Pests and diseases

What are we looking out for?

There are hundreds of pests and diseases that are currently a potential threat to UK trees. The Government has created the UK Plant Health Risk Register which records and rates risks to UK trees (and other plants) from plant pests and diseases.

Working with the UK Plant Health Risk Group (the group that maintains the UK Plant Health Risk Register), Observatree has identified those pests and diseases which are of the highest concern at the moment. They are the ones:

  • most likely to arrive in the UK
  • that have already arrived and we are concerned about their spread
  • which have the potential to cause the most serious and widespread impact on commercial forestry, amenity woodland and ecological systems

Below are the pests and diseases we are most keen to hear about. If you think you have spotted any of their signs, please report them.

Download a poster of all our priority pests and diseases

Pest and disease calendar – A4 (signs and symptoms)

Also see Pest and Disease by Tree Species

Take a look at some other pests and diseases of interest

Acute Oak Decline

  • Infecting mature oak across the UK
  • Oozing of dark fluid from cracks in the bark
  • Thought to be caused by a bacterium

Asian Longhorn Beetle

  • Native to eastern China, Japan and Korea
  • Can infest a wide variety of trees
  • Beetles emerge from spring onwards

Bronze Birch Borer

  • Wood-boring Buprestid beetle
  • Native to North America
  • Serious pest to birch trees

Chalara Dieback of Ash

  • Chronic fungal disease
  • Believed to have originated in Poland
  • Widespread across Europe

Citrus Longhorn Beetle

  • Associated with Japanese maple trees
  • Antennae longer than their bodies
  • Extensive range of hosts

Dothistroma Needle Blight

  • Known as Red Band Needle Blight
  • Needles develop yellow and tan spots
  • Widespread across the UK

Elm Zigzag Sawfly

  • Feeds only on Elm leaves
  • Distinct zigzag eating pattern on leaf
  • Defoliates trees leaving them vulnerable to further attack

Emerald Ash Borer

  • Native to Asia and Eastern Russia
  • Highly destructive to ash trees
  • Feeds on conductive tissue

Great Spruce Bark Beetle

  • Tunnels into Spruce bark
  • Adults are 6-8mm long and 2.5-3mm wide
  • Accidentally introduced to the UK in 1982

Horse Chestnut Leaf Miner

  • First observed in Macedonia
  • Larvae damage leaves and stunt growth
  • Rapidly spread out across Europe

Mountain Ash Ringspot

  • Symptoms first recorded in 1960
  • Distribution over remote areas of Scotland
  • Bright chlorotic ringspots

Oak Lace Bug

  • First observed in Europe in 2000
  • Attaches eggs to the underside of leaves
  • Leaves lose their green colour

Oak Processionary Moth

  • Feeds on Oak leaves
  • Threat to human and animal health
  • Distinctive patterns of movement

Oriental Chestnut Gall Wasp

  • Adult female is 2.5-3mm long
  • Confirmed as present in the UK
  • Mainly spread via infested plant material although females can fly

Phytophthora austrocedri

  • Fungus-like plant pathogen
  • Juniper is the main host in the UK
  • Found in the UK in 2011

Phytophthora lateralis

  • Main cause of Lawson Cypress mortality
  • Attacks and kills at the roots
  • Discovered in the UK in 2010

Pine Processionary Moth

  • Not yet established in the UK
  • Adults of both sexes can fly
  • Colonies are active throughout winter

Plane Lace Bug

  • Eats only plane trees
  • Lays its eggs on the underside of leaves
  • Moving into Northern Europe since 1964

Plane Wilt

  • Weakens and kills plane trees
  • Pathogen is present in Europe
  • No spread in the UK as of yet

Red-necked Longhorn Beetle

  • Native to parts of East Asia
  • 22-38 mm in length with a red neck
  • Mainly found on Cherry

Sirococcus tsugae

  • Found in several GB locations on Cedar
  • Characteristic ‘pink’ dead needles
  • Dispersed by rain splash and strong winds

Sweet Chestnut Blight

  • Fungus grows in and beneath the bark
  • Produces Oxalic acid, lowering pH
  • Cankers eventually girdles the tree