THE arrival of a new tree disease in the UK has set alarm bells ringing. Phytophthora Pluvialis, a pathogen, is now in Europe for the first time and has so far been found in 13 sites across England. 

Discovered in a woodland in Cornwall, it has further been identified in Devon and Cumbria, forcing authorities to take immediate action. 

Boundaries are to be set up and targeted inspections will take place in Scotland in a bid to tackle the issue head on. 

How serious could this be? In short, very. Here's our guide to all we know about Phytophthora Pluvialis so far. 

What is Phytophthora Pluvialis and what species of tree does it affect? 

Phytophthora pluvialis is a fungus-like pathogen known to affect a variety of trees including western hemlock, tanoak, pine (Pinus radiata, Pinus patula and Pinus strobus) and Douglas-fir.

READ MORE: Boundary to be created to prevent spread of Phytophthora Pluvialis

It was originally reported in Oregon, USA in 2013 on tanoak and Douglas fir and was subsequently identified as the pathogen responsible for ’red needle cast’ of radiata pine in New Zealand.

Where did it originate in the UK? 

Phytophthora pluvialis was discovered in a woodland in Cornwall in September 2021, where it was found to be affecting mature western hemlock and Douglas-fir trees. This was the first time it had been recorded in Europe. 

Forestry Journal: General view of a western hemlock stand where P. pluvialis has been detected General view of a western hemlock stand where P. pluvialis has been detected

Following extensive surveillance, further outbreaks have been found in Cornwall, Devon and Cumbria. A total of 13 sites (as of November 23, 2021) have been identified. 

UPDATE: The illness has since been confirmed in Scotland in a woodland near Loch Carron in the north west of the country. 

What are the symptoms? 

Phytophthora pluvialis is known to cause needle cast, shoot dieback, and lesions on the stem, branches, and roots.

Forestry Journal: Dead natural regeneration of western hemlock under mature symptomatic western hemlock on which P. pluvialis has been detected alongside secondary colonisation by honey fungus (Armillaria ostoyae)Dead natural regeneration of western hemlock under mature symptomatic western hemlock on which P. pluvialis has been detected alongside secondary colonisation by honey fungus (Armillaria ostoyae)

What steps are being taken? 

Authorities are clearly worried about the new disease. So much so that in Cumbria, in the north of England, a boundary will be put in place to slow the spread of the illness.

Forestry Journal: Western hemlock demonstrating signs of the disease Western hemlock demonstrating signs of the disease Nicola Spence, the UK chief plant health officer, said this was part of "swift and robust" action and it came just days after Scottish Forestry confirmed targeted inspections will be carried out as a preventative measure. 

READ MORE: Inspections to take place in Scotland as concern mounts over Phytophthora pluvialis

These will primarily focus on the west of the country but landowners and forest managers are being asked to familiarise themselves with the symptoms of this disease and report any suspected infections through Tree Alert.

How serious could this be? 

In short, very. The arrival of Phytophthora pluvialis in the UK has set alarm bells ringing across the industry. 

The worst-case scenario is Phytophthora pluvialis inflicting on Douglas fir and/or Western Hemlock what Phytophthora ramorum did to Japanese larch or turning its attention to a tree species that is not currently on the radar of research scientists in Oregon, New Zealand or Cornwall.

The best-case scenario for P. pluvialis is retreat into relative obscurity like Phytophthora kernoviae.

You can read a more in-depth look at the new disease from Dr Terry Mabbett in December's Forestry Journal.