The UK is now in the grip of a pandemic of killer, mainly non-native, bacterial and fungal tree diseases. Many of them are out of control and spreading but, despite official denials, treatment and control is possible.
The list of non-native diseases is long and growing. It includes Chalara fraxinea (Ash dieback also now known as Hymenoscyphus fraxineus), Phytophthora ramorum (Larch dieback, Sudden Oak Death), Acute Oak Decline caused by a combination of aggressive bacteria, Pseudomonas syringae (Bleeding Canker of the Horse Chestnut), Cryphonectria parasitica(Sweet Chestnut) and Splanchnonema platani (London plane). These pathogens and many more establishing themselves because of changing climatic conditions and because, in the modern world, there is no such thing as effective biosecurity.
We have a reference point to help us understand what is happening and what will happen, from the two phases of Dutch Elm Disease. Ophiostoma ulmi reached the UK in the 1930s and destroyed 10-15% of our elms. It was then followed by Ophiostoma novo-ulmi a more virulent mutation which wiped out over 25 million elms in the 1970s. What we saw was the national destruction of a major tree with just a few very small pockets of survivors. Today, nearly fifty years on, the elm has not recovered despite attempts to breed ‘disease resistant’ species, and the pathogen lives on. There was no viable treatment available at that time. Today, modern science gives us the option to intervene but current government policy remains mistakenly rooted in the past.
Today, nearly all our major tree species are under threat and, unless there is a major change in policy, the same fate as the elm awaits many of them. It is happening to ash now because no direct action was taken to address the disease in 2012 when it was finally discovered, having been present and spreading at least since early 2000.
There are two choices facing us:
One is to stand back, to remain dependent on ‘improved biosecurity’, monitoring and ‘resilience’ (Defra, May 2018, “Tree Health Resilience Strategy”). If we do this, millions of trees will die. Our most threatened species have no natural resistance to these pathogens and ‘resilience’, the central plank of Defra policy which implies an ability to recover from infection is a dangerous illusion.
The alternative is to intervene – treating and saving as many trees as possible and recognising that, faced with invasive pathogens, the only real battleground is within the tree itself. NEM is working on a range of possible solutions.