KC Weed News - April 2008
Topics Below
Weed of the Month: Spotted Knapweed (Centaurea stoebe) , Class B Designate Noxious Weed in King County, Washington
Spotted knapweed could be called the weed that ate Montana. It has been estimated as having a $46 million annual impact on Montana cattle producers. One weed specialist from Montana State University even went so far as having a dog professionally trained to recognize knapweed by smell as a method for early detection. Spotted knapweed was introduced to North America from Eurasia as a contaminant in alfalfa and possibly clover seed, and through discarded soil used as ship ballast. It was first recorded in Victoria, British Columbia in 1883 and spread further in domestic alfalfa seeds and hay before it was recognized as a serious problem. It was collected from King County in 1928 and one botanist noted in 1940 that spotted knapweed was already becoming widespread on gravelly soil nearby in Whatcom County. Although most widespread in the intermountain west, spotted knapweed is now found in almost every state and province in North America.
Because it is widely known in rangelands in the intermountain west, at first glance spotted knapweed might not appear to be as big a problem for wet side western Washington counties like ours. However, thanks in part to contaminated seed, freeways, the movement of hay and construction materials, and the ingenuity of weeds, King County has more than its fair share of spotted knapweed. In fact, it is one of our top four regulated noxious weeds in the county. For more information on this weed in King County, check out our feature page on spotted knapweed in our recent annual report or take a look at the weed map on the county’s iMap page and zoom in to different areas to look for spotted knapweed populations. For more information on the distribution in Washington (as well as some great photos and more links), check out the University of Washington Herbarium website.
Spotted knapweed, closely related to a suite of other Cenaturea species (some weeds, some ornamentals, some both), is most prolific on well-drained soils in full sun and can tolerant really horrid growing conditions, like pure gravel on the side of the highway, for instance. Not surprisingly, most of King County’s sites are closely associated with highways, railroads, ports, and gravel pits. However, being a noxious weed, it is well-adapted to conquering new territory and we also have quite a few populations in unexpected places such as one particularly large site found last year on Vashon Island.
Spotted knapweed is also at home along rivers with sandy or well-drained banks and gravel bars. The White River and the Greenwater Rivers are two local examples with infestations of spotted knapweed. It is also commonly found in open grassy areas, but not usually well-established pastures.
Because spotted knapweed is a perennial, it can tolerate mowing quite well and is notorious for re-flowering after being mowed. In fact, it will re-flower shorter each time until its flowers escape the mower and it can finally produce seeds. Individual plants are not hard to dig up and remove and spotted knapweed is also controllable with a variety of broadleaf herbicides. However, like many noxious weeds, this plant usually grows in dense infestations and produces tons of long-lived seeds. Typically areas infested with spotted knapweed will take many years to clean up, in large part because of the seed bank. Fortunately, spotted knapweed is not highly competitive in well-established grasslands or intact native plant ecosystems in western Washington. As with many weeds, good land management goes a long way to keeping this weed at bay.
For those of you trying to keep up with the scientific names of weeds, you will notice that this plant has changed names more often than most in the past few years. When I started learning about noxious weeds (in the early 1990’s), spotted knapweed was called Centaurea maculosa. Then most references started calling it Centaurea biebersteinii. In the last couple of years, the name has changed once again to Centaurea stoebe, although you will still find both of the other names used in the literature and on the web. So, if you are trying to do searches on this weed, it might be safest to use the common name, which hasn’t changed since this weed first showed up in North America in the middle of the 19 th century (or at least since 1913 according to one reference I found). By the way, if you are trying to find the spots on this knapweed, look at the base of the flower head at the leaf-like structures called bracts that form the flower head. The dark spots on the ends of these bracts are the reason for the name.
If you go to the spotted knapweed page on our website you will see a bunch of pictures, especially young plants because we try to get rid of this plant before it flowers, as well as links to our fact sheet, our Best Management Practices, and a really useful brochure for telling the different knapweed species apart (if you are unfortunate enough to have more than one!). If you find spotted knapweed in King County, please contact us because we are tracking all known locations of this species and because we really want to work with the landowner or road manager to make sure it doesn’t go to seed. Over time, we are seeing a reduction in the amount of spotted knapweed we have in the county, but we are still a long way from eradicating it and will probably continue to see new infestations popping up here and there, so we can use your help in finding new locations.
