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Noxious weeds

King County, Washington

To offer a suggestion or report an error on the King County Noxious Weeds website, please contact Sasha Shaw, education specialist.

KC Weed News - February 2009

(PDF Version for Printing)

Topics Below Bull Thistle Flower - click for more information on bull thistle (Cirsium vulgare)

Weed of the Month: Bull Thistle (Cirsium vulgare), Class C Non-Regulated Noxious Weed in King County, Washington

If you are out walking this time of year and spot a scary looking thistle growing by the side of the road or in a field, chances are that it is a bull thistle. Over-wintering rosettes of this plant are pretty impressive even this time of year when more timid plants are lying dormant or just starting to sprout new growth. The dark green, spiny, hairy, jagged-looking leaves lie low to the ground and might be over-looked if you aren’t watching the ground. However, once these plants start bolting in the spring and summer, they shoot up to as much as five feet tall and form large, branched masses of spiny leaves and magenta flowers. Based on appearance alone, you might think this is one bad thistle. Fortunately for us all, bull thistle only reproduces by seed and can be controlled simply by digging up a few inches of the root or by mowing just before flowering every year.

If you do have a large enough population that would make digging or even cutting impractical, then you might want to look into getting some bugs on your thistles. Bull thistle is one of the better candidates for using biocontrol in King County, especially since we are usually just trying to reduce it, not eradicate it. The bull thistle seed head gall fly (Urophora stylata) lays eggs in closed flower buds and then the larvae burrow into the tissue and reduce the number of seeds produced. You can contact Jennifer Andreas with WSU Extension for more information on this and other biocontrol agents being used to control weeds in Washington State.

Although bull thistle is pretty easy to control and does provide food for many critters (like finches, voles, rabbits, butterflies, bees and others), it can be a serious nuisance in hay fields and pastures. Most domestic livestock typically avoid bull thistle and it can greatly reduce the market value of hay. Those spines are no laughing matter! Luckily, goats and even sheep will eat bull thistle and can help manage it, and more than one horse owner has told me about their horse delicately picking out the sweet, nectar-filled flowers, somehow avoiding the mass of spines all around the flowers. That can really help cut down on the amount of seeds produced.

In King County, bull thistle control is up to the individual land owner. Deciding what to do with your bull thistle depends a lot on what you are doing with your land (and what your neighbors are doing). In pastures and hay fields, controlling bull thistle is pretty important. If you are near pastures and hay fields, it would be a good neighbor thing to do to control bull thistle. Otherwise, it is up to you to decide. Just remember that, like most weeds, the amount of bull thistle will likely only increase if left alone! For more information on this and other noxious weeds, visit our website at or drop us an email at

Weed Tips for February

Pull over-wintering weeds now while the soil is soft and moist. Rosettes of weeds like knapweed, tansy ragwort, garlic mustard, milk thistle, and poison-hemlock are easy to find now and the roots will come out without breaking. Late winter, while the soil is moist and not much is growing out there, is a great time to find and pull noxious weeds. It’s also a great excuse for getting outside!

Mulch before the weeds pop up. If you have ever struggled with garden beds full of pesky annuals like bittercress a.k.a. shotweed (Cardamine hirsuta and related species), then mulching now might be your answer. Bittercress is happily growing right now, undeterred by the winter chill, and will be bolting and seeding before you know it in the early spring. There are many other annual weeds that can be managed well by a nice thick layer of mulch in garden beds and any areas that lack good plant cover to keep the weeds in check.

Watch for gorse, starting to flower later this month. Keep your eyes out for the fragrant yellow flower clusters on large, spiny bushes. Expect to find this plant along coastal areas and in forests on well-drained soils. Pulling or digging up this plant is possible while the soil is loose but you may need a weed wrench and heavy duty gloves.

Warm up with weeding by joining a neighborhood work party. This is a great time of year for pulling ivy, Scotch broom and other invasive weeds, and the best way to do it is with a big group of energetic volunteers. There are work parties going on regularly throughout the county and there is certainly one near you. Check with your local parks department or organizations like Mountains to Sound Greenway, EarthCorps, Green Seattle Partnership, United Way of King County or your local community groups, schools and churches. For more ideas, see our volunteer resources page. If you know of other groups or agencies that are looking for volunteers to join weed control or restoration work parties, email us at and we will add it to our web page.

