There are a large number of non-native and also native plants which are known to be invasive. We list a few weeds that we are regularly contracted to eradicate. We hope the invasive weeds pictures along with descriptions of the plants will assist you in identification of common invasive weeds. However, if you're still struggling with your invasive weed identification, please use the form on this page to contact us and upload pictures so that we can identify it for you.
Non-native invasive plant species are listed in Schedule 9, part II of the Wildlife and Countryside Act 1981. In the main, it lists species that are already established in the wild, but which continue to pose a conservation threat to native biodiversity and habitats, such that further releases should be regulated (under Section 14 of the Act).
There are other native invasive species such as Field Horsetail which are not listed on the Wildlife and Countryside Act. However these also pose a significant problem to home owners and developers alike.
Himalayan Balsam (Impatiens glandulifera)
What is Himalayan balsam?
Himalayan or Indian balsam (Impatiens glandulifera) is an annual herb and was introduced to Britain in 1839. Its common name is “Policeman’s Helmet” due to the shape of the flowers. Other balsam include Orange balsam (Impatiens capensis – from North America) and the rare Touch-Me-Not balsam (Impatiens nolitangere – native to British Isles). Himalayan balsam grows up to 3 metres high with a hollow and bamboo-like stem, pink-red to green in colour with green vertical grooves. Because of the colour and type of the stem it has occasionally been mistaken by the uninitiated for Japanese knotweed. Leaves are long, slender and shiny, with serrated edges and are dark green in colour.
Himalayan balsam produces purplish to pale pink flowers in mid-late summer. On rare occasions flowers are white. Seed pods are carried on long stalks between June and October and resemble an elongated pear. When disturbed or touched they split, resulting in seeds literally exploding from the plant. Each plant can produce around 2,500 seeds that can be propelled up to 7 metres in distance. Seeds that enter watercourses can travel over 10 km before germinating in the spring. The plant is mainly found on riverbanks and damp ground. It spreads predominantly along watercourses but is also spread by human interaction.
What are the Dangers?
Himalayan balsam presents no physical danger to either humans or animals. It does, however, provide a significant ecological impact since it grows in dense stands that suppress native grasses and other flora. In the autumn the plants die off leaving riverbanks bare and highly susceptible to erosion.
There are no legal issues relating to Himalayan balsam.
Control and Eradication of Himalayan Balsam
Relatively weak roots means the plant can be pulled or dug up before the seed pods are produced. Digging operations will need to be carried out for at least two years as seeds can remain viable for several years. Chemical control is also possible, though Environment Agency consent will have to be sought prior to chemical application to plants on riverbanks. Japanese Knotweed Ltd always liaise closely with Environment Agency officials in such circumstances. It should be noted that if Himalayan balsam still exists upstream then control will never be fully effective.
Himalayan Balsam Pictures
Giant Hogweed (Heracleum mantegazzianum)
What is Giant hogweed?
Giant hogweed (Heracleum mantegazzianum) is a member of the Parsley family (Wild Carrot, Fool’s Watercress, Cow Parsley, Hogweed, Wild Angelica, Alexanders, Sweet Cicely, Hemlock) and is native to Asia
- Hollow green/purple stems with fine spines that make them appear furry.
- Dark green coarsely toothed leaves.
- Small white flowers are arranged in flat-top umbrella-like clusters.
- Growth up to 3-5 metres tall with individual umbels measuring up to half a metre across and leaves up to 2 metres across.
The plants’ dense canopy can out-compete native species and cause stream bank erosion in riparian areas when the large shading plant dies back late in the year leaving riverbanks exposed to the elements.
Fattened, oval fruits are produced with a broadly rounded base and each plant supports thousands of individual flowers. Giant Hogweed reproduces through seeds produced in late summer and/or perennial buds that form on the root stalks of the crown. It can produce up to 50,000 seeds per plant (approximately 1,500 per flower head), which can be catapulted distances of up to 4 metres. Seeds can remain inactive in the ground for several years.
The plant can be both a biennial or a perennial, normally flowering around May in the second, third or fourth year after germination.
What are the Dangers?
Giant hogweed growing across or along the route of a public right of way is likely to attract the involvement of the Environment Agency due to the threat it presents to public health.
Hairs on the outside of the stems and poisonous sap on the inside of the stems and leaves can cause severe irritation. The sap reacts with the skin and makes the skin sensitive to ultra-violet light, though no pain or irritation is felt at the time of contact. Any subsequent exposure to sunlight can cause the skin to burn and will result in large, watery blisters that do not become evident until 15 to 20 hours following contact, by which time the damage has been done.
Blisters may develop into purplish or blackened scars and could persist as recurrent photo-dermatitis long after exposure. Contact with the eyes can lead to temporary (or, in some cases, permanent) blindness. Children can be most at risk, as Giant hogweed is highly attractive to them.
Giant hogweed is also a host for both carrot fly and the disease Sclerotinia sclerotiorum, both of which attack many horticultural and arable crops.
