KC Weed News - June 2009
Topics Below 
Weed of the Month: Milk Thistle (Silybum marianum), Class A Noxious Weed in King County, Washington
Mention thistles and most people picture large spiny plants with purple or pink flowers and lots of seeds that blow in the wind. This group of plants is pretty easy to spot, but it may not always be easy to tell them apart. Milk thistle could be mistaken for bull thistle, Canada thistle or even Scotch thistle from a distance. Get close to it, however, and you can definitely see the differences. Full grown milk thistle grows 6 feet tall in large, imposing, dense patches. Rosettes can be several feet across and the flower heads are big too – usually 2 inches wide with long, thick, spine-tipped bracts projecting out from around the purple flowers. But the real giveaway with milk thistle is the leaves. They look like someone poured milk all over them, with streaks of white visible even on the tiny seedlings and very obvious on the large mature leaves. Even though our more common thistles can be tall, none of them have white marbling on the leaves and both Scotch and bull thistle are much more hairy or fuzzy than milk thistle, which has glossy, hairless leaves.
Another distinction of milk thistle is that King County, and in fact all of Washington State, has very little of it, compared with what you will see in California and parts of Oregon. This is a good thing because milk thistle is highly invasive in fields and disturbed areas and can overwhelm pasture grasses without any trouble. It is large and very spiny and can cause injury in animals that graze it (and people that touch it!). Also, when milk thistle dominates a pasture and is eaten in large quantities by livestock, it can cause nitrate poisoning. Milk thistle seeds are fairly heavy and generally fall close to the parent plant, but they are easily carried by mowers, equipment, animals, and in hay. Long seed life in the soil combined with the plant’s toughness and competitiveness make milk thistle very difficult to control once it gets established. All of these factors combined are the reason milk thistle is a Class A noxious weed in Washington, with a statewide effort to eradicate it wherever it shows up, as well as a statewide ban on growing and selling it.
Although milk thistle is sometimes found in gardens being used for medicinal or ornamental use, the first large infestations in King County were found near Enumclaw in the pastures of several dairies. It turns out that hay infested with milk thistle was brought from Oregon or California, and then mowing equipment shared between fields moved the milk thistle around to new pastures and other places in the Enumclaw area and south into Pierce County. Over time, farmers were unable to keep up with this aggressive weed, and large areas became infested. Because of the potential threat of milk thistle and its very limited distribution, the King County Noxious Weed Program began offering assistance to the landowners. When it became clear that we still weren’t making enough headway, we began working a lot more closely with the farmers and doing much of the control work ourselves in order to use the most effective methods and timing over the entire infested area. By developing good relations with the property owners, we are able to find and jump on new sites while they are still small. We have even begun to think that eradication might just be possible.
For the past year, we have had additional help from a grant from the Washington State Weed Board which has helped us to do fall surveying and control as well as spring and summer work. So far this year we have found no new infestations in south King County in spite of increased monitoring. Although it may be too early to say for sure, this is a really good sign and we are hopeful that we have contained the plant by our rigorous efforts to stop all seeding. Another very good sign that we are making progress is how few known sites had milk thistle this year. Out of 49 known sites in south King County, only 18 had any milk thistle plants so far this season, and the weed density at all sites is much reduced.
Trish MacLaren, the weed specialist in south King County who heads up the milk thistle effort, feels that our success can be attributed to:
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cooperation of landowners (cannot stress this enough – they report new infestations, notice when plants are popping up, and help with control)
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using Milestone herbicide (no grazing restrictions even for lactating animals)
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using appropriate application method (boom spraying heavily infested pastures has made a tremendous difference in controlling seedlings missed by spot applications)
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treating infested areas with Milestone in the fall (knocks out fall germination)
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persistence in finding then terminating every plant before it goes to seed (seeds remain viable for at least 9 years)
As you know, weeds don’t obey borders and not surprisingly milk thistle is also found south of us in Pierce County. Recently, Trish reached out in a “Hands Across The White River” cooperative field day to share ideas, challenges and successes with her counterpart in Pierce County. She mapped milk thistle locations using GPS, took photos, and provided herbicide to the Pierce County Noxious Weed Board (thanks in part to the State Weed Board grant). Pierce County has only five known sites and two did not have any plants this year. Similarities are that the milk thistle occurs on or adjacent to active or former dairies. It is great news that both counties are keeping milk thistle controlled and working towards eradication.
