Is Japanese Knotweed Poisonous?

Japanese knotweed, scientific name Fallopia japonica, is a robust, herbaceous perennial that has garnered notoriety for its vigorous growth and the damage it can inflict on property structures. Originating from Asia and introduced to the UK in the 19th century as an ornamental plant, it is now considered one of the most problematic invasive species across the country.

Your concerns about its toxicity, especially considering its pervasive nature, are justified and deserve a clear response.

Surprisingly, while Japanese knotweed has been a bane to homeowners due to its relentless spread and the difficulty of eradication, it poses no direct poisoning threat to humans. The plant does not produce any toxins harmful to people and, in fact, is edible with a taste reminiscent of tart rhubarb. However, its consumption is not commonplace, and it is usually not advocated due to its environmental impact rather than any health risks.

In contrast, the plant’s effect on the environment and biodiversity is significant.

Its dense growth can outcompete native flora, leading to a reduction in local biodiversity. Controlling its spread is a task that requires strategic planning and perseverance, given that even a small fragment of its root system can give rise to a new plant, contributing to its notorious reputation.

From the perspective of human health, though, Japanese knotweed’s poisonous nature is a myth; your primary concern should centre on its environmental implications and potential property damage.

Identification of Japanese Knotweed

Japanese Knotweed (Fallopia japonica), a perennial plant, is distinguishable by its spade-shaped leaves, which can achieve lengths up to 15 centimetres.

The stems, resembling bamboo, are hollow and can grow to 3 metres high. In spring, notice the reddish-purple shoots emerging, while in summer, the flowers bloom in creamy-white clusters.

Physical Characteristics:

• Stems: Hollow, segmented, bamboo-like texture
• Leaves: Green, spade-shaped with a pointed tip
• Flowers: Small, creamy-white, in clusters
• Shoots: Reddish-purple and tender in spring
• Height: Can grow to approximately 3 metres

Growing Habits:

• Habitat: Thriving in a range of soil types, typically near water bodies or in urban waste land.
• Spread: Rapidly expands through rhizomes, which are horizontal underground stems.

Seasonal Changes:

• Spring: Reddish-purple shoots appear.
• Summer: Flowers form and leaves fully mature.
• Autumn: Foliage yellows and the plant begins to die back.
• Winter: Stems turn brown and can remain standing.

When trying to identify this plant, be aware of its ability to spread quickly and its resilience. It can cause considerable damage to building structures if left unchecked.

If you believe you have identified Japanese Knotweed on your property, it’s recommended to seek professional advice for management and removal.

Toxicity Overview

Japanese Knotweed, while not toxic to humans in a traditional sense, warrants caution due to its aggressive growth that can cause ecological imbalances.

Effects on Humans

Your exposure: Japanese Knotweed is not inherently poisonous to you or other humans if touched or ingested. In fact, some cultures use it for culinary and medicinal purposes, considering it safe after proper preparation.

Effects on Animals

Animal Health: Non-toxicity also extends to domestic and wild animals, with no severe adverse effects reported upon consumption. However, the plant’s capability to dominate habitats can indirectly harm wildlife by reducing biodiversity.

Impact on Ecosystem

Japanese knotweed poses significant challenges to ecosystems due to its aggressive growth and resilience.

Invasive Species Concerns

As an invasive species, Japanese knotweed (Fallopia japonica) has a tenacious ability to spread, outcompeting local flora for vital resources. Its dense growth:

• Restricts native plants from accessing sunlight.
• Changes soil composition, making it harder for indigenous species to thrive.
• Reduces biodiversity by forming extensive monocultures.

Environmental Threats

Japanese knotweed’s environmental threats are not limited to plant life; they extend to animal habitats and human activities:

• Alters natural habitats, impacting local fauna.
• Disrupts waterways, which can lead to increased erosion and affect aquatic life.
• Poses a challenge to urban environments by damaging infrastructure like building foundations and roadways.

Control and Management

Effective management of Japanese knotweed involves a combination of chemical and mechanical methods. Your choice of treatment depends on the specific circumstances and the extent of infestation.

Chemical Treatment

Herbicides: The use of glyphosate-based herbicides is a common approach. Treatment requires multiple applications:

• Spring/Summer: Apply when the growth is lush.
• Autumn: Target when the plant is transferring nutrients to the roots.

Safety Note: Always follow the label instructions and consider the impact on surrounding vegetation and water systems.

Mechanical Removal

Excavation: Removal of the plant material and contaminated soil is a direct method. This process should include:

• Safe disposal at licensed facilities to prevent spreading.
• Monitoring post-removal to ensure no regrowth.

Root Barriers: Installing root barriers can prevent the lateral spread of rhizomes, protecting uncontaminated areas:

• Material: Typically robust, impermeable fabrics.
• Depth: Should extend well below the typical rhizome penetration depth.

Legislation and Compliance

Japanese knotweed (Fallopia japonica) is subject to specific regulations in various countries due to its aggressive growth and potential to cause environmental and structural damage. Compliance with these laws is mandatory.

In the UK, the Wildlife and Countryside Act 1981 lists Japanese knotweed as a Schedule 9 species. This designation makes it an offence to “plant or otherwise cause to grow in the wild” this species.

Property owners are responsible for controlling this plant and preventing its spread into wild areas.

When dealing with Japanese knotweed, several legislative documents should guide your actions:

• Environmental Protection Act 1990: Describes Japanese knotweed as ‘controlled waste,’ and dictates its disposal at licensed landfill sites only.
• Anti-social Behaviour, Crime and Policing Act 2014: Grants local councils the authority to issue Community Protection Notices against improper management of the plant, which could lead to its spread.

Key Compliance Points:

• You must not plant or encourage the growth of Japanese knotweed.
• Containment and elimination measures should be conducted carefully to avoid dissemination.
• Waste containing knotweed requires disposal at authorised facilities.
• You may face legal action if your management of Japanese knotweed causes harm to local biodiversity or neighbouring properties.

It is crucial to seek professional guidance when dealing with Japanese knotweed to ensure adherence to all relevant legislation.

Employing recognised eradication methods and engaging accredited professionals for removal and disposal is highly recommended to maintain compliance.