Gardeners are gearing up for battle as an Asian insect capable of wiping out wisterias spreads in the capital.

Defences are up in Chiswick as Fuller’s Griffin Brewery looks to protect the oldest wisteria in the UK from a rapid rise in the number of wisteria scale bugs.

According to Andrew Salisbury, an entomologist for the Royal Horticultural Society (RHS), swathes of the 1cm long, dark brown helmet-shaped insects are able to “suck the plants dry”.

But a spokesman for Fuller’s said it “valued its wisteria very highly” and was constantly checking the condition of the 180-year-old shrub.

He said: “We have one of the foremost wisteria experts looking after it.

“It’s examined very closely twice a year and was examined recently and showed no signs of problems so we are confident it’s in safe hands.”

Mr Salisbury said the pest first showed up on the RHS’s radar in 2001 after it was discovered in Vauxhall. He said there was very little authorities could do to stop the swift increase in numbers.

Until recently the insect had been confined to London but Mr Salisbury admitted it was spreading.

The RHS has confirmed reports of wisteria scale in Hertfordshire this year.

A spokeswoman for Kew Gardens played down the threat posed to the botanic attraction.

She said: “Kew Gardens has a very low level of wisteria scale.

“It is very treatable, and good husbandry keeps it under control. Kew’s wisteria trees are regularly pruned, checked and treated by horticulture staff.”

Mr Salisbury advised gardeners to use systemic insecticides to tackle any outbreaks of the pest. He said the best time to treat the problem was mid summer when wisteria scale eggs hatched.

The RHS urged gardeners to take action before more of the country became infected.

To learn how to control wisteria in your garden visit rhs.org.uk.