Biology and Management of Absinth Wormwood

Figure 1. Distribution of absinth wormwood in the United States and Canada (USDA NRCS 2016)

Figure 1. Distribution of absinth wormwood in the United States and Canada (USDA NRCS 2016)

Absinth wormwood (Artemisia absinthium L.) is a perennial broadleaf plant introduced from Europe. Historically it was cultivated as an herb for the sage flavor of the leaves and production of aromatic oil used in preparation of absinth and vermouth. Absinth wormwood naturalized from intentional horticultural plantings and is well established on rangeland, pastureland, and natural areas in the northern half of the United States and southern Canadian provinces (Figure 1). The plant causes economic losses by reducing grass production and tainting the flavor of milk from livestock grazing the plant. Absinth wormwood pollen can cause allergies and asthma in susceptible individuals when the plant is flowering in late July and August. Absinth wormwood is most often found on dry soils in pastures and rangeland, disturbed areas, wastelands, and roadsides.

IDENTIFICATION

Absinth wormwood is commonly three feet tall at maturity but can grow over five feet in height (Figure 2). The herbaceous plant re-grows from a woody basal crown each spring. Leaves are light to olive green in color, two to five inches long, and divided two or three times into deeply lobed leaflets. Leaves and stems are covered with fine silky hairs that give the plant a grayish appearance. Absinth wormwood is a member of the composite family. Flower stalks appear at each upper leaf node and produce numerous flower heads 1/8 inch in diameter, which appear in mid-summer. Many small, inconspicuous yellow flowers are produced in each head. Each fruit contains one seed, which are scattered easily by wind, water, animals, and in hay. Absinth wormwood is a prolific seed producer but also can spread by short roots.

Figure 2. Absinth wormwood plant (a), flower (b), and leaf covered with fine gray "hair" (c). Photos by Mary Ellen (Mel) Harte, bugwood.org

MANAGEMENT WITH HERBICIDES

Absinth wormwood on rangeland and natural areas is effectively controlled with aminopyralid (Milestone® specialty herbicide), aminopyralid + 2,4-D (GrazonNext® HL specialty herbicide, or clopyralid (Transline® specialty herbicide). The choice of treatments should be based on cost, presence of other target weeds and non-target desirable plants in the same area where absinth wormwood has established.

Milestone at 5 to 7 fluid ounces of product/acre (fl oz/A) or GrazonNextHL at 1.5 to 2 pints of product/acre (pt/A) provide excellent (90 to 100%) control of absinth wormwood when applied in the spring before plants are 12 inches tall or in fall (Figures 1 and 2). Transline at 2/3 pt/A should be applied when the absinth wormwood is greater than 12 inches tall and actively growing. For fall herbicide applications, the plant should be mowed in mid to late-summer to improve application efficiency and increase control.

Transline is more selective than either Milestone or GrazonNext HL and can be applied when non-target tree, shrub or forb selectivity is important. Milestone is more selective on desirable broadleaf plants than GrazonNext HL which contains 2,4-D. 

Figure 3. Average absinth wormwood control with various herbicide treatments applied at multiple sites in North Dakota.


MANAGEMENT WITH OTHER METHODS

Cultural control
Absinth wormwood invades disturbed areas where there is less competition from other plant species. Management should include proper grazing techniques that maintain desirable competitive vegetation on rangelands and prevent invasion of the plant. Disturbed areas should be seeded with desirable plant to prevent re-invasion and spread of the weed.

Manual control
Individual plants or small patches can be controlled by hand pulling or digging roots when soil is moist. The entire root system should be removed to achieve effective control.

Mechanical control
Tillage can prevent establishment of the plant in cultivated cropland; however, root fragments may be spread and re-sprout without continued tillage. Summer fallow followed by fall tillage is more effective than spring tillage.

Mowing alone or mowing plus fertilization will not effectively control absinth wormwood infestations (Moechnig et al. 2009). Mowing several times during the growing season may reduce seed production in absinth wormwood but will also reduce desirable grass production. In a South Dakota study, grass shoot biomass in mowed treatments was less than non-treated areas, and 32 to 64 percent less than that in the most effective herbicide treatments. 


REFERENCES

  1. Lym RG and A Travnicek. 2015. Identification and Control of Invasive and Troublesome Weeds in North Dakota- Absinth wormwood. North Dakota State University, Fargo, ND. W1411.
  2. Lym RG. 2015. Herbicide mixtures applied in the spring or fall for absinth wormwood control. Res. Prog. Rep. Western Soc. Weed Sci. p.11.
  3. Lym RG. 2010. Aminopyralid applied alone or in combination with metsulfuron or picloram for absinth wormwood control. Res. Prog. Rep. West. Soc. Weed Sci. p. 34-36.
  4. Lym RG and LW Samuel. 2006. Control of invasive weeds with aminopyralid in North Dakota. Res. Prog. Rep. Western Soc. Weed Sci. p. 30-35.
  5. Moechnig MJ, DL Deneke, JK Alms and DA Vos. 2009. Absinth wormwood control programs that include mowing, fertilization, or herbicides. Res. Prog. Rep. North Central Weed Sci Soc. 64. p.57.
  6. USDA, NRCS. 2016. The PLANTS Database (http://plants.usda.gov, 20 February 2016). National Plant Data Team, Greensboro, NC 27401-4901 USA.

Additional information on absinth wormwood

Washington State Noxious Weed Board, Absinth Wormwood

University of Washington Burke Museum Herbarium Image Collection - Artemisia absinthium

North Dakota State University, Absinth Wormwood  http://www.nd.gov/ndda/weed/absinth-wormwood


®Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow.

Milestone and GrazonNext HL are not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state.

Milestone: When treating areas in and around roadside or utility rights-of-way that are or will be grazed, hayed or planted to forage, important label precautions apply regarding harvesting hay from treated sites, using manure from animals grazing on treated areas or rotating the treated area to sensitive crops. See the product label for details. State restrictions on the sale and use of Milestone apply. Consult the label before purchase or use for full details. Always read and follow label directions.

Tordon 22K is a federally Restricted Use Pesticides. State restrictions on the sale and use of Transline apply. Consult the label before purchase or use for full details. Always read and follow label directions.

Active ingredients for products mentioned in this article. Product (active ingredient): Milestone specialty herbicide (aminopyralid); GrazonNext HL (aminopyralid plus 2,4-D); Transline (clopyralid); Tordon 22K (picloram); 2,4-D; Banvel and others (dicamba).