Riverside Housing Development
Japanese Knotweed Solutions were first contacted by the developer in March 2005 and asked to carry out an Invasive Species survey.
Site History:
On visiting the site which fronts onto the River Irwell, the survey team reported mass infestation of Japanese Knotweed with ‘significant’ areas of Himalayan balsam. Both banks of the River were covered with well established stands which extended from the banks of the river into the site in broad swathes. The largest stand was 158 metres long by 25 metres wide the smallest was a single stem of Japanese Knotweed within a covered warehouse growing within a pile of debris.
History of Japanese Knotweed:
Japanese Knotweed is a highly problematic plant introduced as an ornamental garden species in the early 1840’s. Due to its excessive growth and the rapidity of its spread it is now classified as the most invasive plant in the UK. It is illegal to … ‘plant or otherwise cause Japanese Knotweed to spread’ – Wildlife and Countryside Act – thus developers must take action to ensure that they do not breach legislation.
History of Himalayan balsam:
Himalayan balsam is another problem plant introduced by the Victorian gardeners as an ornamental plant. Balsam rapidly colonises bare ground and will spread by more than 20 metres in all directions per season if left unchecked. The most significant damage caused by Himalayan balsam are the large areas of open land left over winter. Without any significant root the plant leaves areas susceptible to erosion and collapse.
Initial Works:
Contact was therefore made with the developer immediately to advise that there was a significant problem and that ongoing demolition works (being undertaken at the time of survey) should take every precaution against spreading the plant or causing cross contamination.
Demolition works were put on hold whilst a team from Japanese Knotweed Solutions came onto site and fenced all areas of contamination. Foot wash facilities were set up to ensure that there was no cross contamination and high visibility signage and fencing were erected 7 metres from any surface growth (as per Environment Agency guidelines).
Price was submitted for a three year programme of works with a ten year insurance backed warranty to cover any possible re-growth. Due to the River Irwell being immediately adjacent to the site the chemical strategy was restricted to the use of non-residual herbicides.
Approvals:
Contact was made with the Environment Agency and a Water Quality Management form submitted. Approval for the works was received by return post.
Phase One Year One:
Phase One works were carried out in July of 2005 and involved cutting all existing growth back to a height of 300mm above ground surface. Cutting works were undertaken with hand shears to ensure that no fragments of Japanese Knotweed were spread. All arisings were stacked on fence panels raised 300 mm from the ground surface to encourage air drying and ensure that no contact was made with the ground surface.
All arisings were kept within the existing area of contamination and foot wash used for both access and egress.
Surface growth was left to re-grow to a height of 450mm when leaf cover has begun to establish. Once leaf cover was visible an initial spray of a non -residual glyphosate based herbicide was applied.
Spray was carried out by use of traditional knapsack sprayer with addition of a blue dye to identify areas that have been sprayed.
All of the spray team were holders of the NPTC spray qualification and spray records were completed stating weather conditions and time of application.
Once canes had dried (two weeks later) site was re-visited and all arisings incinerated within the contaminated area.
Phase Two Year One:
Site was re-visited at the start of September 2005.
After a period of six weeks a re-visit to site took place and records made of spray efficacy. In general an 80% die back was noted with all visible shoots showing signs of chemical uptake.
Repeat application of herbicide was undertaken in areas where vegetation had been particularly dense thus allowing some areas to miss spray treatment.
All dead canes were collected and incinerated within the contaminated area.
Phase Three Year Two:
In March 2006 site was re-visited and damage to fencing repaired.
In April 2006 site was re-visited and new growth re-sprayed with a non-residual herbicide.
It was noted at this time that due to the large open areas created by the loss of Japanese Knotweed had created an opportunity for the residual seed from the Himalayan balsam to establish. Himalayan balsam seed is not affected by chemical treatment and can lie dormant in the soil for up to ten years awaiting disturbance or suitable climatic conditions.