Weed Tips for April
Celebrate Earth Day by pulling English ivy . Nothing says Earth Day in the Pacific Northwest like tackling ivy. Just be careful around storm-damaged trees – never pull ivy down from the upper parts of a tree since this might injure the tree and will most certainly injure you if branches fall off. Just pry the vines off the bark of the tree up to where you can comfortably reach and all the way down to the ground. Ivy on the ground can be pulled up with a generous helping of elbow grease, a well-placed shovel, and clippers to cut off roots you can’t dig up.
April is a great time to mulch planting beds. Mulch inhibits weed growth and retains soil moisture. A couple of inches of fresh arborist chips (chipped up tree trimmings) or bark will save you hours of weeding this summer. Avoid piling on too much mulch around trees (10 inches or more is too much) and keep the mulch a few inches away from tree trunks. Too much mulch can act as a barrier—it repels water and deprives the tree of oxygen. Using compost as mulch is great for improving the soil and water retention, but won’t stop weeds, so it is good to add chips or bark on top of compost if you want to avoid pulling weeds.
Watch out for giant hogweed in urban areas, parks, and anywhere else it has been spotted in the past. Check the noxious weed map for King County to see if it has been seen in your area. Hogweed’s large, jagged leaves and thick, purple-blotched stems should be tall enough to spot emerging above most other plants now and the plants will be easier to manage before they get full grown. Look for small seedlings and immature plants around the more obvious mature plants but be sure not to confuse non-native giant hogweed with similar native species cow parsnip and coltsfoot, also about the same size right now. Digging up hogweed this time of year isn’t too difficult, but be sure to use caution to avoid getting the sap on your skin because it can cause painful blisters and scarring. Contact our program if you find this plant in a new location in the county.
April showers bring more than May flowers – disturbed areas in lawns, pastures, woods, and other places will fill in with seedlings of annual and biennial weeds like herb Robert and bull thistle. Spreading perennials like Canada thistle and spotted knapweed will move in quickly as well. Walk trails, fields and yards to spot trouble areas that will need re-seeding or mulch to keep back weeds. And don’t let those little weed seedlings fool you – pulling them now with a hoe or by hand will be much easier than later on when they are monster weeds.
Catch weeds that are starting to flower. When a plant turns to flower production it’s a good sign that the roots are depleted and vulnerable. And waiting until seeds form will make it hard to control plants without spreading seeds. Gorse is flowering now so k eep your eyes out for the fragrant yellow flower clusters on large, spiny bushes. Garlic mustard is up and will be flowering later this month, so check out likely places for returning plants and be sure to contact our program if you find any new populations of garlic mustard! And finally meadow knapweed has started bolting in Kirkland, so it’s a good time to start checking out knapweed sites.
What to Do with Weed Waste
Now that you’ve diligently pulled or dug up all your weeds, noxious and otherwise, you might wonder what to do with all that plant material. This is probably one of the hardest questions because of all the competing issues to consider. You want to minimize the impact of your disposal method but at the same time make sure your weeds don’t come back to haunt you or anyone else. It would be nice if there was an easy answer about how long it takes roots or stems or seeds to stop being viable for new growth, or how hot they need to get in compost, or how small to chip them up, etc. However, it varies considerably by plant and all sorts of other factors. So, we are left with making educated guesses and trying to reduce potential impacts as best we can. If you are faced with this question, feel free to contact us (206-296-0290) and we can help you sort out the pros and cons of different options.
In general, if you are disposing of a regulated noxious weed (one of those Class A, B or C weeds required for control in King County), you can be sure that it is limited in distribution in the county and it is really important to keep it that way. If you move any of these plants away from where they are growing, they should be contained in bags or covered by tarps and taken to a transfer station. Don’t discard these weeds with yard waste in order to make sure they don’t escape and spread to new areas. Fortunately, this is a small percentage of all the weeds people are discarding, so it shouldn’t have a big impact on landfill capacity. Also, for most noxious weeds, if they are removed before they flower, they can generally be left to break down on site, minimizing the risk of moving the weed to a new location (assuming they can’t sprout from stems, in which case you would want to pile them on tarps until they rot or dry out). If you do have regulated noxious weeds to take to a transfer station, we can send you a free voucher to cover the cost at King County transfer stations (this just shows you how important we think it is to keep these weeds completely contained!). Contact our office for more information about these vouchers (206-296-0290).
