HPIPM:Biennial wormwood

Taxonomy

Domain	Eukarya
Kingdom	Plantae
Phylum	Magnoliophyta
Class	Magnoliopsida
Superorder	Asteranae
Order	Asterales
Family	Asteraceae
Subfamily	Asteroideae
Tribe	Anthemideae
Genus	Artemisia

Scientific Name

Artemisia biennis

Common Name

biennial wormwood

Biennial wormwood (Artemisia biennis Willd.)

Compiled by Hilary Parkinson, and Evette Allison, Montana State University, from the following sources:

Hitchock, C and A. Cronquist. 2001. Flora of the Pacific Northwest. University of Washington Press, Seattle.

Kegode, G, R. Zollinger and M. Ciernia. 2007. The Glyphosate, Weeds, and Crops Series: Biology and Management of Biennial Wormwood W-1322, North Dakota State University. Available at: http://www.ag.ndsu.edu/pubs/plantsci/weeds/w1322w.htm

Kegode, G, G Nazre and M Christoffers. 2010. Germination Ecology of Biennial Wormwood (Artemisia biennis) and Lanceleaf Sage (Salvia reflexa) Seeds. Weed Science 58:61-66.

Maurice, D. 2004. New Weed Threats: Biennial Wormwood (Artemisia biennis Willd.). Conference Proceedings. Manitoba Agronomists Conference. Available at: http://www.umanitoba.ca/afs/agronomists_conf/proceedings/2004/maurice_new_weed_threats.pdf\

Ontario Weeds: Biennial wormwood. Ontario Ministry of Agriculture, Food and Rural Affairs. Available at: http://www.omafra.gov.on.ca/english/crops/facts/ontweeds/biennial_wormwood.htm

USDA ARS Plants Database. Plants profile: Artemisia biennis. Accessed 1/28/2010. Available at: http://plants.usda.gov/java/profile?symbol=ARBI2

Identification and Life Cycle

Plants grow as annuals or biennials and emerge from a taproot. Stems are erect with little or no branching, reaching 10-150cm (4-60”) tall or occasionally much taller. Leaves are smooth, hairless, firm with the first leaves of young plants in a basal rosette, short-stalked. Young leaves are pinnately divided and redivided with the final divisions coarsely and sharply toothed. Stem leaves are similar to basal leaves but usually only once-divided with each division coarsely and sharply toothed, alternate (1 per node). By flowering, the lower stem leaves are senescing and the basal rosette of leaves gone; only leaf scars remain. Flower heads are greenish and inconspicuous, clustered on many short branches in the axils of small leaves towards the top of the stem and forming a slender, elongate inflorescence. Each individual flower head is very small, about 2mm (1/12”) across, yellowish-green, without ray florets. Seeds are numerous and very small.

Biennial wormwood often is confused for common ragweed but can be distinguished from common ragweed by a close examination of the leaves. Biennial wormwood leaves have sharp edges and are hairless, whereas common ragweed leaves have smooth and round edges and are hairy. It is also distinguished by its erect habit, sharply toothed, pinnately divided leaves, its numerous short clusters of flower heads along the upper stem forming a slender, and its elongated inflorescence.

Habitats

Biennial wormwood is native to North America, specifically the Rocky Mountains and the Sierra Nevada and Cascade ranges of the northwestern United States and western Canada. It occurs throughout parts of Canada, and the Northern Great Plains region in old fields, waste places, fence lines, meadows, and occasionally around buildings.

Impacts

Serious crop yield reduction can occur since biennial wormwood can escape herbicide control due to misidentification-typically with rag weed. Herbicides like Basagran, and Pursuit that control ragweed do not control wormwood. It is an aggressive and prolific seed-producing plant that has become a problem mainly in soybean and dry edible bean production areas of Minnesota, North Dakota and South Dakota.

Biology and Ecology

Seedling emergence can occur during the entire crop growing season under moist conditions and favorable environmental conditions. Characterization of emergence patterns in eastern North Dakota indicated that the weed began to emerge in late June or early July in corn, dry bean, soybean and sunflower. Biennial wormwood grows slowly after emergence, remaining as a rosette until midsummer, when plants bolt and growth becomes rapid. It flowers from late April to early June depending on soil conditions. A single plant can produce 400,000 seeds. Seed longevity is variable and may relate to soil moisture. During a dry year, seed viability was 65% after 23 months, but during an unseasonably moist year, seed viability was only 8%.

Biological Control

There is no current biological control for biennial wormwood.

Mechanical and Cultural Control

Cultivating young plants can reduce the spread of biennial wormwood. A combination of tillage and chemical applications may be necessary for dense infestations.

Chemical Control

Biennial wormwood has natural tolerance to many soil-applied and post emergence broadleaf herbicides such as some ALS herbicides (flumetsulam, e.g. Python, is an exception), dintroanilines, acetamides, HPPD and PPO inhibitors.

Post emergent herbicides may be applied to seedlings that are less than 3 inches (8cm) in height. Plants greater than 3” tall become more tolerant of postermergent herbicides.

In the table below are some examples of herbicides that can be used to manage biennial wormwood

Consult and follow all herbicide labels for additional rate, application, restriction, and safety information. Additional herbicide information can be found at http://www.greenbook.net.

Herbicide Active Ingredient(s) *Trade Name	Mode of Action	Product per Acre	Application Time or Growth Stage
Range and Pasture
clopyralid, 2,4-D	Group 4: Synthetic auxins
*Curtail		2 qts./A	Do not cut forage for hay within 7 days of application. Do not graze lactating dairy cattle in treated areas for 14 days after application. Spray only one application per season.
clopyralid	Group 4: Synthetic auxins
*Stinger		1/2 - 1 1/3 pts./A	Apply when weeds are young and actively growing. Do not spray on young grasses and forbs unless injury can be tolerated.
Sugarbeet
clopyralid	Group 4: Synthetic auxins
*Stinger		1/4 to ½ pint /A	Apply from weed emergence up to the 5-leaf stage of growth. Wait a minimum of 7 days after application before flood or furrow irrigation. Apply when sugar beets are in the cotyledon to 8-leaf stage of growth and the weeds are young and actively growing. Do not apply within 45 days of harvesting beets or beet tops.
Spring Wheat or Barley
clopyralid, 2,4-D	Group 4: Synthetic auxins
*Curtail		2 - 2 2/3 pts./A	Apply to actively growing wheat or barley once 4 leaves have unfolded on the main stem and tillering has begun, up to the jointing stage. Apply when weeds are less than 3" in height or diameter.
Field Corn
flumetsulam, clopyralid	Group 4: Synthetic auxins
*Hornet WDG		4 -5oz/A	For preplant incorporated applications, apply up to 30 days before planting and incorporate 2-3" deep. Spike stage application: apply from corn emergence until corn is 2" in height and before the first leaf is unfurled. Adequate soil moisture is required for optimum herbicidal activity.
Fallow
clopyralid, 2,4-D	Group 4: Synthetic auxins
*Curtail		2-4 pts./A	Apply to young emerged weeds that are actively growing. For best results, wait 14 to 20 days after application before cultivating or fertilizing. Allow at least 30 days after application before seeding to wheat, barley or grasses.

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality. Updated XXXX

References

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