The Royal Horticultural Society’s 25th annual pest and disease ranking reveals that many gardeners battled familiar foes in 2020, turning to the charity for advice on dealing with slugs and snails, honey fungus and ants.

With more people spending time in their gardens, RHS Gardening Advice saw an 88% increase in pest and disease enquiries last year, many of which had a direct impact on a plant’s appearance including as mildew on flowering cherry, rust on pear, blackspot on roses and glasshouse red spider mite.

Top pests 2020

1: Slugs and snails

2: Vine weevil

3: Box tree caterpillar

4: Ants

5: Woolly aphid

6: Glasshouse red spider mite

7: Fuchsia gall mite

8: Glasshouse thrips

9: Rosy apple aphid

10: Capsid bug & Glasshouse mealybug

Top diseases 2020

1: Honey fungus

2: Pear rust

3: Leaf spot and canker of Prunus

4: Rose black spot

5: Bracket fungi

6: Powdery mildew of Prunus

7: Blossom wilt of fruit trees

8=: Phytophthora root rots

8=: Rose powdery mildew

10: Brown rot of fruit

Honey fungus has consistently topped the disease ranking for a quarter of a century, which can be attributed to its large woody and perennial plant host range and ‘silent killer’ status; the fungus spreads underground attacking roots and decaying bark.

Slugs and snails have also proved to be a mainstay of the ranking but in 2020 returned as the number one garden pest for the first time since 2017 with gardeners reporting damage to crops such as potatoes and beans and ornamentals including clematis and hosta.

There was, however, good news for box as reports of box tree caterpillar, which strip plants of foliage, fell 40%. Separate RHS research also found that its spread slowed last year following rapid growth into the north of England and Wales.

Andrew Salisbury, Principal Entomologist at the RHS, says: “The pests and diseases that gardeners commonly face on their plots has fluctuated over the last 25 years but some age-old problems persist. With gardens taking on a more important role in supporting wellbeing and the environment it’s important that research into management and mitigation of them continues and our rankings help inform this focus. It’s also imperative that we continue to anticipate future threats such as the disease Xylella, which is already present in Europe, and the Marmorated stink bug, to protect our gardens for the future.”

The RHS Plant Health team is currently conducting research on a wide range of plant pests and diseases including identification and management of slugs, mapping and control of box tree moth and honey fungus bio-control, rapid diagnostics, and an improved understanding of fungal behaviour and spread in gardens. This work will move to a new, state of the art facility at RHS Garden Wisley that will open to the public on 24th June 2021. For more information about RHS Hilltop visit www.rhs.org.uk/gardens/wisley/garden-highlights/rhs-hilltop-the-home-of-gardening-science