Dutch elm disease
Encyclopedia
Dutch elm disease is a disease caused by a member of the sac fungi category, affecting elm
trees which is spread by the elm bark beetle. Although believed to be originally native to Asia
, the disease has been accidentally introduced into America
and Europe
, where it has devastated native populations of elms which had not had the opportunity to evolve resistance to the disease. The name Dutch elm disease refers to its identification in the Netherlands
by a Dutch phytopathologist in 1921; the disease is not specific to the Dutch elm
hybrid.
. Three species are now recognized: Ophiostoma ulmi, which afflicted Europe from 1910, reaching North America on imported timber in 1928, Ophiostoma himal-ulmi, a species endemic to the western Himalaya, and the extremely virulent species, Ophiostoma novo-ulmi, which was first described in Europe and North America in the 1940s and has devastated elms in both areas since the late 1960s. The origin of O. novo-ulmi remains unknown, but the species may have arisen as a hybrid between O. ulmi and O. himal-ulmi.
The new species was widely believed to have originated in China
, but a comprehensive survey there in 1986 found no trace of it, although elm bark beetles were very common.
The disease is spread in North America by three species of bark beetles (Family: Curculionidae
, Subfamily: Scolytinae): the native elm bark beetle, Hylurgopinus rufipes, the European elm bark beetle, Scolytus multistriatus, and the banded elm bark beetle, Scolytus schevyrewi. In Europe, while the aforementioned Scolytus multistriatus again acts as vector for infection, it is much less effective than the large elm bark beetle Scolytus scolytus. The native elm bark beetle can be a vector for the disease, but is inefficient compared to the other vectors. Scolytus schevyrewi was found in 2003 in Colorado and Utah, and is now in 10 western states.
with gum and tylose
s, bladder-like extensions of the xylem cell wall
. As the xylem (one of the two types of vascular tissue
produced by the vascular cambium
, the other being the phloem
) delivers water and nutrients to the rest of the plant, these plugs prevent them from travelling up the trunk of the tree
, eventually killing it. (Xylem comprises the bulk of the hard tissue of the interior of trunks and branches of woody plants and is nearly synonymous with "wood". Phloem can be thought of as a thin sheet of tissue wrapped around the central cylinder of xylem, although just beneath the phloem is another thin sheet, the vascular cambium, which produces both phloem and xylem. The bark is external to the phloem.)
in 1927. This first strain was a relatively mild one, which killed only a small proportion of elms, more often just killing a few branches, and had largely died out by 1940 owing to its susceptibility to viruses. The disease was isolated in The Netherlands in 1921 by Bea Schwarz
, a pioneering Dutch phytopathologist, and this discovery would lend the disease its name.
Circa 1967, a new, far more virulent strain arrived in Britain on a shipment of rock elm U. thomasii logs from North America, and this strain proved both highly contagious and lethal to European elms; more than 25 million trees have died in the UK alone. The disease is still migrating northwards through Scotland
, reaching Edinburgh
in the late 1970s, and Inverness
in 2006. By 1990, very few mature elms were left in Britain or much of continental Europe. One of the most distinctive English
countryside trees, the English elm U. procera Salisb. (see John Constable
's painting Salisbury Cathedral from the South-West), is particularly susceptible. Thirty years after the outbreak of the epidemic, nearly all these trees, which often grew to more than 45 m high, are gone. The species still survives in hedgerows, as the roots are not killed and send up root sprouts ("suckers"). These suckers rarely reach more than 5 m tall before succumbing to a new attack of the fungus. However, established hedges kept low by clipping have remained apparently healthy throughout the nearly 40 years since the onset of the disease in the UK.
The largest concentrations of mature elms in Europe are now in Amsterdam
and The Hague
. In 2005, Amsterdam was declared the 'Elm City of Europe': the city’s streets and canals are lined with at least 75,000 elms, including several generations of research-elms (see below: Resistant trees). Some 30,000 of the 100,000 mature trees in The Hague
are elms, planted because of their tolerance of salty sea-winds. Since the 1990s, a programme of antifungal injections of the most prominent 10,000 elms, and of sanitation felling, has reduced annual elm losses in The Hague from 7% to less than 1% (see below: Preventive treatment). The losses are made up by the planting of disease-resistant cultivars. The largest concentration of mature elm trees remaining in England is in Brighton and Hove, East Sussex
, where 15,000 elms still stand (2005 figures), several of which are estimated to be over 400 years old. Their survival is owing to the isolation of the area, between the English Channel
and the South Downs
, and the assiduous efforts of local authorities to identify and remove infected sections of trees immediately when they show symptoms of the disease. Empowered by the Dutch Elm Disease (Local Authorities) (Amendment) Order 1988, local authorities may order the destruction of any infected trees or timber, although in practice they usually do it themselves, successfully reducing the numbers of elm bark beetle Scolytus spp., the vector of elm disease. The largest concentration of mature elms in Scotland is in Edinburgh
, where 5000 elms still stand (2009 figures) out of some 35,000 in 1976. A policy of sanitary felling has kept losses to an average of 1000 a year. Elm was the commonest tree in Paris from the 17th century; before the 1970s there were some 30,000 ormes parisiens. Today, only 1000 mature elms survive in the city, including examples in the large avenues (Avenue d'Italie, Avenue de Choisy, Boulevard Lefebvre, Boulevard de Grenelle, Boulevard Garibaldi) and two very old specimens, one in the garden of the Tuileries in front of the l'Orangerie
and another in the Place Saint-Gervais in front of l'hôtel de ville de Paris
. Losses are now being made up with disease-resistant cultivars, especially the Dutch-French research elm 'Nanguen' (Lutèce), named after the city.
in 1928, with the beetles believed to have arrived in a shipment of logs from The Netherlands destined for use as veneer
in the Ohio
furniture
industry. The disease spread slowly from New England
westward and southward, almost completely destroying the famous elms in the 'Elm City' of New Haven, reaching the Detroit
area in 1950, the Chicago area by 1960, and Minneapolis
by 1970.
