Injurious weeds, also known as harmful weeds, are plants recognised as posing a significant threat to agricultural land in the UK. These plants, although sometimes contributing to biodiversity, can cause damage to crops and be poisonous to animals. Hence the use of the term ‘noxious weeds’ in relation to this group of plants, albeit this is inaccurate as not all are. The UK has established legislative measures to manage these weeds, primarily through the Weeds Act 1959 and the Ragwort Control Act 2003.


Here, we will explain the legislative acts, identify the weeds they cover, and discuss methods for managing and controlling these harmful plants.


What is the Weeds Act 1959?

The Weeds Act 1959, often mistakenly referred to as the ‘Injurious Weeds Act’, is UK legislation designed to control the spread of five specific injurious weeds. Brought forward in 1959, but based on legislation from the 1920’s. The Act was created to highlight the issues with some harmful weeds that, although native to the UK, were thought to be problematic in agricultural and horticultural contexts.

Creeping thistle - a listed injurious or harmful weed in the UK grwoing in a field in South Wales

Creeping thistle Creeping thistle (Cirsium arvense) growing in a field in South Wales (UK)

The UK Government website details how to make a complaint about injurious weeds, and states that The Department for Environment, Food and Rural Affairs (Defra), prioritizes complaints where:

  • Weeds are threatening land used for keeping or grazing horses and other livestock
  • Farmland used to produce conserved forage, or other agricultural activities
  • The complainant has made reasonable efforts to contact the landowner or occupier where the weeds are growing

The Act does not criminalise the presence of these weeds on land but empowers authorities to require landowners to manage and prevent their spread. it outlines the responsibilities of landowners and occupiers in dealing with these weeds, with failure to comply potentially resulting in penalties.

The Weeds Act lists the following injurious weeds:


The Ragwort Control Act 2003

Introduced to amend the Weeds Act 1959. The Ragwort Control Act 2003 focuses on controlling Common Ragwort due to its toxicity to livestock. It came about after John Greenway MP (supported by The British Horse Society)  initiated a Private Member’s Bill to amend the Weeds Act 1959. This resulted in The Ragwort Control Act 2003.

Ragwort in flower. A plant known to be noxious or harmful plant to horses found growing on common land in the UK

Flowering ragwort (Senecio jacobaea) growing on common ground in the UK

The Act provides enforcement mechanisms, including fines for non-compliance, and emphasises the balance between controlling ragwort and preserving its ecological benefits. The Department for Environment, Food & Rural Affairs (DEFRA) published the Code of Practice on Ragwort Control, highlighting the need for responsible management without aiming for total eradication.

It noted a particular relevance ‘for large scale organisations managing significant land areas, including local authorities and public bodies’.


Which are the notifiable weeds in the UK?

Contrary to popular belief, there are no weeds officially classified as ‘notifiable’ in UK law. The confusion arises from misinterpretations of legislative terms. The Weeds Act 1959 covers five specific weeds, but these are not ‘notifiable’ and do not require reporting to authorities.

The commonly misunderstood term ‘noxious weeds’ also contributes to this confusion, but it is important to use the correct terminology to avoid misinformation.


Identification of UK injurious weeds

The visual characteristics of most of the species listed in the Weeds Act 1959 vary quite distinctly. However, two species (dock and thistle), have an additional family member present on the list. Thankfully, all of the injurious weeds in the UK have identifying features that distingusih them. This is an essential step so that the correct control measures can be put in place.

Spear thistle (Cirsium vulgare)

A biennial or perennial plant with spiny leaves, which forms purple or red tufted flowers above dark green spiked leaves. In its first year after germinating, Cirsium vulgare grows as a rosette close to the ground. In the late spring of the second year, spear thistle ‘bolts’, producing spined flowering stems that can reach a height of over 1.5 metres.

Found mainly in pastoral land and along roads, it is easily spread by vehicles as they pass by. Spear thistle control is required due to its vigorous growth and ability to outcompete native vegetation in agricultural fields, pastures, and natural habitats. These characteristics can lead to a reduction of crop yields where the species becomes established.


Flowering spear thistle (Cirsium vulgare) pictured growing in an urban UK setiing, beside a fence

Flowering spear thistle (Cirsium vulgare) pictured growing in an urban UK setiing, beside a fence

Creeping thistle (Cirsium arvense)

A perennial weed with spined, lobed leaves and light purple flowers. Cirsium arvense spreads aggressively through creeping roots that can extend horizontally up to 6 metres and can extend vertically up to 3 metres. Blooming from July to September, its flowers turn white as the seeds ripen.

