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:
- They did not historically occur in our area but have been brought in either intentionally or unintentionally through human action.
- They exhibit aggressive growth that displaces native or desirable vegetation and will continue to spread unless actively controlled.
- They 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.
Containment: These weeds are a priority for management. In some areas, these weeds are so widespread that treatments are not feasible in all locations. For these weeds, infestations will be targeted for eradication when they occur outside of established containment areas. For infestations within containment areas, landowners are encouraged to contact the WeedWise program for technical assistance in developing plans to improve the management of these invasive weeds.
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.
No designation: Some weeds listed below have no designation. This is because the listed weed is either not a state-listed noxious weed or because it is not known to occur in or near Clackamas County.
Clackamas Weed List
| Common Name | Scientific Name | WeedWise Classification | Oregon Classification | Washington Classification | 4-County CWMA | Columbia Gorge CWMA |
|---|---|---|---|---|---|---|
| Velvetleaf | Abutilon theophrasti | priority | B | B | B | B |
| Barbed Goatgrass | Aegilops triuncialis | priority | A,T | not listed | A | W |
| Tree of Heaven | Ailanthus altissima | maintenance | B | C | B | C |
| Garlic mustard | Alliaria petiolata | containment | B,T | A | B | A |
| False indigo bush | Amorpha fruticosa | priority | B | B | not listed | B |
| Wild chervil | Anthriscus sylvestris | maintenance | not listed | B | not listed | B |
| Italian arum | Arum italicum | maintenance | not listed | C | B | B |
| False brome | Brachypodium sylvaticum | containment | B | A | B | A |
| Butterfly bush | Buddleja davidii (Buddleja varabilis) | maintenance | B | B | B | B |
| Flowering rush | Butomus umbellatus | priority | A,T | A | W | A |
| Welted thistle | Carduus crispus | priority | A,T | not listed | not listed | not listed |
| Drooping sedge | Carex pendula | containment | W | not listed | W | B |
| Meadow knapweed | Centaurea × moncktonii (C. pratensis) | maintenance | B | B | B | B |
| Spotted knapweed | Centaurea stoebe (C. maculosa) | maintenance | B,T | B | B | B |
| Rush skeletonweed | Chondrilla juncea | priority | B, T | B | D | B |
| Canada thistle | Cirsium arvense | maintenance | B | C | C | C |
| Bull thistle | Cirsium vulgare | maintenance | B | C | D | C |
| Old man's beard | Clematis vitalba | maintenance | B | C | B | C |
| Poison hemlock | Conium maculatum | maintenance | B | B | B | B |
| English hawthorn | Crataegus monogyna | maintenance | B | C | C | C |
| Yellow nutsedge | Cyperus esculentus | maintenance | B | B | B | B |
| Houndstongue | Cynoglossum officinale | priority | B | B | D | B |
| Scotch broom | Cytisus scoparius | maintenance | B | B | C | B |
| Wild carrot | Daucus carota | maintenance | not listed | C | C | C |
| Spurge laurel | Daphne laureola | priority | B | B | B | B |
| Common teasel | Dipsacus fullonum | maintenance | not listed | C | C | C |
| South American waterweed | Egeria densa | maintenance | B | B | C | B |
| Myrtle spurge | Euphorbia myrsinites | maintenance | B | B | E | B |
| Oblong spurge | Euphorbia oblongata | priority | A,T | A | A | A |
| Goatsrue | Galega officinalis | priority | A, T | A | A | A |
| Shining geranium | Geranium lucidum | maintenance | B | B | B | A |
| Herb robert | Geranium robertianum | maintenance | B | B | C | B |
