Many of our domestic customers ask us if we offer Japanese knotweed removal. We always mention that it is an offence to place Japanese knotweed into the recycle bins as this carries an expensive fine if caught by the local authorities.
Japanese knotweed removal can be carried out in two ways, by application of herbicide or by mechanical means. The latter is usually the most expensive and, in some cases, the least effective. Some companies use excavators to dig out the contaminated soil. Then, they put the soil into a screening machine to separate the plant material from the soil. The small pieces of rhizome/plant fragments in the screened soil are then picked up by operatives. If the soil is heavy clay and sticky it can be very difficult to separate the plant material from the soil. The Japanese knotweed material will then either be incinerated or taken to a specialist landfill site. The Environment Agency and the government always advise that the best way for Japanese knotweed removal is to keep the plant material on-site. Japanese knotweed removal by herbicide treatment keeps the risk of spread off-site to the wider environment to an absolute minimum. However, the larger companies offer Japanese knotweed removal by excavation if treatment by herbicide is too time consuming. In case of many development sites, Japanese knotweed removal by mechanical means may be the only option for the developer.
The main problem with mechanical removal is possible human error as it is very easy for the operative to miss tiny fragments of rhizome in the screened soil. The fragments may be put back onto the land and then start to regrow at a later date after the Japanese knotweed company has left the site. Small fragments could also be transferred between sites on the vehicles and equipment used by developer companies if they are not cleaned sufficiently before leaving the site.
All the Japanese knotweed contaminated soil must be transported to the specialist landfill site. The cost per cubic tonne is sufficient compared with common waste due to the high landfill tax. In addition, there has to be a paper trail and waste transfer licence to accompany the Japanese knotweed removal to the landfill site.
Alternatively, Japanese knotweed can be removed from the infestation area and bunded on other parts of the site. This normally may be carried out by a specialist Japanese knotweed company that dug out the Japanese knotweed contaminated soil down to a depth of 2-2.5 meters and possibly up to seven metres out from the edge of the Knotweed stand. The soil will be placed on an area on-site that is not to be under development. The area will have to be fenced off to limit the access. The clear signage stating contractor details dealing with Japanese knotweed must be provided on the fence. The area will then be treated by application of herbicide and may take several years.
Note, that even after all jobs associated with Japanese knotweed removal by either chemical or mechanical means have been done, there still a probability of new regrowth in the future. The animals, such as foxes and badgers are among the main means of spread of the plant. They can bring rhizome fragments to the area on their fur. Rhizome fragments as small as 0.8 gram are capable of regeneration into new plants. We have been on sites where badgers and foxes have dug their sets and dens in amongst the Japanese knotweed crowns. Many clients are quite shocked when we mention that the likely reason for the plant is in their garden is due to foxes or badgers.
Japanese knotweed removal by scrupulous builders is another way that the plant can be spread the waste material tends to be fly tipped into back streets, disused waste land etc. The council will then clear the waste without checking for Japanese knotweed material. The material may then end up at the local landfill site, thus allowing the plant to re-establish itself.
With Japanese knotweed removal by herbicide poisoning you are guaranteed that the plant stays on-site. It is the most cost-effective way to treat Japanese knotweed. Most professional Japanese knotweed companies offer this service and guarantee to kill the plant even if treatment proceeds from two to three year following by a couple of years monitoring.
There are also situations when Japanese knotweed removal by mechanical means cannot be used as an option due to location and disturbance to the local area. We tend to find that there are large stands of Japanese knotweed along rivers banks. The Japanese knotweed can be been swept down river by the strong currents. To attempt to excavate along the riverbank could cause the river to burst its bank and cause local flooding.
Railways also have a very large problem with Japanese knotweed. The plants can be spread along the railway track by the trains as the plant often grows onto the track and may be easily pulled by the train and dropped further down the track.
It is worth mentioning that in the highlands of Scotland, Japanese Knotweed removal is forbidden and you could face a fine if you are caught trying to remove Japanese knotweed. Otters use dense knotweed stands to secretly move from one mating ground to another, undetected by humans. The otter populations in the protected areas are doing really well.
In summary, Japanese knotweed removal by mechanical means is almost always not cost-effective and imposes the risk of spread of the plant to the wider environment. Japanese knotweed removal by chemical treatment would be a fair safer and cost-effective option.