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Massaria of plane trees: London, an example of management

Plane trees are of particular importance for the city of London. There is no doubt that Platanus x hybrida is the species that characterizes the parks and avenues of the metropolis. For this, the arrival of Massaria (Splanchnonema platani) in Britain, has immediately aroused a loud alarm. It is a fungus that causes extensive injuries on branches surfaces, which might lead them to failure. It is not just a matter of plant disease, but the damage also results in a safety issue. It all started in the 2009, when the London tree management team began to notice large lesions on the branches that emitted exudates. Similar symptoms have been previously reported in continental Europe, particularly in Germany, Austria, the Netherlands and parts of France.

The first identification of Massaria in the capital, however, was in 2011. From the very beginning special resources have been allocated, while the London Tree Officers Association (LTOA) has developed a free card for the recognition of the disease by private individuals. Royal Park and Forest Research have worked for the study of the fungus behavior, also related to climate change.

Classic symptoms. The disease commonly known as Massaria usually infects branches with a diameter smaller than 20 cm. The infected branches, although apparently healthy, can suddenly fail. The damage reveals itself on the upper side of the branch, in the vicinity of the base or often halfway along its length.

Initially, it can be noticed a long pink-brownish strip, which becomes brown with time, turning, finally, to black with clear spores. You may notice a well-defined area where the bark and tissue cells of the branch are attacked; wood generally rots, becoming dry and soft, losing its elasticity.

Since the fungus attack is at the top of the branches, is often impossible to be noticed from the ground, while the branches can show damage identifiable as peeling bark and an orange color on the wood surface. White fungal hyphae are clearly visible.

More aggressive strain. The fungus has been known for more than 100 years as a not too harmful. Now it seems to have changed to a more aggressive strain, since it attacks strong and large branches, in addition to the weaker ones and small.

The causes of stress conditions play an important role: the symptoms are accentuated, in particular, after a period in which the trees have been subjected to long drought and high temperatures. Surveys in Europe show a relationship between the intensity of the symptoms with agronomic and nutritional effects.

It is thought that a tree subjected to drought conditions concentrate water and nutrient on the more productive branches. Those lower and horizontal, with a smaller number of leaves, receive a lower amount of water resources. This condition can be the trigger to ensure that the Massaria becomes active. This explains why in continental Europe, the plane trees of the largest parks, less stressed, have been less affected than street trees.

This is also why the symptoms have worsened in 2011 in London: the city had little rainfall, spring was particularly hot and followed by a dry summer; in autumn, the temperature was above the average. The fungus is capable of causing a rapid breaking of the branches after infection (within three or four months). It is extremely rare that a tree dies from the disease, and felling is not often required, but only the removal of the infected branch.

The challenge of the municipalities

Since the problem translates into safety for citizens who attend of the parks and for traffic security, it is clear that cities need special attention. Only frequent monitoring can ensure the health of plane trees. In London, for example, officers have been trained to control several tenths of thousands trees in the city.

Early diagnosis on infected branches is the main objective to reduce the risk of injury to persons and properties. All this requires trained personnel able to identify the symptoms. The inspection of the plane must be repeated regularly, perhaps with a frequency of every two or three months especially during particularly hot and dry periods.

Vehicles with platforms and/or trained arborists and "tree climbers" are needed, but it is hoped that also photographic methods using drones can be developed. The infected branches should be removed immediately to prevent the spread of the fungus and the trees should be checked at least once a year, if not more frequently.

Fungicides are not available and the defense focuses on reducing the causes of stress. It appears, therefore, of paramount importance the management of newly planted trees. Tests have been developed, not on the direct control of the fungus, but on the proper management of the trees, as to avoid the causes of stress. The tests focused on pruning, application of liquid fertilizers, the use of mycorrhizae and organic mulch.

 

 

This fungus causes the failure of large branches, putting risk on the citizens. The role of stress and the importance of reducing conditions favorable to the onset of the pathogen

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