Dealing with Japanese Knotweed on New Development Sites

Japanese knotweed has gained significant notoriety in recent years, recognised as a major issue for landowners and developers alike.

Despite increased awareness, uncertainty often surrounds the management of knotweed on land slated for development.

Questions like, "Do landowners need a survey to identify Japanese knotweed?" "Are property developers obligated to control it?" and "What are the most effective eradication methods on a development site?" remain common. This blog aims to answer these queries, offering clarity for construction professionals and prospective homebuyers.

Can You Build on Land with Japanese Knotweed?

Construction can proceed on land with Japanese knotweed, provided proper precautions are taken. If the knotweed infestation is located outside the development’s footprint and buffer zones (typically 4-7 metres from the growth), in-situ herbicide treatment supported by a site-specific Management Plan can suffice. Such a plan should include a Completion Report and a certificate confirming the control programme’s success.

However, if the infestation and its rhizomes fall within the planned construction footprint, mechanical excavation becomes necessary. Unfortunately, many developers fail to identify knotweed before beginning construction, leading to costly delays and complications. Misjudging the extent of an infestation is another frequent issue.

While developers are not legally obligated to conduct Japanese knotweed surveys, engaging an invasive plant specialist to perform a comprehensive survey is highly recommended. Reputable companies typically prioritise ethical practices and ensure proper knotweed management before proceeding with development. Avoiding these responsibilities not only risks financial penalties but can also result in legal action.

To mitigate potential issues, developers should make Japanese knotweed surveys a standard part of project planning and due diligence. This proactive approach can save considerable time, money, and resources in the long term.

What Should an Invasive Plant Specialist Do?

A qualified invasive plant specialist plays a critical role in managing Japanese knotweed on development sites. Their expertise ensures that eradication and control efforts are both effective and compliant with environmental regulations. Here are some key responsibilities they should fulfil:

• Understanding Best Practices: Specialists should be well-versed in the latest and most effective eradication and control methods, helping clients understand the options available and easing concerns about knotweed’s presence.
  

• Recommending Site-Specific Solutions: They should offer tailored advice on the most suitable and cost-effective methods for eradication or control, considering the unique characteristics of each site.
  

• Minimising Waste and Costs: Accurate identification of viable knotweed rhizomes, crowns, and stems ensures no unnecessary excavation. This precision reduces the volume of soil requiring disposal, saving costs and aligning with environmental directives.
  

• Protecting Biodiversity: Specialists should adopt practices that benefit native biodiversity, such as managing invasive plants along waterways to protect pollinators and other wildlife.
  

• Promoting Sustainable Practices: By adhering to Integrated Pest Management (IPM) principles and the Irish National Action Plan on Sustainable Pesticide Use, specialists ensure the responsible use of herbicides and compliance with environmental policies.
  

Key Takeaways for Developers

• Conducting a Japanese knotweed survey should be a standard practice for all development projects.
  

• Engaging a knowledgeable invasive plant specialist can save time, money, and legal complications.
  

• Proper identification and management of knotweed reduce environmental impact and support biodiversity conservation.
  

• Ethical and sustainable practices not only protect the environment but also enhance a developer’s reputation.

Taking proactive measures to address Japanese knotweed ensures smooth project execution and contributes to sustainable land management. Developers, landowners, and invasive plant specialists must collaborate to tackle this invasive species effectively, turning a potential challenge into an opportunity for responsible environmental stewardship.