2009 King County Noxious Weed List – Overview of Changes

The King County Noxious Weed Control Board met in January to approve the 2009 King County Noxious Weed List. Although some of the changes were described in last month’s KC Weed News, here are all of the changes to the county list in one convenient place. You can also visit our website for the complete 2009 King County Noxious Weed List.

  1. Three new Class A weeds were added to the King County Class A Noxious Weed List.
    1. Shiny geranium  (Geranium lucidum) is a rapidly spreading cousin of herb Robert (a.k.a. stinky bob). It looks something like the weedy geranium called dove’s foot but has shiny leaves and reddish stems. It spreads in woodlands and forest clearings. In Washington, it is known to occur only in Bayview State Park, Padilla Bay, and a couple of places in Skamania and Clark Counties. 
    2. False brome  (Brachypodium sylvaticum) is a grass that is invading in woodlands in Oregon’s Willamette Valley. Although it can be difficult to identify grasses, this one is shade tolerant and remains bright green throughout summer and fall when many grasses turn brown. It forms squat bunches and has broad, flat, lax leaves. The leaf margins and lower stems have long, soft hairs and the flower spikes droop. So far it is limited to one spot in southern Washington in Skamania County. 
    3. Flowering-rush  (Butomus umbellatus) is an aquatic plant often first introduced to lakes because of its lovely flowers, but spreads to become a huge nuisance and a threat to aquatic ecosystems. In Washington, it is so far known to occur only in a few locations including a large infestation in Silver Lake in northern Whatcom County.  
  2. Upgrade of one Class B to Class A list
    1. Smooth cordgrass  (Spartina alterniflora) – the species of spartina most abundant on Willapa Bay and also present in Padilla Bay and other locations along Puget Sound; not known to occur in King County.  
  3. Two “new” Class C weeds were added to the Non-Regulated Noxious Weed List
    1. Himalayan blackberry  (Rubus armeniacus) and evergreen blackberry (Rubus laciniatus) are invasive, difficult to control, and taking over vast areas of land in the county. 
    2. Although both species have been on King County’s Weeds of Concern or Obnoxious Weeds list for several years, neither species was an official noxious weed in Washington State until this year. 
    3. Both species have been added as Class C noxious weeds to Washington’s weed list. This means that county weed boards have the option to require control of blackberry for all or parts of their county, although that is not likely to happen considering how widespread it is. It also means that when we educate people about noxious weeds, we can include blackberry on that list, and that rules and regulations that allow exceptions for noxious weed control will now apply to invasive blackberry species along with other noxious weeds. 
    4. There is no requirement to control these blackberry species in King County. 
  4. Three weeds currently listed on the State Weed List but not included on the King County list will be added to the Non-Regulated Noxious Weed list
    1. The three weed species are: hairy whitetop (Cardaria pubescens), hoary cress (Cardaria draba), and houndstongue (Cynoglossum officinale). The first two are Class C weeds and houndstongue is a Class B weed. None of them are currently designated for control in King County. 
    2. All three species occur in King County to some extent, but do not appear to be having significant negative impacts at this time. However, they may have localized negative impacts or they may spread further, so program staff will be watching for these species.
  5. Area selected by the King County Noxious Weed Board for mandatory control for four invasive knotweed species.
    1. Japanese knotweed  (Polygonum cuspidatum), Bohemian knotweed (Polygonum bohemicum), giant knotweed (Polygonum sachalinense) and Himalayan knotweed (Polygonum polystachyum) are invasive knotweed species that are currently on the Class B state weed list and are not designated for control in King County. Starting in 2009, public and private landowners will be required to control these knotweed species along the upper and middle Green River and its tributaries, upstream of the Auburn City Limits.
    2. The specific requirement is as follows:  Control of Bohemian, Japanese, giant and Himalayan knotweed is required on the Green River and its tributaries (defined as Type S, F or N aquatic areas in KCC 21A.24.355 ) upstream of the Auburn City Limits, including but not limited to Newaukum Creek, Soos Creek, Big Soos Creek, Jenkins Creek, Covington Creek, and Crisp Creek. Control of these invasive knotweed species is required up to the ordinary high water mark (or to the top of the bank if the ordinary high water mark cannot be identified) and in the adjacent buffer area as specified in KCC 21A.24.358. 
    3. The noxious weed program has been actively controlling knotweed species in the selected area for the past five years as part of a grant-funded Cooperative Weed Management Area project (CWMA) and the presence of knotweed in this area has been greatly reduced. Landowners may request assistance from the noxious weed program and grant-funding is likely to cover the majority of necessary control work for 2009, but the responsibility for ensuring that the control is done will fall to the landowners. Although it has been greatly reduced, knotweed is likely to come back and needs to be monitored for many years following control work, so it is important for landowners to work with the noxious weed program to stay on top of this difficult weed. 
    4. All four species will remain on the Non-Regulated Noxious Weeds list with a footnote added explaining the selected area. Control of knotweed is not required for the rest of King County outside of the designated area. 
  6. Three new species have been added to the King County Weeds of Concern List (these are not on the State Noxious Weed List and this list is for educational purposes only, there are no regulations regarding these species)
    1. Spotted Jewelweed (Impatiens capensis) is an orange-flowered annual that typically grows along lake and creek shores, wetlands and forest edges. It is native to the Eastern United States but not to the Pacific Northwest. It has often been confused with our local native Impatiens species, but research by botanist Peter Zika convincingly showed that spotted jewelweed is not native to the Pacific Northwest and that it is in fact hybridizing with a rare native called spurless jewelweed (Impatiens ecalcarata), and seems to be replacing it. It has similar habitat, biology and impact as the noxious weed policeman’s helmet (Impatiens glandulifera), but it is not as tall and not usually as aggressive. Spotted jewelweed is very abundant and invasive along Cottage Lake Creek (mixed with bittersweet nightshade) and other areas in the Bear Creek watershed. It is also common along many creeks in Seattle and other places throughout King County. 
    2. European Mountain-ash (Sorbus aucuparia) is a non-native tree that often establishes in King County’s natural lands and in urban parks in the county. It spreads by birds eating the seeds. It doesn’t appear to form thickets like English holly, but it is widespread and perhaps replacing native tree species where it escapes. Recommending that it be removed from areas being restored is the primary reason for including it as well as teaching people not to plant this invasive species of mountain-ash.
    3. Common Hawthorn (Crataegus monogyna) is similar to European mountain-ash in that it also spread by birds and escapes into natural areas in rural and urban King County. It seeds in even more prolifically than mountain-ash and is a concern of Mountains to Sound Greenway in their restoration work. It has also been known to hybridize with our native black hawthorn. It is considered a threat to garry oak ecosystems and is considered invasive by California Invasive Plant Council.

