Branches of planes up to a diametre of 15cm (rarely more) break off at their base in fully living stage. Mostly on the upper side of the branches close to their base a long, initially pink-brown, later on brown and finally black (spores!), sharply delimited necrosis; within the necrosis the wood is rotten to the heart.
Affected tree species
This is a microfungus, which has been known for more than 100 years as mostly harmless saprophyte colonising dead fine twigs or playing a certain role in the natural shedding of branches. Only in America, the fungus has been known to cause some damage, but for Europe the symptoms described are new. According to the present knowledge the fungus changes to an aggressive bark and wood rot species of strong branches after extraordinary drought stress, which is able to cause breakage a few weeks after infection. Despite from some cases in France death of whole trees has not been observed so far. The sudden breakage of branches alone creates big problems for the urban authorities. Investigations of the new disease in German cities showed a relation between the disease intensity and site and nutrition factors (increased intensity on dry sites with reduced rooting area): by contrast, planes in larger parks and urban forests are less affected.
Curative measures According to the risk of accidents with breaking branches, the early detection of infected branches is the main challenge. This requires trained personal and has to be repeated. Check of the trees from the soil alone is not sufficient: platforms or tree climbers are needed. Infected branches should be removed immediately, and the tree should be checked afterwards at least one time per year. Chemical measures are unknown, probably not effective. As a prevention planes should be planted only on sites with sufficient water and nutrition supply, and in dry years the trees should be watered until the age of about 25 years.
Plane twigs with superficially discolored bark (infection by Splanchnonema platani
Splanchnonema platani: wood rot within the necroses
Splanchnonema platani: spore masses on the bark surface