The RHS has issued a runner bean warning as a European bug that devastates the fruit of common garden plants has entered the charity’s top ten worst pest list for the first time.
The southern green shield bug feeds on the sap of plants such as tomatoes, raspberries and runner beans, causing misshapen fruit to grow.
Although the emerald green creature usually does not thrive in England as it does across the warmer climates of Europe, the heatwave last year caused it to multiply across gardens.
A sap feeder with some preference for vegetables, especially beans, it became established in Britain in the early 2000s and is thought to have been introduced from mainland Europe.
The immature stages, called nymphs, are distinctively black with white or pink markings and the adult is similar to the harmless native green shield bug but does not feature a brown marking at its rear.
It is thought that the bug could continue to pose an issue across gardens through this year and next.
For 23 years, the Royal Horticultural Society has compiled a list of the most devastating pests and diseases to hit UK gardens.
The most prevalent pest this year is the box tree caterpillar, which has spread from London to Northern Ireland and Wales and is now an issue across the country. This caterpillar devastates box plants and threatens historic gardens.
Stephanie Bird, entomologist at the RHS, said:“Southern green shield bug and box tree caterpillar were likely buoyed last year by the UK’s joint warmest summer on record – resulting in more rapid life cycles and therefore increased prevalence in gardens.
“With the prospect of warmer, drier summers in future these insects could continue their spread and become more problematic. This is particularly true of the sap-sucking Southern green shield bug whose nymphs –which are black with white and red spots – at present become numerous when much of the UK’s beans have already cropped in the late summer and autumn.
“Box tree caterpillar is also still spreading and expanding beyond its current stronghold of the South East and may not have yet reached its full range. It was found for the first time in Northern Ireland and Wales last year and is likely to continue its spread across the North West next year, causing distress for box lovers and threatening historic gardens.
“In the case of the shield bug we would recommend turning a blind eye as much as possible or where it is causing damage, manually removing them.”
Matthew Cromey, Principal Scientist at the RHS, said: “Our pest and disease ranking may be evidence of how climate change is impacting on what we find in our gardens. With the UK predicted to see wetter winters, warmer summers and more extreme weather events, root diseases of trees and shrubs could become even more problematic and the array of pests is likely to change. As the UK faces new plant health problems it’s imperative that the country has the skills needed to predict, exclude and manage the worst.”