Visit the 2009 (Final?) PNW Flower and Garden Show  

Every year I look forward to the lovely, warm, sweet-smelling experience that is the Pacific Northwest Flower and Garden Show. It feels like being transported into spring when I first walk into the show past all the fragrant cut flower arrangements. Sadly, this may be the last year for the show since the organizers are retiring and haven’t found a buyer yet. However, there is still one more year to marvel at the garden displays, shop for garden delights, and, of course, to visit us at the Washington State Noxious Weed Board booth (next to the USDA/WSDA table in the commercial vendor area). As always, there will be lots of great literature on noxious weeds and more importantly, friendly noxious weed specialists from around the state to help answer your weed questions. The show is being held from February 18 to 22 at the Convention Center at 7th and Pike in downtown Seattle.

Save the Dates for King County’s Professional Noxious Weed Workshops

We will be holding our annual noxious weed workshops for vegetation management crews, landscapers, restoration practitioners, agency staff and others on May 6 and May 13 this year. The agenda will include updates and refreshers on identifying and controlling priority noxious weeds, a presentation by Jeff Britt from WSDA on the “Keys to Legal Pesticide Applications and Record Keeping”, updates on using biocontrol in the county, and a special training session on using stem-injection guns to control knotweed. Participants in the stem-injection training can apply to borrow stem-injectors from the noxious weed program for controlling knotweed in their own projects. (By the way, for those of you just interested in knotweed stem-injection training, we will also be offering evening knotweed control workshops in June and July for county residents).

The May 6 session will be held in south King County and the May 13 class will be in north King County, and both will be from 8 to 12. As always, these workshops are free and we will be applying for WSDA recertification credits. The agenda and locations will be posted on our website  when they are finalized.

You can sign up now by contacting Sasha Shaw by phone at 206-263-6468 or by email at Please provide your name, agency or company if any, email address, and phone number. If you are signing up more than one person from a group, please provide names of all of the participants if possible.