Dutch elm disease reached eastern Canada during the Second World War, and spread to Ontario
in 1967, Manitoba
in 1975 and Saskatchewan
in 1981. In Toronto, 80% of the elm trees have been lost to Dutch elm disease; many more fell victim in Ottawa
, Montreal
and other cities during the 1970s and 1980s. Quebec City
still has about 21,000 elms, thanks to a prevention program initiated in 1981. Alberta
and British Columbia
are the only provinces that are currently free of Dutch elm disease, although, in an isolated case, an elm tree in southeastern Alberta
found diseased in 1998 was immediately destroyed. Today, Alberta
has the largest number of elms unaffected by Dutch elm disease in the world ; many streets and parks in Edmonton
and Calgary
are still lined with healthy, mature trees. Aggressive measures are being taken to prevent the spread of the disease into Alberta, as well as other parts of Canada. The City of Edmonton
has banned elm pruning from March 31 to October 1, since fresh pruning wounds will attract the beetles during the warmer months.
The largest surviving urban forest of elm trees in North America is believed to be in the city of Winnipeg
, Manitoba
, where close to 200,000 elms remain - at least double that of Amsterdam
, the "Elm City of Europe". The city of Winnipeg spends $3M annually to aggressively combat the disease using Dursban Turf and the Dutch Trig vaccine, losing 1500-4000 trees per year.
has so far been unaffected by Dutch elm disease, retaining its many stands of introduced elm varieties
.
Arbotect is not effective on root graft infections from adjacent elm trees. It is more than 99.5% effective for three years from beetle infections, which is the primary mode of tree infection.
Alamo (propiconazole
) has become available more recently, though several university studies show it to be effective for only the current season it is injected. Alamo is primarily recommended for treatment of oak wilt
.
that has lost much of its pathogenic capabilities, injected in the elm in spring. The strain is believed to have enough pathogenicity left to induce an immune response in the elm, protecting it against DED during one growing season. This is called induced resistance.
Preventive treatment is costly, and at best will prolong the life of the tree by perhaps five or ten years. It is usually only justified when a tree has unusual symbolic value or occupies a particularly important place in the landscape. The injections have no curative properties on trees which already have Dutch elm disease.
. It is primarily spread in three ways:
s and varieties began in the Netherlands in 1928, followed by the USA in 1937. Initial efforts in the Netherlands involved crossing varieties of U. minor and U. glabra, but later included the Himalayan or Kashmir elm U. wallichiana as a source of antifungal genes. Early efforts in the USA involved the hybridization of the Siberian elm U. pumila with American red elm U. rubra
to produce resistant trees. Resulting cultivars lacked the traditional shape and landscape value of the American elm
; few were planted.
In 2005, the National Elm Trial
(USA) began a 10-year evaluation of 19 cultivars in plantings across the United States. The trees in the trial are exclusively American developments; no European cultivars have been included.
Recent research in Sweden
has established that early-flushing clones are less susceptible to DED owing to an asynchrony between DED susceptibility and infection.
, 'Nanguen' LUTÈCE, and 'Wanoux' VADA, all found to have an extremely high resistance to the disease when inoculated with unnaturally large doses of the fungus. Only 'Columella' was released during the lifetime of the Dutch programme, in 1987; patents for the LUTÈCE and VADA clones were purchased by the French Institut National de la Recherche Agronomique (INRA), which subjected the trees to 20 years of field trials in the Bois de Vincennes
, Paris
, before releasing them to commerce in 2002 and 2006, respectively.
Asian species to feature in the American DED research programs were the Siberian elm U. pumila, Japanese elm U. davidiana var. japonica, and the Chinese elm U. parvifolia
, giving rise to several dozen hybrid cultivars resistant not just to DED, but also to the extreme cold of Asian winters. Among the most widely planted of these, both in North America and in Europe, are 'Sapporo Autumn Gold' and 'New Horizon'. Some hybrid cultivars, such as 'Regal', are the product of both Dutch and American research. Hybridization experiments using the slippery or red elm U. rubra
resulted in the release of 'Coolshade' and 'Rosehill'
in the 1940s and 50s. The species last featured in hybridization as the female parent of 'Repura'
and 'Revera'
, both patented in 1993, although neither has yet appeared in commerce.
In Italy
, research is continuing at the Istituto per la Protezione delle Piante, Florence, to produce a range of disease-resistant trees adapted to the warmer Mediterranean climate, using a variety of Asiatic species crossed with the early Dutch hybrid 'Plantyn'
as a safeguard against any future mutation of the disease. Two trees with very high levels of resistance, 'San Zanobi' and 'Plinio', were released in 2003. 'Arno'
and 'Fiorente'
were patented in 2006 and will enter commerce in 2012. All four have the Siberian elm U. pumila as a parent, the source of disease-resistance and drought-tolerance genes. Further releases are planned, notably of a clone derived from a crossing of Dutch elm Ulmus × hollandica
with the Chinese species U. chenmoui.
and 'Valley Forge'
) are currently available in Europe. No cultivar is "immune" to DED; even highly resistant cultivars can become infected, particularly if already stressed by drought or other environmental conditions where the disease prevalence is high. With the exception of 'Princeton', no trees have yet been grown to maturity. Trees cannot be said to be mature until they have reached an age of 60 years.
Notable cultivars include:
In 2007, the Elm Recovery Project from the University of Guelph in Ontario, Canada reported that cuttings from healthy surviving old elms surveyed across Ontario had been grown to produce a bank of resistant trees, isolated for selective breeding of highly resistant cultivars http://www.canada.com/ottawacitizen/news/story.html?id=33e91594-b329-453d-a4d5-62dba22f33b1&p=1 .
The University of Minnesota USA is testing various elms, including a huge now-patented century-old survivor known as "The St. Croix Elm", which is located in a Minneapolis-St. Paul, MN suburb (Afton) in the St. Croix River valley — a designated National Scenic Riverway.
The slippery or red elm U. rubra
is marginally less susceptible to Dutch elm disease than the other American species, but this quality seems to have been largely ignored in American research. No cultivars were ever selected, although the tree was used in hybridization experiments (see above).
