Recently discovered in a woodland in Cornwall is the pathogen Phytophthora pluvialis. There are over 170 described Phytophthora species, with an estimated 100-500 yet to be uncovered. Interestingly, and rather tellingly, the name Phytophthora derives from the Greek for “the plant-destroyer”. P. pluvialis was first described in 2013, Oregon, USA on tanoak (Nothilocarpus) and Douglas fir (Pseudotsuga menziesii), growing in intimately mixed forests. The disease has also been confirmed on Radiata pine (Pinus radiata), Mexican yellow pine (Pinus patula), Weymouth pine (Pinus strobus), and Western hemlock (Tsuga heterophylla).
Douglas fir, and to a lesser extent Western hemlock, are two of the key conifer species which occur in southern England. Many of the commercial timber stands in the south include one or both species. Without digressing into the fundamental attributes of sustainable forest management, there is a need to balance biodiversity conservation and enhancement, and social inclusion with the commercial aspect which growing valuable conifer brings. Planting purely native broadleaved woodland is a laudable endeavour, but as the old foresters’ saying goes, “the wood that pays is the wood that stays”. This is to say that for landowners a financial return is essential from woodland areas, which often funds less commercially viable, but more environmentally driven work elsewhere. If P. pluvialis develops into a major threat to our lowland conifer forests, the pool of suitable species is reduced further, and may have severe implications on forest and further countryside management across the affected area.
P.pluvialis infection has been confirmed on all stages of tree growth, from seedling to mature specimens. This has serious implications on all examples of host species, from mature stands to nursery stock. The photos (below) show some of the described symptoms of P. pluvialis, which include:
- Needle cast
- Shoot dieback
- Lesions on stem, branch, and roots
The pathogen has currently been identified in Cornwall, Devon, Cumbria, Wales, and north-west Scotland. Whilst these are localised outbreaks, it should be assumed that the disease is, or has the potential to be, country wide.