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Massaria disease of plane trees, caused by the fungus Splanchnonema platani (S. platani), is affecting London plane trees (Platanus x hispanica) in England. It is associated with branches dying back and becoming prone to breaking off and falling.
The fungus used to be known as Massaria platani, which gave rise to the common name of the disease which it causes, until a taxonomic revision resulted in a name change. However, Massaria, or Massaria disease of plane, continues to be recognised as the common name of the disease.
London plane trees are widely planted in towns and cities as shade and amenity trees, so presence of the disease can be a significant public safety issue for their owners, many of which are local authorities. The dead wood has to be removed before it becomes an unacceptable hazard.
The fungus had long been considered to be a weak parasite, and only capable of causing minor damage. It is frequently found on dead twigs and bark which have already been killed by other organisms or non-living causes.
However, during the hot, dry summer of 2003 it was found to be associated with branch death and rapid decay in mature trees in Germany. Since then, similar episodes have been observed in Austria, The Netherlands and parts of France. Scientists are investigating why the fungus has become increasingly associated with more-serious symptoms such as branch decay and failure.
S. platani fungus is common in warmer Mediterranean climates and the southern United States, and in Europe it has been confirmed as far north as The Netherlands. It was found in living plane trees in London and Bristol in 2009, but before that, in 2003, spores of the fungus had been found on fallen dead plane twigs at London's Royal Botanic Gardens, Kew.
S. platani spores are readily spread long distances by the wind. In one notable case, spores were collected by a survey ship stationed over the Mid-Atlantic Ridge between the Caribbean Sea and North Africa. Scientists therefore believe it is entirely possible that it could have been spread on the wind from its Mediterranean heartland to Great Britain.
The disease first appears as a pinkish strip on the upper surface of the branch, and develops into a lesion extending from a union with the parent branch or stem. These lesions can extend many metres, but because they affect the upper part of the branch, infection can be difficult to see from the ground. Branch decline in the summer months can be an indication of infection.
Affected branches suffer death of the bark and cambium (the layer of tissue just under the bark), which can affect up to 30% of the branch circumference. When the fungus produces spores, areas towards the edges of the lesions turn black. Lesions are associated with wood decay, characterised by soft rot, often resulting in the death and / or the fracture of the branch. Arboriculturalists with London’s Royal Parks have seen branch failure within three months of the symptoms first becoming noticeable, but branch failure can occur after one or more years.
We are conducting surveys during 2015 of plane trees in other English cities for evidence of plane tree wilt, caused by the Ceratocystis fimbriata f. platani fungus, and the surveyors will also be looking to see whether there is any evidence of Splanchnonema platani infection.
We are working to raise the awareness of plane tree owners to the apparently increased safety hazard associated with Massaria, and the need to monitor trees' safety and take preventative action if the risk becomes unacceptable.
There is no available treatment for the disease apart from removing diseased branches before they become an unacceptable safety hazard. People who work on plane trees can help to minimise the rate of spread by practising good biosecurity, or plant hygiene, such as cleaning and disinfecting tools, equipment, boots and outer clothing before working on other trees.
S. platani is an ascomycete fungus whose anamorph is Macrodiplodiopsis desmazieresii. A synonym for London plane's scientific name, Platanus x hispanica, is P. x acerifolia.
If you think you have spotted the disease, please check the symptoms section above before reporting it.