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Weed Watcher Program

  • Fight off Gresham’s weedy invaders by participating as a Weed Watcher in our Early Detection, Rapid Response Program. Learn about problem weeds here, and help us stop these plants in their tracks. 

    Effects of invasive weeds 

    Economic impacts 

    • Weeds damage valuable crops and poison livestock.
    • Noxious weeds cost Oregon millions a year.

    Environmental impacts

    • Weeds crowd out native plants and upset fragile ecosystems. 
    • Weeds cause erosion that can affect ecosystems and homes.
    • Weeds speed the decline and extinction of endangered and threatened species.

    Weeds: most wanted list

  • Bohemian Knotweeds (Polygonum spp)
    • Knotweeds grow rapidly to 10 feet or more in height.
    • It thrives in moist places, such as stream banks.
    • It can spread downstream by small stem fragments.
    • There are a number of invasive knotweed species, including Japanese knotweed and giant knotweed (Polygonum cuspidatum and Polygonum sachalinense). 
    Garlic Mustard (Alliaria officinalis)
    • This annual grows quickly in the forest understory and reproduces even quicker.
    • Seeds are often unknowingly spread by humans and animals.
    • The roots release a chemical that inhibits the growth of other plants.
    Kudzu (Pueraria lobata)
    • Kudzu’s nickname is “the weed that ate the south;” let’s keep it out of local forests.
    • This aggressive vine blankets and smothers native vegetation.
    • Brought from Japan and promoted first as an ornamental, then as livestock forage.
    Spurge Laurel (Daphne laureola)
    • This toxic plant can invade the shaded forest floor.
    • It forms thickets and compete with native understory plants.  
    Yellow Archangel (Lamiastrum galeobdolon)
    • This fast growing perennial groundcover escapes from landscaping and spreads rapidly to carpet the forest understory.
    • Despite its attractive foliage and flower, yellow archangel provides poor habitat for wildlife.
  • Contact us 

    For more information about becoming a Weed Watcher, contact Mike Wallace at 503-618-2525 or


    Invasive plant list