Ash dieback is an unhappy prospect for all of us. There are few enough mature trees on Kelston Roundhill as it is, and ash is the one that works best. The trees we just planted included a load of ash. So what do we do about the risk?

Sounds like there are no preventive measures yet. Current advice is keep vigilant and report if we spot it. Small trees would die in the same year; larger ones struggle on for a few years. So the policy is any infected tree gets burned of buried deep. Resources:  Woodland Trust page on Chalara fraxinea (ash die-back), Forestry Commission page 

Update: The Guardian reports

A new website, ashtag.org, and a smartphone app, will be launched on Monday to encourage the public to report trees showing symptoms.

Forestry Commission leaflet (pdf)