What are weeds?

There are a whole host of terms to describe weeds.  The term “weeds” itself can refer to any plant that occurs in an undesirable location. Terms like “non-native“, “exotic“, “alien” or “non-indigenous” refer to plants that occur in areas where they historically did not occur.  These terms make no distinction whether plants are desirable or undesirable.  The term “invasive” refers to a plant or animal that exhibits aggressive growth and displace other species.  Other terms like “noxious” or “nuisance” refer to plants that have special designation by the state or by a municipality the prohibits their sale or cultivation.  With this broad diversity of terms, it is no wonder that many people find themselves confused and wondering how to make sense of it all.

At the WeedWise program, we hope to clarify this issue by focusing on plants we refer to as “invasive weeds”Invasive weeds are plants that live outside their historic geographical range, and whose aggressive growth habit has a detrimental effect on our social, economic, or ecologic resources.  The three key components of invasive weeds are that they:

  1. Did not historically occur in our area, but have been brought in either intentionally or unintentionally through human action.
  2. Exhibit aggressive growth which displaces native or desirable vegetation, and will continue to spread unless actively controlled.
  3. Have a negative impact on our community.

These three characteristics clarify invasive weeds as those plants that pose the greatest threat to our community.  By focusing on invasive weeds the WeedWise program is working to maximize its limited resources to realize the greatest benefit to Clackamas County.

Defining our priorities

All invasive weeds pose a major threat to the residents of Clackamas County, but some of these pests can be more damaging than others.  In addition, the costs to control these invasive weeds greatly exceed the resources available for their management.  As a result, the WeedWise program has prioritized its efforts to target invasive weeds that pose the greatest risk, have the greatest negative impact, and may still be limited enough in their distribution to allow for eradication or containment in Clackamas County.  For these “priority” invasive weeds, the WeedWise program may have resources available to assistance Clackamas County landowners to control or manage these weeds.  For more common invasive weeds, the WeedWise program offers technical information and consultations to improve your efforts and to make your management practices more effective.

WeedWise Classifications

Priority:  These weeds are the highest priority and are actively being targeted for eradication by the WeedWise Program.  Landowners are encouraged to notify the WeedWise program for assistance with these weeds and to actively control them on their property.

Maintenance:  These weeds are damaging and widespread.  The WeedWise Program encourages control by landowners and can assist with the development of a plan to control these weeds.

Containment:  These weeds are a priority for management, but in some areas, these weeds are so widespread that treatments of all infestations is not feasible.  For these weeds, infestations will be targeted for eradication when they occur outside of established containment areas.  Landowners are encouraged to contact the WeedWise program for assistance in controlling these weeds on properties that occur outside the containment areas, and for technical assistance in developing plans for management within containment areas.

