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KC Weed News - June 2007 (PDF Version for Printing) TOPICS BELOW
One of the scariest impacts of noxious weeds like sulfur cinquefoil is their ability to out-compete and replace native plant species. The risk is highest for rare and threatened species that have already lost most of their natural habitat. One striking example of this impact is with western Washington prairie species, many of which are dramatically reduced from the populations present when our region was first settled. I find it sadly ironic that one of these disappearing prairie species, graceful cinquefoil (Potentilla gracilis var. gracilis), closely resembles sulfur cinquefoil, that is itself one of the species invading into the Central Puget Sound prairies. For example, both kinds of cinquefoil are growing on the Fort Lewis Prairie in Pierce County. The Nature Conservancy is actively managing the sulfur cinquefoil and is making progress towards eradicating it, while carefully protecting the native graceful cinquefoil. We are not so lucky in King County. While there are many populations of sulfur cinquefoil invading into what remains of our former prairies, the only populations of graceful cinquefoil that I am aware of were planted intentionally. Good places to see the native graceful cinquefoil are in the lovely native plant garden in front of the Vashon Land Trust office on Vashon Island and in the restoration plantings of Clark’s Prairie by Seward Park in Seattle. Besides invading Central Puget Sound prairies, sulfur cinquefoil is also making a nuisance of itself in several pastures and grassy fields in King County, mostly in the Kent-Covington area, but also east of Redmond and in other scattered places throughout the county. Most populations are found on poor soil, usually rocky and well-drained, but also moist areas and even some high quality pastures. Last year, there were 207 sites in the county with sulfur cinquefoil with an average infestation area of about 4000 sq ft. Given the relatively small size of the infestations, we are optimistic about our chances of keeping this plant generally under control. However, sulfur cinquefoil is very tenacious once established. A 1994 Montana State University Extension publication makes this statement about sulfur cinquefoil: “To date, large infestations have not been effectively controlled.” In our county, most infestations over about 100 sq. ft. have proven to be very persistent in spite of property owners efforts to control them. In addition, there are 45 roadside sites, 28 state highway sites and several railroad infestations in our county, so there is also a high risk of this plant being spread by mowers, vehicles, trains and other right-of-way disturbances. It is easy to find information on sulfur cinquefoil online because of the extent of infestations across North America, particularly in the rangelands of the western states. This plant is native to the eastern Mediterranean region but is also found in western Europe, the Middle East, and in western and central Asia. Sulfur cinquefoil showed up in North America sometime before 1900 and was a well-established weed by the 1950’s in eastern North America and the Great Lakes area. The earliest record in Washington was 1937 and it is now found in at least 28 counties in Washington, including counties on both sides of the Cascades and all the way out to the Olympic Peninsula. This rapid spread is similar to spotted knapweed and other rangeland noxious weeds. In addition to the usual disturbed and over-grazed sites, sulfur cinquefoil is also invading native plant communities that have had minimal human disturbance. One reason for the success of sulfur cinquefoil in grazed fields and pastures is that most animals – elk, deer, horses, cattle – avoid it more than any other plant, even bitter-tasting spotted knapweed. Although it isn’t toxic, sulfur cinquefoil has a high tannin level and is very unpalatable to most animals. Another reason for its success is the woody crown that readily re-sprouts when mowed. Although there are no rhizomes, the plant tends to spread out from the crown as it ages and a single plant can live up to 20 years. In King County, sulfur cinquefoil often persists all winter although it will go dormant after an extended cold streak. Although this plant is easy to identify by its pale-yellow flowers with heart-shaped petals and distinctive 5-lobed leaves, it is also very easy to miss when surveying grassy fields. The leaves are yellow-green and closely match many of our pasture grasses in color. Before flowering and after petals drop, the plants blend into the grass. Flowers are often only present for a short while – late May to mid July – and seeds start forming as early as mid-July and disperse in late July and August. Unfortunately, cutting fields or roadsides in July or August contributes to the spread of this plant as seeds are moved with the mower, sometimes to new, un-infested sites. For information on identification and management of sulfur cinquefoil, check our website or call one of our weed specialists at 206-296-0290. A good detailed resource online is the Forest Service’s information sheet. Because of sulfur cinquefoil’s impacts to pasture productivity and native habitat and its relatively limited distribution, control is required in King County. We encourage you to report sightings of this plant as soon as possible so that we can notify the appropriate agency or property owner. You can call us at 206-296-0290, send us an email or use our online infestation report form. 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. Before the yellow flowers open, pulled tansy ragwort can be left to compost without risk of seeds forming. 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. Watch for flowering giant hogweed in urban areas, parks, and anywhere else it has been spotted in the past. Mature giant hogweed will reach it’s full height of 10 to 15 feet this month and will be easy to spot with its huge umbrella-shaped flower heads. Seeds start forming late June and into July so flower heads should all be carefully cut off and discarded before the seeds mature. CAUTION: 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. Make flowering noxious weeds your first priority . Flowers are quickly followed by seeds and that means many more years of work! Some flowers can go to seed even after they are cut, so it is important to remove flowering noxious weeds before mowing fields and roadsides or to thoroughly clean equipment after mowing. In June, the following noxious weeds begin to flower: sulfur cinquefoil, tansy ragwort, diffuse knapweed, giant hogweed, goatsrue, Spanish broom, and policeman’s helmet. Noxious weeds that are continuing to flower include: meadow knapweed, spotted knapweed, Dalmatian toadflax, orange hawkweed, yellow hawkweed, and milk thistle. By late June, we might start seeing flowering perennial pepperweed and purple loosestrife. 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. In addition to working individually with landowners, the King County Noxious Weed Control Program offers free workshops on invasive and noxious weeds. There are classes scheduled throughout the county in June and July. All classes are free and open to the public. Details are available at www.dnr.metrokc.gov/weeds/classes.htm.
I also encourage community associations to contact our program if they would like to schedule a presentation on noxious weeds in their area. For more information on any of these workshops or to schedule a presentation contact Sasha Shaw at 206-263-6468 or by email. The Noxious Weed Program will be giving out information and advice at two farmers markets and one garden fair this month. On June 23 from 1-4, we will be at the Covington Water District’s WaterWise Garden Fair ( 18631 SE 300th Place, Kent). On June 29, from 10-2, we will be at Pike Place Market in Seattle for Farm Friday and on June 30, from 9-2 at the Issaquah Farmer’s Market at Pickering Barn. We’ll have lots of great literature on weeds and we’ll try our best to answer all weed identification and control questions that come our way. Stop by and say hello if you are in the neighborhood!
May 2007 Program offices are located at 201 S. Jackson St., Suite 600, Seattle, WA 98104. To contact a staff member at the King County Noxious Weed Control Program, please call 206-296-0290 or by reach them by email. |
| Please direct questions & comments regarding noxious weeds to Program Staff, King County Noxious Weed Control Program.
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Updated: June 1, 2007 |
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