Tree Health News - December 2017

4 December 2017

News in brief, in depth and new guidance on pests and diseases from Forestry Commission England.

Read the full newsletter here.

News in brief:

Oak Processionary Moth (OPM) - We’ve reached the end of this year’s OPM season survey and control progamme in the affected areas of London, the South-East and West Berkshire. Having collated the results we held our usual annual ‘wash-up’ event on 23 October to review what worked well and what can be improved for the future. A summary report of our findings will be published on the OPM pages of our website in due course. 

Ramorum disease update - Low level symptoms continue to be observed in the vicinity of previously confirmed infection (larch or rhododendron), mainly affecting individual or small groups of trees, and even single crowns and individual branches. No observations of wide-spread infection have been observed.

Biosecurity FAQs - In her latest post on the ‘Out of the Woodwork’ blog, Dr Katherine Deeks, our biosecurity officer, takes a look at some of the common biosecurity questions she and the team are asked when they’re out and about, delivering talks or training. To find out more and to receive regular biosecurity updates visit the blog site and sign up as a subscriber.

Chalara dieback of Ash - There has been a decline in the number of new sites being reported in England and Wales this year. However we are now starting to see a shift from new sites to more significant impacts on known infection sites in mature ash trees and ash-dominated woodlands and landscapes across the UK – in particular in Norfolk, Suffolk, Sussex, Kent and moving into Hampshire. The overall impact is being seen primarily in terms of trees in woodland, but it should be noted that there is currently limited data on the impact on non-woodland trees.

In Depth:

Better protection against Xylella - The European Union has approved increased protection against the risk of the plant bacterium Xylella fastidiosa crossing national borders, including the United Kingdom’s. 

Although Xylella is best known for devastating olive trees in Italy, it can and does infect a wide range of other plants, including oak, and has been found elsewhere in mainland Europe. 

It would be difficult to eradicate if it was to get into the UK, so in September Michael Gove, the Environment Secretary, wrote to the European Commission stressing that if EU protections were not increased, the UK would consider its own measures. These could include a suspension of high-risk imports. 

The new measures include strengthened requirements on the movements of high-risk plants, and require quicker responses to potential findings of the disease.

Following the vote Mr Gove said: 

“I am pleased this has been taken forward. We will keep the risk level under continuous review to determine whether further measures are needed to keep the disease out of the UK. 

“When we leave the EU we will have an opportunity to examine all our national biosecurity measures on plant imports to ensure they are as robust as possible.” 

The new measures are expected to be published before the end of the year. They will supplement measures already in place in the UK which require arrivals of plants of certain high-risk species to be pre-notified to the plant health authorities, enabling them to carry out targeted inspections and wider surveys for disease. 

The move was supported by a number of other EU Member States, and the full announcement can be read on GOV.UK.

New guidance published:

We have published on our website the following new and updated guidance to aspects of managing and identifying certain pests and diseases.

Juniper guidelines 

These guidelines provide comprehensive advice about planting, regenerating and managing juniper (Juniperis communis) in the context of the threat from Phytophthora austrocedri. Juniper is one of only three conifer species native to the United Kingdom, and these guidelines will be particularly useful to landowners wanting to play their part in conserving this valuable but declining species and habitat. The guidelines are published as a downloadable PDF. 

Pine pitch canker field guide 

We have also published a Pest Alert and a field guide to identifying the symptoms of pine pitch canker, which is caused by the fungus Fusarium circinatum. Also known as pitch canker of pine, it is primarily a disease of pine (Pinus) trees, including Scots pine (Pinus sylvestris). However, Douglas fir (Pseudotsuga menziesii) can also be affected. Both are commercially important in the UK, while Scots pine is also important as a native species of conservation significance. Although pine pitch canker is not known to be present in the UK, it has been reported elsewhere in Europe, so there is a heightened risk of its accidentally entering the country on seeds, planting stock or contaminated machinery. We therefore encourage all tree and nursery professionals and importers of wood and wood products to familiarise themselves with the symptoms, to be vigilant for it, and to report suspected cases. The field guide and the Pest Alert, written by Forest Research scientists, are published as downloadable PDFs. 

Replanting on ramorum disease sites 

Updated guidance on replanting trees on sites where the previous trees, usually larch, have been felled to control ramorum disease, is also now available. Ramorum disease is caused by the organism Phytophthora ramorum, the spores of which can remain active in soil for several years after infected plants have been removed. Replanting with species which are susceptible to it is therefore not advised. Forest Research scientists have drawn on eight years of experience of the disease on larch and other trees to update the guidance, particularly the lists of conifer and broadleaf species which can be used. To access the guidance, which is published as a downloadable PDF, visit and follow the link to the “Advice to owners, agents and the industry” page. 

Emerald ash borer contingency plan 

The contingency plan for an outbreak of emerald ash borer (Agrilus planipennis; EAB) has been reviewed and updated, in line with our commitment to review it at intervals. EAB is a destructive pest of ash trees which has destroyed millions of trees in North America since being introduced from Asia, and has been spreading westwards across the Eurasian landmass towards western Europe. The updated plan includes the latest information about the distribution of the pest in Europe, and about the latest biological control trials in the United States.