Disease control in flowers and shrubs
How to recognise common pests and diseases in ornamentals, how to prevent them, quarantine measures, disease notification and effective treatments.
There are many pests and diseases that could cause serious damage to crops and plants in England if allowed to become established. Therefore there are stringent measures that ensure pests and diseases cannot be brought into the country and, if they are, how they must be dealt with.
It is important that you can recognise early signs of ornamental pests and diseases in your plants in order to deal with the problem and - if necessary - inform your local plant health and seeds inspector.
This guide explains the symptoms, problems and methods of control for various diseases that affect ornamentals, including P ramorum and P kernoviae. It also covers pests that affect ornamentals, such as nematodes, and the licences and regulations you must follow when importing cut flowers.
Statutory action for sudden oak death P ramorum and P kernoviae
Phytophthora ramorum (P ramorum) is an exotic fungus-like plant pathogen which causes damage to trees, shrubs and other plants. It is also known as ‘sudden oak death’.
In the UK it has been found mainly on container-grown rhododendron, viburnum and camellia plants in nurseries. It has also been found on various types of:
- Californian bay laurel
- oak species
- other trees - ash, European beech, horse chestnut, sweet chestnut, sycamore and Winter’s bark
Symptoms of P ramorum vary depending on the plant affected. Signs of infection for:
- rhododendron include blight of shoots, twigs and leaves
- viburnum include stem base infection or brown to black leaf infection
- pieris include brown stem lesions leading to aerial dieback, similar to Rhododendron
- yew include needle blight of young foliage leading to aerial dieback
- trees include blackening of bark, leaves, or shoots. Bark infections appear as large cankers with discoloured outer bark that seeps red sap. When the outer bark is removed, inner bark has dead inner-bark tissue
The disease spreads through asexual spores produced on leaves of susceptible hosts. These can survive in plant debris for two winters and are dispersed by:
- rain splash
- wind driven rain
- ground water
Since the first confirmations, there has been a co-ordinated approach to controlling the disease, which aims to:
- contain the disease
- eradicate the disease
- gather evidence to create future policy
Action is only taken when the disease is confirmed and usually includes the:
- destruction of affected plants
- tracing of related stocks on horticultural plants moving in trade
- increased monitoring of imported host plants
P ramorum is a notifiable pest and statutory action is being taken to prevent its introduction and spread. If you believe the pest may be on your premises, you should immediately contact the Fera (Food and Environment Research Agency) Plant Health and Seed Inspectors Division on 01904 465 625 or email them at email@example.com.
Phytophthora kernoviae (P kernoviae)
P kernoviae is a fungal disease that causes similar damage and has similar symptoms to P ramorum.
P kernoviae produces similar symptoms to P ramorum and has been found present in the same hosts, though most findings have been on rhododendron. The main symptoms are:
- leaf blackening leading to necrotic lesions
- cankers on tree barks
- bleeding lesions on tree trunk - often dark blue to black
The infection can spread from leaf to leaf or plant to plant through:
- water splash
- airborne mist droplets
- movement of contaminated plant material
As P kernoviae is a recently described species, it has only been observed in a limited number of sites. Currently, it is being treated as part of the P ramorum study.
P kernoviae is a notifiable disease and statutory action is being taken to prevent its introduction and spread. If you believe the disease may be on your premises you should immediately contact the Fera Plant Health and Seed Inspectors Division on Telephone: 01904 465 625 or email them at firstname.lastname@example.org.
Fireblight is a serious disease caused by the bacterium Erwinia amylovora of apples, pears, Rosaceae trees and shrubs. Its hosts include:
- June berry
- flowering quince
- mountain ash
It is a quarantine disease, to prevent it moving - particularly into designated ‘protected zones’. However, it is now widespread throughout South and Central England due to its ability to move in planting material or aerially, eg along hawthorn hedges planted near railways, motorways and main roads.
