In recent years there has been an increase in the number of pests and diseases arriving from abroad, largely attributed to the rise in volume and diversity of plants and plant products (e.g. fruit and timber) being imported from an increasingly diverse range of sources. Changes in climate and subsequent phenological changes may also increase the risk of pests and diseases becoming established.

The pests and diseases described on this page are either not known to be present, or are of limited distribution, and some are under eradication in the UK. 

Plants showing symptoms or signs of the pests and diseases below (with the exception of Fuchsia gall mite and Box tree moth) should be reported to the Animal and Plant Health Agency (APHA).

Diseases

 
Chestnut blight
Chestnut blightA fungal disease (Cryphonectria parasitica) that poses a significant threat to sweet chestnut in the UK. It has devastated American chestnut in Northern America and sweet chestnut in Europe.

Symptoms: Cankers swollen or sunken form on the trunk, on which masses of yellow-orange to red-brown pustules (fruiting bodies) form. Branches die back and eventually the tree may be killed.

Where present: Asia, Africa, North America, and Continental Europe. It was observed for the first time in the UK in 2011 in Warwickshire and East Sussex. More recently it has been observed at sites in Devon, Dorset, Kent and east London.
 
RHS advice on sweet chestnut blight
Forestry Commission information on sweet chestnut blight

Image courtesy of USDA Forest Service
Phytophthora
Phytophthora austrocedri on juniper(Many species, but controlled species include Phytophthora ramorum, P. kernoviae and P. austrocedri)

Fungus-like pathogens that produce waterborne spores (zoospores) which are spread by water, in soil and on plants.

Symptoms: Browning and die-back of foliage. Lesions form under the bark causing brown/ black discolouration.

Where present: Some of the controlled species are present in the UK and becoming more widespread (e.g. P. ramorum); others are not present (e.g. P. pinifolia).

Forestry Commission: Phytophthora ramorum
Forestry Commission Phytophthora austrocedri
Forestry Commission Phytophthora lateralis
Forestry Commission Phytophthora kernoviae
 
Rose rosette virus
Rose rosette virusRose rosette virus infects a wide range of cultivated and wild rose species, and is spread by the microscopic mite, Phyllocoptes fructiphilus.

Symptoms: Increased production of thorns and vegetative shoots, usually coloured red; distorted leaves with red pigmentation; stunting, and often death.   

Where present: Canada, USA and India. Not present in the UK.

More information (from Missouri Botanical Garden).

Image courtesy of Missouri Botanical Garden
 
 
Wilt of oak and plane

Plane wiltVascular wilt diseases caused by two different species of the fungus Ceratocystis: (C. fagacearum and C. platani). Oak and plane are the two main hosts.

Symptoms: Both cause wilting of the leaves and die-back of the crown. Staining occurs in the xylem of affected trees.

Where present: Oak wilt widespread in the USA, plane wilt present in mainland Europe. Neither present in the UK.

Forestry Commission information about oak wilt
Forestry Commission pest alert about plane wilt

Image courtesy of Maxime Guérin
 
Xylella fastidiosa

Xylella symptomsThe bacterium Xylella fastidiosa is one of the biggest risks to the UK horticultural industry and wider landscape. It infects a wide range of plants including many species grown in gardens, such as cherry, hebe, lavender, oak and rosemary.  The bacterium causes symptoms including leaf scorch, wilt, dieback and plant death. Unfortunately these symptoms are easily confused with stresses such as frost damage and drought, or other plant diseases. Xylella is spread between plants by insects such as froghoppers and leafhoppers which feed on infected plants. However, long-distance movement of the disease is most likely to occur through trade in infected plant material.

Xylella is native to the Americas where it causes disease in many crops including citrus, coffee and grapevine. Until recently Xylella was absent from Europe but in 2013, Xylella was identified as the cause of death of olive trees in Italy. Since then it has been found in France and Germany (on oleander and polygala), on numerous ornamental plants (including cherry trees) in the Balearic Islands, and most recently in June 2017 it was confirmed in an almond orchard in Alicante, mainland Spain.

RHS Advice on Xylella fastidiosa

Defra guidance document on implications of Xylella fastidiosa for importers and professional users of plants

Reports of Xylella fastidiosa in Europe (the EPPO region)

Xylella fastidiosa host list

IPSN poster showing symptoms of Xylella infection

Image courtesy of Penn State Department of Plant Pathology and Environmental Microbiology Archives, Bugwood.org

 

 
Zebra chip
Zebra chipA bacterium (Candidatus liberibacter solanacearum) spread by psyllids (plant suckers). Five strains (haplotypes) occur: two affecting potatoes and related crops; three affecting carrots and celery.  