In 2001, English elm U. procera was genetically engineered to resist disease, in experiments at Abertay University, Dundee
, Scotland
, by transferring antifungal genes into the elm genome using minute DNA-coated ball bearings. However, owing to the hostility to GM developments, there are no plans to release the trees into the countryside.
The spread of DED to Scotland has revealed a number of Wych elms U. glabra apparently surviving there unscathed, prompting the Royal Botanic Garden Edinburgh
to clone the trees and inoculate them with the fungus to determine any innate resistance (2010).
period about 6000 years ago, and to a lesser extent 3000 years ago. This roughly synchronous and widespread event has come to be known as the 'Elm Decline'. When first detected in the mid-20th century, the decline was attributed to the impact of forest-clearance by Neolithic
farmers, and of elm-coppicing for animal fodder, though the numbers of settlers could not have been large. The devastation caused recently by DED has provided an alternative explanation. Examination of subfossil elm wood showing signs of the changes associated with the disease has suggested that a form of DED "may" have been responsible. Fossil finds from this period of elm bark beetles support this theory. A consensus of opinion today is that the Elm Decline was probably driven by both factors. http://www.geus.dk/departments/environ-hist-climate/posters/rasmussen97-uk.htm
' 1883 book, Nature near London, shows:
Though dead elms also appear in Italian paintings of the late 15th century, this suggestion remains largely speculative, and there is no proof that it was caused by a fungus related to Dutch elm disease.
Elm
Elms are deciduous and semi-deciduous trees comprising the genus Ulmus in the plant family Ulmaceae. The dozens of species are found in temperate and tropical-montane regions of North America and Eurasia, ranging southward into Indonesia. Elms are components of many kinds of natural forests...
trees which is spread by the elm bark beetle. Although believed to be originally native to Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
, the disease has been accidentally introduced into America
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...
and Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, where it has devastated native populations of elms which had not had the opportunity to evolve resistance to the disease. The name Dutch elm disease refers to its identification 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...
by a Dutch phytopathologist in 1921; the disease is not specific to the Dutch elm
Dutch Elm
Although all naturally occurring Field Elm × Wych Elm hybrids are loosely termed 'Dutch elm' , Ulmus × hollandica Major is a distinctive cultivar that in England came to be known specifically as the Dutch Elm...
hybrid.
Overview
The causative agents of DED are ascomycete microfungiMicrofungi
Microfungi are fungi, eukaryotic organisms such as molds, mildews and rusts, which exhibit tube tip-growth and have cell walls composed of chitin, a polymer of N-acetylglucosamine. The microfungi are an artificial, paraphyletic group, distinguished from macrofungi only by the absence of a large,...
. Three species are now recognized: Ophiostoma ulmi, which afflicted Europe from 1910, reaching North America on imported timber in 1928, Ophiostoma himal-ulmi, a species endemic to the western Himalaya, and the extremely virulent species, Ophiostoma novo-ulmi, which was first described in Europe and North America in the 1940s and has devastated elms in both areas since the late 1960s. The origin of O. novo-ulmi remains unknown, but the species may have arisen as a hybrid between O. ulmi and O. himal-ulmi.
The new species was widely believed to have originated in China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, but a comprehensive survey there in 1986 found no trace of it, although elm bark beetles were very common.
Curculionidae
Curculionidae is the family of the "true" weevils . It was formerly recognized in 1998 as the largest of any animal family, with over 40,000 species described worldwide at that time...
, Subfamily: Scolytinae): the native elm bark beetle, Hylurgopinus rufipes, the European elm bark beetle, Scolytus multistriatus, and the banded elm bark beetle, Scolytus schevyrewi. In Europe, while the aforementioned Scolytus multistriatus again acts as vector for infection, it is much less effective than the large elm bark beetle Scolytus scolytus. The native elm bark beetle can be a vector for the disease, but is inefficient compared to the other vectors. Scolytus schevyrewi was found in 2003 in Colorado and Utah, and is now in 10 western states.
Mechanism
In an attempt to block the fungus from spreading farther, the tree reacts by plugging its own xylem tissueXylem
Xylem is one of the two types of transport tissue in vascular plants. . The word xylem is derived from the Classical Greek word ξυλον , meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant...
with gum and tylose
Tylose
Tyloses are outgrowths on parenchyma cells of xylem vessels . When the plant is stressed by drought or infection, tyloses will fall from the sides of the cells and "dam" up the vascular tissue to prevent further damage to the plant.Tyloses can aid in the process of making sapwood into heartwood in...
s, bladder-like extensions of the xylem cell wall
Cell wall
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...
. As the xylem (one of the two types of vascular tissue
Vascular tissue
Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue:...
produced by the vascular cambium
Vascular cambium
The vascular cambium is a part of the morphology of plants. It consists of cells that are partly specialized, for the tissues that transport water solutions, but have not reached any of the final forms that occur in their branch of the specialization graph...
, the other being the phloem
Phloem
In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...
) delivers water and nutrients to the rest of the plant, these plugs prevent them from travelling up the trunk of the tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...
, eventually killing it. (Xylem comprises the bulk of the hard tissue of the interior of trunks and branches of woody plants and is nearly synonymous with "wood". Phloem can be thought of as a thin sheet of tissue wrapped around the central cylinder of xylem, although just beneath the phloem is another thin sheet, the vascular cambium, which produces both phloem and xylem. The bark is external to the phloem.)
Symptoms
The first symptom of infection is usually an upper branch of the tree with leaves starting to wither and yellow in summer, months before the normal autumnal leaf shedding. This progressively spreads to the rest of the tree, with further dieback of branches. Eventually, the roots die, starved of nutrients from the leaves. Often, not all the roots die: the roots of some species, notably the English elm Ulmus procera, put up suckers which flourish for approximately 15 years, after which they too succumb.Europe
Dutch elm disease was first noticed in Europe in 1910, and spread slowly, reaching BritainGreat 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...
in 1927. This first strain was a relatively mild one, which killed only a small proportion of elms, more often just killing a few branches, and had largely died out by 1940 owing to its susceptibility to viruses. The disease was isolated in The Netherlands in 1921 by Bea Schwarz
Marie Beatrice Schol-Schwarz
Dr Marie Beatrice Schol-Schwarz was the Dutch phytopathologist, better known simply as Bea Schwarz, who discovered the causal fungus of Dutch elm disease whilst studying for her doctorate at the University of Utrecht in 1922, where she was Johanna Westerdijk's first PhD student.Born in Batavia,...
