Ash dieback mass screening trials

To identify trees with potential in a disease resistance breeding programme, it is necessary to screen large numbers of individuals which have been exposed to the disease in question. In 2013, Forest Research set up field trials in 14 locations in south-east England where ash dieback was known to be present in the wider environment. The field trials contained around 155,000 ash trees which had been growing in forest nurseries the UK and Ireland but which could no longer be sold to the open market. Plants raised from fifteen different seed sources were obtained, spanning ten of the UK’s native tree seed zones alongside Irish, French and German ash trees. The health status of trees in the trials was monitored for three (14 trials) or four (6 trials) consecutive years following onset of disease symptoms.

This project ran from February 2013 until March 2019, although some of the experiment sites have been retained and taken forward into the Living Ash Project phase II for longer term monitoring.

Site and preparation

Certified disease-free trees have been sourced from various UK nurseries, representing ash from 10 British seed zones, a French source, a German source, a Future Trees Trust seed orchard of ash already selected for their better form and growth rate, and also from two sources in Ireland.

Nearly 155,000 young trees have been planted in replicated trials at 14 sites across 48 hectares in East Anglia and Kent. The sites have been fenced to prevent wildlife access. These areas have been chosen for the trials to give the trees the greatest chance of being exposed to Chalara spores and thereby become infected.

Survival after planting across all sites is around 95%. Growth of some seedlings in the first growing season is as much as 40cm. Where plants have died, it was most likely due to establishment problems and drought . On one site with heavy clay soil, the planting slit had opened up in places and exposed the roots of the trees.

Fruiting bodies of Chalara fraxinea are now being seen in areas of high infection so it’s likely that spores will soon be drifting across East Anglia and Kent, hopefully infecting the ash trees in the trials. Fera are monitoring spore levels in woodlands across the region, which will give us an idea of the numbers of spores at the trial sites.