Fireblight can affect all aerial parts of the host. Symptoms include:
- wilting and death of flower clusters after a blossom infection
- withering and death of young shoots - the tip of the shoot can bend to form a ‘shepherd’s crook’ shape
- leaves with necrotic patches, which spread from the leaf margin or the petiole and midrib, depending on the initial site of infection. These generally remain attached to the plant
- infected fruit turns brown or black and shrivels - however it usually stays attached to the plant
- cankering which may spread into the main stem and kill the plant by girdling. Externally, the cankers are usually sunken in appearance and surrounded by abnormal cracks in the bark. When the bark is removed, a reddish-brown discolouration of the underlying tissues may be revealed, often with a well-defined leading edge to the stained area
It spreads through infected planting material which often does not show symptoms. Initial infection occurs through wounds in young shoots or blossom. The disease can then spread through the main stem and kill the plant.
There are no chemical measures available to control fireblight. Nurseries selling host plants must register and be approved for issuing plant passports. If an infection is located, the Plant Health and Seeds Inspectorate (PHSI) has statutory powers to require removal of infected plants.
Premises that are registered to issue passports for plants being traded into EU Protected Zones must meet additional requirements including buffer zone freedom. If infection is confirmed on or near registered premises, the PHSI has statutory powers to prevent its spread by removal of the affected plants.
Fireblight is a notifiable disease and statutory action is being taken to prevent its introduction and spread. If you believe the disease may be on your premises you should immediately contact the Fera Plant Health and Seed Inspectors Division on 01904 465 625 or email them at email@example.com.
Nematodes are small, transparent, threadlike worms that are a common pest in the UK. Most nematode problems in ornamentals are caused by:
- Aphelenchoides ritzemabosi (A ritzemabosi) and Aphelenchoides fragariae - leaf and bud nematodes often found on nursery stock and herbaceous plants
- Ditylenchus dipsaci (D dipsaci) - stem or bulb eelworm often found on bulbs and herbaceous plants
- Meloidogyne spp - root-knot eelworm
As well as damaging plants through feeding, nematodes can also transmit viruses.
Nematode symptoms and damage
A ritzemabosi attacks plant parts above the ground and can show a number of symptoms including:
- bushy plant appearance - first stems are dwarfed and the plant must grow extra basal stems
- distorted and deformed leaves - feeding in the buds causes growth retardation
- blackened or dead leaves
- infected side shoots
- infection of leaves leading to yellow spots and blotches - a later symptom
- water-soaked bands and blotches on ferns - leaves become dark brown or black and eventually die
Symptoms or damage from D dipsaci include:
- discolouration or distortion of tissues - feeding of nematodes may kill affected plant tissues or the entire plant
- infested bulbs that are soft at the neck and show discoloured brown rings of dead tissue when cut through
- misshapen plant growth with distorted leaves or flowers
Stem nematodes can be spread in bulbs, bulb fragments or leaf debris through:
- wind blown contamination
- movement of surface water
- presence in the soil
Meloidogyne spp symptoms are often the presence of 2-centimetre long galls on roots, which can be an irregular shape. Nematodes attacks disrupt normal root function and plants will show nutrient deficiency, leading to wilting and death.
Nematodes can only be confirmed by laboratory examination.
There are several treatments you can consider to prevent nematode infestation.
Biological control - ‘green manure’ crops can control nematodes if you use them to clean up land before planting. The most effective crops are members of the Brassica family which are effective when chopped and introduced into soil.
Bio-insecticides - French marigold can be used to treat land between crops of field-grown trees and herbaceous plants. The variety ‘Ground Control’ is used in Dutch lily production and a kill rate of up to 95% has been claimed.
Plant on land without crops or weeds to ensure marigold roots are the only nematode food source. A biocide marigolds contain can kill the pests.
Cultural control - good general weed control will prevent the establishment and spread of stem and bud eelworms.
You should consider using hot water treatment to kill any infestations in herbaceous perennials. You should only expose plants to hot water at 44.4°C for 15 minutes to avoid damaging plant tissues. Bulb treatment requires a longer period of time.
