Bleeding Canker of Horse Chestnut
Encyclopedia
Bleeding Canker of Horse Chestnut is a common canker
of horse chestnut trees (Aesculus hippocastanum, also known as conker trees) that is known to be caused by infection with several different pathogens.
Infections by the gram-negative fluorescent bacterium Pseudomonas syringae pathovar aesculi are a new phenomenon, and have caused most of the bleeding cankers on horse chestnut that are now frequently seen in Britain.
) around the trunk and main branches. As it spreads, it cuts off the water supply to the crown; and when it completely encircles the trunk, the tree will die.
This particular infective agent emerged in the past few years, and has now spread rapidly to infect many trees in Western Europe.
Initially the outbreak was attributed to Phytophthora, until DNA tests suggested that a pathovar
of Pseudomonas syringae
was responsible; and this hypothesis was confirmed in 2007 with tests satisfying Koch's postulates
.
The disease has risen markedly in the UK since 2003, and now approximately one half of all horse chestnuts in Great Britain
are affected and showing symptoms to some degree.
The disease is spreading at an alarming rate in the Netherlands
,
where one third of all horse chestnuts are affected to a greater or lesser extent.
A similar upsurge is reported in Belgium and France.
.
Phytophthora was responsible for mass die-off of horse chestnut trees in the 1940s worldwide, and is still the principal agent of bleeding canker on horse chestnuts in North America.
It was considered uncommon in the United Kingdom and only recorded in southern England,
but now accounts for 5-10% of bleeding canker on horse chestnuts in Britain.
Progression is slow, but younger trees can succumb to the disease in just a few years as the smaller diameter of their trunks means that they can be girdled more quickly.
If the outer bark
is cut away at the site of a bleeding canker, the discoloured and dying inner bark (which may be purple or brown or orange in colour) often appears mottled or zoned. A well-defined edge between the discoloured inner bark and the white or pinkish healthy areas suggests an infection that has stabilised; a diffuse boundary indicates that the infection is spreading.
In many cases the disease will progress and will eventually kill the tree, or weaken it to the point that it becomes dangerous and has to be felled.
An injection treatment using the garlic extract allicin is currently being trialed.
Canker
Canker and anthracnose are general terms for a large number of different plant diseases, characterised by broadly similar symptoms including the appearance of small areas of dead tissue, which grow slowly, often over a period of years. Some are of only minor consequence, but others are ultimately...
of horse chestnut trees (Aesculus hippocastanum, also known as conker trees) that is known to be caused by infection with several different pathogens.
Infections by the gram-negative fluorescent bacterium Pseudomonas syringae pathovar aesculi are a new phenomenon, and have caused most of the bleeding cankers on horse chestnut that are now frequently seen in Britain.
Pseudomonas syringae pathovar aesculi
In the past few years, the bacterial pathogen Pseudomonas syringae pv. aesculi has a emerged as a new and virulent agent for this disease in Western Europe. Specific to horse chestnut trees, this pathogen infects the bark (cambiumCambium (botany)
A cambium , in botany, is a tissue layer that provide undifferentiated cells for plant growth. It forms parallel rows of cells, which result in secondary tissues....
) around the trunk and main branches. As it spreads, it cuts off the water supply to the crown; and when it completely encircles the trunk, the tree will die.
This particular infective agent emerged in the past few years, and has now spread rapidly to infect many trees in Western Europe.
Initially the outbreak was attributed to Phytophthora, until DNA tests suggested that a pathovar
Pathovar
A pathovar is a bacterial strain or set of strains with the same or similar characteristics, that is differentiated at infrasubspecific level from other strains of the same species or subspecies on the basis of distinctive pathogenicity to one or more plant hosts.Pathovars are named as a ternary or...
of Pseudomonas syringae
Pseudomonas syringae
Pseudomonas syringae is a rod shaped, Gram-negative bacterium with polar flagella. It is a plant pathogen which can infect a wide range of plant species, and exists as over 50 different pathovars, all of which are available to legitimate researches via international culture collections such as the...
was responsible; and this hypothesis was confirmed in 2007 with tests satisfying Koch's postulates
Koch's postulates
Koch's postulates are four criteria designed to establish a causal relationship between a causative microbe and a disease. The postulates were formulated by Robert Koch and Friedrich Loeffler in 1884 and refined and published by Koch in 1890...
.
The disease has risen markedly in the UK since 2003, and now approximately one half of all horse chestnuts in Great Britain
Great Britain
Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...
are affected and showing symptoms to some degree.
The disease is spreading at an alarming rate in the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
,
where one third of all horse chestnuts are affected to a greater or lesser extent.
A similar upsurge is reported in Belgium and France.
Phytophthora and other fungal pathogens
Some bleeding cankers on horse chestnuts are caused by fungal pathogens including principally the fungus PhytophthoraPhytophthora
Phytophthora is a genus of plant-damaging Oomycetes , whose member species are capable of causing enormous economic losses on crops worldwide, as well as environmental damage in natural ecosystems. The genus was first described by Heinrich Anton de Bary in 1875...
.
Phytophthora was responsible for mass die-off of horse chestnut trees in the 1940s worldwide, and is still the principal agent of bleeding canker on horse chestnuts in North America.
It was considered uncommon in the United Kingdom and only recorded in southern England,
but now accounts for 5-10% of bleeding canker on horse chestnuts in Britain.
Symptoms
The first symptom is a sticky liquid oozing from blemishes on the bark of infected trunks. Later, the bark peels away, exposing a characteristically brown-orange stained inner bark below, and the whole tree shows a yellowing of foliage and premature leaf drop. Eventually the crown dies.Progression is slow, but younger trees can succumb to the disease in just a few years as the smaller diameter of their trunks means that they can be girdled more quickly.
If the outer bark
Bark
Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines and shrubs. Bark refers to all the tissues outside of the vascular cambium and is a nontechnical term. It overlays the wood and consists of the inner bark and the outer bark. The inner...
is cut away at the site of a bleeding canker, the discoloured and dying inner bark (which may be purple or brown or orange in colour) often appears mottled or zoned. A well-defined edge between the discoloured inner bark and the white or pinkish healthy areas suggests an infection that has stabilised; a diffuse boundary indicates that the infection is spreading.
Treatment
There is as yet no tried and tested treatment, and cutting out the infected branches may even be counter-productive. In some cases the disease will stop spreading and the tree will recover—and it is for this reason that experts recommend that infected trees should not be felled at first signs of infection.,In many cases the disease will progress and will eventually kill the tree, or weaken it to the point that it becomes dangerous and has to be felled.
An injection treatment using the garlic extract allicin is currently being trialed.