If you notice milk thistle growing anywhere in King County, please contact us or report it right away so we can keep it from spreading. If there are only a few plants, it is pretty easy to dig them up. Although spiny and large, milk thistle has tap roots not rhizomes so digging is effective. However, even buds and especially open flowers will form viable seeds after being dug up or mowed, so please remove, bag and discard all flower heads of milk thistle in the garbage, not in the yard waste. Plants without flower heads can be chopped up with a shovel and left on the ground or thrown out with the flower heads. Roots can carry seeds so please don’t put them in the yard waste or transport them away from where the plants were growing.
For more information, photos and control tips, see our milk thistle page and follow links to the milk thistle weed alert and the Best Management Practices or call us at 206-296-0290.
Weed Tips for June
Watch out for garlic mustard: new infestations have been found in Black Diamond and North Bend. Garlic mustard is on the move in King County. It has been found in two new locations far outside of Seattle – on private property in North Bend and at Lake Sawyer in Black Diamond – and even for the first time on the Olympic Peninsula. This last population was found by someone who saw the King 5 story on our garlic mustard control at Golden Gardens Park and realized they had it in their own yard. If you don’t know this plant yet, please check out our website or visit our weed booth at one of our events in June or July (see below for dates and locations). Please email us at noxious.weeds@kingcounty.gov or call us at 206-296-0290 if you do find this plant anywhere in the county so we can move quickly to stop it. Garlic mustard is forming seed pods this month but there is still time to pull plants before the seeds mature.
Spread the word to friends and neighbors about giant hogweed. It's sad to hear about children who get burns from playing with hogweed stems or gardeners using a weed whacker on hogweed and getting blisters all over their bare legs. If you have giant hogweed in your neighborhood, make sure to tell everyone to watch out for this plant and to call the noxious weed program for help if they don’t know how to remove it safely. Check the noxious weed map for King County to see if it has been seen in your area. This month, hogweed’s large, thick, purple-blotched stalks will be rising above the giant jagged leaves and starting to flower. Digging up hogweed when it is full grown is tricky. Make sure to wear gloves and long sleeves and pants and carefully cut down the flowering stem without getting the juice on you. Then remove the leaves enough to get access to the roots. Dig up as much root as you can, at least 6 inches deep if possible. If there is a risk of anyone coming into contact with the plant or if there are flowers, place the hogweed in a sturdy plastic bag and discard in your garbage. Please contact our program if you find this plant or need assistance removing it.
Pull tansy ragwort before you see yellow. Bolting tansy ragwort is taking energy from the roots. This means weak roots that are easy to pull out of the ground. If you pull it before the yellow flowers open, it can be left to compost without risk of seeds forming. However, make sure to keep pulled plants away from livestock – tansy ragwort remains toxic when dry and is more palatable after being pulled. Look for tansy ragwort anywhere it was growing last year – seeds last up to 16 years in the soil, so you are sure to get new plants where it was last year. Remember to look for low-growing rosettes as well as tall, bolting plants.
Act quickly to stop flowering weeds from going to seed. The last hot, sunny period is really speeding things up in the weed world and lots of plants are starting to flower all at once. When weeds are flowering, it means there’s no time to lose. Preventing seeding means saving time and money and it’s also the easiest time to spot hard-to-find weeds. Noxious weeds that are flowering now or will be soon include: garlic mustard, Dalmatian toadflax, spotted knapweed, meadow knapweed, milk thistle, orange hawkweed, yellow hawkweed, poison-hemlock, Scotch broom, and herb Robert. Many more noxious weeds will start flowering later in June including: diffuse knapweed, sulfur cinquefoil, giant hogweed, tansy ragwort and goatsrue.