Clackamas Weed List

Common NameScientific NameWeedWise ClassificationOregon ClassificationWashington Classification4-County CWMAColumbia Gorge CWMA
Barbed GoatgrassAegilops triuncialispriorityA,Tnot listedAW
Garlic mustardAlliaria petiolatapriorityB,TABA
Flowering rush Butomus umbellatuspriorityA,TAWA
Welted thistleWelted thistlepriorityA,Tnot listednot listednot listed
Rush skeletonweedChondrilla junceapriorityB, TBDB
HoundstongueCynoglossum officinalepriorityBBDB
Spurge laurelDaphne laureolapriorityBBBB
Oblong spurgeEuphorbia oblongatapriorityA,TAAA
GoatsrueGalega officinalispriorityA, TAAA
Giant hogweedHeracleum mantegazzianumpriorityA, TAAA
Orange hawkweedHieracium aurantiacumpriorityA,TBAA
Meadow hawkweedHieracium caespitosumpriorityB,TBAB
African ruePeganum harmalapriorityA,Tnot listedAW
Sulphur cinquefoilPotentilla rectapriorityBBAB
KudzuPueraria montanapriorityA,TAAA
Blessed milk thistleSilybum marianumpriorityBAAA
GorseUlex europaeuspriorityB,TBAA
Garden yellow loosestrifeLysimachia vulgarispriorityA,TBAW
Spiny cockleburXanthium spinosumpriorityBCDC
Syrian bean-caperZygophyllum fabagopriorityAAAA
Russian KnapweedAcroptilon repenspriorityBBAB
Pheasant eyeAdonis aestivalispriorityBnot listednot listednot listed
Jointed goatgrassAegilops cylindricapriorityBCnot listedC
Ovate GoatgrassAegilops ovatapriorityAnot listedAW
CamelthornAlhagi pseudalhagipriorityABAA
Yellow tuftAlyssum corsicumpriorityA,Tnot listedAW
Yellow tuftAlyssum muralepriorityA,Tnot listedAW
RagweedAmbrosia artemisiifoliapriorityBnot listedDB
Common buglossAnchusa officinalispriorityB,TBAB
Giant reedArundo donaxpriorityWnot listednot listedA
Hoary allysumBertoa incanapriorityA,TBAB
White bryoniaBryonia albapriorityABAA
Plumeless thistleCarduus acanthoidespriorityA,TBAA
Musk thistleCarduus nutanspriorityBBEB
Italian thistleCarduus pycnocephaluspriorityBADA
Slender-flowered thistleCarduus tenuifloruspriorityBADA
Smooth distaff thistleCarthamus baeticuspriorityAnot listedAW
Woolly distaff thistleCarthamus lanatuspriorityA,Tnot listedAW
Purple starthistleCentaurea calcitrapapriorityA,TAAA
Iberian starthistleCentaurea ibericapriorityA,Tnot listedAA
Yellow starthistleCentaurea solstitialispriorityBBAB
Squarrose knapweedCentaurea virgatapriorityA,Tnot listednot listedA
Jubata grassCortaderia jubatapriorityBCWB
Japanese dodder Cuscuta japonicapriorityAnot listedAW
Purple nutsedgeCyperus rotunduspriorityAnot listedAA
Cape ivyDelairea odoratapriorityAnot listedAW
Cutleaf teaselDipsacus laciniatuspriorityBnot listednot listedW
Paterson's curseEchium plantagineumpriorityA,Tnot listedAW
Leafy spurgeEuphorbia esulapriorityB, TBBA
HalogetonHalogeton glomeratuspriorityBnot listednot listedW
SpikeweedHemizonia pungenspriorityBCnot listedC
Yellow hawkweedHieracium × floribundumpriorityA,TBAA
Mouse-ear hawkweedHieracium pilosellapriorityA,TBAA
King-devil hawkweedHieracium piloselloidespriorityA,TBAA
HydrillaHydrilla verticillatapriorityAAWA
Common frogbitHydrocharis morsus-ranaepriorityAnot listedAW
Small-flowered jewelweedImpatiens parvifloraprioritynot listedAAA
KochiaKochia scopariapriorityBBnot listedB
Lens-podded whitetopLepidium chalepensispriorityBnot listedAB
Hoary cressLepidium drabapriorityBCAB
Perennial pepperweedLepidium latifoliumpriorityB,TBAB
Hairy whitetopLepidium pubescenspriorityBCnot listedC
West Indian spongeplantLimnobium laevigatumpriorityAAAW
MatgrassNardus strictapriorityA,Tnot listedAW
Yellow floating heartNymphoides peltatapriorityA, TBAA
Scotch thistleOnopordum acanthiumpriorityBBAB
Taurian thistleOnopordum tauricumpriorityA,Tnot listedAW
Common reed Phragmites australis ssp. australispriorityBBAB
Himalayan knotweedPolygonum polystachyumpriorityBBnot listedB
RavennagrassSaccharum ravennaepriorityAAAA
Silverleaf nightshadeSolanum elaeagnifoliumpriorityAAAA
BuffaloburSolanum rostratumpriorityBCDC
JohnsongrassSorghum halepensepriorityBAEA
Smooth cordgrassSpartina alterniflorapriorityA, TAAW
Common cordgrassSpartina anglicapriorityA,TAAW
Dense-flowered cordgrassSpartina densiflorapriorityA,TAAW
Saltmeadow cordgrassSpartina patenspriorityA,TAAW
