Tillamook County Soil and Water Conservation District

Tillamook County Invasive Weed List

Tillamook County SWCD has organized invasive weeds into 3 categories: Early Detection Species, Common Invasive Species from Gardens, and High Priority Species.  We have highlighted certain species from each of these 3 categories below:

Early Detection Species

These four weeds are currently the highest priority for the district due to their highly invasive nature and their low abundance within the county. Species in this category are candidates for eradication from the county and known sites are being aggressively treated. If you suspect that you have spotted a species on this list, please contact the Invasive Weed Coordinator, Troy Abercrombie, via phone: 503-842-2848 Ext. 103 or email: tillamookweeds@gmail.com

Garlic mustard (Alliaria petiolate).
ODA: B list.
Prevalence: Not common in our county, but problematic elsewhere.
Why it is a priority: Spreads through prolific seed production and by plant pieces being moved around.
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2. Giant Hogweed (Heracleum mantegazzianum)
ODA: A List
Prevalence: At least 2 known site in Tillamook County
Why it is a priority: It is incredibly invasive in riparian areas, but can grow in many habitats. The sap is toxic and can severely burn your skin if exposed to sunlight.
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3. Lesser Celandine (Ranunculus ficaria):
ODA: B List
Prevalence: one reported site in Tillamook County
Why it is a priority: Persists due to mini tuber production, and not yet established in the county.
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4. Gorse (Ulex europaeus)
ODA: B list
Prevalence: Limited to a few known sites in Tillamook County.
Why it is a priority: Gorse is basically scotch broom with thorns. Very invasive. Very flammable.
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Common Invasive Species From Gardens

Always be wary of introducing unknown plants to your property. You can check to see if a plant is invasive be searching for the words “(plant name) control” and see if there is information about removing the plant. If there is information about it, there is a good chance it is invasive. The four plants in this list are common in Tillamook County and exceptionally invasive.

Yellow archangel (Lamiastrum galeobdolon)
ODA B List
Prevalence: Fairly common onrnamental weed in Tillamook County.
Why it is a problem: Spreads into forest understory and can grow from cuttings and yard waste.
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Periwinkle or Vinca (Vinca minor)
ODA B List
Prevalence: Common landscaping plant, used as ground cover.
Why it is a problem: It frequently escapes and creates dense monocultures.
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Yellow-flag iris (Iris pseudacorus)
ODA B List
Common riparian area weed in Tillamook County.
Why it is a problem: It tends to take over sensitive habitat in estuaries and slow moving waterways.
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Italian arum (Arum italicum)
Not Listed by ODA
Prevalence: Common horticultural plant, a few incidental sightings.
Why it is a problem: Spreads via tubers and very difficult to remove once established.
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High Priority Species

These species have a high impact economically and environmentally. Control of these four species on private property is encouraged.

Japanese knotweed (Fallopia japonica) and/or Bohemian Knotweed (a hybrid of Japanese and Giant Knotweed)
ODA B List
Prevalence: Ubiquitous in waterways in north Tillamook County, less well-established in south Tillamook County.
Why it is a problem: Prevents trees from re-seeding stream sides, causes erosion, alters nutrient cycling and can damage building foundations.
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Giant knotweed (Fallopia sachalinensis)
ODA B List
Prevalence: Fairly common ornamental weed in Tillamook County.
Why it is a problem: It creates dense colonies that exclude native vegetation and greatly alter natural ecosystems. Established populations are extremely persistent and difficult to eradicate, even very small fragments can form new plants.
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Himalayan knotweed (Persicaria wallachii or Polygonum polystachyum)
ODA B List
Prevalence: The least common of the 3 knotweeds in Tillamook County.
Why it is a problem: Forms dense colonies that exclude native vegetation, although less adapted to shade than the other two knotweed species.
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Policeman’s helmet (Impatiens glandulifera)
Prevlaence: Becoming established in Tillamook County. Many large populations have been observed.
Why it is a problem: It displaces other plants and its shallow roots do not hold the river banks the it colonizes.
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