Wisteria in danger from invasive bug

Wisteria in danger from invasive bug

Britain's wisteria is under increasing threat from an Asian insect capable of wiping out swathes of the beautiful climbing plant, the Royal Horticultural Society has warned.

By Louise Gray, Environment Correspondent
Published: 7:00AM BST 05 May 2010


The shrub's lavender and violet flowers are just coming into bloom on cottages and in parks and gardens across Britain, signalling the arrival of spring and summer.

However, the Royal Horticultural Society (RHS) is issuing a warning to gardeners about the rise of a dark brown insect called wisteria scale, which is rapidly spreading across the country.

The sap-sucking bug, which is capable of killing branches or wiping out entire wisteria plants, first came to the UK in imported plants from Asia in 2001. However, it has been increasing in prevalence each year and is now spreading throughout the home counties.
The RHS is now urging gardeners to invest in non-organic chemical pesticides to get rid of the insects before more of the country becomes infected.
At 10mm in diameter, wisteria scale is much bigger than native bugs that affect wisteria. The scale grows a grey sack around itself then lays thousands of eggs underneath it before they hatch and crawl up to feed - sucking the sap and eventually killing it the plant.
Andrew Halstead, principal entomologist at the RHS, said the problem is worse than ever this year.
"It first came to Britain nine years ago and it will get worse. Scale are not very mobile so it will spread slowly but it will spread."
Mr Halstead said it was up to ordinary gardeners to route the problem out before it gets any worse.
"It is something gardeners need to watch out for particularly if they are in the London area because they are very much on the front line. If you see it on your plant you need to do something about it.
"Once you have scale it is very difficult to eradicate them but if you can keep the population down you can stop the worst damage occurring."
Wisteria scale will not kill the plant immediately so many plants that are infected will still be flowering and need to be checked for the telltale bug or its black-grey eggs. It is especially important to try to get rid of the scale at this time of year just before it breeds and the young or 'nymphs' are spread on birds' feet and feathers.
Soap and water is commonly used by gardeners to get rid of aphid-like bugs commonly known as 'scale'. But it is actually illegal to use soap in large quantities on the natural environment. Instead gardeners can use organic substances like fatty acids or plant oils. Smaller parts can also be removed by scrubbing with a toothbrush or squashed by hand.
However Mr Halstead said none of this will work on wisteria scale as the bugs are able to hide behind the shrub against the wall.
He advised using a much stronger chemical like Provado Ultimate Bug Killer or Bug Clear Ultra.
"If you have this problem you would be better off using systemic pesticide that gets absorbed by the plant and taken up by the plant as they feed," he said.
The oldest wisteria in the UK on Fuller's Brewery in Chiswick is unaffected but gardeners are keeping a close eye on the plant in famous gardens and National Trust properties. There are even fears the bug could spread to sycamore and fruit trees.
Wisteria floribunda, which can climb as high as 20 metres above the ground and spread out 10 metres wide. It flowers for about a month each May.
Andrew Williams, head gardener at Magdalene College in Cambridge, said the wisteria had flowered on time this year which shows nature is catching up after a late start to spring because of the exceptionally cold winter.
"Luckilly our plants have not been effected. It would be a real shame as they are so beautiful," he said.