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Amsterdam, the city of elms: the fight against graphiosis

Debora BleekerThe elms are a typical landmark of Amsterdam; elms have been planted since about 1600. The arrival of the DED, about 100 years ago, was the trigger to develop an advanced system for control of the disease. At the Elm International Conference, held in Florence in early October, we met Debora Bleeker, responsible for the elm policy in Amsterdam, who was so kind to answer some questions about the elm tree management in that city.

Debora Bleeker, Why there is so much sensitivity to the DED in Amsterdam?
There have always been a large number of elm trees in Amsterdam. They started planting in the sixteenth century, as can be seen on paintings existing from that time. Today there are about 75,000 elms and  they account for almost 25% of the trees in the public space. This is why there is a high sensitivity to the DED. In 2012 331 trees were felled, that is only 0.4% of the total tree number in the city. The elm is essential for the city, not only because of the historical point of view but also for its botanical characteristics, its fast-growing rate,  the big variety in colour of leaves and shape of the crown and its adaptability to our climate (a brackish environment near to the coast). It fits very well, also, to the typical stresses of the urban environment.

Amsterdam is successful in the struggle against this infectious disease. How is it organized?
The various boroughs are responsible for inspecting the elm trees in the streets and public parks. The inspection frequency is at least twice during the season of greatest spread of DED.  Diseased trees are removed in the proper manner within ten working days and always replaced with more resistant elm varieties. When removing elm trees, either diseased or healthy, the trees are uprooted, debarked and/or chipped directly on site. The clearing of trees with DED in small private gardens is funded by the city. All of this is laid down in a municipal by-law and costs the city close to 1 million euros (this includes the work of the city authorities). Our approach to the control of the disease has remained unchanged since 1970 and is applied to many other cities. Amsterdam currently has four other tree diseases or pests harmful to deal with: the oak processionary moth, Bleeding Canker of Horse Chestnut, Massaria disease of plane trees and ash dieback. These diseases are associated with risks of safety, public health or infection and must be fought to prevent their further spread.

How does Amsterdam control the elm bark beetle?
To  monitor the elm bark beetle 66 aluminum traps have been installed on lamp posts throughout Amsterdam. Pheromones are applied to the traps, along with a non-drying glue. From experience, we have set a limit of 80 beetles per trap in a 2.5-month period. If several hundred beetles are found on a trap, there is every reason to assume that DED or dead elms can be found in the vicinity. A search will almost always reveal a breeding site for beetles. In 2012, 2366 beetles were captured, about 600 less than the previous year. This is the best result since 1990, after the national program for the control of DED was discontinued, and the number of bark beetles in Amsterdam had exploded.
One thing is certain: the disease has been for nearly a century in our region and cannot be eradicated, though it can be well controlled with some effort.

Links to this post:

"The DED in Australia: control and risk of spreading" 

"Third International Conference Elm. Download the "book of abstracts"






Interview with Deborah Bleeker, responsible for the elm policy in Amsterdam