Report designated Class A and B noxious weeds on roads and trails. County, city and state crews are all busy working on noxious weeds along roadsides, trails and parks. However, even with their hard work and our own efforts to send them locations of regulated noxious weeds, we can't be everywhere and some sites get missed. If you see a patch of tansy ragwort or any other regulated noxious weed growing on public land or a roadside, please contact our office and we will make sure the right agency or property owner gets notified quickly. We can be reached at 206-296-0290 or you can use our online infestation report form.
Dry soil makes pulling a problem. Weed roots break off much more when the soil is dry and hard. This time of year you will probably need to use a digging tool or shovel to get the roots out for most weeds. If possible, you might want to try watering the weeds first, not to give them water but to make it easier to remove the roots. For areas that have been pulled, add mulch to slow down the re-growth and buy you some much needed time before having to pull again. Or consider other weed management methods for the summer months. Regular cutting can reduce many weed problems and prevent seeding for most plants (just don’t try this with tansy ragwort – it just flowers shorter and shorter each time!). Or try sheet mulching over unwanted grass or weedy areas – lay cardboard over area and cover with a thick layer of arborist chips. Then get some lemonade, find some shade, and watch the weeds die.
We will be holding four workshops for homeowners on knotweed control in July. We want to show what's involved in effectively getting this plant controlled and how and where to use different methods. It can be frustrating to keep trying to get rid of knotweed and not have it work, year after year. Hopefully we can help you figure out what to do that will work better. These workshops will be very hands on and interactive. We will also be providing specific training on using the knotweed stem injectors effectively. Participants in this training will be eligible to borrow our stem injectors for use on their own land. We are targeting four watersheds where we have cooperative, grant-based knotweed control projects underway: Snoqualmie River, Cedar River, Green River-Soos Creek, and the South Fork Skykomish.River Watersheds. However, everyone is welcome to attend any of the workshops, you don't have to live in one of these watersheds. The more people working on controlling knotweed, the less damage it will be doing in our county.
The workshops are all free and open to the public. We do ask that you register for the Skykomish class but registration is not needed for the others. Contact Sasha Shaw (sasha.shaw@kingcounty.gov) or Monica Walker (monica.walker@kingcounty.gov) for more information or call 206-296-0290. See our website for more details.
Knotweed Workshop Dates and Locations:
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July 21, 6:30-8:00 p.m., Skykomish, location to be determined (registration required for this workshop)
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July 28, 7:00-8:30 p.m., Maple Valley Lions Club (at the Cedar River Council Meeting), 20899 SE 184th St., Maple Valley
Be the "Early Detection" part of "Early Detection-Rapid Response": Volunteer as a Weed Watcher
We often hear about the importance of finding new weed infestations early and responding quickly to stop them while we still can. Well, now you can do just that. In our two weed watcher programs we are focusing on a short list of target weeds growing in certain areas. Then we will be taking the data and acting on it so you will have the satisfaction of making a real difference.
Lake
Weed
Watcher Program:
If you have a canoe or small boat and would like to help keep noxious weeds out of our small lakes, then consider joining our lake weed watcher program. Our goal is to catch water weeds before they have a chance to cause major problems. All it takes is attendance at one of two trainings in late June and two summertime lake surveys. We’ll teach you how to identify the target weeds and their native look-alikes, and we’ll provide all the equipment and materials you’ll need (other than a boat). The half-day trainings will be in Black Diamond on June 20 and in Bellevue on June 27. For more information or to sign up for a training, contact Katie Messick at 206-263-6461 or katie.messick@kingcounty.gov.
Trail Weed Watcher Program:
If hiking on trails is more your passion, then consider joining our Middle Fork Snoqualmie Weed Watcher group. The Mid Fork Weed Watchers are part of an ongoing cooperative effort with Mountains to Sound Greenway Trust and the King County Noxious Weed Program to find and remove invasive plants from the Middle Fork Snoqualmie Valley, including state and federal forest lands and wilderness areas. We need people who can hike a trail or two this summer and take note of where they see invasive plants growing. It helps to have a GPS and some plant knowledge, but we will train you so don’t worry about being an expert. If you can’t make it to the training, let me know and I’ll work out a way to get you up to speed and out on the trails.
