Ash dieback

Chalara fraxinea more commonly known as Ash dieback first hit the headlines back in 2012/2013. Coverage of this 'new disease' went national with reports on the 'outbreak' posted regularly in the news and papers. Since then it hasn't been such a prominent issue with less coverage in the media. We thought we'd use this post to revisit and discuss the disease and give anyone interested some up to date information.

About Chalara ash-dieback 

As the name suggests the disease affects Ash, a common tree across the UK. There are a number of species of Ash that thrive in the UK, the most commonly encountered being the European ash, Fraxinus excelsior. This species is affected along with Narrow-leaved ash (Fraxinus augustifolia) which is also susceptible.

Chalara is caused by the fungus Hymenoscyphus fraxineus the spores from which are produced from infected leaves. It causes extensive die back in the canopy and leads ultimately to its death. Early defoliation can be a good indication of infection along with dead, black hanging leaves and diamond shaped lesions on the bark. Below is a short but excellent video by the Forestry Commission describing the symptoms.

Chalara fraxinea - a brief history

Chalara ash dieback was first discovered in Europe in the early 1990's and in Britain in 2012. Since its initial discovery in a tree nursery in Buckinghamshire more sites with infected trees have been discovered and this trend is likely to continue as the disease spreads across the UK.

Initially it was believed that the fungus first entered the UK via imported trees from Europe, however studies are now being undertaken to investigate the possibility of it being transported from mainland Europe via wind, on birds and even by people on their footwear returning back from holiday.

Scientists believe the risk of local spread is most likely via the carriage of fungal spores from the disease on the wind whereas spread over longer distances is likely to be through the movement of diseased plants. That's why there is a ban on all imports from overseas and all internal movements of ash seeds, plants and trees.

Although it has been around for some time there is still no cure for Chalara; the future for the UKs Ash is therefore bleak. Scientists are working hard to discover a cure but hopes rely predominantly on finding resistant or tolerant trees and using these to breed others.

To summarise:

Chalara can affect all types of Ash tree; spores from the fungus causing the disease are transmitted from infected to healthy trees via direct contact and the wind. There is no cure for Chalara and it will eventually kill the infected tree, genetic variance will hopefully lead to resistant trees being discovered and breeding new trees from these. If you discover or suspect an infected tree you should report this to tree_health_england@forestry.gsi.gov.uk