Slugs & Snails and Honey Fungus Top the Royal Horticultural Society List of Gardeners’ Most Troubles

Wednesday 1 March 2017

Hot, moist year causes rise of humidity-loving pests and diseases

Slugs and snails, and honey fungus, were named the top plant pest and disease of 2016, based on enquiries received by the Royal Horticultural Society (RHS) Gardening Advice Service.

Last year slugs and snails, which had been the number one pests for eight of the past 10 years, were pushed off the top spot by the box tree moth, but in 2016 the pests came back with a vengeance, generating a record number of enquiries and regaining the number one spot.

As in the previous 21 years, honey fungus was named the most troublesome plant disease by gardeners, with RHS scientists identifying its presence on 70 host genera.

But while the top spots were predictable, it was the emergence of pests such as glasshouse thrips and fuchsia gall mite that gave the top 10 an unfamiliar look. Fuchsia gall mite moved five places up the table from 8th position in 2015 to being named the 3rd most problematic pest of 2016. Glasshouse thrips had an even more spectacular rise, moving from outside the top 10 in 2015 to 4th place last year.

Fuchsia gall mite, first detected in mainland Britain in 2007, is now widespread in southern England and has become a serious problem for fuchsia growers. The microscopic mites infest new growth at the shoot tips, where they suck sap and secrete chemicals that prevent the normal development of leaves and flowers. As the infestation increases, foliage becomes distorted until the plants no longer produce normal leaves or flower buds.

Glasshouse thrips were primarily a problem within greenhouses until 2008 when the pest began to be reported on outdoor shrubs. Last year this thrips broke into the top 10 for the first time. It is thought that most of the outbreaks of glasshouse thrips occurred on shrubs in sheltered positions in warm urban areas, although further research is required to determine why they have become such a problem outdoors.

Also known as thunder flies, thrips are small insects that feed by sucking sap from leaves and flowers. Adult glasshouse thrips have narrow, dark brown bodies up to 2mm long with an orange-tipped abdomen. Thrips infestations are characterised by a silvery discoloration of the upper surface of leaves.

The mild weather last year had a major bearing both on bacterial and scab plant diseases, which both broke into the top 10.

Bacterial diseases, which thrive in moist, mild conditions, secured 8th place in the table, with RHS scientists dealing with twice as many enquiries about fireblight as the previous year.

Fireblight is a bacterial disease that kills the shoots of apples and pears and their ornamental relatives, giving the plant the appearance of having been scorched by fire. Symptoms include the wilting and dying of blossoms at flowering time and, as the infection spreads down the inner bark of the plant, shoots shrivel and die.

Scab diseases, which were outside the top 10 in 2015, were named the 9th biggest disease problem facing gardeners last year, with the RHS recording a 65 percent increase in the number of enquiries. Scab diseases disfigure plants by producing unsightly dark spots on the leaves. Blossoms and fruit can also be attacked, and the vigour of the plant reduced as a result of premature defoliation.

Apple scab is one of the most important diseases of apple trees and their fruit. Other hosts commonly affected by scab diseases include loquat, olive, pear, poplar, pyracantha, rowan and willow.

Speaking about the results, RHS Head of Plant Health Gerard Clover said: “Dealing with pests and diseases is an integral part of gardening and always has been.

“However, gardeners are not powerless against the threats posed by pests and diseases. Simple steps such as choosing more resistant varieties and taking an integrated approach to dealing with them, which could involve using a combination of controls together such as biological and cultural, can help gardeners fight back.”

For more information, please contact Garfield Myrie in the RHS Press Office on 020 7821 3060 or email

Images of the top pests and diseases are available to download at Please email the RHS Press Office at for instructions on how to create an account.



Notes to editors



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 bring 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 more than 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: For more information call: 020 3176 5820, 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