Under The Wildlife and Countryside Act 1981 / Wildlife (Northern Ireland) Order 1985 it is an offence to introduce Giant hogweed into the wild. This includes transferring soil contaminated with hogweed material (such as seeds) from one location to another. Under the Environmental Protection Act 1990, Duty of Care Regulations 1991, hogweed infested soil or plant material must be removed to a licensed landfill site for disposal accompanied by appropriate Waste Transfer documentation.
Control and Eradication of Giant Hogweed
Due to the longevity and quantity of the seeds, full eradication can take a number of years to achieve. To be effective all control measures should be undertaken each year before the plant produces seeds (early spring to early summer).
Eradication of Giant hogweed through herbicide treatment alone can take a minimum of three years - and could take up to ten, due to the proliferation of seeds that form a dormant ‘seed bank’ over successive years. Any chemical application to plants found growing near watercourses will require the granting of written consent from the Environment Agency prior to treatment. Japanese Knotweed Ltd always liaises closely with Environment Agency officials in such circumstances.
Great care should be taken whilst conducting any Giant hogweed works to ensure the plant does not come into contact with the skin or eyes. A face-shield, gloves and suitable protective clothing should be worn during any Giant hogweed operations, and it is advisable to have at least two operatives conducting works in case one of them slips and falls into the plant’s foliage. If at all possible, avoid working in direct sunlight when dealing with Giant hogweed.
The plant may be hand dug, but care must be taken to remove as much root material as possible, as a plant can grow from a section of root carrying auxiliary buds. Alternatively, the hogweed can be mechanically excavated, as long as due allowance is made for the extensive seed bank. Following excavation new seedling growth should be controlled by use of herbicide. Cutting of the plant is not an efficient long-term solution and is not recommended on any plant exceeding 1.5 metres in height due to the risk of direct contact.
Giant Hogweed Pictures
Field Horsetail (Equisetum arvense)
What is Field Horsetail?
Field Horsetail (Latin name ‘Equisetum arvense’) is often referred to as Mare’s tail and is an invasive native herbaceous perennial plant (weed). Horsetail is easily recognised throughout the summer and autumn by its upright (5-60cm height) light green, fir tree like shoots (pointed green shoots with folded needle like leaves pointing upward around the stem). These shoots are rough to the touch as they have a natural hard casing. In spring, the plant first appears as light brown stems (20-50cm tall) with a fertile spore producing cone structure at the end of the stems. A single cone can produce 100,000 spores. As a perennial the above ground growth completely dies off in the winter.
Horsetail has an underground stem structure called rhizomes. These creeping rhizomes may go down as deep as 2m (7ft) below the surface and spread out laterally. This enables the plant to spread not only by spore dispersal but underground rhizome growth as well. In fact the main method of spread is by vegetative reproduction of detached rhizomes and tubers.
What are the Dangers?
Horsetail is a pernicious weed capable of rapidly colonising a diverse range of sites as it’s extremely hardy. It spreads quickly, out-competing other plants to form a dense carpet of foliage. Surprisingly due to the relative fragility of the individual stems it also presents a damage risk to hard standing.
Unfortunately it is common to see hard standing (block-paving, macadam roads and pavements) damaged by Horsetail growth, where the rhizome has exploited gaps in these surfaces. Developers who have failed to identify and remove Horsetail under construction therefore do find this plant re-appearing through newly laid driveways and footpaths!
Control and Eradication of Horsetail or Mare’s tail
Control can be achieved by professional application of suitable herbicides. However the hard casing of the plant, its deep extensive rhizome system and spore dispersal make it very hard to eradicate. The application of herbicides should be seen as a control measure only in nearly all cases and unlikely to achieve complete eradication.
Complete eradication can be achieved via the digging out (excavation) of the plant, which requires our expertise to ensure that the entire rhizome is identified and removed. This is the preferred method for development sites to reduce the risk of subsequent hard standing damage post construction completion.
Where Horsetail has already caused hard standing damage we would only recommend repairing this damage once the Horsetail has been dug out (perhaps accompanied by the installation of protective root barrier). If the Horsetail was to be treated with herbicide only the risk of re-growth and repeat damage to the hard standing is high.
Field Horsetail Pictures
Common Ragwort (Senecio jacobaea)
What is Ragwort?
Common ragwort (Senecio jacobaea) is usually a biennial plant, producing a rosette in the spring of the 1st year and flowers between May and October of the 2nd year - although disturbance to the plant can cause it to live for longer periods. It has characteristic dark green leaves, tough stems and yellow daisy-like flowers. Rosettes consist of a circular cluster of leaves with a ragged appearance (hence the name), usually deep green on top and cottony underneath. The rootstalk, leaf stalks and lower parts of the stem may have a purple/red colour.
