Many methods currently used to control knotweed are based on very limited information, often with little follow-up to confirm if the knotweed was actually dead.

Researchers from the College of Science have therefore set up a series of rigorous scientific field trials to compare different knotweed control methods.

They are working in partnership with Complete Weed Control, a link which ensures that the project combines scientific and practical expertise.  The research is part-funded by the European Social Fund, via the Welsh Government.

21 different Japanese knotweed control methods are being tested, including current best practice and novel control methods.   The trials, which draw on almost 50 years of research, are the largest Japanese knotweed field trial ever conducted in Europe or North America.

Picture:  aerial shot of one of the field trial sites, showing different patches treated with different methods

Watch BBC TV coverage of the research

About Japanese knotweed

•    It begins to grow in early spring and can grow in any type of soil, no matter how poor
•    It can grow as much as 20 centimetres per day, and can reach a height of 1.5 metres by May and 3 metres by June.
•    It spreads through rhizome (underground root-like stem) fragments and cut stems.
•    It was originally introduced by the Victorians as an ornamental plant



‌Picture:  Research team members Dan Jones (left) with Dr Gareth Bruce

Dan Jones from the College of Science at Swansea University, lead researcher on the project, said:

“Even when the knotweed looks like it’s under control, it doesn’t mean it is.  There’s always a chance that it’ll grow back.

60% of the plant is below ground and without investigating that we can’t be sure it’s gone.
 
We’re looking at different herbicides and application methods, and at how they work in combination.

An estimated £200 million has been spent across the UK tackling knotweed.   But we aren’t necessarily improving the situation, and we can be polluting the environment needlessly.

We need to move towards more effective and efficient solutions, to tackle the problem properly

That’s why a scientific approach is so important.  We’re working on our data and analysis at the moment, and should be able to publish results next year, to identify which treatments are most effective.”


Ian Graham from Complete Weed Control, a partner in the research project, added:

“Misinformation is a big problem.  Prior to these trials, we’ve been lacking something concrete, carried out in a scientific manner, to allow us to make sensible decisions about what to do.

So we’re not looking just at opinions and conjecture, we’re actually looking at what happens under the ground.    

Only now are we starting to see the implications of past attempts to tackle Japanese knotweed.  What may have looked like an effective job may turn out not to be so

In spite of very heavy levels of spending, we’re no further forward than we were.  That’s why we need to find a better way of dealing with Japanese knotweed.”

Picture:  Ian Graham demonstrating the scale of Japanese knotweed, in an interview with the BBC