Do we still need to record and report Chalara dieback of Ash?

Chalara dieback of Ash was first reported on Common ash (Fraxinus excelsior) in the UK in late 2012. Since those first reports it has rapidly spread and can now be found across the UK and is very likely one of the first tree diseases you will come across. Given its widespread distribution do we still need to report it or pay close attention to trees apparently infected by it?

Reporting chalara Ash dieback: apart from the exceptions listed below, only report Chalara Ash dieback via TreeAlert if you think you have seen it in a yet unrecorded 10km grid square according to this map.

The highest numbers of unrecorded squares are now in Scotland, but there are still some in England and a few in Northern Ireland. Wales has been very thoroughly mapped thanks largely to the efforts of a single Observatree volunteer!

Healthy trees: Trees which appear to be disease free could help to provide insight into tolerance to the disease. If you find an Ash that appears to not have any of the symptoms associated with chalara ash dieback *and* is otherwise healthy, register it with TreeAlert and report it as a healthy tree. Be mindful that few ash trees currently exhibit the crown density seen prior to Chalara arriving in the UK.

Other issues with Ash: There’s a real risk that if we stop paying attention to ash trees because we think they have Chalara dieback of ash, we might miss other issues. Just as with us, if trees are under stress their ability to fend off pests and diseases is lowered. Thus, Ash which are showing symptoms associated with ash dieback can be afflicted by other pests and diseases.

Take time to inspect trees apparently infected with chalara dieback for the D-shaped exit holes which can indicate the presence of Emerald Ash Borer (Agrilus planipennis). Stressed or dying ash trees might also be attacked by Agrilus convexicollis, another non-native Agrilus which was found in Surrey in 2023 – for more information see the Ash host of the month.

As part of their activities Observatree volunteers report on Sentinel trees, individual trees which are inspected for signs of pests and diseases around 4 times a year over many years. Started in 2017, this is helping to build a long-term picture of tree health across the UK. As well as helping to track the spread of tree pests and diseases it will also yield useful information about how the disease progresses in individual trees, and particularly if they recover. As the data set grows it will become a valuable resource for research scientists, helping them to understand the tree-disease interaction.

For more information about Chalara dieback of Ash and Emerald ash borer see the Observatree priority pests and diseases webpage.