Most plants die off following flowering, making way for immediate colonisation by the seedlings. The seeds have a downy appendage making them readily dispersible by the prevailing wind. They can also be dispersed via water or inadvertently transported by humans or livestock. Each plant can produce up to 150,000 seeds with a 70% germination rate – with seeds remaining dormant in the soil for up to 20 years. Mature ragwort can grow up to 1-2 metres in height and it proliferates on roadside verges, railway tracks, wasteland and pasture. It prefers light soils of low fertility, particularly in over- or under-grazed pasture.
Ragwort can often be identified by the presence of Cinnabar moth caterpillars (Tyria jacobaeae), as these caterpillars feed almost exclusively on ragwort. The caterpillars are distinctive, black with gold stripes, and grow up to 30mm long.
What are the Dangers?
Ragwort is one of the most frequent causes of plant poisoning of livestock in Britain, with equines and bovines being more susceptible than others – particularly the young. It can also be poisonous to people and has been suspected of causing liver damage in those who seek to pull the plant without the benefit of protective clothing.
Ragwort poisoning can occur at any time of year. Ragwort acts as a cumulative poison, eventually destroying the liver, and a small intake of ragwort over a long period can be just as damaging as a large intake on a single occasion. Clinical symptoms of poisoning by ragwort are loss of condition (weight loss, dull coat, depression), poor appetite and constipation, photosensitisation (sunburn) and sometimes jaundice. The development of nervous behaviour, restlessness and aimless uncoordinated movement are some of the common terminal symptoms. Animals may appear blind, press their heads against solid objects and develop an abnormal gait and stance. Animals can die after as little as a week, though some can survive several months. Little can be done for an animal once the clinical symptoms appear.
Livestock tend to avoid eating ragwort on good pastures but it is advisable, as a precaution, to ensure horses do not have access to plants. The poisons in ragwort are not destroyed by drying out and the plant becomes much more palatable when cut or wilted, as it loses its bitter taste. Therefore all cut material must be removed from site. Common sources of ragwort poisoning are dried grass, hay and silage where it can lie undetected and be consumed readily.
Common ragwort is the only ragwort species specified in The Weeds Act of 1959 (other species of Senecio are not so widespread). Under The Weeds Act, the Secretary of State may serve an enforcement notice on the occupier of land on which injurious weeds are growing, requiring the occupier to take action to prevent the spread of these weeds. Responsibility for weed control rests primarily with the landowner. Further information on a landowners responsibilities in regard to The Weeds Act can be found in the Department for Environment Food and Rural Affairs (DEFRA) leaflet "The Weeds Act 1959 – Preventing The Spread of Harmful Weeds", which is available from DEFRA publications and also on the DEFRA website.
The Ragwort Control Act came into force on 20 February 2004 as an amendment to The Weeds Act and enabled the Secretary of State to draw up a Code of Practice to prevent the spread of ragwort. By promoting good practice and good neighbourliness the Code aims to reduce significantly the risk posed by ragwort poisoning. It is particularly relevant for large-scale organisations, including local authorities and public bodies, and provides comprehensive guidance on how to develop a strategic and more cost-effective approach to weed control. It gives advice on the identification of Common ragwort, risk assessment and priorities for ragwort control, control methods, their suitability and efficiency, environmental considerations and health and safety issues. Under the Ragwort Control Act, the Code is admissible in enforcement proceedings under The Weeds Act, which will make it easier to prosecute those who disregard the need to control ragwort. Similarly, those who have followed the guidance laid down in the Code would be able to use this in their defence in any Court proceedings.
It should be noted that the Code does not seek to eradicate ragwort completely. It is important to remember that, where there is no threat to animal welfare, Common ragwort is a native species and makes an important contribution to the biodiversity of the countryside.
Control and Eradication of Ragwort
Active control of Common ragwort is the only way to avoid the risk of ragwort poisoning. Control needs to be ongoing and, preferably, combined with good pasture management. Over-grazing and under-grazing creates open patches of land where ragwort can readily establish itself. Ragwort will not establish where there is a dense vigorous grass sward. Such a pasture can be best achieved through controlled grazing and/or regular fertiliser applications. This encourages root development of grasses and makes a valuable contribution to preventing re-infestation.
Cutting and stem removal at the early flowering stage reduces seed production but does not destroy the plant. It is acceptable in an emergency situation but is generally not recommended long-term as it encourages more vigorous re-growth. Pulling or digging is a popular method of control but experts believe its effectiveness as anything other than an emergency short-term measure is severely limited. If carried out, this operation needs to be performed before flowering has completed and it is important to remove as much of the root as possible since ragwort can regenerate from its root fragments. All wilted and dead Ragwort from the pasture should be removed and burned. Always wear gloves when carrying out this operation.
No single herbicide application will completely eliminate a ragwort infestation due to successive germinations of the weed. Treatment with selective herbicides can be made in the spring but, as ragwort is a biennial, control measures will have to be conducted for at least 2 years (and probably longer). To be fully effective, treatments should be applied early in the first year of the plant’s growing cycle (rosette). Once it has begun to produce flowers eradication will become a time-consuming and long-term process.