, a pioneering Dutch phytopathologist, and this discovery would lend the disease its name.
Circa 1967, a new, far more virulent strain arrived in Britain on a shipment of rock elm U. thomasii logs from North America, and this strain proved both highly contagious and lethal to European elms; more than 25 million trees have died in the UK alone. The disease is still migrating northwards through Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
, reaching Edinburgh
Edinburgh
Edinburgh is the capital city of Scotland, the second largest city in Scotland, and the eighth most populous in the United Kingdom. The City of Edinburgh Council governs one of Scotland's 32 local government council areas. The council area includes urban Edinburgh and a rural area...
in the late 1970s, and Inverness
Inverness
Inverness is a city in the Scottish Highlands. It is the administrative centre for the Highland council area, and is regarded as the capital of the Highlands of Scotland...
in 2006. By 1990, very few mature elms were left in Britain or much of continental Europe. One of the most distinctive English
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
countryside trees, the English elm U. procera Salisb. (see John Constable
John Constable
John Constable was an English Romantic painter. Born in Suffolk, he is known principally for his landscape paintings of Dedham Vale, the area surrounding his home—now known as "Constable Country"—which he invested with an intensity of affection...
's painting Salisbury Cathedral from the South-West), is particularly susceptible. Thirty years after the outbreak of the epidemic, nearly all these trees, which often grew to more than 45 m high, are gone. The species still survives in hedgerows, as the roots are not killed and send up root sprouts ("suckers"). These suckers rarely reach more than 5 m tall before succumbing to a new attack of the fungus. However, established hedges kept low by clipping have remained apparently healthy throughout the nearly 40 years since the onset of the disease in the UK.
Amsterdam
Amsterdam is the largest city and the capital of the Netherlands. The current position of Amsterdam as capital city of the Kingdom of the Netherlands is governed by the constitution of August 24, 1815 and its successors. Amsterdam has a population of 783,364 within city limits, an urban population...
and The Hague
The Hague
The Hague is the capital city of the province of South Holland in the Netherlands. With a population of 500,000 inhabitants , it is the third largest city of the Netherlands, after Amsterdam and Rotterdam...
. In 2005, Amsterdam was declared the 'Elm City of Europe': the city’s streets and canals are lined with at least 75,000 elms, including several generations of research-elms (see below: Resistant trees). Some 30,000 of the 100,000 mature trees in The Hague
The Hague
The Hague is the capital city of the province of South Holland in the Netherlands. With a population of 500,000 inhabitants , it is the third largest city of the Netherlands, after Amsterdam and Rotterdam...
are elms, planted because of their tolerance of salty sea-winds. Since the 1990s, a programme of antifungal injections of the most prominent 10,000 elms, and of sanitation felling, has reduced annual elm losses in The Hague from 7% to less than 1% (see below: Preventive treatment). The losses are made up by the planting of disease-resistant cultivars. The largest concentration of mature elm trees remaining in England is in Brighton and Hove, East Sussex
East Sussex
East Sussex is a county in South East England. It is bordered by the counties of Kent, Surrey and West Sussex, and to the south by the English Channel.-History:...
, where 15,000 elms still stand (2005 figures), several of which are estimated to be over 400 years old. Their survival is owing to the isolation of the area, between the English Channel
English Channel
The English Channel , often referred to simply as the Channel, is an arm of the Atlantic Ocean that separates southern England from northern France, and joins the North Sea to the Atlantic. It is about long and varies in width from at its widest to in the Strait of Dover...
and the South Downs
South Downs
The South Downs is a range of chalk hills that extends for about across the south-eastern coastal counties of England from the Itchen Valley of Hampshire in the west to Beachy Head, near Eastbourne, East Sussex, in the east. It is bounded on its northern side by a steep escarpment, from whose...
, and the assiduous efforts of local authorities to identify and remove infected sections of trees immediately when they show symptoms of the disease. Empowered by the Dutch Elm Disease (Local Authorities) (Amendment) Order 1988, local authorities may order the destruction of any infected trees or timber, although in practice they usually do it themselves, successfully reducing the numbers of elm bark beetle Scolytus spp., the vector of elm disease. The largest concentration of mature elms in Scotland is in Edinburgh
Edinburgh
Edinburgh is the capital city of Scotland, the second largest city in Scotland, and the eighth most populous in the United Kingdom. The City of Edinburgh Council governs one of Scotland's 32 local government council areas. The council area includes urban Edinburgh and a rural area...
, where 5000 elms still stand (2009 figures) out of some 35,000 in 1976. A policy of sanitary felling has kept losses to an average of 1000 a year. Elm was the commonest tree in Paris from the 17th century; before the 1970s there were some 30,000 ormes parisiens. Today, only 1000 mature elms survive in the city, including examples in the large avenues (Avenue d'Italie, Avenue de Choisy, Boulevard Lefebvre, Boulevard de Grenelle, Boulevard Garibaldi) and two very old specimens, one in the garden of the Tuileries in front of the l'Orangerie
Orangery
An orangery was a building in the grounds of fashionable residences from the 17th to the 19th centuries and given a classicising architectural form. The orangery was similar to a greenhouse or conservatory...
and another in the Place Saint-Gervais in front of l'hôtel de ville de Paris
Hôtel de Ville, Paris
The Hôtel de Ville |City Hall]]) in :Paris, France, is the building housing the City of Paris's administration. Standing on the place de l'Hôtel de Ville in the city's IVe arrondissement, it has been the location of the municipality of Paris since 1357...
. Losses are now being made up with disease-resistant cultivars, especially the Dutch-French research elm 'Nanguen' (Lutèce), named after the city.
