Royal Horticultural Society Announces the Top 10 Garden Pests and Diseases of 2015

Friday 18 March 2016

• Slugs and snails knocked off the top spot by invasive hedge-eating caterpillar • Honey fungus named the most problematic plant disease for the 20th year in a row • Record temperatures and rainfall lengthened the season of pests and diseases

For the first time in nearly a decade slugs and snails did not top the list of the most troublesome garden pest of the year, based on enquiries received by the Royal Horticultural Society (RHS) Gardening Advice team. The title of top pest of 2015 has gone to a native of East Asia that was first discovered in the UK in 2011, the box tree caterpillar.

A voracious feeder of box (Buxus), the larvae of the box tree moth are 4cm long and feed on the leaves of the host box plant under a blanket of pale fine webbing which can cover infected plants.

First found in 2011 the pest is now prevalent in the home counties and is spreading across south-east England.

Although not the number one reported annoyance for gardeners in 2015, snails and slugs came a strong second in the charity’s annual top pest list, with enquiries remaining high.

Slug and snail damage mainly occurs in the spring and autumn but can become a problem during any damp period. The creatures affect a wide range of ornamental plants and vegetables, especially potato tubers, hostas and daffodils, seedlings are particularly susceptible.

For the 20th year running honey fungus was the most commonly reported garden disease, with its presence recorded on 76 plant genera in 2015.

Considered one of the most destructive fungal diseases in UK gardens, honey fungus attacks and kill the roots of many woody and perennial plants. The most characteristic symptom of the presence of honey fungus is white fungal growth between the bark and wood, usually at ground level. Clumps of honey-coloured toadstools sometimes appear briefly on infected stumps in autumn.

The second most reported plant disease, like the box tree caterpillar also affects box plants, leaving them with bare patches and die-back. Box blight, caused by the fungus Cylindrocladium, is the scourge of hedges, parterres and topiary. Box blight poses a serious threat to the UK’s horticultural heritage, as box plants provide the structure of many historic formal English gardens.

High temperatures and rainfall over the spring saw a spike in enquiries to the RHS about box blight, as the environmental factors combined to create the perfect condition for the disease to thrive. Unusually warm wet weather in December saw an unexpected increase in enquiries at a time when the expected cold weather would suppress the disease.

As in previous years, the close relationship between the weather and the presence and longevity of garden pests and disease was evident. During 2015 the UK experienced its hottest-ever day and the warmest and wettest December on record. December 2015 saw temperatures reach those usually associated with April and May.

RHS Head of Plant Health Gerard Clover said: “Dealing with pests and diseases is a reality for gardeners, but by sharing their observations, insights and samples with RHS scientists they are helping us identify those areas where we need to focus our research efforts to better control pests and diseases.

“We are currently undertaking research that we hope will mean that slugs and snails will become less of a problem in the future, as we work to determine the most effective ways of controlling them.

“The project will provide gardeners with the robust, evidence based information they’ll need to confidently take on slugs and snails.

“We are also working with the National Trust, whose properties include many historic gardens, to manage the threat of box blight and are looking to identify ways to mitigate the effects of box tree moth”

Top 10 Garden Pests of 2015


Top 10 Plant Diseases


Notes to editors

For more information and images, please contact Garfield Myrie at or call 0207 821 3060

Notes to Editors:
For more information on how to identify and control garden pests and diseases visit: or

About the RHS
The Royal Horticultural Society was founded in 1804 by Sir Joseph Banks and John Wedgwood to inspire passion and excellence in the science, art and practice of horticulture. Our vision is to enrich everyone’s life through plants, and make the UK a greener, healthier, happier and more beautiful place. We believe everyone in every village, town and city should benefit from growing plants to enhance lives, build stronger, healthier, happier communities and create better places to live.

We held our first flower shows in 1820, were granted a Royal Charter in 1861 and acquired RHS Garden Wisley, our flagship garden, in 1903. From our first meetings in a small room off London’s Piccadilly, we have grown to become the world’s largest gardening charity. At our gardens and shows and through our scientific research, publications, libraries and our education and community programmes we inspire a passion for gardening and growing plants, promote the value of gardens, demonstrate how gardening is good for us and explain the vital roles that plants undertake.

The RHS is committed to bringing the joy of gardening to millions more people, inspire the next generation of gardeners and invest in the future to safeguard a £10.4 billion industry employing over 300,000 people. We are entirely funded by our members, visitors and supporters. RHS membership is for anyone with an interest in gardening. Support the RHS and help us secure a healthy future for gardening. For more information call: 0845 130 4646, or visit

RHS membership is for anyone with an interest in gardening. Support the RHS and secure a healthy future for gardening. For more information call: 0845 130 4646, or visit

RHS Registered Charity No. 222879/SC038262.


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About the RHS

The RHS believes that gardening improves the quality of life and that everyone should have access to great garden experiences. As a charity we help to bring gardening into people's lives and support gardeners of all levels and abilities; whether they are expert horticulturists or children who are planting seeds for the very first time.

RHS membership is for anyone with an interest in gardening. Support the RHS and secure a healthy future for gardening. For more information call: 0845 130 4646, or visit

RHS Registered Charity No. 222879/SC038262