505256
Credit: Invasive Species Council of British Columbia

505256

Invasive plants aren't just nuisances, they're deadly monsters that encroach on everything, from highways to water banks and private properties. These are just a few of British Columbia's most despised species

Don’t be fooled by their dainty flowers and vibrant colours; invasive plants are anything but innocent! According to the Invasive Species Council of British Columbia, these aggressive plants can “permanently alter ecosystems, reduce property values, impact natural resource sectors of the economy, and in the worst case, cause the extinction of native species.”

Far away from natural predators and pathogens, these alien plants, which have made their way one way or another from their native area to BC, tend to multiply rapidly and wreak havoc on BC’s vulnerable landscape. To protect the local flora and fauna, it’s crucial to identify the “invaders” and effectively eliminate them.

Here are BC’s most “unwanted” plants to seek out and eradicate.

Giant Hogweed <em>(Heracleum mantegazzianum)</em>
Credit: Invasive Species Council of British Columbia

Giant Hogweed (Heracleum mantegazzianum)

Adorned with white flowers and huge jagged-edged leaves, the Giant Hogweed shoots up to a towering height of five metres (16 ft.) This plant dominates the Lower Mainland, eastern parts of Vancouver Island, the Gulf Islands, and parts of the Kootenays.

The sap of the Giant Hogweed is extremely dangerous when touched. Rashes and blistering can persist for up to 10 years(!) after contact, while contact with eyes results in temporary or permanent blindness.

To remove the hogweed, a professional is highly recommended. If you must do it yourself, wear eye protection and waterproof gloves and gear at all times when removing flower heads and cutting root crowns. Do not touch your skin with the gloves and clean or dispose of them afterward.

Common Tansy <em>(Tanacetum vulgare)</em>
Credit: Invasive Species Council of British Columbia

Common Tansy (Tanacetum vulgare)

With 20-200 flower heads, the Common Tansy boasts vibrant yellow petals and stems as high as 1.8 metres (6 ft.). It is widely distributed across the province, but is particularly prominent on the southeast coast of Vancouver Island, Squamish/Pemberton, Gulf Islands, Sunshine Coast, Bulkley-Nechako, Central and East Kootenay, Columbia-Shuswap, North Okanagan Regional Districts, Greater Vancouver, and the Fraser Valley.

Considered noxious by the Weed Control Act, infestations of the common tansy can be toxic for farm animals. They can also displace native plants.

Be warned: Occasional mowing will only trigger an increase in plant growth. You must use both herbicide and mowing to effectively eradicate the Common Tansy.

Spotted and Diffuse Knapweed <em>(Centaurea biebersteinii and Centaurea diffusa)</em>
Credit: Invasive Species Council of British Columbia

Spotted and Diffuse Knapweed (Centaurea biebersteinii and Centaurea diffusa)

Labelled noxious under the BC Weed Control Act, Spotted and Diffuse Knapweeds negatively transform the landscapes of the Omineca, Peace River, Kootenay, Okanagan, Thompson and Cariboo regions.

Spotted Knapweed possesses purple or white flowers with black tipped flower head bracts, while the diffuse knapweed have white, rose-purple or lavender blossoms in clusters.

Knapweeds intensify erosion and runoff, and displace native plants. When dead, its materials increase the chance of wild fires.

Eliminate the plant by hand pulling, cutting or mowing. Remove all roots to prevent regrowth and revisit the spot every so often to avert further growth.

Yellow and Orange Hawkweeds <em>(Hieracium spp.)</em>
Credit: Invasive Species Council of British Columbia

Yellow and Orange Hawkweeds (Hieracium spp.)

Rapidly spreading throughout the eastern and western BC, invasive Hawkweeds are threatening the forest regions of the Northern Rockies, the Peace River Regional Districts and the eastern regions of the Rocky Mountains.

While the majority of Hawkweeds have bright-yellow blossoms, the only Hawkweed identified as noxious by the Weed Control Act is vibrantly orange. The Orange Hawkweed dominates the East Kootenay, Central Kootenay, Thompson-Nicola, Bulkley Nechako, Cariboo Regional Districts and Columbia-Shuswap.

Menaces to both the forest and livestock industry, Hawkweeds displace native plants, reduce forage, and invade undisturbed natural areas.

To get rid of small infestations, dig out the flower and its roots, but ensure that none of the plant parts scatter as they can easily regrow from these fragments.

Japanese Knotweed <em>(Fallopia japonica)</em>
Credit: Carol Pope

Japanese Knotweed (Fallopia japonica)

Capable of growing through house foundations and cement, the Japanese Knotweed possesses stout reddish-brown stems, rough heart-shaped leaves and seasonal greenish-white flowers. Its favourite hangouts include roadsides, waste sites, wooded areas and waterways in the lower Fraser Valley region.

A born survivor, this plant can grow up to 3 metres (10 ft.) in a year and can worm its way into new territories simply with root fragments. It clogs waterways and deteriorates native plant communities.

To eradicate the Japanese Knotweed, you must remove existing stems, cover the area with plastic tarps during the fall and, finally, dig up rhizomes to prevent further growth. Since it will not compost properly, this knotweed must be bagged and buried deep in a landfill.

Scotch Broom <em>(Cytisus scoparius)</em>
Credit: Carol Pope

Scotch Broom (Cytisus scoparius)

Reaching as high as 3 metres (10ft.), the Scotch Broom can be recognized by its ridged green or brownish green stems, and vivid yellow flowers. It flourishes in sandy soils, haunting the terrains of Vancouver Island, Queen Charlotte Islands, the southern interior and the Lower Mainland.

The Scotch Broom releases toxic substances into its surroundings, restraining the growth of native plants and causing seasonal allergies. It establishes menacing colonies and hinders the activities of large animals. The worst part? Each pod contains 3 to 12 seeds, seeds that can survive over 30 years!

Eliminate the Scotch Broom by removing it before the flowering stage. Hand-pull the smaller ones and keep your eyes on the area every so often. For deep-rooted plants, remove with large tools, such as a shovel or gas-powered or hand saw.

Yellow Flag Iris <em>(Iris pseudacorus)</em>
Credit: Invasive Species Council of British Columbia

Yellow Flag Iris (Iris pseudacorus)

From 40 to 150 cm tall, the Yellow Flag-iris is distinguished by bold yellow flowers and long erect leaves. This species is generally located along riverbanks, marshes, and lakes in southern parts of BC.

The Yellow Flag-iris does not only reduce water flow, but also displaces native plants, consequently damaging the wildlife habitat. What’s more, the rhizomes are poisonous when ingested by cattle.

The most effective technique to eradicate this species is hand-pulling or cutting for a number of years until it is completely removed. Since its leaves and rhizomes lead to skin irritation, it’s vital that you wear gloves and protective clothing. Do not compost; always throw it away as garbage.