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.

[9] Dutch elm disease was first noticed in continental Europe in 1910, and spread slowly and eventually extended to all other countries except Greece and Finland.

[12] Barendina Gerarda Spierenburg compiled records of trees displaying symptoms from 1900 - 1905 onwards in the Netherlands and her publication[13] of this information in 1921 was one part of the start of extensive research and practical measures to try to halt the disease.

[14] Following this, in the 1920s and 30s Christine Buisman, working in the Netherlands and USA, identified the sexual stage of the fungal pathogen and also developed methods for experimental infections of elm seedlings that led to selection of resistant trees.

In around 1967, a new, far more virulent, strain arrived in Britain, apparently via east coast ports on shipments of rock elm U. thomasii logs from Canada destined for the small-boat industry, confirmed in 1973 when another consignment was examined at Southampton Docks.

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.

[32][33] DED was first reported in the United States 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.

Quarantine and sanitation procedures held most cases within 150 mi (240 km) of metropolitan New York City until 1941 when war demands began to curtail them.

[36] The disease first appeared on the planted rows of American elm trees (Ulmus americana) on the National Mall in Washington, D.C., during the 1950s and reached a peak in the 1970s.

The NPS combated the disease's local insect vector, the smaller European elm bark beetle (Scolytus multistriatus), by trapping and by spraying with insecticides.

While this method was effective in New York State and adjacent areas, its cost made it uneconomical except in large cities where elms were considered valuable attractions.

Dutch Trig is nontoxic, consisting of a suspension in distilled water of spores of a strain of the fungus Verticillium albo-atrum that has lost much of its pathogenic capabilities, injected in the elm in spring.

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.

Consequently, tests were conducted on specimens in a controlled environment, either in greenhouses or customized plant chambers, facilitating more accurate evaluation of both internal and external symptoms of disease.

[61] The differences in method and inocula possibly explain why the American cultivar 'Princeton', displaying high resistance in the US, has often succumbed to Dutch elm disease in Europe.

[62] Many attempts to breed disease-resistant cultivar hybrids have involved a genetic contribution from Asian elm species that are demonstrably resistant to this fungal disease.

The programme had three major successes: 'Columella', 'Nanguen' Lutèce, and 'Wanoux' Vada,[63] all found to have an extremely high resistance to the disease when inoculated with unnaturally large doses of the fungus.

japonica, and the Chinese elm U. parvifolia, which gave rise to several dozen hybrid cultivars resistant not just to DED, but also to the extreme cold of Asian winters.

In Italy, research was initiated 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.

In 1993, Mariam B. Sticklen and James L. Sherald reported the results of NPS-funded experiments conducted at Michigan State University in East Lansing that were designed to apply genetic engineering techniques to the development of DED-resistant strains of American elm trees.

[67] In 2007, AE Newhouse and F Schrodt of the State University of New York College of Environmental Science and Forestry in Syracuse reported that young transgenic American elm trees had shown reduced DED symptoms and normal mycorrhizal colonization.

[68] By 2013, researchers in both New York State and North Carolina were conducting field trials of genetically engineered DED-resistant American elms.

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.

[69] In Europe the testing of clones of surviving field elms for innate resistance has been carried out since the 1990s by national research institutes, with findings centrally assessed and published.

[70] The first results of this ongoing project suggest that in some countries a very small number of native field elm genotypes have comparatively high levels of tolerance to DED.

In Spain, for example, of around 5,000 native elms evaluated to 2013, some 25 genotypes (0.5% of those tested) fall into this category; and it is now hoped that the controlled crossing of the best seven of these (genetically and aesthetically) will produce Ulmus minor hybrids with effective 'field resistance' and market appeal.

In 1994 a Research Information Note (no 252) was published, written by John Gibbs, Clive Brasier and Joan Webber, and in 2010 a Pathology Advisory Note, as well as throughout the period a stream of more academic papers: notable results have been the observation that the progress of the disease through Scotland has been quite slow, and that genetic engineering has been tried to improve the resistance of the English elm.

The spread of DED to Scotland has focussed attention on a small number of wych elms U. glabra surviving in areas of high infectivity, prompting the Royal Botanic Garden Edinburgh to begin a programme of selecting trees, with a view to determining innate resistance (2009).

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.

"[87] Sir Thomas Browne, writing in 1658, noted in The Garden of Cyrus an elm disease that was spreading through English hedgerows, and described symptoms reminiscent of DED.