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Posted: August 4, 2018

Home Invasion: Japanese Knotweed

While volunteer groups are out pulling Purple Loosestrife and East Kootenay Invasive Species Council (EKISC) is out selectively spraying Orange Hawkweed, there’s something else lingering on everyone’s mind: Knotweed.

Ask anyone who has experience trying to tackle this plant, it’s a nightmare. Such a nightmare for homeowners in UK that they are being denied house insurance and seeing the value of their home plummet due to this highly invasive plant.

What’s the problem? 

Knotweeds are among the top 10 invasive species for control in B.C. and one of the 100 worst around the globe, as identified by the International Union for Conservation of Nature. Knotweed was first introduced to North America in the 1800’s and was sold in nurseries as an ornamental. Knotweed species have a strong root system and can spread up to 20 meters laterally and to a depth of 3 meters; they have the ability to grow through concrete and asphalt, threatening home foundations and roadways. It is also known to change river flows and interrupt spawning beds.

The compounding problem: control. “These plants are incredibly tough and persistent,” says Jessie Paloposki, Education and Communications Manager for the East Kootenay Invasive Species Council (EKISC), “People are always blown away by the almost superpower-like characteristics of these plants. Plant fragments as small as .07 of a gram can take hold and form new plant colonies.”

To make matters even more complicated, the real estate market here in Canada is following the footsteps of our neighbours in the UK. Homeowners who have Knotweed on their property, and are thinking of selling, should tackle any knotweed problem before marketing their home.

David Hollingworth, associate director at broker London & Country Mortgages in the UK says, “Often the mere mention of Knotweed sees buyers run screaming for the hills. By being proactive, sellers can improve the chances of a sale and soothe nervous buyers.”

What is being done?

EKISC maintains a list of knotweed locations, prioritizes treatment locations based on environmental sensitivity, organizes chemical treatment through a certified pesticide applicator and landowner contact where required, arranges for plant disposal and ensures all data is entered into the provincial Invasive Alien Plant Program database.

A total of nine known sites are currently being treated.

It is strongly recommended that Knotweed is treated with systemic herbicides to ensure that the roots are killed. Treating a Knotweed infestation can take several years, with treatments in spring and/or fall of each treatment year until the plant no longer sprouts from the roots.

To learn more about knotweed treatment and local professional services, please contact EKISC.

Environmental protection laws and exemptions

BC Weed Control Act specifically requires property owners to ensure that certain listed species, including Knotweed, are not growing on their property or are controlled from spreading from their property. “If you’ve got this plant in your neighbourhood, contact EKISC to report it and take we can advise you on how best to manage it.”

The Regional District of East Kootenay (RDEK) also has a Neighbourhood Invasive Plant Program (NIPP) that provides homeowners with funding to manage invasive plants. Often management includes the use of herbicide.

“Some cities in the RDEK have enacted by-laws banning the use of cosmetic pesticides; what many people don’t know is that plants, such as Knotweed, that are designated as noxious weeds under the provincial Weed Control Act are exempt from these by-laws,” says Jessie.

Quick ID

Hollow bamboo-like stems with elongated spots;

Creamy white flowers in clusters from leaf joint;

heart or triangle-shaped leaves are lighter green on underside;

Grows rapidly and forms dense thickets.

EKISC has resources and workshops available for homeowners, real estate agents, and land developers.

They can help with:

  • Recommendations and tools available to developers and real estate professionals regarding invasive species on private lands;
  • Local government jurisdiction and enabling legislation for local invasive species control programs;
  • Determining responsibility and management of private property impacted by invasive species, and
  • Key resources and reporting tools available on invasive species in B.C.


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