North America
The disease was first reported in the United StatesUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
in 1928, with the beetles believed to have arrived in a shipment of logs from The Netherlands destined for use as veneer
Wood veneer
In woodworking, veneer refers to thin slices of wood, usually thinner than 3 mm , that are typically glued onto core panels to produce flat panels such as doors, tops and panels for cabinets, parquet floors and parts of furniture. They are also used in marquetry...
in the Ohio
Ohio
Ohio is a Midwestern state in the United States. The 34th largest state by area in the U.S.,it is the 7th‑most populous with over 11.5 million residents, containing several major American cities and seven metropolitan areas with populations of 500,000 or more.The state's capital is Columbus...
furniture
Furniture
Furniture is the mass noun for the movable objects intended to support various human activities such as seating and sleeping in beds, to hold objects at a convenient height for work using horizontal surfaces above the ground, or to store things...
industry. The disease spread slowly from New England
New England
New England is a region in the northeastern corner of the United States consisting of the six states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut...
westward and southward, almost completely destroying the famous elms in the 'Elm City' of New Haven, reaching the Detroit
Detroit, Michigan
Detroit is the major city among the primary cultural, financial, and transportation centers in the Metro Detroit area, a region of 5.2 million people. As the seat of Wayne County, the city of Detroit is the largest city in the U.S. state of Michigan and serves as a major port on the Detroit River...
area in 1950, the Chicago area by 1960, and Minneapolis
Minneapolis, Minnesota
Minneapolis , nicknamed "City of Lakes" and the "Mill City," is the county seat of Hennepin County, the largest city in the U.S. state of Minnesota, and the 48th largest in the United States...
by 1970.
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
in 1967, Manitoba
Manitoba
Manitoba is a Canadian prairie province with an area of . The province has over 110,000 lakes and has a largely continental climate because of its flat topography. Agriculture, mostly concentrated in the fertile southern and western parts of the province, is vital to the province's economy; other...
in 1975 and Saskatchewan
Saskatchewan
Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....
in 1981. In Toronto, 80% of the elm trees have been lost to Dutch elm disease; many more fell victim in Ottawa
Ottawa
Ottawa is the capital of Canada, the second largest city in the Province of Ontario, and the fourth largest city in the country. The city is located on the south bank of the Ottawa River in the eastern portion of Southern Ontario...
, Montreal
Montreal
Montreal is a city in Canada. It is the largest city in the province of Quebec, the second-largest city in Canada and the seventh largest in North America...
and other cities during the 1970s and 1980s. Quebec City
Quebec City
Quebec , also Québec, Quebec City or Québec City is the capital of the Canadian province of Quebec and is located within the Capitale-Nationale region. It is the second most populous city in Quebec after Montreal, which is about to the southwest...
still has about 21,000 elms, thanks to a prevention program initiated in 1981. Alberta
Alberta
Alberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...
and British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
are the only provinces that are currently free of Dutch elm disease, although, in an isolated case, an elm tree in southeastern Alberta
Alberta
Alberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...
found diseased in 1998 was immediately destroyed. Today, Alberta
Alberta
Alberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...
has the largest number of elms unaffected by Dutch elm disease in the world ; many streets and parks in Edmonton
Edmonton
Edmonton is the capital of the Canadian province of Alberta and is the province's second-largest city. Edmonton is located on the North Saskatchewan River and is the centre of the Edmonton Capital Region, which is surrounded by the central region of the province.The city and its census...
and Calgary
Calgary
Calgary is a city in the Province of Alberta, Canada. It is located in the south of the province, in an area of foothills and prairie, approximately east of the front ranges of the Canadian Rockies...
are still lined with healthy, mature trees. Aggressive measures are being taken to prevent the spread of the disease into Alberta, as well as other parts of Canada. The City of Edmonton
Edmonton
Edmonton is the capital of the Canadian province of Alberta and is the province's second-largest city. Edmonton is located on the North Saskatchewan River and is the centre of the Edmonton Capital Region, which is surrounded by the central region of the province.The city and its census...
has banned elm pruning from March 31 to October 1, since fresh pruning wounds will attract the beetles during the warmer months.
The largest surviving urban forest of elm trees in North America is believed to be in the city of Winnipeg
Winnipeg
Winnipeg is the capital and largest city of Manitoba, Canada, and is the primary municipality of the Winnipeg Capital Region, with more than half of Manitoba's population. It is located near the longitudinal centre of North America, at the confluence of the Red and Assiniboine Rivers .The name...
, Manitoba
Manitoba
Manitoba is a Canadian prairie province with an area of . The province has over 110,000 lakes and has a largely continental climate because of its flat topography. Agriculture, mostly concentrated in the fertile southern and western parts of the province, is vital to the province's economy; other...
, where close to 200,000 elms remain - at least double that of Amsterdam
Amsterdam
Amsterdam is the largest city and the capital of the Netherlands. The current position of Amsterdam as capital city of the Kingdom of the Netherlands is governed by the constitution of August 24, 1815 and its successors. Amsterdam has a population of 783,364 within city limits, an urban population...
, the "Elm City of Europe". The city of Winnipeg spends $3M annually to aggressively combat the disease using Dursban Turf and the Dutch Trig vaccine, losing 1500-4000 trees per year.
Australia
Owing to its geographical isolation and effective quarantine enforcement, AustraliaAustralia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
has so far been unaffected by Dutch elm disease, retaining its many stands of introduced elm varieties
Elms in Australia
The cultivation of elms in Australia began in the first half of the 19th century when European settlers imported species from their former homelands...
.
Chemical
The first fungicide used for preventive treatment of Dutch elm disease was Lignasan BLP (carbendazim phosphate), which was introduced in the 1970s. This had to be injected into the base of the tree using specialized equipment, and was never especially effective. It is still sold under the name "Elm Fungicide". Arbotect (thiabendazole hypophosphite) became available some years later, and it has been proven effective. Arbotect must be injected every two to three years to provide ongoing control; the disease generally cannot be eradicated once a tree is infected. There is a process called tracing that was invented by Rainbow Treecare in Minneapolis. It has proven to be effective at saving infected elms as long as the Dutch elm disease fungus has not grown into the roots.Arbotect is not effective on root graft infections from adjacent elm trees. It is more than 99.5% effective for three years from beetle infections, which is the primary mode of tree infection.