| English ivy | Hedera helix | maintenance | B | C | C | B |
| Irish ivy | Hedera hibernica | maintenance | B | C | C | B |
| Giant hogweed | Heracleum mantegazzianum | priority | A, T | A | A | A |
| Orange hawkweed | Hieracium aurantiacum | priority | A,T | B | A | A |
| Meadow hawkweed | Hieracium caespitosum | priority | B,T | B | A | B |
| St. John's wort | Hypericum perforatum | maintenance | B | C | C | C |
| Hairy cat's ear | Hypochaeris radicata | maintenance | not listed | C | C | C |
| Jewelweed | Impatiens capensis | maintenance | W | C | C | W |
| Policeman's helmet | Impatiens glandulifera | containment | B | B | B | B |
| Yellow flag iris | Iris pseudacorus | maintenance | B | C | B | B |
| Yellow archangel | Lamium galeobdolon | maintenance | B | B | B | B |
| Large-flowered primrose willow | Ludwigia grandiflora | containment | B, T | not listed | not listed | B |
| Primrose willow | Ludwigia hexapetala | containment | B, T | B | not listed | B |
| Water primrose | Ludwigia peploides ssp. montevidensis | containment | B, T | A | A | A |
| Purple loosestrife | Lythrum salicaria | containment | B | B | B | B |
| Fragrant water lily | Nymphaea odorata | not listed | C | D | C | |
| Small broomrape | Orobanche minor | maintenance | B | not listed | D | A |
| African rue | Peganum harmala | priority | A,T | not listed | A | W |
| Japanese butterbur | Petasites japonica | not listed | not listed | W | B | |
| American pokeweed | Phytolacca americana | W | not listed | B | A | |
| Ribbongrass | Phalaris arundinacea var. picta | maintenance | B,T | C | not listed | C |
| Reed canarygrass | Phalaris arundinacea | maintenance | W | C | not listed | C |
| Bohemian knotweed | Fallopia × bohemica ( Polygonum × bohemicum ) | containment | B | B | C | B |
| Japanese knotweed | Fallopia japonica ( Polygonum cuspidatum ) | containment | B | B | B | B |
| Giant knotweed | Fallopia sachalinensis ( Polygonum sachalinensis ) | containment | B | B | B | B |
| Curly-leaf pondweed | Potamogeton crispus | maintenance | not listed | C | C | C |
| Sulphur cinquefoil | Potentilla recta | priority | B | B | A | B |
| Kudzu | Pueraria montana | priority | A,T | A | A | A |
| Lesser celandine | Ranunculus ficaria | maintenance | B | B | B | B |
| Armenian (Himalayan) blackberry | Rubus armeniacus (R. bifrons, R. procerus, R. discolor) | maintenance | B | C | C | C |
| Evergreen blackberry | Rubus laciniatus | maintenance | not listed | C | C | C |
| Tansy ragwort | Senecio jacobaea | maintenance | B | B | B | B |
| Common groundsel | Senecio vulgaris | maintenance | not listed | C | not listed | C |
| Blessed milk thistle | Silybum marianum | priority | B | A | A | A |
| Perennial sowthistle | Sonchus arvensis ssp. arvensis | maintenance | not listed | C | D | C |
| Common tansy | Tanacetum vulgare | maintenance | not listed | C | C | C |
| Gorse | Ulex europaeus | priority | B,T | B | A | A |
| Garden yellow loosestrife | Lysimachia vulgaris | priority | A,T | B | A | W |
| Spiny cocklebur | Xanthium spinosum | priority | B | C | D | C |
| Syrian bean-caper | Zygophyllum fabago | priority | A | A | A | A |
| Biddy-biddy | Acaena novae-zelandiae | priority | B | not listed | not listed | W |
| Russian Knapweed | Acroptilon repens | priority | B | B | A | B |
| Pheasant eye | Adonis aestivalis | priority | B | not listed | not listed | not listed |
| Jointed goatgrass | Aegilops cylindrica | priority | B | C | not listed | C |
| Ovate Goatgrass | Aegilops ovata | priority | A | not listed | A | W |
| Camelthorn | Alhagi pseudalhagi | priority | A | B | A | A |
| Blackgrass | Alopecurus myosuroides | not listed | C | A | W | |
