Documents: Special Interest: Orchids:

2002 a bumper year for bugs

...five new-to-Britain pests identified by the RHS Top Ten Garden Pests 2002
by Royal Horticultural Society
February 23, 2003

Entomologists at the Royal Horticultural Society identified five new-to-Britain invertebrates in 2002 from samples sent by RHS members to the advisory service at RHS Garden Wisley.

The arrival of new pests is usually due to the importation of infested plants or plant material from abroad. One of the new arrivals, berberis sawfly, originates from central and southern Europe and has probably become established here now due to our changing climate.

Andrew Halstead, Senior Entomologist at the Royal Horticultural Society, said; " 2002 was an unprecedented year for new-to-Britain plant pests identified at Wisley. Increased importation of plants and plant material to Britain is the main cause of recent rises in 'aliens' appearing in the country. The RHS, through its members' advisory service, is tracking such 'aliens' and reporting them to the Plant Health and Seeds Inspectorate (PHSI), the DEFRA body responsible for trying to prevent alien plant pests and diseases entering Britain."

He continued; "Once a pest is established in gardens, it is generally too late for an eradication programme. We advise gardeners about available pesticides and / or biological and other controls and we continue to research the best ways such 'pests' can be dealt with."

The RHS received 30% more enquiries about garden 'pests' in 2002 than the previous year suggesting that gardeners are becoming more aware of the biodiversity in their gardens and want to find out more about it. Over 3,500 member enquiries were answered about 'pests' alone - the RHS advisory service annually deals with over 35,000 individual enquiries. (One-to-one gardening advice is offered as a benefit of RHS membership.) RHS advice on a variety of topics, including garden pests and diseases, can be found at www.rhs.org.uk/advice

Also announced this week are the Top Ten 'Garden Pests' concerning gardeners in 2002. Slugs and snails top the list for the third year running with many gardeners asking about more environmentally friendly ways of discouraging the unwanted molluscs.

New-to-Britain Pests 2002

Wisteria scale (Eulecanium excrescens)
Samples of this unusually large scale, up to 10mm long, were first received at Wisley from a London SE11 garden in June 2001 but the identity of the scale was not determined until April 2002. This scale is not only new to Britain but also new to Europe. It originates from Asia but also occurs in the USA. In Britain it is mainly a problem on Wisteria but elsewhere it attacks a wide range of fruit trees, including apple, almond, cherry, peach, walnut, and other woody plants such as sycamore and elm. So far the scale appears to be confined to south west London (Vauxhall, Chelsea and Earls Court). Wisteria can develop such severe infestations that they are killed. The wisteria scale has one generation a year with eggs hatching in early summer.

Elaeagnus sucker (Cacopsylla fulguralis)
Elaeagnus has few pests so the arrival to the advisory service of Elaeagnus shoots covered in sooty mould immediately aroused suspicions of a new pest. The first sample was received in March 2002 from a garden at Selsey, Sussex and was soon followed by others from Brighton in Sussex, Leigh on Sea in Essex, Cobham and Woking in Surrey. It has also been found as far north as Yorkshire. This pest sucks sap from the foliage and shoot tips which become soiled with honeydew and sooty mould. Heavy infestations cause early leaf fall. Elaeagnus sucker originates from eastern Asia and was first recorded in Europe in 1999 in France. It has several generations during the summer but the worst damage appears to occur during the spring.

Berberis sawfly (Arge berberidis)
Berberis sawfly originates from central and southern Europe although it has become more widespread in northern Europe in recent years, becoming a pest in Holland in 1996. Reports of defoliated Berberis bushes were received at Wisley in 2001 but by then the larvae had left the plants to pupate. The first adult sawfly was sent to Wisley from a garden at Church Langley, Essex in April, 2002. Further samples of larvae have since been sent to Wisley from other gardens in the London suburbs of Hertfordshire, Middlesex and Buckinghamshire. Berberis sawfly has two or possibly three generations during the summer. It causes severe defoliation in May-June and late July-September. Its main hosts are Berberis thunbergii and B. vulgaris, and Mahonia species can also be attacked.

Horse chestnut leaf-mining moth (Cameraria ohridella)
This tiny moth probably originates from Asia and was unknown in Europe until 1985 when it was found in Macedonia. It then spread rapidly throughout much of northern and central Europe. The first British sample came from a garden in Wimbledon in July 2002. This leaf miner has several generations during the summer; probably three in Britain but as many as five in warmer parts of Europe. The caterpillars cause brown blotch mines in the leaves that can be confused with damage caused by the fungus, Guignardia aesculi. Heavy attacks cause early leaf fall and loss of vigour. Several Aesculus species are attacked; other host plants are Acer pseudoplatanus, A. platanoides and A. pavia.