Spanish broomSpartium junceumpriorityBAFA
Water soldiersStratiotes aloidespriorityAnot listedAnot listed
Medusahead ryeTaeniatherum caput-medusaepriorityBnot listedCC
European water chestnutTrapa natanspriorityAnot listedAA
PuncturevineTribulus terrestrispriorityBBCB
ColtsfootTussilago farfarapriorityABAA
VelvetleafAbutilon theophrastipriorityBBBB
False indigo bush Amorpha fruticosapriorityBBnot listedB
Biddy-biddyAcaena novae-zelandiaepriorityBnot listednot listedW
Portuguese broomCytisus striatuspriorityB,Tnot listedWW
French broomGenista monspessulanapriorityBAWA
Dyers woadIsatis tinctoriapriorityBAnot listedA
Dalmatian toadflaxLinaria dalmaticapriorityB, TBBB
Delta arrowheadSagittaria platyphyllapriorityAnot listedAnot listed
Ricefield bulrushSchoenoplectus mucronatuspriorityWADA
SwainsonpeaSphaerophysa salsulapriorityBCnot listedC
SaltcedarTamarix ramosissimapriorityB,TBWB
Eurasian watermilfoilMyriophyllum spicatummaintenanceBBCB
Tree of HeavenAilanthus altissimamaintenanceBCBC
Wild chervilAnthriscus sylvestrismaintenancenot listedBnot listedB
Italian arumArum italicummaintenancenot listedCBB
Butterfly bushBuddleja davidii (Buddleja varabilis)maintenanceBBBB
Meadow knapweedCentaurea × moncktonii (C. pratensis)maintenanceBBBB
Spotted knapweedCentaurea stoebe (C. maculosa)maintenanceB,TBBB
Canada thistleCirsium arvensemaintenanceBCCC
Bull thistleCirsium vulgaremaintenanceBCDC
Old man's beardClematis vitalbamaintenanceBCBC
Poison hemlockConium maculatummaintenanceBBBB
English hawthornCrataegus monogynamaintenanceWCCC
Yellow nutsedgeCyperus esculentusmaintenanceBBBB
Scotch broomCytisus scopariusmaintenanceBBCB
Wild carrot Daucus carotamaintenancenot listedCCC
Common teaselDipsacus fullonummaintenancenot listedCCC
South American waterweedEgeria densamaintenanceBBCB
Myrtle spurgeEuphorbia myrsinitesmaintenanceBBEB
Shining geraniumGeranium lucidummaintenanceBBBA
Herb robertGeranium robertianummaintenanceBBCB
English ivyHedera helixmaintenanceBCCB
Irish ivyHedera hibernicamaintenanceBCCB
St. John's wort Hypericum perforatummaintenanceBCCC
Hairy cat's earHypochaeris radicatamaintenancenot listedCCC
JewelweedImpatiens capensismaintenanceWCCW
Yellow archangelLamium galeobdolonmaintenanceBBBB
Small broomrapeOrobanche minormaintenanceBnot listedDA
RibbongrassPhalaris arundinacea var. pictamaintenanceB,T Cnot listedC
Reed canarygrassPhalaris arundinaceamaintenanceWCnot listedC
Curly-leaf pondweedPotamogeton crispusmaintenancenot listedCCC
Lesser celandineRanunculus ficariamaintenanceBBBB
Armenian (Himalayan) blackberryRubus armeniacus (R. bifrons, R. procerus, R. discolor)maintenanceBCCC
Evergreen blackberryRubus laciniatusmaintenancenot listedCCC
Tansy ragwortSenecio jacobaeamaintenanceBBBB
Common groundselSenecio vulgarismaintenancenot listedCnot listedC
Perennial sowthistleSonchus arvensis ssp. arvensismaintenancenot listedCDC
Common tansyTanacetum vulgaremaintenancenot listedCCC
Perennial peavineLathyrus latifoliusmaintenanceBnot listedCC
Oxeye daisyLeucanthemum vulgaremaintenancenot listedCCC
Yellow toadflaxLinaria vulgarismaintenanceBCBC
Parrots featherMyrophyllum aquaticummaintenanceBBBB
Yellow flag irisIris pseudacorusmaintenanceBCBB
Diffuse knapweedCentaurea diffusamaintenanceBBBB
Brown knapweedCentaurea jacea maintenancenot listedBFB
Big-headed knapweedCentaurea macrocephalamaintenanceWAnot listedA
Malta starthistleCentaurea melitensismaintenancenot listedBnot listednot listed
Black knapweedCentaurea nigra maintenancenot listedBnot listedB
Vochin knapweedCentaurea nigrescensmaintenancenot listedAnot listedA
Field bindweedConvolvulus arvensismaintenanceB,TCCC
Common crupinaCrupina vulgarismaintenanceBAnot listedW
Smoothseed alfalfa dodderCuscuta approximatamaintenanceBCnot listedC
Bigseed dodderCuscuta indecoramaintenanceBnot listednot listednotlisted
Five-angled dodderCuscuta pentagonamaintenanceBnot listednot listednotlisted
Spanish heath Erica lusitanicamaintenanceBnot listedWW
Creeping yellow cressRorippa sylvestrismaintenanceBnot listednot listedA
Mediterranean sageSalvia aethiopismaintenanceBAnot listedA