Alamo (propiconazole
Propiconazole
Propiconazole is a triazole fungicide, also known as a DMI, or demethylation inhibiting fungicide due to its binding with and inhibiting the 14-alpha demethylase enzyme from demethylating a precursor to ergosterol. Without this demethylation step, the ergosterols are not incorporated into the...
) has become available more recently, though several university studies show it to be effective for only the current season it is injected. Alamo is primarily recommended for treatment of oak wilt
Oak wilt
Oak wilt is a fungal disease that can quickly kill an oak tree. It is caused by the fungus Ceratocystis fagacearum. Symptoms vary by tree species but generally consist of leaf discoloration, wilt, defoliation, and death. The fungus is spread from diseased to healthy trees by insect vectors or via...
.
Biological
Because of the ban on the use of chemicals on street and park trees in the Netherlands, the University of Amsterdam developed a biological vaccine by the late 1980s. Dutch Trig is nonchemical and nontoxic, consisting of a suspension in distilled water of spores of a strain of the fungus Verticillium albo-atrumVerticillium albo-atrum
Verticillium albo-atrum is a plant pathogen.-External links:* *...
that has lost much of its pathogenic capabilities, injected in the elm in spring. The strain is believed to have enough pathogenicity left to induce an immune response in the elm, protecting it against DED during one growing season. This is called induced resistance.
Preventive treatment is costly, and at best will prolong the life of the tree by perhaps five or ten years. It is usually only justified when a tree has unusual symbolic value or occupies a particularly important place in the landscape. The injections have no curative properties on trees which already have Dutch elm disease.
Practical information for elm tree owners
DED is caused by a fungusFungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
. It is primarily spread in three ways:
- By beetle vectors which carry the fungus from tree to tree — the beetle does not kill the tree, the fungus it carries does.
- Through connection of an infected tree's roots with a neighboring healthy tree.
- By pruning of a healthy tree with saws which have been used to take down diseased trees. This third method of spread is common and not recognized by many tree pruning and removal services. Arborists at Kansas State UniversityKansas State UniversityKansas State University, commonly shortened to K-State, is an institution of higher learning located in Manhattan, Kansas, in the United States...
claim that cleaning blades with a 10% solution of a household bleachBleachBleach refers to a number of chemicals that remove color, whiten, or disinfect, often via oxidation. Common chemical bleaches include household chlorine bleach , lye, oxygen bleach , and bleaching powder...
will prevent this type of spread. Owners of healthy trees should be vigilant about the companies they hire to prune healthy trees. Blades need to be disinfected between use to remove dead trees and use to prune healthy trees.
Resistant trees
Research to select resistant cultivarCultivar
A cultivar'Cultivar has two meanings as explained under Formal definition. When used in reference to a taxon, the word does not apply to an individual plant but to all those plants sharing the unique characteristics that define the cultivar. is a plant or group of plants selected for desirable...
s and varieties began in the Netherlands in 1928, followed by the USA in 1937. Initial efforts in the Netherlands involved crossing varieties of U. minor and U. glabra, but later included the Himalayan or Kashmir elm U. wallichiana as a source of antifungal genes. Early efforts in the USA involved the hybridization of the Siberian elm U. pumila with American red elm U. rubra
Ulmus rubra
Ulmus rubra, the Slippery Elm, is a species of elm native to eastern North America...
to produce resistant trees. Resulting cultivars lacked the traditional shape and landscape value of the American elm
American Elm
Ulmus americana, generally known as the American Elm or, less commonly, as the White Elm or Water Elm, is a species native to eastern North America, occurring from Nova Scotia west to Alberta and Montana, and south to Florida and central Texas. The American elm is an extremely hardy tree that can...
; few were planted.
In 2005, the National Elm Trial
National Elm Trial
The National Elm Trial is an American volunteer effort to evaluate a range of newly developed elm cultivars as replacements for elms destroyed by Dutch elm disease...
(USA) began a 10-year evaluation of 19 cultivars in plantings across the United States. The trees in the trial are exclusively American developments; no European cultivars have been included.
Recent research in Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
has established that early-flushing clones are less susceptible to DED owing to an asynchrony between DED susceptibility and infection.
Hybrid cultivars
Many attempts to breed disease resistant cultivar hybrids have usually involved a genetic contribution from Asian elm species which have demonstrable resistance to this fungal disease. Much of the early work was undertaken in the Netherlands. The Dutch research programme began in 1928, and ended after 64 years in 1992, during which time well over 1000 cultivars were raised and evaluated. The programme had three major successes: 'Columella'Ulmus 'Columella'
Ulmus Columella is a Dutch cultivar raised by the Dorschkamp Research Institute in Wageningen from a selfed seedling of the hybrid 'Plantyn' sown in 1967...
, 'Nanguen' LUTÈCE, and 'Wanoux' VADA, all found to have an extremely high resistance to the disease when inoculated with unnaturally large doses of the fungus. Only 'Columella' was released during the lifetime of the Dutch programme, in 1987; patents for the LUTÈCE and VADA clones were purchased by the French Institut National de la Recherche Agronomique (INRA), which subjected the trees to 20 years of field trials in the Bois de Vincennes
Bois de Vincennes
The Bois de Vincennes is a park in the English landscape manner to the east of Paris. The park is named after the nearby town of Vincennes....
, Paris
Paris
Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...
, before releasing them to commerce in 2002 and 2006, respectively.
Asian species to feature in the American DED research programs were the Siberian elm U. pumila, Japanese elm U. davidiana var. japonica, and the Chinese elm U. parvifolia
Ulmus parvifolia
Ulmus parvifolia, commonly known as the Chinese Elm or Lacebark Elm, is a species native to China, Japan, North Korea and Vietnam...
