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Invasive Species Week 2021

Updated: May 12, 2023

This week is Invasive Species Week, so we’d like to raise awareness of some of the more common Invasive Weeds that ERS deals with, starting with the most well known one, Japanese Knotweed:

Japanese Knotweed

Typical Japanese Knotweed growth in various seasons

Japanese Knotweed can be identified by the red asparagus-like spears of early growth, followed by bamboo-like canes with alternating leaves with white flowers in summer. In winter the leaves die off leaving light coloured, brittle canes.

Japanese Knotweed can spread aggressively and is difficult to remediate due to its extensive underground network of rhizomes from which new plants can regrow. New growth can exploit weaknesses in concrete, tarmac and brick structures, which is why its presence can have a negative impact on property prices.

ERS are experts at Japanese Knotweed treatments and our work comes with a 10 year insurance backed guarantee.

Giant Hogweed

Typical Giant Hogweed growth in various seasons

Number 2 on our Invasive Species Week list is Giant Hogweed. As the name suggests, this phytotoxic plant can grow up to 5m tall!

Aside from the height and its resemblance to the much smaller native Common Hogweed, Giant hogweed can be identified by its large, sharply divided, serrated leaves and its hollow green stem with hairy bristles and purple blotches.

All parts of the Giant hogweed plant contain phytotoxic sap which causes a severe rash when exposed to sunlight. If you come into contact with it, wash the area thoroughly, keep it covered from sunlight and seek medical advice.

Himalayan Balsam

Himalayan Balsam is typically found near watercourses but also in wooded areas

Number 3 on our list is Himalayan Balsam. This vigorously growing weed is commonly found along watercourses where it forms dense stands, blocking out sunlight and out-competing native plants.

Himalayan balsam can be identified by its finely serrated-edged whorls of leaves and trumpet shaped pink or purple flowers. The stems are hollow and brittle and the plants can grow up to 2.5m in height.


Rhododendron ponticum in flower, growing out of a wall

At Number 4 on list is Rhododendron ponticum, an invasive member of the Rhododendron family of ornamental plants.

Rhododendron ponticum is a versatile plant found across moorlands, woodlands, hillsides and riverbanks, as well as in gardens and parks. Its nectar is toxic to European honey bees* and it can also harbour harmful Phytophthora pathogens which can spread to and kill native woodland trees.

Rhododendron ponticum can be identified by its leathery, dull green leaves and light, woody stems. Mature plants can reach 8m in height and produce pink to purple clumps of flowers between May and June.

American Skunk Cabbage

American Skunk Cabbage in flower and after flowering

The final common invasive weed we’d like to highlight for Invasive Species Week is American Skunk Cabbage.

It can be easily identified by its rosette of large leathery green leaves and yellow hood-like flowers which have a strong skunk odour, giving the plant its name.

American Skunk Cabbage forms dense stands in wet, muddy areas surrounding ponds, streams and marshy woodlands, and can outcompete many of the sensitive native species growing in these habitats.

So is this a definitive list?

By no means! In fact, there are 77 species of invasive plants listed in the Property Care Association’s Invasive Non-Native Species (INNS) list.

ERS has experience at dealing with many of these invasive plants, including heavily invested sites and environmentally sensitive areas, and we have a range of treatment options available depending on the plant and the site. If you are interested in any of our Invasive Weeds services, please take a look at our Invasive Weeds webpage or download our handy brochure on identification and treatment options.

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