If control measures are unsuccessful then nationwide spread is highly likely. The establishment of P. pluvialis has been widespread in countries with similar climates. Very little is known about distribution methods, other than the similarities to other Phytophthora. Phytophthora are oomycetes, otherwise known as water moulds, and thrive in wet and humid conditions. Our relatively wet and humid climate, especially on the West coast, provides ideal conditions for growth, as seen in the location of the outbreaks mentioned above.
For commercial timber stands it is to be expected that infection will cause significant yield loss, principally through considerable needle cast. There is also the possibility, though this has not yet been recorded, that seedling production of those affected species will be affected. As Douglas fir is one of our primary timber species, especially in the south, this has serious ramifications on the landscape into the future. It is not yet known whether P. pluvialis will be a primary causal disease agent in the UK, in all current infections other pathogens are also present.
Natural regeneration as an establishment practise may become impossible in these affected forests, especially those, such as Western hemlock stands, where natural regeneration is a key method of restocking. The photo below shows an example of a previously healthy understory of Western hemlock, now completely dead. Usually, to increase a woodland’s resilience to disturbances, multiple species are planted. It should be assumed that as the native ecosystem is a mixed species forest, mixed forests in the UK will be similarly affected.