Client had been advised that this was a likely scenario and allowance had been made within the price for chemical treatment of Himalayan balsam at no additional cost. It is essential that spray treatment is carried out prior to allowing the plant to set seed.
At this time a re-growth of less than 5% Japanese Knotweed was noted.
Phase Four Year Two:
Site was re-visited at the start of September 2006.
A re-visit to site took place and records were again made of spray efficacy. In general a 95% die back was noted with all visible shoots showing signs of chemical uptake.
Repeat application of herbicide was undertaken in areas where vegetation had been particularly dense thus allowing some areas to miss spray treatment.
Himalayan balsam surface growth had been eradicated.
Phase Five Year Three:
In March 2007 site was re-visited and damage to fencing repaired.
In April 2007 site was re-visited and new growth re-sprayed with a non-residual herbicide.
It was noted at this time that again due to the large open areas created by the loss of Japanese Knotweed the residual seed from the Himalayan balsam had established.
JKSL again undertook a chemical treatment of Himalayan balsam at no additional cost.
At this time a re-growth of less than 5% Japanese Knotweed was noted.
Phase Six Year Three:
Site was re-visited at the start of September 2007.
A re-visit to site took place and records were again made of spray efficacy. In general a 100% die back was noted with all visible shoots showing signs of chemical uptake.
Himalayan balsam surface growth had been eradicated.
Aftercare Package:
Site is now covered under an aftercare package for ten years which includes an annual re-visit and any additional ‘in situ’ chemical treatment works as required to eradicate Japanese Knotweed. A written report is issued following each visit.
New Superstore
JKSL were called in to survey extensive stands of Japanese Knotweed which had gone un-noticed on a proposed new superstore development. Due to initial survey works not identifying the presence of JK, control measures had not been accounted for in the master planning of the project, no budgetary allowance had been made and no time allowance included within the already tight timescales for the works. The main contractor was also on a penalty clause of £250K per week if the opening deadline was missed.
Initial thoughts by the main contractor were based upon excavation and removal of contaminated material to a licensed tip. The cost estimate to excavate and remove the JK came to £2.8 million.
The project works were discussed with Japanese Knotweed Solutions and in close liaison with the Environment Agency alternate solutions were sought. Excavation and removal of JK contaminated material is not only highly costly but also increases the risk of cross contamination. The method is also not environmentally sound as valuable landfill is used as well as increasing road traffic with the numbers of wagons required to move the vast amount of material produced.
The superstore had been approved within sight of a residential estate and as such was subject to strict planning issues with regards to the landscape works. It was proposed to provide landscape bunding to the periphery of the site and to provide screen planting along the mound.
JKSL suggested in-situ treatment of the JK with a herbicide using both foliar applied treatment and direct injection of chemical. Dead surface growth could then be incinerated within the existing areas of contamination. Treated stands could then be carefully excavated and used as sub-soil within the bunded areas. Clean top-soil could then be placed on top of the contaminated material and screen planting incorporated in to the clean top soil. Any potential re-growth would be within landscaped areas and not within the development area – as such an ongoing maintenance plan was proposed and a ten year warranty issued.
This methodology was in line with the EA Code of Practice and cost in the region of £120K, a massive reduction in the proposed £2.8 million off site costs.
Flood Alleviation Project
The Environment Agency had committed itself to a series of flood alleviation measures on a watercourse within a major conurbation. High profile flooding caused a major problem for the Agency by increasing public demand on the timescales for the work. JKSL were called in to survey JK along the watercourse and strategies for eradication were discussed.The only chemical strategy approved by the EA is use of Glyphosate based herbicides which require repeat applications of chemical over what is quoted as a three to five year period.
JKSL have carried out detailed works to improve the efficacy of their chemical treatment and offered their experience to the EA. Works were approved and chemicals applied both in foliar applied sections and with a direct injection system. Works to date have shown a marked improvement in performance with timescales being reduced from three to five years to 12 to eighteen months for complete eradication.
