Weed Season Is Upon Us!

Whether you are a city dweller, suburbanite, farmer, or livestock owner, weeds are an issue. Some weeds are more pervasive than others. But there are a few weeds that present extreme challenges to us all.

The following top 5 are particularly invasive or toxic.

Bindweed (Native hedge, Field, and Hybrid)

King County clarified with a name change and species in 2022. Current Latin name is native! Prior to 2018, all were confused as Calystegia sepium, but now distinguished into three different species with the names: Native hedge bindweed (Calystegia sepium ssp. angulata), Large bindweed (Calystegia sylvatica) and Hybrid bindweed (Calystegia silvatica ssp. disjuncta C. xlucana).

Hedge bindweed, also called morning glory, is a perennial herbaceous vine that twines around other vegetation or fences for support and has large, white trumpet shaped flowers. Stems are light green to red, slender, twined, branched and mostly hairless. Below ground the plant has extensive, white fleshy rhizomes and fibrous roots, and it may extend into the ground up to 10 feet. It spreads by clonal offshoots from its rhizomes and by seed. It resembles field bindweed but with larger flowers and leaves. It is considered an invasive plant in King County and is on the King County Weeds of Concern list. Control is recommended where natural resources are being protected or as part of a stewardship plan. However, this plant is very difficult to eliminate so it may only be possible to suppress it while allowing other plants to establish. May be confused with Field bindweed.

Field bindweed is a perennial herbaceous plant with creeping and twining stems that grow along the ground and up through other plants and structures. It has an extensive system of rhizomes that can grow deep into the soil. It can be confused Native hedge bindweed. Field bindweed can grow in a wide range of conditions from full sun to full shade and is drought-tolerant. It is found in fields, turf, farmland, and residential areas. It reproduces via roots, rhizomes, and stem fragments, as well as by seeds that persist in soil 20 years or more. It becomes extremely difficult to eradicate once it is established due to very deep, extensive rhizomes and long-lived seed bank. Dense plantings of sod or shade-producing crops can reduce bindweed problems because it is not very competitive under shady conditions.

Non-native hybrid (Calystegia silvatica ssp. disjuncta C. xlucana) bindweed is a King County weeds of concern. It is not classified as noxious weeds in Washington State. Control is recommended where possible and new plantings are discouraged. Hedge bindweed species were recently differentiated between native and nonnative varieties in local herbaria.

All bindweeds should not be placed into yard waste bins or compost piles as they can spread very easily without proper compost processes taking place. Contact the noxious weed program for advice on managing large infestations of any kind of bindweed.

Blackberry (Himalayan, Evergreen and Vested/European)

Himalayan blackberry is a thorny, thicket-forming shrub in the Rose family that produces large, edible blackberry fruits. Leaves are somewhat evergreen, divided into 3-5 leaflets (palmately compound) that are rounded (ovate) and have toothed edges. Stems (canes) can grow 20 to 40 feet long and 13 feet tall, root at the tips when they touch the ground, and have stout, hooked, sharp prickles with wide bases. The plant creates dense thickets that are impassable and sprawls over surrounding vegetation. It has large, deep, woody root balls that sprout at nodes.

Evergreen blackberry (Rubus laciniatus) is another invasive, non-native blackberry that has ragged looking leaves that are deeply lacerated or incised.

Vested/European blackberry (Rubus vestitus) was added by King County as a Weed of Concern after it was proposed by a member of the public at last year’s hearing and due to its invasive behaviors in addition to its potential to expand the footprint of invasive blackberries in King County.

All species of blackberry have edible fruits, but the fruits of the native trailing blackberry (Rubus ursinus) are smaller, much tastier, and NOT a noxious weed!

Special Note: In unincorporated King County outside of wetlands, aquatic areas, wildlife network areas and their buffers, a King County Clearing and Grading Permit is not required to clear areas of blackberry if:

  1. The annual area to be cleared is less than 7000 square feet
  2. If the clearing is conducted in accordance with an approved Forest Management Plan, Farm Management Plan or Rural Stewardship Plan. Within wetlands, aquatic areas, wildlife network areas and their buffers, Clearing and Grading permits are not required if the area to be cleared is less than 7000 square feet and clearing is conducted in accordance with one of the stewardship plans mentioned above or is removed by hand labor.

Clearing in excess of these limits will require a permit, however there will be no cost for this permit provided control practices defined in this BMP and the King County Noxious Weed Regulatory Guidelines are followed.

Knotweed (giant, hybrid aka Bohemian, itadori/Japanese and Himalayan)

In the Pacific Northwest, the four species of invasive knotweed are difficult to tell apart. They are all large, robust perennials that spread by long creeping rhizomes to form dense thickets. These tall, bamboo-like plants were introduced from Asia via England. Control of knotweed is challenging and often requires a watershed approach to be effective along waterways.


Poison hemlock (Conium maculatum), a Class B noxious weed, is a widespread toxic biennial plant in the Carrot Family often found in open sunny areas, fields, vacant lots, and on roadsides. Poison-hemlock is acutely toxic to people and animals, with symptoms appearing 20 minutes to three hours after ingestion. All parts of the plant are poisonous and even the dead canes remain toxic for up to three years.

Tansy Ragwort

Tansy ragwort (Jacobaea vulgaris), a regulated Class B noxious weed, is a toxic biennial found throughout King County. Eating it can sicken or even kill cattle, horses, some goats, pets, and people. And it also can cause skin irritation, so use gloves when removing and handling it.

Please visit King County Noxious Weeds for assistance on eradicating these species, and many more. The website has many resources for identifying weeds of all types. You can also Report-a-Weed. if you find Knotweed, Poison-hemlock, or Tansy Ragwort.

Details compiled from King County and King County Noxious Weeds
Featured photo collage credit: King County Noxious Weeds

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