[6] In 2009, based on morphological and DNA sequence comparisons, Chalara fraxinea was suggested to be the asexual stage (anamorph) of the ascomycete fungus Hymenoscyphus albidus.

[7] In 2010, through molecular genetic methods, the sexual stage (teleomorph) of the fungus was recognized as a new species and named Hymenoscyphus pseudoalbidus.

[9] The sexual, reproductive stage, (teleomorph) grows during summer on ash petioles in the previous year's fallen leaves.

[11] Genetic analysis of the fungus Lambertella albida which grows harmlessly on petioles of the Manchurian ash (Fraxinus mandschurica) in Japan, has shown that it is likely to be the same species as Hymenoscyphus fraxineus.

[12] In December 2012, teams from The Sainsbury Laboratory (TSL) and the John Innes Centre in Norwich sequenced the genome of the fungus.

"[22] In 2012, it was reported that the disease was reaching its peak in Sweden and Denmark, and that it was entering a post-decline (or chronic) phase in Latvia and Lithuania.

[25] A Danish study found that substantial genetic variation between ash trees resulted in significant differences in their susceptibility to the disease.

These necrotic lesions then enlarge in stretched, perennial cankers on the branches, wilting, premature shedding of leaves and particularly in the death of the top of the crown.

[30] The mycelium can pass through the simple pits, perforating the middle lamella but damage to either the plasmalemma or cell walls was not observed.

[11] The removal of trees in infected areas has little effect as the fungus lives and grows on leaf litter on the forest floor.

[14] A ban on imports of ash from other European countries was imposed in October 2012 after infected trees were found in established woodland.

Environment Secretary Owen Paterson announced that the disease was acknowledged to be a long-term presence in the UK, and that efforts would be concentrated on slowing its spread.

[46] In February 2016 the BBC program "Countryfile" presented a case study of enhanced resistance to ash dieback following soil treatment by injecting enriched "Biochar" - a type of charcoal.

[47][48] In December 2016, writing in Nature,[49] Dr Richard Buggs reported that the common ash (Fraxinus excelsior) had been genetically sequenced for the first time and UK specimens appeared more resistant than Danish ones.

[52] In June 2019, Defra published a report summarising the current state of knowledge regarding ash dieback, and identified priority areas for future research.

[55] On 12 October 2012 the Department of Agriculture, Food and the Marine confirmed the first recorded instance of the fungus in Ireland, at a plantation in County Leitrim.

[56] By 23 September 2013, a survey conducted by the Irish Government revealed that the disease had been identified at ninety-six sites across the Republic of Ireland.

[57] As of August 2021, Teagasc warns that: "The disease is now prevalent throughout most of the island of Ireland and is likely to cause the death of the majority of the ash trees over the next two decades.