You can also reduce the risk of flower damage by storing bulbs at 30°C for three weeks before treatment.
Leaf and bud nematodes can be transferred in cuttings and spread on propagation tools, dead and dying plant material and poorly composted material. You can avoid excessive moisture in propagation and space plants to avoid leaf contact. You should use disinfectants to routinely clean tools, equipment and surfaces.
You can follow similar prevention guidelines for all nematode species. You should ensure that:
- narcissus bulbs are sourced from a certified crop wherever possible and must be accompanied by a plant passport which confirms bulbs are free from stem nematodes. There is currently no certification scheme for tulips but they must have a plant passport. All passport plant stocks are inspected in the growing season by the Defra Plant Health and Seeds Inspectorate
- crops susceptible to attack by stem nematode should only be grown in the same field every four years. Groundkeeper bulbs should be destroyed
- machinery used during bulb production is regularly cleaned and disinfected. Bulb waste from grading should not be returned to agricultural land
- growing crops are regularly inspected for signs of stem nematode damage. Suspect bulbs and the bulbs next to them should be destroyed (destroy bulbs within a 1 metre radius - nematodes can move up to 1 metre in a season)
- all narcissus stocks are hot-water treated
- infected plants and fallen leaves are carefully removed from the garden or greenhouse and burned. Soil in affected nursery plantings should be fumigated
Pest and disease threat when importing ornamentals and cut flowers
You must follow certain plant health controls when importing cut flowers into the UK to prevent the introduction of plant pests and diseases.
For plant health purposes the three categories plant materials fall into are:
- prohibited - poses such a serious risk that import is only permitted under authority of a licence issued by the Fera or the Forestry Commission
- controlled - this includes cuttings, rooted plants and trees that are not prohibited, as well as bulbs, most fruits, certain seeds and some cut flowers. You usually need a phytosanitary certificate from the plant protection service of the exporting country
- unrestricted - presents little or no risk and is not subject to routine plant health controls. Includes nearly all flower seeds, some cut flowers and fruit, and most vegetables for consumption or processing - except potatoes
You can sometimes import prohibited or controlled plants under licence from Fera. You must make this application before you import and you may have to pay a fee. Fera can issue licences for the import, movement and keeping of:
- plants and plant material for scientific or trialling purposes
- soil and growing medium for physical or chemical analysis
- other plant material which would otherwise be prohibited entry
Imports of certain forest trees, wood, bark and some wood products are subject to legislation implemented by the Forestry Commission.
How to apply
To apply for an import licence, you must complete the relevant application form and return it to the following address:
Shared Services Directorate
PO Box 347
The costs you will incur when you apply for a licence are for:
- licences to import, move and keep prohibited soil or growing medium for physical or chemical analysis - £220
- renewal of the authority - £12
- renewal of the authority with changes to scientific or technical assessment - £100
- inspection of licensed premises to monitor compliance - £27 per hour
You need to enclose a copy of standard operating procedures for the work you are undertaking and can only get a licence issued in the name of an individual who is a permanent member of staff.
You should submit your application as soon as possible, at least one month before the licence is needed. Licences are valid for 12 months and must be renewed before they expire.
You may need a plant passport to move plants, seeds and plant products within the EU. You can find information on plant passports on the Fera website.
Quarantine measures are taken to keep foreign pests out of areas where they could cause damage to crops, trees and wild plants. Measures are based on a scientific assessment of the risks. Certification ensures that high quality planting material, substantially free from plant pests and diseases, is available to growers.
‘Pests’ are organisms that affect the health of plants by feeding on them or causing disease. They can be:
- other invertebrates
- other pathogens
Whether an organism is a potential quarantined pest is judged by a pest risk assessment (PRA).
A PRA uses biological, scientific and economic evidence to determine whether a pest should be regulated, and what measures should be taken against it.
PRAs follow an international standard and consider evidence such as:
- simple expert judgements - for example, what it feeds on, what its hosts are
- assessments of biological factors
- climate maps
- estimated costs and benefits of the measures needed to keep a pest out of an area
- costs and measures for eradicating an outbreak
They are written by plant health experts to inform public policy decision makers of the issues.
