Whilst I was a trainee at the Yorkshire Wildlife Trust, I gained qualifications allowing me to use pesticides/herbicides, but never got the chance to use these skills. The Invasive Non-Native Species (INNS) project is now at the stage where it is carrying out treatments, and I have been along several times over the last month to help out.
Japanese Knotweed was originally brought to the UK as an ornamental plant, as it looks rather like bamboo and has pretty white flowers. It has large, bright green shield shaped leaves that zig-zag up a pink stem. Although it is infertile, it easily spreads from broken plant fragments, particularly the rhizomous roots. It is often dug up and illegally dumped, which actually makes the problem worse as the plant then occurs in two places! It is easily spread along roads, rivers and railways via broken off fragments.
As with other invasive plants such as Himalayan Balsam and Giant Hogweed, where they occur along rivers this can be problematic. As well as spreading downstream, they grow fiercely and outshade native plants.
When the invasive plants die back over winter, bare soil is left; this is susceptible to erosion and the whole process exacerbates flooding.
Each invasive plant has a different method of treatment. For Japanese Knotweed, the best method is to inject herbicide directly into the stem of the plant. Special industrial size syringes are used, and each individual stem has to be injected with a calibrated measure of the viscous liquid. This ensures that the chemical goes straight down into the root, meaning that the plant is killed in the root ball and not just above the surface. This will stop it from growing back and spreading further. Another benefit is that, unlike spraying, the chemical only goes into the Japanese Knotweed - no other plants should be damaged, meaning regrowth of native plants will be quicker. There is also virtually no risk to passing people and animals, as the chemical is all inside the plant. 
Protective clothing, boots and gloves have to be worn, making the task quite warm and uncomfortable. A lot of time is spent scrabbling about in the undergrowth on your knees, trying to avoid sharp stones, twigs, rubbish and dog poop, often on steep sided river banks so there is the added task of keeping balance and not slipping into the water. It is not the easiest or most glamorous task!
There are large infestations of Japanese Knotweed on the Rivers Colne and Holme in West Yorkshire, which is where some of the recent work has been carried out. Earlier in the week I was on a stretch of the River Colne between Marsden and Slaithwaite, near the Huddersfield Narrow Canal. There was a massive, continous broad swathe of the weed right along the river bank. After a full days work we managed to treat about a third of it, so further visits will be needed. A few minutes upstream was a patch of river bank that I helped to treat several weeks ago. It was good to go back and have a look at the effect of our work. All of the Japanese Knotweed had died back, leaving just brown twigs. The photos to the right show the before and after pictures.
It is a mammoth project to try and rid Yorkshire of invasive plant species, but I feel I have played a small part in the battle.
To help, you can report any invasive species that you see using the PlantTracker app on smart phone or via the website. This helps get a better understanding of where invasive plants are, and by mapping them and getting an overall view by river catchment, appropriate action can be planned.
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