For many common, widespread weeds like English ivy, Scotch broom or blackberry, you can often leave them to break down on site if you have the room. But for weeds with seeds, weeds that spread by stems and root fragments (knotweed, bindweed, etc) or if you just need to get rid of a big pile of weeds (or have a small yard), then sending these weeds off with your yard waste is a great idea. When they get taken to a commercial composting facility like Cedar Grove, virtually all of the viable plant material and seeds are destroyed in the composting process. Home composting doesn’t usually get hot enough to destroy seeds and some rhizomes, but it is a good option for stems and young plants with no flowers (except for plants like bindweed, nightshade, and yellow archangel that can root from stem fragments). And, unlike with the regulated noxious weeds, if one or two seeds escape, it probably won’t make much of a difference because of how widespread these weeds already are. If you don’t have city pick up for yard waste, you can also take your material to a city or county transfer station and usually pay less to discard yard waste than other materials. Both of Seattle’s transfer stations have yard waste disposal. King County has three transfer stations that accept yard waste at a reduced rate: Enumclaw, Cedar Falls, and Shoreline. Visit the King County Solid Waste website for more information. For a list of private and public facilities that accept yard waste, check out the page on What do I do with landscaping/landclearing materials?.
Staff News – Meet the 2008 Weed Crew
The 2008 weed season has begun and the King County Noxious Weed Program is fully staffed once again. Our seasonal regional weed specialists are already heading out to the field to track down high priority Class A and B noxious weeds and to work with landowners and property managers to get these problem plants controlled. Each specialist is assigned a region of the county that includes both incorporated and unincorporated areas. Our program is very fortunate to have a crew of highly motivated weed specialists who enjoy talking to people and helping them to find answers to their noxious weed problems. If you would like to meet your regional weed specialist, please do not hesitate to call our program at 206-296-0290 or send them an email at noxious.weeds@kingcounty.gov.
- Karen Peterson : North Seattle, Shoreline, Lake Forest Park, Kenmore, Bothell, Woodinville, Bellevue
- Frances Lucero : Kirkland, Redmond, Sammamish, Fall City, Carnation, Duvall, Skykomish
- Monica Walker : Central and East Seattle, Mercer Island, Knotweed Project Manager
- Maria Winkler : West Seattle, Harbor Island, Tukwila, Vashon Island
- Jessica McKenney : Burien, SeaTac, Normandy Park, Des Moines, Federal Way, western Kent
- Kimiora Ward : Issaquah, Newcastle, Renton, Snoqualmie, North Bend
- Matt Below : eastern Kent, Covington, Maple Valley, Black Diamond
- Trish MacLaren : Auburn, Milton, Algona, Pacific, Enumclaw
We also have three weed specialists who work year round throughout the county. They can be reached at our program line 206-296-0290 or directly by email:
And finally, for information on the Weed Board, program business, educational activities or general weed questions, please contact:
King County Lake Stewardship Program Gets to Work on a New Milfoil Infestation
The insidious noxious weed Eurasian watermilfoil (Myriophyllum spicatum) has found its way into Cottage Lake, a lovely place in north King County east of Woodinville, that was formerly free of this aquatic weed. In September 2007, staff from the King County Lake Stewardship Program surveyed Cottage Lake from a canoe to quickly assess submersed and emerged aquatic plants in the lake, keeping a keen eye out for any previously undocumented noxious aquatic weed infestations. Surveyors first spotted Eurasian watermilfoil in the shallow water off the shore of the public park, just minutes after launching their canoe.
“At first we didn’t let ourselves believe it was Eurasian milfoil,” said Michael Murphy, an Environmental Scientist with the Lake Stewardship Program who performed the survey with colleague Beth Cullen. “We tried to convince ourselves it was a native variety with odd morphology. But we knew…” Since milfoil plants of the same species can have widely variable characteristics from lake to lake and even plant to plant, Murphy sent a sample to Jenifer Parsons, an aquatic plant specialist at the Washington Department of Ecology. Parsons confirmed the bad news.
Murphy and Cullen estimated the infestation covered less than two acres of the shallow areas of the lake, with plants or small patches present in low densities around much of the lake’s margins. But there is hope. Because the infestation is still early, King County is eligible for funding from Ecology to attempt to eradicate the weeds with herbicide.
