The London Tree Officers Association (LTOA) and the Bartlett Tree Research Laboratory at Reading University have so far failed to find evidence of plane wilt caused by the fungus Ceratocystis platani on apparently stressed or diseased London planes.
The disease has been present in French and Italian plane trees since the mid-20th century, but was only confirmed in Spain in 2010. Thought to have originated in the USA, it is lethal and has decimated amenity plane trees on both sides of the Atlantic.
The iconic and widely planted London plane (Platanus x acerifolia) is considered "extremely susceptible" to C. platani according to Defra, which earlier this month banned the import and sale of plane trees from nurseries not certified as free of the disease.
A statement from the LTOA said: "Laboratory study is expensive and time-consuming, and has to be combined with the sort of careful observation by an experienced eye that our members and the scientists at Bartletts possess.
"We are looking for symptoms of wilt but we know that our urban planes are in constant danger from many factors which threaten them - root severance, chemical contamination or a number of other fungal, bacterial, viral, insect and mechanical problems. Some of these can appear similar and some can pre-dispose our trees to further attack."
The two will continue their partnership, and the LTOA has set up a working party to report on best protective measures and co-ordinate any response.