The battle lines have been drawn. On one side, vicious and deadly invaders, on the other, an army of driller killers prepared to use brute force in their fight for victory.

It’s not the latest video game or Netflix blockbuster. Instead, it’s the normally gentle natured gardening teams at heritage organisation National Trust of Scotland, who have just upped the ante in the battle against a group of vicious plant nasties that simply must die.

At the heart of Project Wipeout, the combative name given to a sweeping programme that sees teams injecting unwanted species with herbicides or, more low-tech, ripping them out of the ground by hand – is the fight to save Scotland’s native species from a fate worse than death.

For the relentless march of certain invasive non-native species has become so overwhelming in some areas of the Trust’s estates, that it has virtually obliterated their delicate native rivals from the face of the earth.

The problem is particularly troublesome in Scotland’s sensitive rain forests, where mosses and lichens have been swamped, and in waterways at risk of being clogged by huge areas of unwelcome invaders.

Now teams of plant destroyers have been unleashed at eight of the Trust’s key sites across Scotland, with a view to tackling out of control species such as Rhododendron ponticum, Japanese knotweed and American skunk cabbage.

In just a few weeks, they cleared around 40 hectares of troublesome intruders using a range of removal methods including drilling plants’ individual stems and injecting them with a chemical cocktail, to sending plant squads over cliffs and into a 60m deep gorge to reach the most awkward roots.

It’s hoped they have already created enough space and light in previously clogged areas of some estates to encourage springtime growth of native bluebells, primroses and wood anemone.

The two-year, £620,000 programme is being carried out at Inverewe, Corrieshalloch Gorge, Torridon, Balmacara and Kintail in Wester Ross, at Brodie Castle in Moray, Brodick Castle on Arran and at Culzean Castle in South Ayrshire.

It is the Trust’s biggest ever assault on non-native invasive species, with hopes that it will virtually eradicate the species at the eight key estates, leaving garden teams with what is likely to be a never-ending task of keeping on top of any signs of regrowth.

The Trust’s Natural Heritage Advisor Rob Dewar says killing the plant invaders was essential if native species are to be allowed to thrive. “Unfortunately, we have to take plants out of the system and clear them away, but it’s to help natural plants to come through,” he says.

One of the biggest headaches is caused by the spread of Rhododendron ponticum, introduced to Scotland in the 1700s as an ornamental plant and admired for its huge blooms.

Left uncontrolled, it can go on to dominate habitats to the virtual exclusion of all other plant life, while its extensive root system and leaf litter is toxic to many plants. It also harbours Phytophthora, a fungus-like pathogen that affects many other trees and plants.

To tackle it, NTS staff have developed a range of attacks, from using simple mattocks to rip at its roots or their hands to rip young plants from the ground, to more cunning methods including drilling a well into individual stems and then filling it with small solutions of herbicide.

Although painstakingly slow, the method avoids the need to spray sensitive woodland sites with chemicals which could have an adverse impact on the very native plants the teams are trying to nurture.

“Rhododendron ponticum has a lovely flower, but it only blooms for two weeks of the year,” adds Rob. “After that, if you put your head underneath them, there’s nothing living below. You have a totally dense canopy that shuts out all the sunlight.

“At Brodie Castle, there was nothing left on woodland floor,” he continues. “We have gone in with chainsaws and chippers and cleared the decks so we can restore the woodland.”

Most moorlands and woodlands will be allowed to regenerate naturally, with carpets of colourful bluebells and primroses or moorland heather replacing dense areas of rhododendron shrubs. In others, new native species such as hazel and holly will be planted.

Extreme lengths have been employed to tackle some plants: at Corrieshalloch Gorge teams have had to be lowered over cliffs to reach Japanese hogweed took root on inaccessible ledges within the 60m-deep gorge.

The Trust is also using innovative methods such as retorn kilns which will process rhododendron waste into biochar which can be returned to the soil – helping foe become friend.

“The biochar feeds back into the soil to improve macro fauna and the soil’s structure, air and water retention,” adds Rob. “So we are dealing with invasive species difficulty and waste product by feeding back into the soil.”

However, the invaders often have their own anti-weapon and survival devices, including exploding seed pods and very determined roots.

In the case of Japanese knotweed, which was introduced to Europe from the Far East in the mid-19th century as an ornamental ‘architectural’ plant, hacking at it can result in just a tiny fragment of discarded root sprouting into a new plant.

“Japanese knotweed has such deep roots that we’ve developed a ‘gun’ with a needle that disperses some herbicide which we inject in each stem,” says Rob, adding the technique has been used to tackle growth at Brodie Castle.

“At Corrieshalloch Gorge, we found that fragments of Japanese knotweed had washed along a culvert under a road and then down the sheer, vertical cliff face to establish itself.

“It’s tough work,” he adds.

Similar work is being done to halt the spread of American skunk cabbage which, despite its pretty yellow lantern-shaped flowers has a skunk-like odour that has been likened to rotting flesh making it particularly attractive to flies.

Introduced as ornamental flowers for garden ponds and burns, the seeds are so robust they can survive in sea water, raising fears that it could easily be established in open water.

Work is underway to remove the plant at Balmacara estate, where it has taken hold over a 1.5km site.

As well as tackling invasive non-native species on Trust land, work has also been carried out on neighbouring properties in Wester Ross, to help curb growth and support communities’ fight against the intruders.

Project Wipeout has been funded by players of People’s Postcode Lottery, the NatureScot Biodiversity Challenge Fund, Baillie Gifford and an anonymous donor.

It has been so successful that NTS experts will share details of their removal methods at an online conference on Tuesday which has been arranged with Wester Ross UNESCO Biosphere to examine problems caused by invasive species in Scotland.

However, such is the enemy’s determination to survive, Rob concedes that the battle against some species, such as Rhododendron are from over.

“It will come back eventually,” he adds. “We have to be pragmatic. Some of our properties have big areas.

“But if we turn the other cheek and don’t deal with it, in a few years’ time it will be an even bigger problem.”