Pests and Diseases: Threats to our tree populations

Adam Sharman has led RFS Workshops on Tree Health - Pests and Diseases. Here he asks whether you are ready for the challenges ahead.

By Adam Sharman · March 1, 2018

It would be quite easy to turn this post into a soapbox for a rant about Grey Squirrel (Sciurus carolinensis).  I attended the RFS’ Eastern Region Winter Lecture recently, delivered by the venerable Bede Howell on Quercus sp. timber production and he explained that in France, they do not have grey squirrel; a most enviable position.

A second species that could easily be targeted is deer. There are strong arguments to be made for a cull to control numbers. The damage they do to ground flora as well as trees is significant and can run into thousands of pounds each year, not including damage to vehicles and insurance premiums.

Whilst they are a significant threat to many of our native tree species here in the UK, there are many other threats a diligent tree manager needs to be aware of.

The Political Angle

Being an island, we are at constant threat from new pests and diseases. These could be in live plant form, seeds and transplants, mulch and in raw timber form. The Animal and Plant Health Agency (APHA) works tirelessly at ports to ensure that any new threats are identified at entry and then preventative action is taken as necessary. But it is not just in these plant materials that threats lurk – it is packing materials, such as pallets and crates, too.

Packaging materials have been an easy way to distribute for many decades. Indeed, it was during WW2 that American crates brought with them the fungal spores of Splanchnonema platani, more commonly known as Massaria of London Plane (Platanus x acerifolia). 

Trees are under constant threat from a variety of pests and diseases. They have developed ways to defend themselves, but  pest or disease will often win the battle. Despite this, there are steps the woodland or forest manager can take to try and prevent the spread. Above: honey fungus 

Biotic and Abiotic Threats

Threats to trees can be divided into biotic and abiotic hosts – simply, those that are living and those that are not.

  • · Biotic threats are insect, mammal, fungi or bacterial.
  • · Abiotic can be the wind, road salt or mechanical damage, for example.

Depending on the location of your woods, you could be managing threats from both of these classifications.

Help Prevent the Spread

Whilst many threats are difficult to control once they infiltrate, there are some actions that can be taken. For example, fungal and bacterial spores can spread in the wind, on woody material, but also shoes, dogs’ paws, tools and vehicle tyres. Precautions such as spraying off tyres, equipment and shoes with disinfectant spray can help prevent helping spread an infection. If your woods have public access, signage encouraging walkers to be vigilant may also assist.


Education is important. Learning to identify threats and then learning how to manage them will increase your vigilance. Looking for changes, supported by your knowledge of your woods will put you in a better position to try to manage a threat before it becomes a much more serious affliction.


Having a working knowledge (because no one can become an expert over night!) of pests and diseases will help your management skills.

Forest resilience is one of the hottest topics in forestry right now. Making the correct choice regarding species selection (whilst at the same time being able to predict the future) is part of the job spec of a woodland or forestry manager.

We are an island nation. We rely (arguably too much) on imported product. By default, we are exposing ourselves to a raft of new pests and diseases every day. Therefore, being vigilant to these threats will assist with protecting the future of our forests.