This Quick scan was prompted by the first report of Phytophthora pluvialis in the EU (in Belgium) in 2024. 

The species is probably native to North-Western USA and has been introduced into New Zealand, the United Kingdom (UK) and Belgium. In the UK, P. pluvialis was reported for the first time in 2021. 

Known host plants are Larix kaempferi, Notholithocarpus densiflorus, Pinus patula, Pinus pinea, Pinus radiata, Pinus strobus, Pseudotsuga menziesii and Tsuga heterophylla. 

Phytophthora pluvialis can likely establish in parts of the EU including the Netherlands. Phytophthora pluvialis has probably already established in parts of Belgium and may have a wider distribution in Europe than currently known.

Frequent rainfall and high relative humidies are favourable for establishment and spread of the pathogen. Coastal areas that have been assessed to be favourable for the development of other tree affecting Phytophthora species that can spread by fog and wind-driven rain (P. ramorum, P. kernoviae and P. lateralis) may also be favourable for P. pluvialis. A more detailed assessment is needed to assess the potential area of distribution in the EU and the endangered area. 

Phytophthora pluvialis can cause various symptoms of which needle cast is most common. Infection can lead to growth reduction of the tree. • In NL, at least 10% of the forest area is covered by susceptible conifer species. The potential impact of P. pluvialis is, however, uncertain. It is assessed to be lower than for the UK because of less favourable climatic conditions and the absence of symptoms in the two trees found infected in Belgium (neighbouring country). However, winters are expected to become milder and more humid due to climate change making the conditions more favourable for P. pluvialis. The potential impact of P. pluvialis may, therefore, increase in the future.