Cypress gall mite (Trisetacus chamaecypari)
A North American eriophyid mite that infests the shoot tips of Cupressus, Chamaecyparis and x Cupressocyparis leylandii. Affected shoots are yellowish white in colour and contain numerous microscopic creamy white mites. Damaged shoot tips dry up and die, leaving 2-3mm of brown dead growth at the shoot tips. This pest was sent to Wisley from a garden at Altrincham, Cheshire in October 2002.

Top Ten Garden Pests 2002

The Royal Horticultural Society's one-to-one gardening advice is one of the most popular benefits of RHS Membership. A team of horticultural advisors based at RHS Garden Wisley, Surrey, annually receive over 35,000 individual enquiries from RHS members. They also travel to all the RHS flower shows to dispense gardening advice to visitors.

By tracking the number of enquiries about individual problems, advisors can find out what has been troubling gardeners and monitor trends.

  1. Slugs and snails (various species)
    Many plants, especially seedlings and soft young growth on herbaceous plants and vegetables, are vulnerable to these pests. For the third year running, slugs and snails have been the number one garden pest.

  2. Vine weevil (Otiorhynchus sulcatus)
    Invariably a top three pest in recent years, vine weevil may become less troublesome in the future. The use of imidacloprid-based pesticides or the newly available cold-tolerant nematode for biocontrol of the larvae gives gardeners the opportunity for effective control. The larvae are destructive root feeding pests, especially of plants growing in pots. Adult beetles eat notches from the leaf margins of many plants.

  3. Rabbits (Oryctolagus cuniculus)
    Rabbit enquiries increased last year. Gardening in rabbit-infested areas can be a frustrating occupation as there are few plants that are entirely immune. New plantings are particularly attractive to rabbits and usually require protection with netting.

  4. Ants (several species)
    Although ants cause little direct damage to plants they often cause annoyance in gardens, especially when their nesting activities disrupt lawns and low growing plants in flower borders. Ant enquiries in 2002 were higher than usual.

  5. Deer (several species)
    Like rabbits, deer will damage a wide range of flowers, fruits and vegetables. Because of their larger size it is even more difficult to prevent deer gaining access to gardens. Both deer and rabbits are becoming more widespread and numerous in Britain.

  6. Soft scale (Coccus hesperidum)
    This sap-feeding insect occurs on many plants, but especially citrus, ivy, Ficus benjamina, ferns and bay trees. Infested foliage becomes sticky with honeydew excreted by the insects which live on the underside of the foliage. Soft scale is invariably the most troublesome of the various scale insects found on houseplants and in gardens.

  7. Woolly aphid (Eriosoma lanigerum)
    This sap-feeding insect is mainly a problem on fruiting and crab apples but it also occurs on pyracantha and cotoneaster. It produces fluffy white colonies on the bark of the trunk and branches. This aphid was more troublesome than usual in 2002.

  8. Glasshouse red spider mite (Tetranychus urticae)
    This tiny sap-feeding mite attacks many glasshouse and houseplants, and it also damages some garden plants during mid-late summer. Affected plants develop finely speckled foliage and can be killed or prematurely defoliated by heavy attacks.

  9. Cypress aphid (Cinara cupressi)
    Conifer hedges of Cupressus, Chamaecyparis and x Cupressocyparis leylandii often suffer extensive die-back and a frequent cause of this is the feeding activities of the cypress aphid in early summer. The die-back often does not become apparent until late summer, by which time it is too late for any treatment. It can take several years for a hedge to recover and badly damaged plants may need replacing.

    The prevalence of cypress aphid in some years, such as 2002, and the other well-publicised problems associated with Leyland cypress, means that very careful thought should be given to the selection of conifers for hedging purposes. The RHS has recently published a new Conservation & Environment Guidelines leaflet on hedges. It can be downloaded in full from the RHS website at www.rhs.org.uk/research/c_and_e_hedges.pdf

  10. Glasshouse mealybugs (several species)
    Many glasshouse and houseplants are susceptible to mealybugs. These small sap-feeding pests cover themselves with a fluffy white waxy substance. They often hide in relatively inaccessible parts of the plant, making them difficult to control, especially on tall conservatory plants.


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