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When: Sunday, June 14, 9:00 a.m. to 5:00 p.m.
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Where: North Bend Ranger Station (in the conference hall behind the main building)
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Logistics: Starts in classroom, then in the field. Be ready for a short hike and bring lunch, water, GPS and compass if you have them, and something to write on.
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Come Learn About Weeds while You Shop for Yummy Local Foods
We will be setting up our noxious weed information booth at several Farmers Markets over the next couple of months and would love to see you. We will have lots of handouts, live weed specimens of many local weed pests, and, of course, we will have our friendly weed experts there to answer your questions. Our schedule over the next couple of months is:
Don't Be a Vector - Invasive Species are Great at Hitchhiking
Those of us who work with weeds are the people with the best opportunity to spread them. Seeds and other plant parts (propagules) get caught in the soles of our shoes, on shoelaces, clothing and hair, in the tires of our vehicles, the dirt on our tools, even on our pets. When we leave the site of a weed infestation, we can carry these a long distance, ultimately starting a new infestation in a new place. Fortunately, it’s very easy to prevent this. Simply follow two rules when you’ve been around weeds: 1) INSPECT yourself, your vehicle, your tools and anything else that may be a good seed carrier; and, 2) if you see anything, CLEAN it off BEFORE you leave the site. All it takes is a simple boot brush to get the dirt off your shoes and tools, plus a little water if the area is muddy. The five extra minutes it takes to check for seeds may save you days of work in the future. All you need to do is INSPECT and CLEAN. It's that easy!
Restoration and the Arts Come Together in the West Duwamish Greenbelt
The Nature Consortium brings a fresh new angle to urban forest restoration by combining art and nature in their volunteer events and festivals. Their motto sums it up well: “teaching environmental lessons through the creative arts and hands-on conservation projects”. Performing artists "play in the woods" during many of their work parties, and include singers, instrumentalists, and dancers. And every summer they celebrate nature and the arts at their Arts in Nature Festival at Camp Long, being held this year on August 22-23.
The Nature Consortium's Urban Forest Restoration Project is committed to long-term stewardship and restoration of the West Duwamish Greenbelt, the largest remaining contiguous forest within Seattle city limits, consisting of 182 acres in park land and another 300 acres in privately owned land. It encompasses the extended forest along the eastern slopes of West Seattle that is visible from I-5. The Greenbelt is home to foxes, red-legged frogs, hawks, and bald eagles. Unfortunately it is also inundated with invasive species like English ivy and Himalayan blackberry and much of the forest cover is in declining health and has few conifer trees needed for long term forest health. The Nature Consortium’s main restoration goal is reintroducing native conifer species to the greenbelt and they also focus on invasive plant removal, site maintenance and environmental education. Support for the project comes from Seattle Dept. of Parks & Recreation, Green Seattle Partnership, King County Council, Patagonia, Peck Family Foundation, Lucky Seven Foundation, and Coffee.net/Seattle.
The Nature Consortium hosts volunteer work parties in the West Duwamish Greenbelt year round 5-6 times per week, including every Saturday from 10am-2pm. Each work party begins with a short informal forest ecology workshop. Spring and summer events are devoted to maintenance and monitoring, and during the fall and winter they remove invasive species, mulch, and plant native plants and trees in the West Duwamish Greenbelt.
They require an RSVP for all work parties as the locations and times vary. Email the volunteer coordinators at volunteer@naturec.org or call 206.923.0853 (provide name, phone, email, and work party date of interest.). If you have a group of 10 or more, email Mark Tomkiewicz (buphalo) at buphalo@naturec.org or call 206.930.9025 to book a date for your own group work party. Tools, gloves and light refreshments are provided at all work parties.
Weeds in the News: The Good, The Bad, and The Ugly
THE GOOD – Success and Motivational Stories:
THE BAD – Garlic Mustard Just Gets Worse and Worse:
THE UGLY – Battle of the Weeds and Fascinating Ways Plants Can Hurt Us:
NOTE: For these news stories and more see our Weeds in the News page on our website.
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