Labrador trained to detect invasive Japanese knotweed

There’s been no shortage of double-act super-sleuths over the years — Holmes and Watson, Starsky and Hutch, Morse and Lewis.

And now there’s Mick and Mack, two fox red Labrador retrievers, whose mission is to sniff out Japanese knotweed, one of the most invasive plants.  

It can break through mortar, brickwork, joints in concrete, drains, sewers, driveways and even cavity walls.

This week the Government announced it is backing a scheme to spot the stuff before it runs riot. 

The plan is to use a high-speed camera on top of a vehicle to film up to 120 miles of roadside a day.

But Mick and Mack might not be overly impressed. This crack pair of 14-month-old brothers have only been working for a few weeks, but they’re already at the top of their game.

It is thought that around four per cent of Britain’s homes are affected by knotweed, either directly or indirectly via a neighbouring property, according to a 2018 YouGov survey. 

Its discovery knocks around 10 per cent off the value of a home.

That means, based on the average house price of £231,855, and on the understanding that there are 889,600 homes with gardens in the UK, that knotweed reduces the value of the country’s housing stock by approximately £20 billion.

Woking-based firm Environet UK, which specialises in the treatment of knotweed, came up with the idea of knotweed-detecting dogs towards the end of last year.

Mick and Mack are the first in the UK, and to watch them in action is exhilarating, not least because they clearly love what they do.

Peter Watson, 40, is their trainer. ‘They’re from the Drakeshead bloodline, which is the aristocracy of the retriever world — bred to hunt and with lots of drive,’ he says.

The Drakeshead kennels in Lancashire has bred many field trial champions.

Today, Mick and Mack have been summoned to a pretty Georgian house in West Horsley, Surrey, owned by David and Liz Botley. 

They are thinking of moving somewhere smaller now their three daughters have left home.

They’ve read horrific accounts of buyers suing vendors after the discovery of Japanese knotweed, sometimes many years after the completion of the sale.

Last year, a construction company had to pay a grand total of £220,000 to a couple after knotweed was found in the garden of their £1.9 million new-build property on the outskirts of Manchester.

‘It’s about peace of mind more than anything,’ says Liz, whose husband is a chartered surveyor and knows all too well the devastation knotweed can cause.

Sellers must declare if their property is affected by Japanese knotweed via The Law Society’s TA6 form. 

In a 2018 survey, 4 per cent of people admitted they would deny they had the plant, however.

On the TA6 form, a seller has three choices: yes, no or not known. ‘Not known’ is the most popular answer because it protects a seller from any future legal action if knotweed is subsequently found, and places the onus on buyers to carry out their own checks.

Which is where Mick and Mack come in. ‘They live for this sort of thing,’ says Peter, who started training dogs aged 16 when he joined the family firm, RFA Security, which until now has mainly been involved in detecting explosives.

There’s something of the good cop, bad cop going on with his bouncy charges. ‘Mack is delicate, whereas Mick can be a bit of a thug. He goes flat out all the time.’

Mack goes first. He’s in a harness, which, Peter says, is the dog’s ‘uniform’ that tells him he’s working rather than out for a jolly.

‘Fetch on!’ he says. Mack’s nose goes down and, presumably, the Botleys’ anxiety goes up.

Mack glides over every blade of grass. ‘Where is it?’ says Peter. ‘Where is it?’ After 15 minutes or so, it’s obvious the knotweed isn’t anywhere. 

The process is repeated with Mick, with the same result.

Now comes the interesting part. To prove that the dogs could not have overlooked even the smallest trace of knotweed, Peter puts a tiny leaf of it in a thimble-sized cup and conceals it in the garden.

‘Fetch on!’ he tells Mack, who works the flower beds again until he suddenly freezes, staring down at the knotweed hidden under the soil. Even his tail is motionless.

‘Show me!’ barks Peter like a sergeant major. Mack points to the spot for about 20 seconds. 

Peter rewards him by dropping a tennis ball on the ground, which Mack scoops up triumphantly. 

After the knotweed is hidden in a different part of the garden, we see the same outcome with Mick.

‘That’s such a relief,’ says Liz. ‘Now we can tick the “No” box on the TA6 with confidence. Watching the dogs in action was a thrill. Their sense of smell is amazing.’

Dogs like Mick and Mack have 300 million receptors in their noses, and proportionally speaking, the area of their brains dedicated to scent is 40 times larger than that of humans. They can detect knotweed even if it’s buried four feet down.

We all know about dogs sniffing out drugs and explosives, but increasingly they are being trained to detect cancer, malaria and Parkinson’s. There are even trials to see if they can trace Covid-19.

Training Mick and Mack took less than three months — and was based on their love of tennis balls.

In the early days, a ball was placed next to a small amount of knotweed. The size of the ball was gradually reduced, until the knotweed became a stronger scent than the ball. 

Eventually, there was no ball at all, though the dogs still associated the knotweed with it. 

Japanese knotweed was introduced here from Japan in 1850, when it was regarded as a rare beauty thanks to its white flowers.

It can grow at a rate of 10cm per day, reaching up to three metres by late summer. It spreads horizontally underground for up to seven metres if its growth is blocked vertically, seeking to break through the surface wherever it can. 

It can be sprayed with glyphosate-based herbicide but that doesn’t eradicate it. Even if it’s dug out, traces of its root could remain and germinate.

You can never be 100 per cent sure it’s gone,’ says Nic Seal, founder of Environet UK, which hires Peter’s company to do the searches. ‘So we offer five or ten-year guarantees, which banks insist on before they’ll lend money.’

These guarantees confirm that Nic’s company will deal with the knotweed if it grows back.

A homeowner can expect to pay £900 with a five-year guarantee for a search on a garden of up to half an acre, or £1,800 for a ten-year guarantee. If knotweed is found, removal costs from £5,000.

Mark Montaldo, from CEL Solicitors in Liverpool, specialises in knotweed litigation. He says in the past few weeks he has received more enquiries than normal. 

‘People have spent so much time in their gardens just as the knotweed growing season has been reaching its peak,’ he says.

Nic, after noticing a big increase in traffic to his website, expects to be helping many more households anxious to know if they have developed a problem during lockdown. Mick and Mack must be chomping at the bit.