Wormwood

Wormwood

Artemisia absinthium
2117065-smallest

Status in Squamish:

PREVENTION-WATCHLIST

Status in Whistler:

PREVENTION-WATCHLIST

Status in Pemberton:

STRATEGIC-CONTROL
Vectors of Spread:
Synonyms

Wormwood is also known as:

  • Absinth
  • Wormwood Sage
  • Absinth Sage
  • Madder Wormwood
ID Characteristics

General: Wormwood is a perennial, aromatic herb and a member of the daisy (Asteraceae) family.

Flowers: Are pale yellow and tubular. They develop in drooping heads in the axils of the leaves.

Stems: Are ascending to erect, clustered and finely hairy. Wormwood stems sometimes have a woody base, and grow to be 0.4 – 1.2m tall.

Leaves: Are alternate, lacy, pinnately-cut with rounded tips, grey-green, 2.5 – 10cm long. They emit a strong sage-like scent when crushed. The leaves are finely hairy, giving them a greyish appearance.

Roots: Wormwood forms a taproot that can reach up to 5 cm in diameter, as well as shallow lateral branches extending up to 1.8m in all directions.

Similar Species

Native: 

Biennial Wormwood (Artemisia biennis) drawing

By Britton, N.L., and A. Brown. http://plants.usda.gov Public Domain

Biennial Wormwood (Artemisia biennis), which, as its name indicates, lives for 2 years. It is generally taller and greener than Wormwood, and its leaves are pointier.

 

 

 

 

 

 

Non-Native:

Common Wormwood (Artemisia vulgaris) in flower

Artemisia vulgaris (Wikipedia)

Common Mugwort or Common Wormwood (Artemisia vulgaris), which has white flowers and pointy leaf tips. It is also greener than Wormwood.

Report

Please report any sighting of Wormwood by clicking here.

Habitat and Origin

Wormwood is native to Eurasia and Northern Africa. It was introduced to North America in the early 19th century for medicinal purposes.

Wormwood will survive in both dry and moist soils, but it thrives in poor, dry soils with full sun. It is generally found on dry, open waste areas or overgrazed rangelands, but also along roads and fencerows as well as in pastures.

Current Distribution

Wormwood distribution map

Propagation & Vectors of Spread

Wormwood reproduces primarily by seed. It is a prolific seed producer, and seeds can remain viable in the soil for 3 – 4 years. Seedlings can emerge at any point from late spring to early fall. It can also reproduce vegetatively, by cuttings.

Wormwood is a perennial; the above-ground portion of the plant dies back in late fall, but the crown of the plant remains intact and produces buds and new shoots each spring.

Wormwood’s spread is aided by the horticultural industry, as the plant is still sold as a garden ornamental.

Ecological, Economic, & Health Impacts

Health:

  • Wormwood pollen is a source of allergy and asthma problems.
  • Toxic if consumed in large quantities.

Ecological: 

  • Exhibits allelopathic properties: inhibits the growth of other plants, thereby reducing biodiversity.
  • Outcompetes desirable grasses and other plants in established pastures.

Economic:

  • Reduces agriculture crops and forage yield production.
  • Taints the milk of cattle that graze it.
What Can I Do?

Wormwood is currently found in the Pemberton area, but has not yet been found in Squamish or Whistler, so PREVENTION of further spread is key:

Learn to identify Wormwood: use the images presented in this profile page to learn how to identify Wormwood.

What to do if you spot it: You can report any Wormwood sighting by clicking here.

DO:

  • Regularly monitor properties for weed infestations.
  • Minimize soil disturbances and use seed mixes with dense, early colonization to re-vegetate exposed soil and resist invasion.
  • Check wildflower mixes to ensure that they do not contain Wormwood.
  • Ensure all flowering heads or buds are bagged or covered to prevent spread during transport to designated disposal sites.

DO NOT:

  • Do not unload, park or store equipment or vehicles in infested areas; remove plant material from any equipment, vehicles or clothing used in such areas and wash equipment and vehicles at designated cleaning sites before leaving infested areas.
  • Do not plant Wormwood in a garden, no matter how well-contained its enclosure may seem.
  • Do not compost any flowering heads or buds. Instead, dispose of Wormwood in the general/household waste stream at the landfill as the seeds will be able to persist the composting process.
  • Do not move soil, gravel, or fill that has been contaminated with Wormwood.

Control

Mechanical 

  • Hand-pull or dig up individual plants or small patches; make sure all the roots have been removed.
  • It is often easier to dig up the roots when the soil is moist.
  • Mowing may prevent seed production, as long as it is done prior to seed set and repeated several times throughout the season.

Chemical

  • Aminopyralid, clopyralid, dicamba, glyphosate and 2,4-D are effective for controlling Wormwood.
  • Best results are obtained by spraying the foliage and stems of actively growing plants when they are at least 30 cm tall.
  • Since Wormwood is hairy, the use of a surfactant is essential.
  • We recommend that any herbicide application is carried out by a person holding a valid BC Pesticide Applicator Certificate. Before selecting and applying herbicides, you must review and follow herbicide labels and application rates; municipal, regional, provincial and federal laws and regulations; species-specific treatment recommendations, and site-specific goals and objectives.

Biological control

There is no biocontrol available for this plant.

References

Alberta Invasive Species Council, Absinthe Wormwood Factsheet, https://abinvasives.ca/wp-content/uploads/2017/11/FS-AbsintheWormwood.pdf

Electronic Atlas of the Flora of British Columbia, Artemisia absinthium, http://linnet.geog.ubc.ca/Atlas/Atlas.aspx?sciname=Artemisia%20absinthium

King County, Absinth wormwood identification and control, https://www.kingcounty.gov/services/environment/animals-and-plants/noxious-weeds/weed-identification/absinth-wormwood.aspx

Northwest Invasive Plant Council, Absinth Wormwood Factsheet, http://nwipc.org/documents/Absinth_Wormwood_Facts.pdf

Northwest Invasive Plant Council, Wormwood, http://nwipc.org/plants/wormwood

Washington State Noxious Weed Control Board, Absinth Wormwood, https://www.nwcb.wa.gov/weeds/absinth-wormwood