Gardening Advice line sees 88 per cent increase in enquiries
The RHS’s 25th annual garden pests and diseases ranking reveals that many gardeners battled familiar foes in 2020 – slugs, snails and honey fungus. RHS Gardening Advice saw an 88 per cent increase in pest and disease enquiries last year. These included mildew on flowering cherries, rust on pears, black spot on roses and red spider mite.
Honey fungus has been top of the disease ranking every year. It has a large host range of woody and perennial plant hosts. Not for nothing is it called the ‘silent killer’. The fungus spreads underground attacking roots and decaying bark.
Slugs and snails have also been a constant menace but in 2020 returned as the top garden pest for the first time since 2017. Gardeners reported damage to potatoes, beans and ornamentals including clematis and hosta.
There was good news for box as reports of box tree caterpillar, which strip plants of foliage, fell 40 per cent. Separate RHS research found that its spread slowed last year following rapid growth into the north of England and Wales.
‘Flucuating levels of pests and diseases’
Andrew Salisbury, Principal Entomologist at the RHS, says: “The pests and diseases that gardeners commonly face on their plots have 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.
“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 researching a wide range of plant pests and diseases. These include 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 facility, Hilltop, at RHS Garden Wisley, which will open to the public on June 24, 2021. For more information, visit www.rhs.org.uk.
Pests and diseases 2020
| Top pests 2020 | Top diseases 2020 | ||
| 1 | Slugs and snails | 1 | Honey fungus |
| 2 | Vine weevil | 2 | Pear rust |
| 3 | Box tree caterpillar | 3 | Leaf spot and canker of Prunus |
| 4 | Ants | 4 | Rose black spot |
| 5 | Woolly aphid | 5 | Bracket fungi |
| 6 | Glasshouse red spider mite | 6 | Powdery mildew of Prunus |
| 7 | Fuchsia gall mite | 7 | Blossom wilt of fruit trees |
| 8 | Glasshouse thrips | 8= | Phytophthora root rots |
| 9 | Rosy apple aphid | 8= | Rose powdery mildew |
| 10 | Capsid bug & Glasshouse mealybug | 10 | Brown rot of fruit |
Pest ranking 2019 vs 2020
| Top pests 2020 | Top pests 2019 | ||
| 1 | Slugs and snails | 1 | Box tree caterpillar |
| 2 | Vine weevil | 2 | Vine weevil |
| 3 | Box tree caterpillar | 3 | Slugs/snails |
| 4 | Ants | 4 | Fuchsia gall mite |
| 5 | Woolly aphid | 5 | Alder leaf beetle |
| 6 | Glasshouse red spider mite | 6 | Woolly aphid |
| 7 | Fuchsia gall mite | 7= | Rosy apple aphid |
| 8 | Glasshouse thrips | 7= | Viburnum beetle |
| 9 | Rosy apple aphid | 9 | Glasshouse red spider mite |
| 10= | Capsid bug and Glasshouse mealy bug | 10 | Plum leaf-curling aphid |
Disease ranking 2019 vs 2020
| Top diseases 2020 | Top diseases 2019 | ||
| 1 | Honey fungus | 1 | Honey fungus |
| 2 | Pear rust | 2 | Phytophthora root rots |
| 3 | Leaf spot and canker of Prunus | 3 | Box blight |
| 4 | Rose black spot | 4 | Pear rust |
| 5 | Bracket fungi | 5 | Brown rot of fruit |
| 6 | Powdery mildew of Prunus | 6 | Leaf spot and canker of Prunus |
| 7 | Blossom wilt of fruit trees | 7 | Apple and pear scab |
| 8= | Phytophthora root rots | 8= | Rose black spot |
| 8= | Rose powdery mildew | 8= | Blossom wilt of fruit trees |
| 10 | Brown rot of fruit | 10 | Powdery mildew of Prunus |
For more information on garden pests and diseases, visit www.rhs.org.uk.
