The epidemiology of the ash dieback pathogen, Hymenoscyphus fraxineus, in Northern Ireland

There were significant differences in lesion length between individual H. fraxineus isolates, but the diversity in the N. Irish H. fraxineus population mirrored that of the European population. <br><br>Urea was investigated to determine if it aided in the decomposition of ash leaves and thus might have potential as a control measure for ash dieback. Urea applications did not enhance the degradation of ash leaves; the rachises (on which the apothecia of H. fraxineus are produced) remained largely intact.

It was therefore concluded that urea was unlikely to be effective in reducing ash dieback.<br><br>In 2015 a site recently planted (2006) with ash in Co. Antrim, N. Ireland was found through routine plant health inspections to be infected with H. fraxineus. This site was used for an in-depth case study.

Previously published work had suggested that apothecia could only form on fallen, infected ash rachises; raising the question of the initial source of infection of N. Ireland ash trees and inoculum build up if ash was imported as leafless whips. A unique finding from the site was that apothecia were observed on ash stems, branches and roots (in addition to the leaf rachises). This could explain the environmental spread of ash dieback into N. Ireland.

A disease timeline was constructed for the site, showing that there was a disease lag time between two and three years from planting to symptom development. <br>