The Pacific Northwest Invasive Plant Council is Up and Running

When we are fighting weeds in our own little areas, we sometimes feel alone and separate from the rest of the world. At these times, it really helps to have a regional resource like the new Pacific Northwest Invasive Plant Council ( This new IPC (can be pronounced “ip-see”) encompasses weed issues, research and activities in Washington, Oregon, British Columbia, Alaska, Yukon and the Northern Territories. There is a moderated list serve that provides an avenue for sharing information on research, new weeds, and other issues of importance to the region. The website is a clearinghouse of information and it is being expanded daily with new resources and information. The organization itself is just getting underway but growing steadily and has already developed a list of projects to focus on.

  • Early Detection Rapid Response (EDRR) – this will include support of existing efforts through mapping and information sharing and also developing new programs where they are needed.
  • Clearinghouse for information on invasive plants for the PNW region, including information from the field as well as what researchers are working on.
  • List of Plants of the Greatest Ecological Concern for the PNW. This will be a list of plants evaluated through a Weed Risk Assessment protocol and will include plant species that may not be regulated, yet are considered to be potentially invasive and an impending problem in the future.
  • Education through workshops and the website for general public, horticulturists, teachers, practitioners, et al.
  • Nursery certification program. This program will focus on the pathway of new invasives from the horticulture industry.

Native Plant Steward Program in East King County

The Washington Native Plant Society is teaming up with several east side cities and King County to bring their popular native plant stewardship program to the eastside. This program teaches participants all about native plants and in return they volunteer their time.  Top professionals will teach all about native plants, habitat restoration and native plant landscaping. The training is FREE! In exchange, Stewards commit to completing at least 100 hours providing environmental education to others and working on restoration projects in one of five eastside communities. The ten week training program will be held on Fridays from April 24 to June 26, 2009 in Bellevue. For more information contact the Washington Native Plant Society at 206-527-3210,, or visit their website:

Job Opening for State Noxious Weed Education Specialist

The Washington State Noxious Weed Control Board is now in the process of hiring an Outreach and Communications Specialist in Olympia (or Yakima). The position is open until filled, but applicants are encouraged to apply as soon as possible. Here is an excerpt from the position description:

Acts as the chief outreach and communications specialist for the Washington State Noxious Weed Control Board (WSNWCB). Coordinates and supplements the educational and outreach efforts of county and regional noxious weed control boards and weed districts and coordinates with neighboring states to promote noxious weed and weed law awareness. Represents the Board to the general public, media, and technical audiences. Performs other duties as assigned by the Executive Secretary.

This full-time position requires statewide travel and occasional evening and weekend work. The position is exempt from civil service. Starting salary range is $38,000 to $43,000, DOE. Washington State also offers a comprehensive benefit package that includes membership in the state retirement system, a tax-deferred compensation program, leave package, and a full array of health, dental, disability, and life insurance coverage.

For a complete job description and application information, please visit the WA State Weed Board website at or contact Alison Halpern at

Contract Position Opening for WNPS Stewardship Program Coordinator

The Washington Native Plant Society is requesting qualifications from interested persons to coordinate its Native Plant Stewardship Program in King County. This is a paid contract position and applications will be accepted through February 12, 2009. The Coordinator hired under this contract will be responsible for coordinating all aspects of the spring training and for management and oversight of native plant steward volunteers and their projects, including documentation of their hours through March 1, 2010. The project beginning date is March 2, 2009 and the completion date is March 1, 2010. The contract amount is $18,000 - $20,000 and the work location will be predominately Bellevue and East King County. More information and application instructions are at the WNPS website or contact WNPS at 206-527-3210 or

Hawaii Gets Proactive in their Weed Fight

It’s a well known fact in weed science that the best way to stop a new weed is to catch it early. Sadly, this is rarely done. Probably the main reason is that limited resources tend to make us focus on the most obvious problems. When an invasive plant is just getting started, no one really notices it and it’s hard to argue that it’s worth spending valuable resources on something that hasn’t caused any problems yet. But just imagine how much environmental damage we would have saved if knotweed had been stopped when it first came into our state. I recently read a report on on invasive plant work in Hawaii that sounds like a step in the right direction, a focus on pro-active weed control.  The report described what is happening on Oahu to shift the focus of invasive plant control to a greater focus on prevention and early response to new invaders. I especially like the idea of the creation of a “Detection Community” – a network of plant enthusiasts, scientists, agency staff and community members who are working together to find and remove new weeds before they get going. It sounds like there is still plenty of work to do, but at least things are moving in a positive direction.