| Yellow tuft | Alyssum corsicum | priority | A,T | not listed | A | W |
| Yellow tuft | Alyssum murale | priority | A,T | not listed | A | W |
| Ragweed | Ambrosia artemisiifolia | priority | B | not listed | D | B |
| Annual bugloss | Anchusa arvensis | not listed | B | not listed | B | |
| Common bugloss | Anchusa officinalis | priority | B,T | B | A | B |
| Absinth wormwood | Artemisia absinthium | not listed | C | not listed | C | |
| South African capeweed | Artotheca calendula | W | not listed | not listed | W | |
| Giant reed | Arundo donax | priority | B | not listed | not listed | A |
| Common barberry | Berberis vulgaris | not listed | C | not listed | W | |
| Hoary allysum | Berteroa incana | priority | A,T | B | A | B |
| White bryonia | Bryonia alba | priority | A | B | A | A |
| Fanwort | Cabomba caroliniana | not listed | B | not listed | W | |
| Plumeless thistle | Carduus acanthoides | priority | A,T | B | A | A |
| Turkish thistle | Carduus cinereus | priority | A | not listed | not listed | not listed |
| Musk thistle | Carduus nutans | priority | B | B | E | B |
| Italian thistle | Carduus pycnocephalus | priority | B | A | D | A |
| Slender-flowered thistle | Carduus tenuiflorus | priority | B | A | D | A |
| Smooth distaff thistle | Carthamus baeticus | priority | A | not listed | A | W |
| Woolly distaff thistle | Carthamus lanatus | priority | A,T | not listed | A | W |
| Whitestem distaff thistle | Carthamus leucocaulos | W | not listed | not listed | W | |
| Wild safflower | Carthamus oxyacantha | W | not listed | not listed | W | |
| Longspine sandbur | Cenchrus longispinus | not listed | C | not listed | C | |
| Purple starthistle | Centaurea calcitrapa | priority | A,T | A | A | A |
| Diffuse knapweed | Centaurea diffusa | maintenance | B | B | B | B |
| Iberian starthistle | Centaurea iberica | priority | A,T | not listed | A | A |
| Brown knapweed | Centaurea jacea | maintenance | not listed | B | F | B |
| Big-headed knapweed | Centaurea macrocephala | maintenance | W | A | not listed | A |
| Malta starthistle | Centaurea melitensis | maintenance | not listed | B | not listed | not listed |
| Black knapweed | Centaurea nigra | maintenance | not listed | B | not listed | B |
| Vochin knapweed | Centaurea nigrescens | maintenance | not listed | A | not listed | A |
| Yellow starthistle | Centaurea solstitialis | priority | B | B | A | B |
| Feather-headed knapweed | Centaurea trichocephala | W | not listed | not listed | W | |
| Squarrose knapweed | Centaurea virgata | priority | A,T | not listed | not listed | A |
| Oriental clematis | Clematis orientalis | not listed | A | not listed | A | |
| Field bindweed | Convolvulus arvensis | maintenance | B,T | C | C | C |
| Jubata grass | Cortaderia jubata | priority | B | C | W | B |
| Pampass grass | Cortaderia selloana | W | C | W | C | |
| Common crupina | Crupina vulgaris | maintenance | B | A | not listed | W |
| Smoothseed alfalfa dodder | Cuscuta approximata | maintenance | B | C | not listed | C |
| Bigseed dodder | Cuscuta indecora | maintenance | B | not listed | not listed | notlisted |
| Japanese dodder | Cuscuta japonica | priority | A | not listed | A | W |
| Five-angled dodder | Cuscuta pentagona | maintenance | B | not listed | not listed | notlisted |
| Purple nutsedge | Cyperus rotundus | priority | A | not listed | A | A |
| Portuguese broom | Cytisus striatus | priority | B,T | not listed | W | W |
| Cape ivy | Delairea odorata | priority | A | not listed | A | W |
| Cutleaf teasel | Dipsacus laciniatus | priority | B | not listed | not listed | W |
| Tree echium | Echium pininana | W | not listed | not listed | W | |
