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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.

2014 King County Noxious Weed List

(click here to download brochure)

Regulated Class A noxious weeds
(eradication required throughout Washington State including King County)

Common name Scientific name State class
common crupina Crupina vulgaris  A
cordgrass, common Spartina anglica  A
cordgrass, dense flower (external link) Spartina densiflora  A
cordgrass, salt meadow Spartina patens  A
cordgrass, smooth Spartina alterniflora  A
dyers woad Isatis tinctoria  A
eggleaf spurge (external link)  Euphorbia oblongata  A
false brome Brachypodium sylvaticum  A
floating primrose-willow  Ludwigia peploides  A
flowering-rush Butomus umbellatus  A
French broom Genista monspessulana   A
garlic mustard Alliaria petiolata  A
giant hogweed Heracleum mantegazzianum  A
goatsrue Galega officinalis  A
hydrilla Hydrilla verticillata  A
johnsongrass (external link)  Sorghum halepense  A
knapweed, bighead Centaurea macrocephala  A
knapweed, Vochin Centaurea nigrescens  A
kudzu Pueraria montana var. lobata  A
meadow clary Salvia pratensis  A
oriental clematis Clematis orientalis  A
purple starthistle Centaurea calcitrapa  A
reed sweetgrass Glyceria maxima  A
ricefield bulrush Schoenoplectus mucronatus  A
sage, clary Salvia sclarea  A
sage, Mediterranean Salvia aethiopis  A
shiny geranium Geranium lucidum  A
silverleaf nightshade (external link)  Solanum elaeagnifolium  A
Spanish broom Spartium junceum  A
spurge flax (external link)  Thymelaea passerina  A
Syrian bean-caper Zygophyllum fabago  A
Texas blueweed Helianthus ciliaris  A
thistle, Italian (external link)  Carduus pycnocephalus  A
thistle, milk Silybum marianum  A
thistle, slenderflower Carduus tenuiflorus  A
variable-leaf milfoil Myriophyllum heterophyllum  A
wild four o'clock (external link) Mirabilis nyctaginea  A

Regulated Class B noxious weeds
(control is required for these species in King County)

Common name Scientific name State class 
blueweed, viper's bugloss (external link) Echium vulgare  B
Brazilian elodea (see note 1 below)  Egeria densa  B
bugloss, annual Anchusa arvensis  B
bugloss, common Anchusa officinalis  B
camelthorn (external link) Alhagi maurorum  B
common reed (non-native genotypes) Phragmites australis  B
Dalmatian toadflax Linaria dalmatica ssp. dalmatica  B
fanwort Cabomba caroliniana  B
gorse Ulex europaeus  B
grass-leaved arrowhead (external link) Sagittaria graminea  B
hairy willowherb Epilobium hirsutum  B
hawkweeds: all non-native species and hybrids of the meadow subgenus (see note 2 below) Hieracium, subgenus Pilosella  B
hawkweeds: all non-native species and hybrids of the wall subgenus (see note 2 below) Hieracium, subgenus Hieracium  B
hawkweed, orange Hieracium aurantiacum  B
hawkweed oxtongue (external link) Picris hieracioides  B
hoary alyssum (external link)  Berteroa incana  B
houndstongue Cynoglossum officinale  B
indigobush Amorpha fruticosa  B
knapweed, black Centaurea nigra  B
knapweed, brown Centaurea jacea  B
knapweed, diffuse Centaurea diffusa  B
knapweed, meadow Centaurea jacea x nigra  B
knapweed, Russian Acroptilon repens  B
knapweed, spotted Centaurea stoebe  B
kochia Kochia scoparia  B
loosestrife, garden Lysimachia vulgaris  B
loosestrife, purple Lythrum salicaria  B
parrotfeather Myriophyllum aquaticum  B
perennial pepperweed Lepidium latifolium  B
policeman's helmet Impatiens glandulifera  B
rush skeletonweed Chondrilla juncea  B
saltcedar Tamarix ramosissima  B
spurge, leafy Euphorbia esula  B
sulfur cinquefoil Potentilla recta  B
tansy ragwort (see note 3 below) Senecio jacobaea  B
thistle, musk Carduus nutans  B
thistle, plumeless (external link) Carduus acanthoides  B
thistle, Scotch Onopordum acanthium  B
velvetleaf Abutilon theophrasti  B 
water primrose Ludwigia hexapetala  B
white bryony (external link) Bryonia alba  B
wild chervil (external link) Anthriscus sylvestris  B
yellow floating heart Nymphoides peltata  B
yellow nutsedge Cyperus esculentus  B
yellow starthistle Centaurea solstitialis  B
1. Brazilian elodea is designated for control throughout King County except in Lake Washington, Lake Sammamish, Lake Union, Lake Fenwick, Lake Doloff and the Sammamish River.
2. Non-native yellow-flowered hawkweeds (Hieracium species): the 11 separate listings of yellow-flowered hawkweeds that were previously on the noxious weed list are now consolidated into two Class B listings by subgenus - meadow (Pilosella) and wall (Hieracium). In general, the meadow subgenus species have stolons present, have no or few leaves on the stems, and have leaf edges that are smooth or minutely toothed. The wall subgenus species in contrast generally lack stolons, have stem leaves, and have leaf edges that are conspicuously toothed or lobed.
3. Tansy ragwort is not designated by the State Weed Board for control in King County, but has been selected by the King County Weed Board for required control in all areas of King County.

