Sep 2022

Below is a detailed list of the top four invasive weeds to be aware of in the Commercial Development Sector other than Japanese Knotweed. We go into depth about what to be aware of at certain times of the year, how to identify them, the idiosyncrasies of each species and the best actions to take.


Field Horsetail (Equisetum arvense)


Is a native herbaceous perennial plant, but very invasive and spreads by both spores and rhizomatus stem system (like Japanese Knotweed). If untreated can and does give rise to damage to Tarmac areas resulting in significant costs. Deep rhizome system and tubers that can be more than 2m down and so excavation is difficult. Difficult to control with systemic herbicides as it is a primitive plant and herbicides are designed for modern plants, but it can be done over a number of years.


  • When in hard surface areas of the development site it is best to consider physical controls, such as root barrier membranes to protect the Tarmac areas.
  • Can be controlled in open landscape areas with herbicide but can take five years or more.
  • Can be confused with Mare’s Tail (Hippuris vulgaris) but this an aquatic perennial herb found in streams and shallow waters.
  • Looks quite different in the Spring to later in the Summer.


Field horsetail in spring
Field horsetail in spring
Field Horsetail in summer
Field Horsetail in summer

Hemlock (Connium maculatum)


Poisonous and invasive


Is not on the Schedule 9 of the Countryside and Wildlife Act (1981) but is poisonous and invasive.

Can be controlled with herbicide control programmes and is important to prevent from flowering to break the lifecycle and eventually the dormant seedbank retained in the soil.

Has a zigzag form so could be confused with Japanese Knotweed (Reynoutria japonica), but has fern like leaves and a distinctive purple speckling on the stem.


Hemlock in flower
Hemlock in flower
Hemlock stem showing the distinctive purple speckling
Hemlock stem showing the distinctive purple speckling


Giant Hogweed ( Heracleum mantegazzianum)


Giant Hogweed is a Non Native Invasive Weed listed on the Schedule 9 of the Wildlife and Countryside Act (1981) which, like Japanese Knotweed (Reynoutria japonica) , requires the owner of the land to ensure that this plant does not spread into neighbouring land.

Giant Hogweed is very invasive and presents a health risk to all those using the site as the sap is phototoxic and can result in significant blistering of the skin which can be so severe as to require hospitalisation.

Can be controlled through excavation or herbicide control.


Winter stem of Giant Hogweed
Winter stem of Giant Hogweed


Hemlock Water Dropwort ( Oenanthe crocata)


Extremely poisonous and could be considered the most poisonous plant in the United Kingdom.


  • Fatal to both humans and livestock.
  • A perennial found in wetland areas and although more common in the South and West has been found elsewhere, such as the Midlands.
  • Presents a serious health risk to all those using the site.
  • Can be controlled using both excavation and or herbicide control programmes.


Excavated Hemlock Water Dropwort showing roots sometimes referred to as 'Dead man's fingers'
Excavated Hemlock Water Dropwort showing roots sometimes referred to as ‘Dead man’s fingers’


Site Check for Invasive Weeds


Contact us to discuss arranging a site visit report to check your site for Japanese Knotweed and other invasive weeds likely to give rise to problems on your development site.

Invasive weed checker

Book an appointment for a quick call

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The Postcode Areas We Serve

Gloucester and Swindon

Birmingham and the Midlands

Bristol and the South West

Cardiff and South Wales

Japanese Knotweed
Giant Hogweed
Himalayan Balsam
Hemlock Water Dropwort