After a community meeting to discuss control options, King County and members of the community group Friends of Cottage Lake decided an herbicide treatment was appropriate and applied for a grant. In late March, King County was awarded $10,000 from Ecology to begin eradication efforts. In cooperation with the Friends of Cottage Lake, King County has begun planning eradication efforts, which will likely consist of several surveys and at least two herbicide spot‑treatments in summer 2008. To ensure all milfoil in the lake is treated, King County will also apply herbicide to areas of dense fragrant water lily to reduce the lily canopy prior to treatment of milfoil.
For information about the Cottage Lake milfoil eradication project, please contact Michael Murphy at 206-296-8008 or michael.murphy@kingcounty.gov.
Volunteer for Earth Day Pulling Invasive Weeds
This is a great time to pull weeds in parks – not too cold and not too hot, the soil is still nice and loose, and there are lots of events to choose from. Earth Day is on a Tuesday this year – April 22 – so most of the events are on April 19 or other weekends in April.
On the eastside, check out the Earth Day Event in Bridle Trails State Park, Saturday, April 19, 9-12. Join other volunteers removing invasive blackberry and holly from this forested park in the heart of the Eastside. Adults, families, teenagers, and scouts welcome. Drinks, snacks, and lunch provided. Bring gloves and hand pruners. Bridle Trails State Park , at entrance on 116 th Ave. N.E. at N.E. 53 rd St., Kirkland. For more info call 425-827-6595 or go to www.bridletrails.org. For more great events in Kirkland, including one at Cotton Hill Park with a herd of goats helping out, check out the schedule at the Green Kirkland webpage.
For a great Earth Day event in Seattle with both fun and work, check out Earth Day with Duwamish Alive! on April 19 sponsored by People for Puget Sound (and lots of other organizations and agencies). The City of Seattle has declared the whole month of April as Earth Month so check out Seattle’s 2008 Earth Month Events for lots of great activities all month long. The City of Shoreline also has a great list of Earth Day events, check it out on their events calendar (scroll down to the Earth Day section) or download the event flyer.
For volunteering in King County Parks, check out their volunteer restoration event calendar. For volunteer events all along the Mountains to Sound Greenway, check out the Greenway Trust Volunteer Events Calendar. Two more great resources for volunteer events are EarthCorps’ Volunteer Calendar and Cascade Land Conservancy’s Events Calendar. For volunteering in your city, contact your local parks department for work parties – there’s always lots to do this time of year! And if I left your events off, I apologize. Just drop me an email next year around March and I’ll get it in next time. Happy volunteering everyone!
Weed Info Booths in April and May
April 12
April 19
April 22
May 10
Sign up for King County Noxious Weed Workshops
We are taking registrations for our annual noxious weed workshops for vegetation management crews and others who need to identify and manage noxious weeds. This year we are pleased to have WSU researcher Tim Miller in addition to several of our own noxious weed specialists to teach a broad range of topics on noxious weeds. Topics include: state noxious weed list; identifying new and unusual noxious weeds; control of key weeds including garden loosestrife, purple loosestrife, phragmites, hawkweeds, knapweeds and thistles; noxious weed control on rights-of-way, disturbed areas and wastelands; weed identification with live specimens; WSU research results for control of a variety of noxious weeds; and a review of knotweed control on King County rivers. The full agenda is on our workshops page. Both classes are free and open to the public. WSDA pesticide license recertification credits have been requested for these classes (4 credits requested). Register at 206-263-6468 or sasha.shaw@kingcounty.gov. Please provide your name, agency or company, number of attendees and your contact information.
- North Session: Wednesday, May 7, 8 am to 12 pm, Northshore Utility District, Northshore Room, 6830 NE 185th St., Kenmore, WA 98028
- South Session: Wednesday, May 14, 8 am to 12 pm, City of Kent Shops Building, upstairs meeting room, 5821 W. James St., Kent, WA 98032
King County Website Update
The domain name for all of King County’s websites is changing from metrokc.gov to kingcounty.gov by the end of 2008. We have a quick link set up for our home page: www.kingcounty.gov/weeds but we don’t have the addresses for the other pages yet. As the transfer moves forward, the links in this newsletter and earlier additions may not work, but the main address above will continue to work and you can always navigate to the individual pages from the index page. Hopefully this will not cause too much of an inconvenience. Please feel free to contact Sasha Shaw (206-263-6468) if you encounter any problems with accessing our website.
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