, giving rise to several dozen hybrid cultivars resistant not just to DED, but also to the extreme cold of Asian winters. Among the most widely planted of these, both in North America and in Europe, are 'Sapporo Autumn Gold' and 'New Horizon'. Some hybrid cultivars, such as 'Regal', are the product of both Dutch and American research. Hybridization experiments using the slippery or red elm U. rubra
Ulmus rubra
Ulmus rubra, the Slippery Elm, is a species of elm native to eastern North America...
resulted in the release of 'Coolshade' and 'Rosehill'
Ulmus 'Rosehill'
The hybrid cultivar Rosehill was originally raised by the Rose Hill Nurseries of Kansas City, Missouri, from a selection of Ulmus pumila × Ulmus rubra seedlings made in 1951.-Description:...
in the 1940s and 50s. The species last featured in hybridization as the female parent of 'Repura'
Ulmus 'Repura'
Repura is an American cultivar raised by the Wisconsin Alumni Research Foundation as selection '1193-4', derived from a crossing of 'Regal' and a crossing of Ulmus rubra with the hybrid Ulmus pumila × Ulmus davidiana var...
and 'Revera'
Ulmus 'Revera'
Revera is an American cultivar raised by the Wisconsin Alumni Research Foundation as selection '1193-3', derived from a crossing of 'Regal' and a crossing of Ulmus rubra with the hybrid Ulmus pumila × Ulmus davidiana var...
, both patented in 1993, although neither has yet appeared in commerce.
In Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
, research is continuing at the Istituto per la Protezione delle Piante, Florence, to produce a range of disease-resistant trees adapted to the warmer Mediterranean climate, using a variety of Asiatic species crossed with the early Dutch hybrid 'Plantyn'
Plantyn (elm hybrid)
Plantyn was one of three Dutch hybrid elms released in 1973. Derived from a crossing of the Dutch hybrids '202' and '302' , it was to prove of great significance in later developments...
as a safeguard against any future mutation of the disease. Two trees with very high levels of resistance, 'San Zanobi' and 'Plinio', were released in 2003. 'Arno'
Ulmus 'Arno'
Ulmus Arno is a cultivar derived from a crossing of the Dutch hybrid cultivar 'Plantyn' with the Siberian Elm Ulmus pumila clone S.2. It was raised by the Istituto per la Protezione delle Piante in Florence, patented, and released to commerce in 2007.-Description:'Arno' is of erect habit with...
and 'Fiorente'
Ulmus 'Fiorente'
Ulmus Fiorente is a hybrid cultivar derived from a crossing of the Siberian Elm Ulmus pumila clone S.10 with Ulmus minor C.02 by the Istituto per la Protezione delle Piante , part of the Italian National Research Council, in Florence...
were patented in 2006 and will enter commerce in 2012. All four have the Siberian elm U. pumila as a parent, the source of disease-resistance and drought-tolerance genes. Further releases are planned, notably of a clone derived from a crossing of Dutch elm Ulmus × hollandica
Ulmus × hollandica
Ulmus × hollandica Mill. , often known simply as Dutch Elm, is a natural hybrid between Wych Elm Ulmus glabra and Field Elm Ulmus minor which commonly occurs across Europe wherever the ranges of the two parent species overlap. In England, according to the field-studies of R. H...
with the Chinese species U. chenmoui.
North America
Ten resistant American elm U. americana cultivars are now in commerce in North America, but only two ('Princeton'Ulmus americana 'Princeton'
The American Elm Ulmus americana cultivar Princeton was originally selected in 1922 by New Jersey nurseryman William Flemer for its aesthetic merit...
and 'Valley Forge'
Ulmus americana 'Valley Forge'
The American Elm Ulmus americana cultivar Valley Forge was raised by the Agricultural Research Service in Maryland and released to wholesale nurseries without patent restrictions by the U. S. National Arboretum in 1995.-Description:...
) are currently available in Europe. No cultivar is "immune" to DED; even highly resistant cultivars can become infected, particularly if already stressed by drought or other environmental conditions where the disease prevalence is high. With the exception of 'Princeton', no trees have yet been grown to maturity. Trees cannot be said to be mature until they have reached an age of 60 years.
Notable cultivars include:
- 'Princeton'Ulmus americana 'Princeton'The American Elm Ulmus americana cultivar Princeton was originally selected in 1922 by New Jersey nurseryman William Flemer for its aesthetic merit...
, is a cultivar selected in 1922 by Princeton Nurseries for its landscape merit. By happy coincidence, this cultivar was found to be highly resistant in inoculation studies carried out by the USDA in the early 1990s. As trees planted in the 1920s still survive, the properties of the mature plant are well known. - 'American Liberty'Ulmus americana 'American Liberty'The American Elm Ulmus americana cultivar American Liberty is in fact a group of six genetically distinct cultivars under a single name, although they are superficially similar . The Liberty elm is reportedly suitable for street planting, being tolerant of de-icing salts and air pollution...
, is, in fact, a set of six cultivars of moderate to high resistance produced through selection over several generations starting in the 1970s. Although 'American Liberty' is marketed as a single variety, nurseries selling the "Liberty Elm" actually distribute the six cultivars at random and thus, unfortunately, the resistance of any particular tree cannot be known. One of the cultivars, 'Independence'Ulmus americana 'Independence'The American Elm Ulmus americana cultivar Independence was raised by Eugene B. Smalley and Donald T. Lester at the University of Wisconsin–Madison from a crossing of the American Elm cultivar Moline and American Elm clone W-185-21, to become one of the six clones forming the American Liberty...
, is covered by patent (U. S. Plant patent 6227). The oldest 'American Liberty' elm was planted in about 1980. - 'Valley Forge'Ulmus americana 'Valley Forge'The American Elm Ulmus americana cultivar Valley Forge was raised by the Agricultural Research Service in Maryland and released to wholesale nurseries without patent restrictions by the U. S. National Arboretum in 1995.-Description:...
, released in 1995, has demonstrated the highest resistance of all the clones to Dutch elm disease in controlled USDA tests. - 'Lewis and Clark'Ulmus americana 'Lewis & Clark'The American Elm Ulmus americana cultivar Lewis & Clark is a relatively new development from the North Dakota State University Research Foundation breeding programme, released in 2004 to commemorate the 200th anniversary of the eponymous expedition...
