In 2009, the Coos Watershed Association sprayed knotweed patches for almost 30 individual landowners and 8 businesses along the Millicoma and Coos Rivers and in the towns adjacent to the Coos Bay. Additionally, due to press coverage of the knotweed program this year, we were able to help 7 other people and learn about other knotwed patches in the area.

Please note that we are currently focusing our control efforts on knotweed infestations in the Coos Watershed (i.e. Coos Bay and North Bend) and do not have program funding to treat the Coquille Watershed (i.e. Coquille, Bandon, Fairview). 

An early detection adaptive management plan for a Cooperative Weed Management Area (CWMA) is being developed by the Coos Soil and Water Conservation District in coordination with the Coos County Weed Advisory Board.  CoosWA supports the creation of a CWMA and anticipates that large scale projects like its ongoing Coos River knotweed project could be used as a model for neighboring watershed weed management plans.

There are two types of invasive kntoweed in the Coos watershed: Japanese and Himalayan knotweed. Both types of knotweed are extremely aggressive and grow very quickly, displacing native, beneficial vegetation along rivers in the Coos watershed. The Coos Watershed Association offers a free knotweed removal program during the summer months.

Japanese knotweed is characterized by a wide, heart-shaped leaf, and Himalayan knotweed has an elongated leaf. Knotweed is characterized by bamboo-like, green or reddish stems, and bright green leaves 1-12” wide with smooth edges. This invasive plant begins its growth in April, and by July it can reach a height of 12 feet! Large spikes of small, white flowers bloom in late summer. In the winter months, although the plant lies dormant and dead, brown stems may remain standing.

Knotweed is most commonly found in the flood plains along rivers and creeks. However, it will thrive in any moist soil or river cobble in full or partial light.

Much of the knotweed in the Coos watershed, especially along the Coos River, was spread during the 1996 floods. Knotweed spreads through rhizomes - root and stem segments - which transport easily in tidally-influenced river systems. Fragments as small as 1/2-inch can start a new plant and just one patch of knotweed can produce hundreds of new plants. Stream banks were rapidly colonized by the weed, and if not carefully controlled, will continue to spread. Beavers also contribute to the spread of knotweed because they cut it down and promote the spread of rhizomes.

Knotweed is an ornamental plant native to Asia. When it colonizes in areas such as the Coos watershed, it out competes and permanently displaces native vegetation. It grows extremely fast - one small plant can grow up to a foot a week. Native animals and fish cannot use it for food or shelter. Therefore, knotweed destroys terrestrial and aquatic habitat that would otherwise be suitable for wildlife. The food chain could also be disrupted because knotweed takes nitrogen out of the soil without replacing it with leaf litter.

Knotweed threatens current and potential restoration planting sites on the Coos River, Millicoma River, and their tributaries. Past experience has shown that plantings need to be maintained for 3-5 years after establishment before they are self-sustaining. The Coos Watershed Association treats knotweed with an aquatic-safe herbicide cocktail that can be applied to the foliage from May to October. The herbicide will be applied on the knotweed leaves by a licensed applicator with a backpack sprayer, and every precaution will be taken to avoid spraying the surrounding trees and shrubs. Treating knotweed earlier in the growing season prevents a dense canopy from forming. Patches that are successfully treated and killed can be re-vegetated with native conifer and hardwood trees. Trees provide shade for fish habitats and have root structures that help slow erosion, and filter toxins.

The Coos Watershed Association offers a knotweed control program during the summer months at no charge to the landowner. If you find knotweed on your property, no matter what size, call (541) 888-5922. It is important that you avoid cutting down the knotweed because it can regrow even stronger and small cuttings of the plant can resprout elsewhere if not contained.

Last year, with the permission of 25 landowners, CoosWA was able to spray knotweed along several rivers in the Coos watershed and are currently treating additional properties this season. CoosWA is also available to consult with you about what native plants to plant after invasive plants are removed and can help with restoration projects on your property when funds are available.

Tyler Pedersen, CoosWA’s lowlands restoration projects manager, contributed greatly to this article.

• The Coos Watershed Association's Riparian Areas Restoration Fact Sheet (PDF, 1.5 MB)
• The Oregon Department of Agriculture's page on Japanese knotweed
• The Oregon Department of Agriculture's page on Himalayan knotweed
• Knotweed brochure by the Nature Conservancy (PDF, 585 KB)
• Oregon Invasive Species Online Hotline
• Oregon State University Extension Service's Knotweed fact sheet (PDF, 559 KB)
• Oregon State University Extension Service's publication Invasive Plants and your Streamside Garden (PDF, 200 KB)

CoosWA rents small, medium, and large weed wrenches free of charge with a $25 refundable deposit. Weed wrenches are particularly useful to remove Scotch Broom. Please call our office for more information on this program.

Here is a useful webpage all about weed wrenches.

• Bull Thistle (PDF, 633 KB)
• Butterfly Bush (PDF, 515 KB)
• Canada Thistle (PDF, 598 KB)
• English Ivy (PDF, 536 KB)
• Gorse (PDF, 508 KB)
• Himalayan Blackberry (PDF, 588 KB)
• Purple Loosestrife (PDF, 144 KB)
• Scotch Broom (PDF, 174 KB)
• Tansy Ragwort (PDF, 502 KB)

One resident along the Coos River who had their knotweed sprayed this season said:

"Thanks, to all of you who rescued me and our beautiful river."

Below are photos of both Japanese and Himalyan knotweed at different stages of growth, and photos of the spraying process.

Japanese knotweed is characterized by wide, heart-shaped leaves and has white blooms during July through October. (Photo by Britt Slattery, USFWS)

This photo taken in the Coos watershed shows how Japanese knotweed can quickly grow into large bushes. (Photo by CoosWA staff)

Untreated Japanese knotweed (foreground) and treated Japanese knotweed after one week (background). (Photo by Tyler Pedersen, CoosWA)

Himalayan knotweed has more elongated leaves than the Japanese type. Himalayan knotweed also has long spikes of white blooms during part of the year. (Photo by Glenn Miller, ODA)

This close-up shows the bamboo-like structure of the stalks of Himalayan knotweed. (Photo by Glenn Miller, ODA).

Treated knotweed must be monitored for several seasons, and re-sprayed as needed. This photo shows Himalayan knotweed regrowth after treatment. (Photo by Tyler Pedersen, CoosWA)

Spraying is performed by a licensed technician. This photo shows Rex Miller from Agri-Tech Design spraying knotweed on the South Fork Coos River. (Photo by Tyler Pedersen, CoosWA)

The Coos Watershed Association uses a water-safe herbicide to treat knotweed and every precaution is taken by the technician to avoid spraying other plants. (Photo by Tyler Pedersen, CoosWA)