North Africa grassVentenata dubia ( V. avenacea )maintenanceBCnot listedC
Large-flowered primrose willowLudwigia grandifloracontainmentB, Tnot listednot listedB
Primrose willowLudwigia hexapetalacontainmentB, TBnot listedB
Water primroseLudwigia peploides ssp. montevidensiscontainmentB, TAAA
False bromeBrachypodium sylvaticumcontainmentBABA
Drooping sedgeCarex pendulacontainmentWnot listedWB
Policeman's helmet Impatiens glanduliferacontainmentBBBB
Purple loosestrifeLythrum salicaria containmentBBBB
Bohemian knotweedFallopia × bohemica ( Polygonum × bohemicum )containmentBBCB
Japanese knotweedFallopia japonica ( Polygonum cuspidatum )containmentBBBB
Giant knotweedFallopia sachalinensis ( Polygonum sachalinensis )containmentBBBB
Fragrant water lilyNymphaea odoratanot listedCDC
Japanese butterburPetasites japonicanot listednot listedWB
American pokeweedPhytolacca americanaWnot listedBA
BlackgrassAlopecurus myosuroidesnot listedCAW
Annual buglossAnchusa arvensisnot listedBnot listedB
Absinth wormwoodArtemisia absinthiumnot listedCnot listedC
South African capeweedArtotheca calendulaWnot listednot listedW
Common barberryBerberis vulgarisnot listedCnot listedW
FanwortCabomba caroliniananot listedBnot listedW
Whitestem distaff thistleCarthamus leucocaulosWnot listednot listedW
Wild safflowerCarthamus oxyacanthaWnot listednot listedW
Longspine sandburCenchrus longispinusnot listedCnot listedC
Feather-headed knapweedCentaurea trichocephalaWnot listednot listedW
Oriental clematisClematis orientalisnot listedAnot listedA
Pampass grassCortaderia selloananot listedCnot listedC
Tree echiumEchium pininanaWnot listednot listedW
Viper buglossEchium vulgareWBnot listedB
Water hyacinthEichhornia crassipesWnot listednot listednot listed
Russian oliveElaeagnus angustifolianot listedCnot listedC
Hairy willow-herbEpilobium hirsutum not listedBnot listedB
Toothed spurgeEuphorbia dentataWnot listednot listedW
Common fennelFoeniculum vulgarenot listedBCB
Reed sweetgrassGlyceria maximanot listedAnot listedA
BabysbreathGypsophila paniculatanot listedCnot listedC
Texas blueweedHelianthus ciliarisnot listedAnot listedA
Polar hawkweedHieracium atratumnot listedBnot listedW
Whiplash hawkweedHieracium flagellarenot listedBnot listedW
Queen-devil hawkweedHieracium glomeratumnot listedBnot listedW
Common hawkweedHieracium lachenaliinot listedBnot listedB
Pale hawkweedHieracium lactucellanot listedBnot listedW
Smooth hawkweedHieracium laevigatumnot listedBnot listedW
Spotted hawkweedHieracium maculatumnot listedBnot listedW
Wall hawkweedHieracium murorumnot listedBWW
European hawkweedHieracium sabaudumnot listedBnot listedW
Black henbaneHyoscyamus nigernot listedCnot listedC
LepyrodiclisLepyrodiclis holosteoidesnot listedCnot listedW
Rose campionLychnus coronariaWnot listednot listedW
Wand loosestrifeLythrum virgatum not listedBnot listedW
Scentless mayweedMatricaria perforatanot listedCnot listedC
Wild four o'clockMirabilis nyctagineanot listedAnot listedW
Variable-leaf milfoilMyriophyllum heterophyllumnot listedAnot listedA
Hybrid watermilfoil Myriophyllum spicatum × M. sibiricum not listedCnot listednot listed
Mile-a-minute weedPersicaria perfoliataWnot listednot listedW
Hawkweed oxtonguePicris hieracioides not listedBnot listedB
Austrian fieldcressRorippa austriacanot listedCnot listedC
Sweet briar roseRosa rubiginosa ( R.eglanteria )Wnot listednot listedW
Grass-leaved arrowheadSagittaria graminea not listedBnot listedW
Meadow clarySalvia pratensisnot listedAnot listedW
Clary sageSalvia sclareaWAnot listedW
Cereal ryeSecale cerealenot listedCnot listedC
White cockleSilene latifolia ssp. albanot listedCnot listedC
Sticky nightshadeSolanum sisymbriifoliumWnot listednot listedW
Field BurrweedSoliva sessilisnot listedCnot listedW
Spurge flaxThymelaea passerinanot listedBnot listedW
Narrowleaf cattailTypha angustifolianot listedCnot listedC
Southern cattailTypha domingensisnot listedCnot listedW
Miniature cattailTypha minimanot listedCnot listedW
White cattailTypha x glaucanot listedCnot listedW
Japanese eelgrassZostera japonicaWCnot listedW
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