(Prairie Expedition TM ), released in 2004, was cloned from a tree found growing in North DakotaNorth DakotaNorth Dakota is a state located in the Midwestern region of the United States of America, along the Canadian border. The state is bordered by Canada to the north, Minnesota to the east, South Dakota to the south and Montana to the west. North Dakota is the 19th-largest state by area in the U.S....
which had survived unscathed when all around had succumbed to disease.
In 2007, the Elm Recovery Project from the University of Guelph in Ontario, Canada reported that cuttings from healthy surviving old elms surveyed across Ontario had been grown to produce a bank of resistant trees, isolated for selective breeding of highly resistant cultivars http://www.canada.com/ottawacitizen/news/story.html?id=33e91594-b329-453d-a4d5-62dba22f33b1&p=1 .
The University of Minnesota USA is testing various elms, including a huge now-patented century-old survivor known as "The St. Croix Elm", which is located in a Minneapolis-St. Paul, MN suburb (Afton) in the St. Croix River valley — a designated National Scenic Riverway.
The slippery or red elm U. rubra
Ulmus rubra
Ulmus rubra, the Slippery Elm, is a species of elm native to eastern North America...
is marginally less susceptible to Dutch elm disease than the other American species, but this quality seems to have been largely ignored in American research. No cultivars were ever selected, although the tree was used in hybridization experiments (see above).
Europe
Among European species, there is the unique example of the European white elm U. laevis, which has little innate resistance to DED, but is eschewed by the vector bark beetles and only rarely becomes infected. Recent research has indicated it is the presence of certain organic compounds, such as triterpenes and sterols, which serves to make the tree bark unattractive to the beetle species that spread the disease.In 2001, English elm U. procera was genetically engineered to resist disease, in experiments at Abertay University, Dundee
Dundee
Dundee is the fourth-largest city in Scotland and the 39th most populous settlement in the United Kingdom. It lies within the eastern central Lowlands on the north bank of the Firth of Tay, which feeds into the North Sea...
, Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
, by transferring antifungal genes into the elm genome using minute DNA-coated ball bearings. However, owing to the hostility to GM developments, there are no plans to release the trees into the countryside.
The spread of DED to Scotland has revealed a number of Wych elms U. glabra apparently surviving there unscathed, prompting the Royal Botanic Garden Edinburgh
Royal Botanic Garden Edinburgh
The Royal Botanic Garden Edinburgh is a scientific centre for the study of plants, their diversity and conservation, as well as a popular tourist attraction. Originally founded in 1670 as a physic garden to grow medicinal plants, today it occupies four sites across Scotland — Edinburgh,...
to clone the trees and inoculate them with the fungus to determine any innate resistance (2010).
The 'Elm Decline'
From analysis of fossil pollen in peat samples, it is apparent that elms, an abundant tree in prehistoric times, all but disappeared from northwestern Europe during the mid-HoloceneHolocene climatic optimum
The Holocene Climate Optimum was a warm period during roughly the interval 9,000 to 5,000 years B.P.. This event has also been known by many other names, including: Hypsithermal, Altithermal, Climatic Optimum, Holocene Optimum, Holocene Thermal Maximum, and Holocene Megathermal.This warm period...
period about 6000 years ago, and to a lesser extent 3000 years ago. This roughly synchronous and widespread event has come to be known as the 'Elm Decline'. When first detected in the mid-20th century, the decline was attributed to the impact of forest-clearance by Neolithic
Neolithic
The Neolithic Age, Era, or Period, or New Stone Age, was a period in the development of human technology, beginning about 9500 BC in some parts of the Middle East, and later in other parts of the world. It is traditionally considered as the last part of the Stone Age...
farmers, and of elm-coppicing for animal fodder, though the numbers of settlers could not have been large. The devastation caused recently by DED has provided an alternative explanation. Examination of subfossil elm wood showing signs of the changes associated with the disease has suggested that a form of DED "may" have been responsible. Fossil finds from this period of elm bark beetles support this theory. A consensus of opinion today is that the Elm Decline was probably driven by both factors. http://www.geus.dk/departments/environ-hist-climate/posters/rasmussen97-uk.htm
Historic period
A less devastating form of the disease, caused by a different fungus, had possibly been present in Britain for some time, as this passage in Richard JefferiesRichard Jefferies
John Richard Jefferies was an English nature writer, noted for his depiction of English rural life in essays, books of natural history, and novels. His childhood on a small Wiltshire farm had a great influence on him and provides the background to all his major works of fiction...
' 1883 book, Nature near London, shows:
- There is something wrong with elm trees. In the early part of this summer, not long after the leaves were fairly out upon them, here and there a branch appeared as if it had been touched with red-hot iron and burnt up, all the leaves withered and browned on the boughs. First one tree was thus affected, then another, then a third, till, looking round the fields, it seemed as if every fourth or fifth tree had thus been burnt. [...] Upon mentioning this I found that it had been noticed in elm avenues and groups a hundred miles distant, so that it is not a local circumstance.
Though dead elms also appear in Italian paintings of the late 15th century, this suggestion remains largely speculative, and there is no proof that it was caused by a fungus related to Dutch elm disease.
External links
- Walter E. Burton "Army of Experts Wage War on Dutch Elm Disease" Popular Science Monthly, May 1937
- Elm Recovery Project - Guelph University (Canada)
- Dutch elm disease - info from the Government of Alberta
- Dutch elm disease - info from the Government of British Columbia
- DED info from Rainbow Treecare Scientific Advancements
- The Mid-Holocene Ulmus decline: a new way to evaluate the pathogen hypothesis
- Dutch Elm Disease - Gallery of Pests
- KIM PALMER, Minneapolis, Minnesota USA Star Tribune
- Species Profile- Dutch Elm Disease (Ophiostoma ulmi and Ophiostoma novo-ulmi), National Invasive Species Information Center, United States National Agricultural LibraryUnited States National Agricultural LibraryThe United States National Agricultural Library is one of the world's largest agricultural research libraries, and serves as a National Library of the United States and as the library of the United States Department of Agriculture...
. Lists general information and resources for Dutch Elm Disease.