Phytophthora ramorum — Ramorum Dieback of Larch

Phytophthora ramorum (P. ramorum) is a fungus-like pathogen of plants that is causing extensive damage and mortality to trees and other plants in parts of the United Kingdom. It has also been found in a number of European countries, but mostly on plants and shrubs, especially rhododendron, viburnum and camellia, and has caused significant damage and mortality to many trees and other plants in parts of the USA.

However, few trees in the UK were affected until 2009, when P. ramorum was found infecting and killing large numbers of Japanese larch trees in South West England. Then in 2010 it was found on Japanese larches in Wales, Northern Ireland and the Republic of Ireland, and 2011 it was confirmed at locations in western Scotland.

This sudden change in the pathogen's behaviour was the first time in the world that P. ramorum had infected and sporulated (reproduced) on large numbers of a commercially important conifer tree species. It was also an unexpected setback to efforts to tackle ramorum disease.

We and our partners have moved quickly to respond to this development. Full details about the pathogen and what's being done to research it, minimise its impact, and support affected woodland owners are available at the links on this page.

Symptoms

Larch can suffer from a number of diseases, not all of them serious, so before reporting a suspected case, check the symptoms of ramorum disease carefully. Typical signs include needle wilting and browning, shoot dieback, and resinous cankers on branches and stems.

Key Documents

Among the key documents and guidance available are:

• Symptoms guide. Larch can suffer from a number of diseases, not all of them serious, so before reporting a suspected case, check the symptoms of ramorum disease in the Forestry Commission symptoms guide.
• Replanting advice. Restocking (replanting) affected sites with larch or other species that are susceptible to P. ramorum is not recommended, so guidance sets out options for the woodland owner.
• Biosecurity precautions. Advice on precautions to take when visiting or working in an infected woodland to limit the risk of accidentally spreading the disease on clothes, tools or vehicles.

P. ramorum Found on Sitka Spruce

The Forest Service of the Irish Department of Agriculture, Fisheries & Food has reported the first finding of a Sitka spruce (Picea sitchensis) in the wild infected with Phytophthora ramorum. Sitka spruce is the most widely grown timber-producing tree species in the United Kingdom.

Plant Health Inspections

Inspections of trees and woodland by Forestry Commission plant health inspectors play an important role in efforts to manage outbreaks of ramorum disease. Guidance for Plant Health Inspectors can help you understand what to expect if an inspector needs to visit your premises.

Learn more about how phosphite fungicide treatments combat Phytophthora, or see our full library of case studies and research.