East Asian box tree caterpillar, that feeds on box plants, has beaten slugs and snails to become gardeners’ top foe, says Royal Horticultural Society

This article is more than 4 years old

This article is more than 4 years old

Slugs and snails are traditionally the gardener’s worst foe but they have been knocked off the top spot for pests by an invasive hedge-eating caterpillar.



Last year was the first time in nearly a decade that slugs and snails were not top of the UK’s list of most troublesome pests, based on the number of enquiries received by the gardening advice team at the Royal Horticultural Society (RHS).

The RHS said the title of top pest 2015 went to the box tree caterpillar, a native of East Asia that was first discovered in the UK in 2011 and which feeds vociferously on box plants under a blanket of pale fine webbing which can cover infected plants.

The pest - the larvae of the box tree moth - is now widespread in the home counties and is spreading across south-east England, the gardening experts said.

It was a bad year for box last year, as box blight, “the scourge” of hedges, parterres and topiary, was also one of the most commonly reported garden diseases, the RHS said.

Box blight, caused by a fungus which attacks plants leaving them with bare patches and die-back, poses a serious risk to UK horticultural heritage as box plants provide the structure of many historic formal gardens, according to experts.

It came only second in diseases to honey fungus, which attacks and kills the roots of many different woody and perennial plants, and can most often be spotted as white fungal growth between the bark and wood, usually at ground level.

The experts said high temperatures and rainfall in the spring led to a spike in enquiries about box blight as the weather created perfect conditions for the disease.

And the warmest, wettest December on record meant there was an unexpected rise in enquiries about the disease when it would normally be suppressed by cold conditions.

The other top 10 plant diseases based on enquiries to the RHS were leaf spots, Phytophthora diseases, rust, volutella blight of box, powdery mildews, other root and stem rots, wilts and viruses.

Slugs and snails were second in the list of top 10 pests, followed by aphids, large cabbage white butterflies, vine weevil, cushion scale, lily beetle, rosemary beetle, fuschia gall mite and woolly aphid.

RHS head of plant health Gerard Clover said: “Dealing with pests and diseases is a reality for gardeners, but by sharing their observations, insights and samples with RHS scientists they are helping us identify those areas where we need to focus our research efforts to better control pests and diseases.

“We are currently undertaking research that we hope will mean that slugs and snails will become less of a problem in the future, as we work to determine the most effective ways of controlling them.

“We are also working with the National Trust, whose properties include many historic gardens, to manage the threat of box blight and are looking to identify ways to mitigate the effects of box tree moth.”