There can be a number of conclusions following a PRA, including that:
- specific treatments can be recommended, such as control measures
- exclusion or eradication is not warranted for low risk organisms
The Food and Environment Research Agency diagnostic tool
There are many forms of pests and diseases that affect ornamentals in the UK and have an economic impact on your business. They can vary in severity depending on the plant affected, so it is important that you recognise symptoms of diseases early to treat the problem and prevent it from spreading.
You can submit a sample to Fera’s Plant Clinic, who will then help you to diagnose any plant problems quickly. You can read about Fera’s Plant Clinic on the Fera website.
Diagnostic tools and techniques
SamTrack is Fera’s free online sample tracking system which allows you to easily access your sample information. It allows you to check:
- when Fera have received your sample
- who is dealing with your sample
- any pests or diseases that have been identified
- a summary of samples you have sent
- information outside normal working hours
To send them a sample you should:
- register for SamTrack on the Fera website
- select a sample
- complete a sample submission form - download sample submission forms from the Fera website (PDF, 274KB)
- pay the invoice once your results have been received - you can find a sampling price list on the Fera website
You must follow specific rules when packaging your samples. You can find sample selecting and packing information on the Fera website.
You should send your sample to Fera at the following address:
The Food and Environment Research Agency
You can also call the Plant Clinic Helpline on 01904 462 324.
You will receive disease and pest information about your sample within three working days from Fera’s receipt.
For more information, you can email the Fera Plant Clinic at firstname.lastname@example.org.
Organisations that can help
Controlling the spread of pests and diseases in flowers and shrubs is essential, and there are a number of bodies that can offer help and support.
Fera’s PHSI is responsible for import and export inspections of plants, plant products and certain other products such as soil, issuing phytosanitary certificates and scientific licences. You can call the Defra Plant Health Division on Telephone: 01904 455 174 or contact your local PHSI. Download a list of PHSI offices from the Fera website (PDF, 25KB).
One of the major roles of Defra is to help the farming industry operate as efficiently as possible. Defra administers European Commission support policies that provide around £3 billion to UK agriculture. They also oversee a number of agencies that work with arable farmers, imports and exports of crops, and implement pest and disease controls. You can call the Defra Helpline on 03459 33 55 77.
The Health and Safety Executive’s Chemicals Regulation Directorate (CRD), formerly Defra’s Pesticides Safety Directorate, is responsible for ensuring the safe use of pesticides or plant protection products - and their approval process - for agricultural, horticultural and home garden use.
Only approved pesticides can be sold, supplied, used, stored or advertised in the UK.
CRD is also responsible for biocides, industrial chemicals and detergents to protect the health of people and the environment.
For further information on pesticides, you can call the Chemicals Regulation Directorate Helpline on 01904 455 775.
The Organic Food Federation promotes organic methods and maintains high standards and best practice within the farming sector. For more information, you can call the Organic Food Federation on 01760 720 444.
In England, the Farm Advisory System advises farmers about cross compliance. For further information, call the Cross Compliance Helpline on 0345 345 1302. Alternatively, for information on cross-compliance requirements, see the guide on cross compliance: the basics.
For more general enquiries, you can call the Defra Helpline on 03459 33 55 77.
The RPA is responsible for licences and schemes for growers as well as for running the Single Payment Scheme (SPS). For more information about SPS and how it can help your farming business, you can call the RPA Helpline on 0345 603 7777.
The National Farmers Union (NFU) represents the farmers and growers of England and Wales. It aims to promote successful and socially responsible agriculture and horticulture, while ensuring the long term viability of rural communities.
Fera Plant Health and Seed Inspectors Division
01904 465 625
Chemicals Regulation Directorate Helpline
01904 455 775
Defra Plant Health Division
01904 455 174
03459 33 55 77
0345 603 7777
Cross Compliance Helpline
0345 345 1302
Organic Food Federation
01760 720 444