IT may be the nemesis of every gardener in the land, but one of Scotland's leading botanists says the fight against Japanese knotweed is a waste of time and money.

James Dickson, retired professor of archaeobotany and plant systematics at Glasgow University and currently honorary senior research fellow of environmental and evolutionary biology at the university, says hundreds of millions of pounds are being wasted each year trying to wipe out weeds like Japanese knotweed – classified as an invasive species in Europe and America – and giant hogweed.

He also insisted it is a myth that the foreign plant drives out and destroys local species.

Dickson is best known for his studies of Oetze, the 5000-year-old "Iceman" found in the Alps in 1991. He analysed the body's stomach contents to unravel the Stone Age man's background and lifestyle.

Dickson believes attempts to eradicate non-native plants are pointless and the growth of knotweed and hogweed is now "beyond control".

He said: "There is a war of attrition going on and I think it's futile because even if there were the funds and the manpower available to combat it, some [invasive species] are always going to escape.

"I think there's a hysteria surrounding these plants and how to deal with them. Colossal sums of money are spent trying to get rid of them. But we should actually be addressing them in a minimalist way - At the minute I don't think the matter is well thought out."

The plants have long been blamed for a decline in native species and are reported to cost the UK economy more than £166 million a year.

The construction industry suffers the bulk of the costs of combating Japanese knotweed, which is listed by the World Conservation Union (IUCN) as one of the world's 100 worst invasive species. Plant-attacking fungus and insects are used in an effort to eradicate the weed.

Japanese knotweed and giant hogweed were introduced by the Victorians as garden plants in the 1800s, but quickly spread across the country. According to the British Non-native Species Secretariat, 3.1% of Scottish rivers and canals are infested with Japanese knotweed, which spreads at a rate of up to a metre a month and can damage roads and buildings.

Giant hogweed, which grows up to 5m tall, also spreads rapidly as it produces thousands of seeds which are easily dispersed by wind and water. Its sap can cause blistering if it gets on to skin in sunlight.

Jim McColl, of the BBC's Beechgrove Garden programme, said that while he accepts Dickson's assertion that attempts to eradicate the plants are probably futile, he feels the nation's gardeners must try to limit the spread of the plants.

He said: "They are destroying the natural biodiversity of some areas and destroying natural habitats, so I think we need to continue with some form of action."

But Dickson said the weeds do not drive out native plants.

He said: "In the last 200 years, 100 species have disappeared from the Glasgow area, but not one of them has left because of Japanese knotweed or any other non-native plant - There's space for everybody."