Based on numbers of enquiries to the members' advice service, this annual RHS ranking reveals the pests and diseases rife in UK gardens in 2017.
- Honey fungus was ranked number one disease for 22nd year in a row, and box (Buxus) suffered three top ten plant health issues
- Fuchsia gall mite and diseases of edible crops are expected to take hold in 2018
Now in its 22nd year, the annual ranking is a guide to new and growing areas of concern for gardeners and includes a number of pests and diseases first identified by the RHS - such as kerria twig and leaf blight, which features in the top ten for the first time this year.
In 2017, box tree caterpillar returned to the number one spot after dropping to number seven in 2016. Increasingly common in London and the Home Counties, the caterpillar feeds on the leaves of box from within a protective webbing - causing severe defoliation.
In what was a bad year for the plant, it also battled box blight and Volutella blight – both of which cause twig and leaf death. While the box tree caterpillar is expected to continue its spread, the issue of blight may be decreased by growing awareness among gardeners of how to manage it, and the breeding of resistant varieties.
Honey fungus has retained the disease top spot for the 22nd year running, which can be attributed to its numerous and diverse host range that includes popular garden plants such as roses, rhododendrons and Prunus. Current RHS research is intended to help gardeners better manage the disease, which attacks and kills the roots of perennial plants before decaying the wood.
Pests and diseases to watch in 2018 include fuchsia gall mite which makes its fourth and highest appearance in the top ten, having first been discovered in the UK in 2007. Reported for the first time in South Wales and Cheshire in 2017, the microscopic mites cause the shoots and flowers of fuchsias to distort.
Changing weather conditions, the withdrawal of fungicides and the use of highly susceptible cultivars, is also expected to see a rise in the number of diseases of edible crops such as apple and pear scab that causes dark, scabby markings on fruit and pear rust that causes bright orange spots on leaves.
Top ten plant pests and diseases 2017
|1 Box tree caterpillar
||1 Honey fungus
|2 Fuchsia gall mite
||2 Phytophthora root rots
|3 Vine weevil
|4 Slugs and snails
||4 Powdery mildews
|5 Alder leaf beetle
||5 Box blight
|6 Viburnum beetle
||6 Volutella blight of box
|7 Tortrix moth
||7 Leaf spot and canker of Prunus
|=8 Glasshouse mealybug
||8 Verticillium wilt
|=8 Pear blister mite
||9 Blossom wilt of fruit trees
|10 Woolly aphid
||10 Kerria twig and leaf blight
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Old foes and new threats
Gerard Clover, RHS Head of Plant Health, said: “This year’s pest and disease ranking points to the continuing problems inflicted on gardens by old foes like honey fungus but also new and emerging threats like box tree caterpillar, fuchsia gall mite and kerria twig and leaf blight. With new pests and diseases emerging in continental Europe, it has never been more important that people get to grips with what is going on in their gardens.”
To help mitigate the risk posed by pests and diseases, the RHS is adopting six new principles that will guide its activity across gardens, shows and plant centres and hiring three new senior staff who will oversee plant health issues. This includes Xylella fastidiosa which has been labelled a ‘game changer’ for gardeners and the horticultural industry.
► Plant health in gardens
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