Plane trees (Platanus x hispanica) in Britain are reported to be suffering from Massaria disease, which causes large lesions on the upper surfaces of major branches and can cause branch drop. The cause is thought to be the fungus Splanchnonema platani (formerly called Massaria platani).
This resource page will help you to identify Massaria disease and the fungus that may cause it.
In 2009 tree management teams in London began to notice large lesions and branch drop on the branches of plane trees. Similar symptoms had recently been seen on lesions of plane trees in mainland Europe, most notably in Germany, Austria, the Netherlands and parts of France.
Spores of the fungus Splanchnonema platani, formerly called Massaria platani, were found to be associated with the lesions. However it is not yet clear whether this is the primary cause of Massaria disease.
Forest Research is collecting fresh samples of lesions from planes trees to establish the cause of Massaria disease, and to see if lesions result from S. platani or subsequent infections with opportunistic basidiomycetes such as Auricularia spp.
Tubby, K. V. and Rose, D. R. (2009). Problems facing plane trees. Arboriculture Association Newsletter. 144, Spring. 18–19.