Wormwood

Wormwood (Artemisia absinthium)

Report

Photo credit: Chris Evans, Illinois Wildlife Action Plan, Bugwood.org

Management Strategy

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. Its scent is similar to sage.

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. Stems and leaves emit a sage-like smell when crushed.

Leaves: Are lacy with rounded tips and finely hairy, which gives them a grey-green appearance. The leaves grow in an alternate pattern up the stems.

Roots: Wormwood forms a taproot that can reach up to 5 cm in diameter, as well as long, shallow branching lateral roots.

Seeds: Are small and shaped like sunflower seeds, with a broader base and a narrower tip.

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. Biennial wormwood 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) has white flowers and pointy leaf tips. It is also greener than wormwood.

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.

How it Spreads

Wormwood reproduces primarily by seed. It is a prolific seed producer, each stem producing up to 50,000 seeds annually. Seeds can persist in the soil for 3 – 4 years, rapidly forming a seed bank. Seedlings can emerge at any point from late spring to early fall.

Some sources also indicate that Wormwood cuttings can generate new plants.

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.

The small seeds are also scattered by wind, water and animals. Wormwood seeds are also spread in contaminated soil.

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.

Stop the Spread

Wormwood is found in the Sea to Sky region and its distribution is beyond landscape-level control. When Wormwood is present at high-priority locations and negatively impacting them, their control is considered a high priority.

Otherwise, the goal is to prevent it from spreading to new (uninfested) areas, and to control it where possible to limit its impact on biodiversity.

Learn to identify wormwood: use the images presented on this page to learn how to identify wormwood.

What to do if you spot it: You can report any wormwood sighting by visiting our reporting page.

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:

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.
Plant wormwood in a garden, no matter how well-contained its enclosure may seem.
Compost any flowering heads or buds. Instead, dispose of wormwood in the general/household waste stream at the landfill as the seeds are likely to survive the composting process.
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 (prior to seed set) may prevent seed production but won’t eradicate the plant.
If mowing, make sure it is done regularly as plants will resprout and grow new flowering stems.

Chemical

Aminopyralid, clopyralid, dicamba, glyphosate, picloram and 2,4-D are effective for controlling Wormwood.
However, note that picloram is not suitable for wet, coastal soils.
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.