Another unwelcome invader
A short article in the January 2022 edition of the Royal Horticultural Society magazine, Garden, grabbed my attention, so I set about finding out more.
The article reported a new-to-the-UK tree disease caused by a fungus-like pathogen, Phytophthora pluvialis, spotted in forests in Cornwall, the West Country and the Lake District. But by the time I was on the case, the disease was spreading closer to home - in forests near Loch Carron, Ross and Cromarty.
Phytophthora, ominously meaning ‘plant destroyer’, is a genus of fungus-like organisms containing around 170 known species with a worldwide distribution.
The genus, which includes the pathogens that cause potato blight and sudden oak death, has been responsible for massive crop failures, economic loss and environmental damage.
Phytophthora are called ‘fungus-like’ since they behave like fungi but differ from them, and from all animals and plants, in several key features of their reproduction and chemical makeup. This places them in an ill-defined group of misfits called protists, which also includes amoebae, kelp and slime moulds.
Phytophthora pluvialis was discovered in Oregon, USA, in 2013, where it resides in soil and watercourses, and mainly infects Douglas fir.
Its recognition in Cornwall during 2021 was the first identification of this particular Phytophthora species in Europe.
Thought to have arrived here on imported live plants, its spores germinate in water and can be spread, for instance, on shoes, tyres and animal paws.
The pathogen infects a variety of trees, including western hemlock, Douglas fir and several pine species, causing needle shedding, shoot dieback and lesions on the branches, trunks and roots of infected trees.
Forestry and Land Scotland and its policy section Scottish Forestry took rapid action – surveillance to detect infected forests, restrictions on the movement of timber and trees, and asking the public to report suspicious tree lesions.
But since the European climate is ideal for P pluvialis to thrive, and its favoured trees are commonly grown here, like so many other plant pathogens, it seems likely that this one is here to stay for the long term.
Forestry and Land Scotland asks foresters and the public to be vigilant for signs of Phytophthora pluvialis.
Anyone who thinks they might have spotted signs of the disease should report it using the online TreeAlert system on the on www.forestresearch.gov.uk website.