Noxious weeds are found everywhere in Pierce County - in rural, urban and suburban areas; on developed and undeveloped land.  They crowd out desirable vegetation, reduce agricultural productivity, compromise public health and safety, lower property values, increase flood hazards, and destroy native plant and animal habitat.

These non-native invasive species arrive in our region in a variety of different ways.  Many are escaped garden plants, others arrive through agricultural crops, contaminated hay or seed, aquariums and water gardens, or from vehicle tires along transportation corridors.

Every year noxious weeds cost Pierce County millions of dollars in maintenance and control costs, lost agricultural production, and environmental degradation.  Once these invasive plants get established, it is very expensive and time-consuming to remove them.




Top Ten Noxious Weeds That Threaten Pierce County

Common Fennel
  • Licorice scented perennial 4-10 ft. tall
  • Leaves are dark green and feathery
  • Umbrella shaped clusters of small yellow flowers
  • Tap roots can reach depths of 10 feet
  • Outcompetes native plants and reduces native wildlife habitat
  • Once established it is difficult to control, due to strong competitive abilities and persistent seed bank

Dalmation Toadflax
  • Perennial herb 2.5 to 5 feet tall
  • Waxy, heart shaped, light green leaves
  • Bright yellow flowers tinged with orange center, looks like a snapdragon
  • Persistent, aggressive invader, pushes out native grasses and other perennials
  • Rapidly colonizes open sites
  • Contains poisonous alkaloid, toxic to livestock

Wild Chervil
  • Biennial plant grows from 1 to 4 ft. tall
  • Hollow ridged stems with fern-like leaves
  • Small, white umbrella shaped flower clusters
  • Serious threat to native plants and agriculture
  • Highly adaptable, will grow in almost any type of soil
  • Has an aggressive growth habit, quickly creates a monoculture
  • Most of Pierce County is highly susceptible to Wild Chervil infestation

Tansy Ragwort

  • Invasive, persistent, toxic biennial
  • 1st year: rosette stage; dark green basal leaves, ruffled in appearance
  • 2nd year: one or more flowering stalks bolt up to 6 ft. tall
  • Numerous yellow, daisy-like, flowers with 13 petals
  • Contains toxins that cause chronic irreversible liver damage; a threat to livestock and agriculture.

Poison Hemlock

  • Toxic biennial plant up to 10 ft. tall
  • 1st year: basal rosette with fern like leaves.
  • 2nd year: produces hollow, hairless stems with purplish splotches and dark green, glossy, fern-like leaves
  • Umbrella shaped clusters of small, white flowers
  • All plant parts are extremely poisonous to humans and livestock
  • Wear gloves and protective clothing when handling this plant, can cause contact dermatitis
  • Do not burn or compost this plant


  • There are 3 species of knapweed that threaten Pierce County: spotted, diffuse, and meadow knapweed
  • 1st year: rosettes form
  • 2nd year: flowering stalks elongates
  • Spine tipped, or fringed bracts (leaf-like structure at the base of the flower) 
  • Flowers are lavender to pink and sometimes white
  • Very aggressive species, one of the most dominant weeds of the west, can infest large areas very quickly
  • Contains phyto-toxins which inhibit the growth of surrounding native plants, allowing knapweed to form monocultures
  • Has very long tap roots

  • A dense, spiny, evergreen shrub, 3-10 ft. tall, closely resembles scotch broom
  • Aggressive, invasive plant crowds out other vegetation, forms dense thickets
  • Has sharp thorn-like leaves up to 3 in. long
  • Clusters of bright yellow, pea-like flowers form into pods containing 1 to 4 seeds
  • Plants form a center of dry, dead vegetation, that coupled with its high oil content creates a serious fire hazard

Perennial Pepperweed
  • Bushy, perennial plant usually1 to 3 ft. tall, but may reach up to 6 ft.
  • Alternate, waxy leaves with white mid-vein
  • Rounded clusters of small white flower at branch tips
  • Displaces desirable native plants
  • Poses serious threat to natural areas, wildlife habitat, pastures, and coastal areas
  • Destabilizes river and stream banks, increases soil erosion

Giant Hogweed
  • Huge perennial plant from15-20 ft. tall.
  • Hairy, hollow stems 2 to 4 in. in diameter, with dark reddish, purple splotches 
  • Large compound leaves, up to 5 ft. wide with jagged edges
  • White umbrella shaped, flower-heads up to up to 2.5 ft. wide
  • Clear watery sap causes ultraviolet skin sensitivity, resulting in severe burns, blisters and scars
  • Sap can squirt up to 5 ft. when stem is cut or broken.
  • Do not handle without gloves, goggles and protective clothing



top ten worst weeds in Pierce County, WA
 Shiny Geranium
  • Low growing annual, 10 to 12 inches high
  • Stems are tinged bright red
  • Leaves are rounded, divided into lobed sections that have 3 lobes at the tip and are shiny and bright green, turning red in late summer and fall 
  • Pink flowers grow in pairs and have 5 petals
  • Invades woodlands, forest openings, open grasslands and native habitat