Slugs, snails and honey fungus top RHS most troublesome pests and diseases of 2016

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.?

Top 10 pest enquiries of 2016 and 2015

Top 10 disease enquiries of 2016 and 2015