some cases, the brooms are quite large in size and are easily spotted. There may be only one broom in a tree, or they may be many scattered throughout the tree. Witches' brooms occur on many different woody plant species, including deciduous trees such as hackberry, maple, and willow, and conifers such as pine and spruce. The term witches' broom comes from the German word Hexenbesen, which means to bewitch (hex) a bundle of twigs (besom). Brooms during this time were made of bundles of twigs. In medieval times, mysterious and unexplainable occurrences were often blamed on witchcraft. A willow branch was recently submitted to the Plant Disease Clinic that had a dense cluster of twigs, a symptom referred to by plant pathologists as a "witches' broom".
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