Japanese knotweed is simply one of things in life that should not be brushed under the carpet with a botched attempt at removal, unless of course you want to incur delays and major expense at a later stage. While it may seem like a large task to remove Japanese knotweed, you are better off sorting the problem out at the beginning, before any works start. We have a number of Japanese knotweed removal methods that can be used to ensure complete removal.Many attempts at "controlling" Japanese knotweed are counterproductive. They kill off some of the plant, leaving the majority of the rhizome system below ground in a state of temporary dormancy, ready to resurface when you least expect it. There may be no obvious evidence of the knotweed above ground, but you can be pretty sure that viable rhizome remains. This is what we see in a lot of DIY attempts. The plant looks dead, but it is in fact dormant. Imagine a development site where viable knotweed rhizome remains hidden in the ground, possibly to a depth of 2m or more, having laterally spread into areas you might think are unaffected. Once you disturb these soils whether by ignorance, accident or intentionally, you would almost certainly fragment and spread the knotweed rhizomes to other areas of your site. This would significantly increase the scale of the problem, and hence the cost of remediation. All too frequently we are called in to help with removing Japanese knotweed, because other less experienced operators have failed to completely kill off the knotweed.
The legal implications of a knotweed infestation
Make sure you understand the law before tackling Japanese knotweed. If you caused the knotweed to be spread off-site, you could find yourself at the wrong end of criminal proceedings under either the Wildlife and Countryside Act 1981, or the Environmental Protection Act 1990 "duty of care". Offences under these Acts can result in custodial sentences. If you consign knotweed infested soils off site other than strictly in accordance with these legislative requirements, whether intentionally or not, you will run the risk of prosecution.
The technical implications of removing knotweed
Botched attempts at treatment or removal make it considerably more difficult for professionals to completely remove the knotweed for you. Trying to find and remove every piece of viable rhizome is akin, albeit with a difference, to finding and removing all fragments of asbestos that may or may not be in the ground. The big difference being that asbestos does not grow, so usually stays buried out of sight, whereas viable Japanese knotweed rhizomes are living and will grow to the surface, pretty much irrespective of what is put in its way. Imagine it growing through your asphalt driveways/roads just as you are nearing completion of the build – it would have pretty dire consequences on the saleability of the property and in many cases financing.
Where knotweed exists, either within the curtilage of a property or on adjoining land, virtually all UK banks and building societies will refuse lending until it is removed and Insurance Backed Guarantees (IBGs) "from a reputable company" are in place. We know because we receive up to 20 calls a day from distressed vendors of properties who have usually just lost a buyer due to funding being refused. Please don't think that funding will never be granted - once an insurance backed guarantee is in place, the lending should be granted.
The financial implications of a removing Japanese knotweed
Not surprisingly, the financial consequences can be pretty steep. It is not just the cost of remediation you should consider. Many main contractors/developers will be reluctant to take on the risk associated with a site infested with Japanese knotweed. Those prepared to take the risk inevitably price the risk, which of course gets reflected in the purchase/tender price.
If the risk remains with the client and knotweed is subsequently found, then additional costs during the construction stage are almost inevitable to cover professional fees, considerable management time, additional site precautions and delays to the contract, plus of course the cost of remediation. The cost of remediation in these circumstances escalates due to the urgency, as the more cost-effective alternatives to dig & dump may not be available.
Removing the problem prior to letting the main contract is the best solution all round.