Mild weather in a hot, moist year causes the rise of humid-loving pests and diseases
Top pest 2016
Plenty of moisture during 2016 brought slugs and snails back to the top of the list for garden pest of the year, based on enquiries received by the RHS Gardening Advice team.
Slugs and snails
Last year slugs and snails were pushed off the top spot by the box tree moth, but in 2016 the pests came back with a vengeance and a record number of enquiries.
But while the top spots were predictable, it was the emergence of pests such as glasshouse thrips and fuchsia gall mite that changed the look of the list.
Fuchsia gall mite
Fuchsia gall mite moved up to third most problematic pest of 2016. First detected in mainland Britain in 2007, it 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.
The rise of glasshouse thrips was even more spectacular, coming from outside the top 10 in 2015 to fourth place in 2016. Also known as thunder flies, glasshouse thrips were primarily a problem within greenhouses until 2008 when the pest began to be reported on outdoor shrubs. It is thought that most outbreaks 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. Adult glasshouse thrips have narrow, dark brown bodies up to 2mm long with an orange-tipped abdomen and insects that feed by sucking sap from leaves and flowers. Infestations are characterised by a silvery discoloration of the upper surface of leaves.
Top 10 pests 2016
Top plant disease for 2016
No change at the top - honey fungus has now been the most troublesome plant disease for 21 years. RHS scientists have identified its presence on 70 host genera.
The mild weather last year also had a major bearing on bacterial and scab plant diseases, which both broke into the top 10.
- Bacterial diseases, which thrive in moist, mild conditions, came eighth place in the table, with RHS scientists dealing with twice as many enquiries about fireblight as the previous year.
- Scab diseases, moved from outside the top 10 in 2015, to the ninth biggest disease problem facing gardeners in 2016 - the RHS recording a 65 percent increase in the number of enquiries.
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.
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.
Top 10 diseases 2016
RHS Head of Plant Health Gerard Clover observed:
“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.”