Typically found in agricultural fields, pastures, and along roadsides, creeping or ‘field thistle’ quickly establishes itself in disturbed soils. It outcompetes other vegetation by height, but also has allelopathic properties. By releasing natural biocides that inhibit other plants it enhances its competitive edge, and can reduce crop yields.


Flowering creeping thistle (Cirsium arvense), with butterfly, growing on UK common land

Flowering creeping thistle (Cirsium arvense), with butterfly, growing on UK common land

Curled dock (Rumex crispus)

Curled dock is a perennial plant with distinctive wavy-edged leaves and reddish-brown flowers. Emerging as a rosette of leaves close to the ground, which eventually produces a tall flower spike. This can reach up to 1.5 metres in height, and produce heart-shaped seeds that can remain viable in the soil for over 50 years. This makes curled dock a persistent weed once established.

Common in pastures, meadows, and disturbed lands, curled dock competes aggressively for resources, reducing crop yields and pasture quality. Its long-lived seeds contribute to its resilience, and effective management (at least in part) requires preventing the plant from seeding.


The tall seed spikes of curled dock (Rumex crispus) prominent in a rural UK setting

The tall seed spikes of curled dock (Rumex crispus) prominent in a rural UK setting

Broad-leaved dock (Rumex obtusifolius)

Broad-leaved dock is similar to curled dock but features broader leaves and greenish-white flowers. This perennial weed also starts as a rosette and develops a tall flower spike. The seeds of broad-leaved dock are also highly viable, with a long lifespan that makes it difficult to eradicate once established.

Found in pastures, meadows, and along roadsides, broad-leaved dock can significantly reduce agricultural productivity. It is particularly problematic in disturbed soils, where it quickly establishes and spreads. The need for the control of broad-leaved and curled dock comes from theior ability to outcompete crops and other native plants for nutrients and water.


Close up of the fruiting-perianth of broad leaved dock (Rumex obtusifolius)

Close up of the fruiting-perianth of broad leaved dock (Rumex obtusifolius)

Common Ragwort (Senecio jacobaea)

A biennial or perennial plant with finely lobed leaves and bright yellow flowers. In its first year, it forms a rosette of leaves, and in the second year, it produces a flowering stem up to 1.5 metres high. Its seeds can remain viable in the soil for up to 20 years.

Ragwort is often found in pastures, grasslands, and along roadsides. The need for ragwort control and removal stems from its toxicity to livestock. It can pose a significant risk when present in dried feeds like hay. Despite its agricultural impact, ragwort is an important nectar source for pollinators and supports diverse insect life.


Flowering ragwort growing on common land in the UK

Flowering ragwort growing on common land in the UK

Methods for controlling harmful weeds

Effective injurious or harmful weed control requires a range of approaches, tailored to the specific plant and context. Methods include:

Herbicides: Use selectively and minimally to avoid environmental damage. Glyphosate is effective but non-selective, while selective herbicides target specific plants. For example, 2,4-D is a selective herbicide commonly used for controlling broadleaf weeds like docks.

  • Mechanical Control: Digging out plants, particularly effective for small infestations. However, for plants with extensive root systems, like Creeping Thistle, mechanical control may require repeated efforts to be successful.
  • Preventing Seeding: Removing seed heads to break the life cycle of weeds. For instance, the seeds of docks can remain viable in the soil for over 50 years, so preventing seeding is essential to long-term control.
  • Cultural Control: Implementing practices such as crop rotation and maintaining healthy, competitive vegetation to suppress weed growth. This approach can reduce the reliance on chemical controls.
  • Biological Control: Utilising natural predators or diseases to manage weed populations. For example, certain insects are known to feed on ragwort, helping to reduce its prevalence.

Integrated Weed Management (IWM) combines these methods for more effective and sustainable control. Always consider the ecological impact before deciding on control measures.

Need help with injurious weeds? Our specialists are equipped to help you identify and control invasive and harmful plants. Whether you need assistance with creeping thistle, common ragwort, or any other injurious weed, we are on hand to help. Call 0203 174 2187 or 01202 816134 to talk to one of our consultants today.


Lead image: Close up of spear thistle flowers and leaves
All pictures © tintac



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