Symptoms: Solanaceous plants (potatoes, tomatoes etc.) show stunting, chlorosis, leaf scorching and purpling of foliage. Fruits fail to set or are misshapen. Potato tubers display striped browning when cooked, hence the name zebra chip. Carrots become stunted, with discoloured, curling leaves.
Zebra chip on potato tubers
Where present: North and Central America, New Zealand (on solanaceous crops) and Europe (on carrots and celery). Not present in the UK.

CABI invasive species datasheet
EPPO datasheet

Images courtesy of Ministry for Primary Industries, New Zealand

 

Pests

 

Oriental chestnut gall wasp
Oriental Chestnut Gall WaspOriental chestnut gall wasp (Dryocosmus kuriphilus) is a small insect (2.5-3mm) with a black body and orange-brown legs whose larvae feed within the buds of trees.

Symptoms: Green, rose-coloured or red galls up to 4cm in diameter on the buds, leaves, and leaf stalks. Leaf distortion as a result of the growth of the galls. Leaves affected by the gall wasp can drop early, or remain on the tree throughout the winter

Where present: Originating from Asia, this species arrived in Europe in 2002 and was first recorded in the UK in 2015 - it is now fairly widespread throughout south east England.
 
RHS advice on oriental chestnut gall wasp
Forestry Commission information on oriental chestnut gall wasp

 
 
Box tree moth
Box tree moth (caterpillar)Box tree caterpillars are moth larvae that feed on box plants. The pest (Cydalima perspectalis) is native to Japan, Korea and China but established in Europe in 2005. It was discovered in UK gardens in 2011.

Symptoms: Severe defoliation of box. Caterpillars are green/yellow with a black head and thick black and white stripes along their body, infested plants are covered in webbing.

Where present: Present in the UK; widespread in London and surrounding areas.

CABI invasive species datasheet
RHS advice page

 

Fuchsia gall mite
Fuchsia gall miteA microscopic gall mite (Aculops fuchsiae) from South America that causes severely distorted growth on fuchsias. The mites infest new growth at the shoot tips where they suck sap and secrete chemicals that prevent normal growth. Probably arrived in the UK on fuchsia cuttings.

Symptoms: Growth at the shoot tips becomes a mass of yellowish green or reddish-pink distorted tissue.

Where present: USA and Europe (France, Guernsey, Jersey). Widespread in southern England.

RHS advice page
CABI invasive species datasheet

 

Longhorn beetles (Asian and Citrus)

Asian longhorn beetleThe larvae of Asian and Citrus longhorn beetles (Anoplophora glabripennis and A. chinensis) feed within trunks, branches and roots of a wide range of deciduous trees and shrubs. The tunnelling can cause substantial damage to healthy trees. Can be confused with native longhorn beetles but these are unlikely to affect healthy trees.

Symptoms: The most obvious sign of activity are circular ‘exit’ holes around 10mm in diameter. The larvae of Citrus longhorn beetles feed on the lower trunk and roots whilst Asian longhorn beetles are found higher up the tree.

Where present: Canada, USA, China and Korea (Asian longhorn beetle); Asia and Italy (Citrus longhorn beetle). Not present in the UK; an Asian longhorn beetle colony in Kent is thought to have been eradicated.

RHS advice page
Forestry Commission pest alert

Image: Asian longhorn beetle, courtesy of Forestry Commission.

 

Processionary moths
Oak processionary mothOak processionary moth (Thaumetopoea processionea) and Pine processionary moth (T. pityocampa).

Oak processionary moth (OPM) and pine processionary moth (PPM) are defoliating pests of oak and pine, respectively. The caterpillars have allergy-inducing hairs that can cause breathing problems and rashes.

Symptoms: Can defoliate oak or pine trees. The caterpillars are covered in long white hairs, and move in distinctive nose to tail processions. OPM caterpillars produce white webbing nests in oak trees in early summer. PPM caterpillars produce nests in winter on pine trees.

Where present: OPM is widespread in west London plus outbreaks in Surrey and Hertfordshire; containment and eradication measures are in place. PPM is not present in the UK but is present in countries in Africa and Europe (including France, Italy and Spain).

RHS advice page on oak processionary moth
Forest Research  - oak processionary moth
Forestry Commission information on pine processionary moth


 
 
Red palm weevil
Red palm weevilRhynchophorus ferrugineus is an important pest of crop and ornamental palm species including coconut and date palm. Since the 1980s it has rapidly expanded its geographical range westwards.

Symptoms: Larvae and adults hollow out the interior of the palm tree, often the plant shows no sign of deterioration unless the damage is severe. The plant is then susceptible to collapse. Infestation often leads to the death of trees.

Where present: Africa, Asia, Europe (including France, Italy and Spain), Oceania and the USA. Not present in the UK.

CABI invasive species datasheet
Red palm weevil factsheet USDA APHIS

 


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