Identification TipsShowy, bright yellow flowers grow in clusters near thetop of the plantSoftly hairy leaves and stems on erect plants growing 3to 6 feet tallLeaves are lance or egg-shaped and usually 3 in a whorl(sometimes 2 or 4)Flowers have 5 petals that are joined at the baseThe base of the flowers is ringed by green sepals thathave distinct orange-brown edgesSeeds found in dry, egg-shaped capsules

BiologyUpright perennial with roots forming on creeping stemsthat are partly or entirely underground (rhizomes)Rhizomes can be up to 15 feet longReproduces by seed and by vegetative growthSomewhat slow to invade into new areas but onceestablished, highly competitive and able to spreadaggressively into stands of established vegetationAble to out-compete even tough plants such as cattailsand purple loosestrifeThrives in wet sites with full sun but also shade-tolerantand able to grow in sites that dry out in the summerFlowers July to August

ImpactsDamages shoreline and wetland ecosystems byreplacing beneficial native plantsReduces habitat needed by waterfowl, wildlife, birds andfish, including several species of salmonReduces recreational opportunities

DistributionOccurs on lakeshores, waterways and in wetlandsMostly found on Lake Sammamish, Lake Washingtonand the Sammamish River. Also Lake Burien andin the lower Snoqualmie River valley.Occasionally found growing as an ornamental

Garden LoosestrifeGarden LoosestrifeGarden LoosestrifeGarden LoosestrifeGarden Loosestrife Lysimachia vulgaris Primrose Family

Class B Noxious Weed: Control Required

KING COUNTY NOXIOUS WEED CONTROL PROGRAM WEED ALERT

King County Noxious Weed ControlProgram Line: 206-477-WEEDwww.kingcounty.gov/weeds

Questions?

KING COUNTY NOXIOUS WEED CONTROL PROGRAM WEED ALERT

Garden loosestrife originated fromEurope and has no natural enemiesin North America.

A large infestation of gardenloosestrife in Marymoor Park ischoking out native vegetation.

What You Can DoDo your part by checking regularly for garden loosestrife on your property and along publicwaterways and wetlands. If a new infestation on public lands is spotted, please contact the KingCounty Noxious Weed Control program.

Control MethodsMost control methods need to be applied overseveral years to be successful. Often, a combinationof methods will be more effective than one by itself.

Prevention: Avoid varieties sold as ornamentals.If boating in areas with loosestrife, check boat hulls,motors and other equipment for plant fragments thatcan be transported to new waterways.

Manual: Small infestations can be dug, bagged anddisposed of, taking care not to disperse seeds. Besure to dig up as much rhizome as possible. Matureflowering stems can be cut at base in late summer toprevent seed production. Brush off boots and clothes before leaving the infested area.

Mechanical: Cutting or mowing by itself is not an effective control option for garden loosestrife.New shoots and roots will develop from cut plants. Black plastic covering or landscaping fabic is aninterim option for dense seedling infestations. It does not kill mature plants, but it does slow growthand seed production.

Chemical: Chemical control options may differ for private, commercial and government agencyusers. Follow all label directions and local regulations regarding herbicide use in sensitiveareas. Certain herbicides cannot be used in aquatic areas or their buffers. If herbicides are used,make sure that their label specifies your type of site. All aquatic herbicides are restricted-useherbicides. Purchase and application of these herbicides can only be done by licensed aquaticherbicide applicators. Permits are required before applying aquatic herbicides. Aquatic formulationsof glyphosate or triclopyr are effective but may require repeat applications. Follow up in the secondyear is crucial for successful control. For site specific herbicide recommendations, please contactthe King County Noxious Weed Control Program.

Don’t be fooledDon’t be fooledDon’t be fooledDon’t be fooledDon’t be fooled::::: garden loosestrife looks verysimilar to yellow loosestrife (Lysimachia punctata) andgrows in the same habitat. It is also somewhat invasive,but has not been elevated to the same status as gardenand purple loosestrife within King County. Yellowloosestrife has yellow, star-like blooms all along theflower stem (not just at the top). Blooms begin in mid-June. It also is shorter than garden loosestrife, usuallyonly reaching a height of 4 feet.

Garden loosestrife rings lakes and wetlands,out-competing beneficial vegetation andforming a dense, underground mat ofrhizomes.

Revised June 2007

Yellow loosestrife(right and below) isoften confused withits more aggressivecousin, gardenloosestrife.

kingcounty.gov/weeds ~ 206-477-WEED (206-477-9333) or TTY: 711 ~ noxious.weeds@kingcounty.gov

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