Using dogs to detect invasive weeds

Employing dogs is growing in popularity as a means of tackling invasive weeds


  • Helga Heylen

22 June 2020

Never before have invasive weeds cost the environment, economy and taxpayer more. However, we have every reason to believe we can manage them better if we follow the trailblazing New Zealand government-funded model, where conservation dogs are the number one tool in detecting invasive species. No other method is nearly as fast, accurate, inexpensive and eco-friendly. The concept of conservation dogs originates in New Zealand, where these dogs are considered the primary tool in protecting biodiversity, closely linked to conservation.

Dogs do not rely on sight to identify invasives as humans do: the secret is in the snout. Conservation dogs are unsurpassed in finding infestations early by scent alone. Not only are their noses between ten and 100,000 times more sensitive than ours, they can work year-round in Europe's temperate climate – a big improvement in efficiency from traditional methods that are season-dependent for the most part and rely on visual cues.

To understand their potential, it may help to think of other detection dogs, such as narcotics dogs working in airports. The Pentagon even used dogs to detect explosives in Afghanistan after first investing heavily in technologies, and the animals and their handlers proved far more successful.

Meanwhile, cadaver detection dogs – which are generally part of a different specialist search and rescue organisation, or charity called upon by the police – are fastest at locating human remains, and electronic sensors are still to be optimised to get even remotely comparable results. We might also think of medical detection dogs, sniffing out cancer at an early asymptomatic stage.

Nose to the ground

In Japan, knotweed is not invasive and grows in harmony with its environment, controlled by local insects and fungi. In the mid-19th century it was introduced into European gardens without its natural enemies, however, and when left unaddressed is not only a serious threat to ecosystems, crops, and structures such as bridges and roads, but it can also have a major adverse impact on the value of any affected property.


Of all European countries, the extent of the problem is best understood in the UK. Early detection is key to limit the time, money, resources and use of herbicide needed to get rid of it. A study by Dan Jones, managing director of invasive plant species consultancy, Advanced Invasive, carried out on behalf of Swansea University, shows that managing Japanese knotweed costs more to deal with than all other invasives added together.

But why is control such a problem? The main issue lies underground with the rhizome, a tiny fragment of which can quickly create a new colony. This commonly happens when landowners or those working in construction move soil containing traces off site.

In Ireland, conservation dogs are trained to detect small fragments of Japanese knotweed – any part of the plant in any season even when dormant before it breaks the surface – and they can do so reliably down to a depth of 1m. Best for such field work tend to be high-energy rescue dogs, such as mixed breeds like labradorxbeagle, spanielxlabrador or an active dog that is considered ‘too much dog’ to be a pet. Other than searching sites, dogs in Ireland are also trained to check truckloads of earth, equipment and tyres for multiple scents. Dogs are a cost-effective, highly sensitive and non-invasive way to detect any part of the weed. They generally find targets up to 40 times faster than is possible with any other method. Trials show that what five people cover in eight hours, a dog does better in just one.

Dogs offer results instantly, with near-perfect accuracy. For terrain that is hard to access or densely overgrown, they can even work unleashed without a handler. Equipped with Bluetooth GPS harnesses, they log their stop-and-stare alert, allowing weed management teams to go in after with exact coordinates of the infestations. Dogs’ precision therefore greatly reduces the need for personnel, time and herbicide use.

Conservation dogs are ideal partners for the construction industry, helping with surveys and site clearance. They complement and speed up the work of surveyors, developers, ecologists and researchers in a thorough and cost-effective way.

Helga Heylen is managing director at Conservation Dogs Ireland  helga@conservationdogsireland.ie

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