| Paterson's curse | Echium plantagineum | priority | A,T | not listed | A | W |
| Viper bugloss | Echium vulgare | W | B | not listed | B | |
| Water hyacinth | Eichhornia crassipes | W | not listed | not listed | not listed | |
| Russian olive | Elaeagnus angustifolia | not listed | C | not listed | C | |
| Hairy willow-herb | Epilobium hirsutum | not listed | B | not listed | B | |
| Spanish heath | Erica lusitanica | maintenance | B | not listed | W | W |
| Toothed spurge | Euphorbia dentata | W | not listed | not listed | W | |
| Leafy spurge | Euphorbia esula | priority | B, T | B | B | A |
| Common fennel | Foeniculum vulgare | not listed | B | C | B | |
| French broom | Genista monspessulana | priority | B | A | W | A |
| Reed sweetgrass | Glyceria maxima | not listed | A | not listed | A | |
| Babysbreath | Gypsophila paniculata | not listed | C | not listed | C | |
| Halogeton | Halogeton glomeratus | priority | B | not listed | not listed | W |
| Texas blueweed | Helianthus ciliaris | not listed | A | not listed | A | |
| Spikeweed | Hemizonia pungens | priority | B | C | not listed | C |
| Yellow hawkweed | Hieracium × floribundum | priority | A,T | B | A | A |
| Polar hawkweed | Hieracium atratum | not listed | B | not listed | W | |
| Whiplash hawkweed | Hieracium flagellare | not listed | B | not listed | W | |
| Queen-devil hawkweed | Hieracium glomeratum | not listed | B | not listed | W | |
| Common hawkweed | Hieracium lachenalii | not listed | B | not listed | B | |
| Pale hawkweed | Hieracium lactucella | not listed | B | not listed | W | |
| Smooth hawkweed | Hieracium laevigatum | not listed | B | not listed | W | |
| Spotted hawkweed | Hieracium maculatum | not listed | B | not listed | W | |
| Wall hawkweed | Hieracium murorum | not listed | B | W | W | |
| Mouse-ear hawkweed | Hieracium pilosella | priority | A,T | B | A | A |
| King-devil hawkweed | Hieracium piloselloides | priority | A,T | B | A | A |
| European hawkweed | Hieracium sabaudum | not listed | B | not listed | W | |
| Hydrilla | Hydrilla verticillata | priority | A | A | W | A |
| Common frogbit | Hydrocharis morsus-ranae | priority | A | not listed | A | W |
| Black henbane | Hyoscyamus niger | not listed | C | not listed | C | |
| English holly | Ilex aquifolium | maintenance | W | W | C | not listed |
| Small-flowered jewelweed | Impatiens parviflora | priority | not listed | A | A | A |
| Dyers woad | Isatis tinctoria | priority | B | A | not listed | A |
| Kochia | Kochia scoparia | priority | B | B | not listed | B |
| Perennial peavine | Lathyrus latifolius | maintenance | B | not listed | C | C |
| Lens-podded whitetop | Lepidium chalepense | priority | B | not listed | A | B |
| Hoary cress | Lepidium draba | priority | B | C | A | B |
| Perennial pepperweed | Lepidium latifolium | priority | B,T | B | A | B |
| Hairy whitetop | Lepidium pubescens | priority | B | C | not listed | C |
| Lepyrodiclis | Lepyrodiclis holosteoides | not listed | C | not listed | W | |
| Oxeye daisy | Leucanthemum vulgare | maintenance | not listed | C | C | C |
| West Indian spongeplant | Limnobium laevigatum | priority | A | A | A | W |
| Dalmatian toadflax | Linaria dalmatica | priority | B, T | B | B | B |
| Yellow toadflax | Linaria vulgaris | maintenance | B | C | B | C |
| Rose campion | Lychnus coronaria | W | not listed | not listed | W | |
| Wand loosestrife | Lythrum virgatum | not listed | B | not listed | W | |
| Scentless mayweed | Matricaria perforata | not listed | C | not listed | C | |
| Wild four o'clock | Mirabilis nyctaginea | not listed | A | not listed | W | |
