Update on the situation of Phytophthora pluvialis in the United Kingdom, and first record on Larix trees
Phytophthora pluvialis (EPPO Alert List) was first detected in the EPPO region in 2021 in the United Kingdom affecting western hemlock (Tsuga heterophylla) and Douglas-fir (Pseudotsuga menziesii) (EPPO RS 2021/227, RS 2022/060). During surveys done in England in 2022, P. pluvialis was also detected in a group of about 10 Japanese larch (Larix kaempferi). The symptoms were similar to those observed on western hemlock and Douglas-fir: multiple cankers on branches, and in some instances main stems, defoliation and needle blight. Pathogenicity tests were performed on two- to three-year-old larch trees of European larch (L. decidua) and hybrid larch (L. eurolepis), and showed that these species are potential hosts.
As of January 2024, there were 6 demarcated areas in England (Cornwall and Devon, Cumbria, Gloucestershire, Herefordshire, Shropshire, Surrey), 3 in Scotland (Argyll and Bute, Isle of Bute, Ross-shire), and 5 in Wales (Carmarthenshire, Crychan, North West and Mid Wales, Powys, South East Wales). A map of the demarcated areas is available at https://www.gov.uk/guidance/phytophthora-pluvialis. As the risk of movement with wood material was shown to be low, restriction of movement of host plants now only applies to plants for planting and no longer applies to wood or isolated bark.
Sources
Pérez-Sierra A, Chitty R, Eacock A, Wylder B, Biddle M, Quick C, Olivieri L, Crampton M (2024) First report of Phytophthora pluvialis causing cankers on Japanese larch in the United Kingdom. New Disease Reports 49, 12246. https://doi.org/10.1002/ndr2.12246
England: https://www.gov.uk/guidance/phytophthora-pluvialis
Wales: https://www.gov.wales/phytophthora-pluvialis