Regulated Class C noxious weeds
(control is required for these species in King County)

Common name Scientific name State class
absinth wormwood Artemisia absinthium  C
buffalobur Solanum rostratum  C

Non-regulated Class B and C noxious weeds
(Class B and C noxious weeds that are not designated for control in King County, control recommended but not required in King County)

Common name Scientific name State class
blackberry, evergreen Rubus laciniatus  C
blackberry, Himalayan Rubus armeniacus  C
butterfly bush Buddleia davidii  B
common barberry (external link) Berberis vulgaris  C
common catsear (external link) Hypochaeris radicata  C
common fennel (except bulbing variety azoricum) (external link) Foeniculum vulgare  B
common groundsel (external link) Senecio vulgaris  C
common St. Johnswort (see note 1 below) Hypericum perforatum  C
common tansy Tanacetum vulgare  C
common teasel Dipsacus fullonum   C
curly-leaf pondweed (external link) Potamogeton crispus  C
Eurasian watermilfoil Myriophyllum spicatum  B
field bindweed Convolvulus arvensis  C
fragrant water lily Nymphaea odorata  C
hairy whitetop (external link) Cardaria pubescens  C
herb Robert Geranium robertianum  B
hoary cress (external link) Cardaria draba  C
ivy, Atlantic Hedera hibernica  C
ivy, English Hedera helix 'Baltica', Hedera helix 'Pittsburgh', Hedera helix 'Star'  C

knotweed, Bohemian (see note 2 below)

Polygonum x bohemicum  B
knotweed, giant (see note 2 below) Polygonum sachalinense  B
knotweed, Himalayan (see note 2 below)  Polygonum polystachyum  B
knotweed, Japanese (see note 2 below) Polygonum cuspidatum  B
lesser celandine Ficaria verna  B 
old man's beard Clematis vitalba  C
oxeye daisy Leucanthemum vulgare  C
perennial sowthistle Sonchus arvensis ssp. arvensis  C
poison-hemlock Conium maculatum  B
reed canarygrass Phalaris arundinacea  C
Scotch broom (see note 3 below) Cytisus scoparius  B
spurge laurel Daphne laureola  B
thistle, bull Cirsium vulgare  C
thistle, Canada Cirsium arvense  C
tree-of-heaven (external link) Ailanthus altissima  C
wild carrot Daucus carota  C
yellow archangel Lamiastrum galeobdolon  C
yellow flag iris Iris pseudacorus  C
yellow toadflax Linaria vulgaris  C
1. Permit from KC Weed Board required to grow common St. Johnswort as a crop in King County.
2. Control of Bohemian, Japanese, giant and Himalayan knotweed is required on the Green River and its tributaries upstream of the Auburn City Limits and on the Cedar River and its tributaries upstream of the Renton City Limits (tributaries included are those defined as Type S, F or N aquatic areas in KCC 21A.24.355). Control of these invasive knotweed species is required up to the ordinary high water mark (or up 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. This requirement to control knotweed is contingent upon the noxious weed program or program partners providing knotweed control services in the selected area for affected private landowners who request assistance.
 3. Control of Scotch broom is required on King County's section of SR-2 and on I-90 between mile marker 34 and the King/Kittitas county line.

King County weeds of concern
(This list is for educational purposes only; these species are not classified as noxious weeds in Washington State. These species often impact and degrade native plant and animal habitat. Control is recommended where possible and new plantings are discouraged.)

Common name Scientific name State class
bittersweet nightshade Solanum dulcamara NONE
buttercup, creeping Ranunculus repens NONE
buttercup, tall Ranunculus acris NONE 
common hawthorn Crataegus monogyna NONE
English holly Ilex aquifolium NONE
English laurel Prunus laurocerasus NONE
European mountain-ash (external link) Sorbus aucuparia NONE
hedge bindweed, morning glory (external link)  Convolvulus sepium NONE
multiflora rose Rosa multiflora NONE
spotted jewelweed (external link) Impatiens capensis NONE

King County Noxious Weed List

Download brochure

Related information

Related agencies

Program offices are located at 201 S. Jackson St., Suite 600, Seattle, WA 98104. To contact staff, see the Noxious Weed Control Program Directory, send an email, or call 206-477-WEED (206-477-9333).