| Variable-leaf milfoil | Myriophyllum heterophyllum | not listed | A | not listed | A | |
| Eurasian watermilfoil | Myriophyllum spicatum | maintenance | B | B | C | B |
| Hybrid watermilfoil | Myriophyllum spicatum × M. sibiricum | not listed | C | not listed | not listed | |
| Parrots feather | Myrophyllum aquaticum | maintenance | B | B | B | B |
| Matgrass | Nardus stricta | priority | A,T | not listed | A | W |
| Yellow floating heart | Nymphoides peltata | priority | A, T | B | A | A |
| Scotch thistle | Onopordum acanthium | priority | B | B | A | B |
| Taurian thistle | Onopordum tauricum | priority | A,T | not listed | A | W |
| Mile-a-minute weed | Persicaria perfoliata | W | not listed | not listed | W | |
| Common reed | Phragmites australis ssp. australis | priority | B | B | A | B |
| Hawkweed oxtongue | Picris hieracioides | not listed | B | not listed | B | |
| Himalayan knotweed | Polygonum polystachyum | priority | B | B | not listed | B |
| Austrian fieldcress | Rorippa austriaca | not listed | C | not listed | C | |
| Creeping yellow cress | Rorippa sylvestris | maintenance | B | not listed | not listed | A |
| Sweet briar rose | Rosa rubiginosa ( R.eglanteria ) | W | not listed | not listed | W | |
| Ravennagrass | Saccharum ravennae | priority | A | A | A | A |
| Grass-leaved arrowhead | Sagittaria graminea | not listed | B | not listed | W | |
| Delta arrowhead | Sagittaria platyphylla | priority | A | not listed | A | not listed |
| Mediterranean sage | Salvia aethiopis | maintenance | B | A | not listed | A |
| Meadow clary | Salvia pratensis | not listed | A | not listed | W | |
| Clary sage | Salvia sclarea | W | A | not listed | W | |
| Ricefield bulrush | Schoenoplectus mucronatus | priority | W | A | D | A |
| Cereal rye | Secale cereale | not listed | C | not listed | C | |
| White cockle | Silene latifolia ssp. alba | not listed | C | not listed | C | |
| Silverleaf nightshade | Solanum elaeagnifolium | priority | A | A | A | A |
| Buffalobur | Solanum rostratum | priority | B | C | D | C |
| Sticky nightshade | Solanum sisymbriifolium | W | not listed | not listed | W | |
| Field Burrweed | Soliva sessilis | not listed | C | not listed | W | |
| Johnsongrass | Sorghum halepense | priority | B | A | E | A |
| Smooth cordgrass | Spartina alterniflora | priority | A, T | A | A | W |
| Common cordgrass | Spartina anglica | priority | A,T | A | A | W |
| Dense-flowered cordgrass | Spartina densiflora | priority | A,T | A | A | W |
| Saltmeadow cordgrass | Spartina patens | priority | A,T | A | A | W |
| Spanish broom | Spartium junceum | priority | B | A | F | A |
| Swainsonpea | Sphaerophysa salsula | priority | B | C | not listed | C |
| Water soldiers | Stratiotes aloides | priority | A | not listed | A | not listed |
| Medusahead rye | Taeniatherum caput-medusae | priority | B | not listed | C | C |
| Saltcedar | Tamarix ramosissima | priority | B,T | B | W | B |
| Spurge flax | Thymelaea passerina | not listed | B | not listed | W | |
| European water chestnut | Trapa natans | priority | A | not listed | A | A |
| Puncturevine | Tribulus terrestris | priority | B | B | C | B |
| Coltsfoot | Tussilago farfara | priority | A | B | A | A |
| Narrowleaf cattail | Typha angustifolia | not listed | C | not listed | C | |
| Southern cattail | Typha domingensis | not listed | C | not listed | W | |
| Miniature cattail | Typha minima | not listed | C | not listed | W | |
| White cattail | Typha x glauca | not listed | C | not listed | W | |
| North Africa grass | Ventenata dubia ( V. avenacea ) | maintenance | B | C | not listed | C |
| Japanese eelgrass | Zostera japonica | W | C | not listed | W |
