Artemisia biennis
(biennial wormwood)

Identity

Preferred Scientific Name

• Artemisia biennis Willd.

Preferred Common Name

• biennial wormwood

Other Scientific Names

• Artemisia australis Ehrh. ex DC.
• Artemisia biennis var. biennis
• Artemisia biennis var. diffusa Dorn
• Artemisia canescens Willd.
• Artemisia cernua Dufour ex Willk. & Lange
• Artemisia cernuiflora Dufour ex Willk. & Lange
• Artemisia eschscholtziana Besser
• Artemisia inconspicua Spreng.
• Artemisia jacquinii Raeusch.
• Artemisia microcephala Hillebr.
• Artemisia pyromacha Viv.
• Artemisia ramosa Lag. ex Willk. & Lange
• Artemisia seriphium Pourr. ex Willk. & Lange

International Common Names

• English: biennial sagewort; false tansy; slender mugwort
• French: armoise bisannuelle; herbe St-Jean

Local Common Names

• Germany: Zweijähriger Beifuß
• Netherlands: rechte alsem; tweejarige alsem

Summary of Invasiveness

The large seed production, small sticky seeds and adaptation to disturbed habitats facilitated the early and rapid spread of A. biennis beyond its natural range in North America, along transportation corridors and in association with human activities. In recent decades it has become invasive in some agricultural areas in North America. The increasing prevalence of A. biennis in agricultural lands seems to be associated with several factors, including: a shift to annual growth habit; increasing adoption of reduced tillage systems; crop diversification; and, a tolerance to several classes of herbicides. In Europe, the plant has become a local weed, but has not yet been reported as invasive in crops. However, increased frequency has been observed in some countries and changes in land use and agricultural practices suggest the potential for emerging problems in Europe in the future.

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Asterales
•                         Family: Asteraceae
•                             Genus: Artemisia
•                                 Species: Artemisia biennis

Notes on Taxonomy and Nomenclature

The genus Artemisia is a highly diverse and taxonomically complicated genus with about 500 species worldwide (Schultz, 2006). Infrageneric classification puts A. biennis in the subgenus Artemisia, which is characterized by heterogamous flower heads with female outer florets, bisexual and fertile central florets, and a glabrous receptacle (Vallès and McArthur, 2001; Pellicer et al., 2010). A. biennis is closely related to the Eurasian species A. tournefortiana and the two species are sometimes grouped together as conspecific. A. magellanica is also closely related and is too sometimes grouped with A. biennis. For example, Ling (1995) included both A. tournefortiana and A. magellanica, as well as other taxa, within his broad concept of A. biennis. The various species concepts to which the name has been applied in the literature can be confusing and caution is needed when interpreting its use.

One unusual variation with atypically short leaves and many short branches originating from the base of the main stem, A. biennis var. diffusa (Dorn, 1988), is usually treated as a minor variant of no taxonomic significance (Ling, 1995; Schultz, 2006).

Description

A. biennis is an annual or biennial herbaceous plant. Stems are 1–3 m tall (although flowering plants may be as little as a few cm tall), erect and more or less spike-like, simple or somewhat branching at the base from a firm taproot. The stems are glabrous throughout, striate and often reddish.The leaves are alternate, glabrous, sessile, pinnatifid into narrow lobes with the lower leaf segments also pinnatifid, lobes of all but the uppermost toothed. Inflorescence a compound spike-like panicle, leafy throughout, with dense clusters of more or less globose capitula (flower heads) which are nearly sessile along short branches arising from upper leaf axils. Each flower head consists of a hemispheric involucre 2–3 cm long, made of 8–14 glabrous bracts. There are 6–22 or more outer pistillate (ray) florets, and 15–40 central bisexual disc florets. Corollas very small, pale yellow to whitish, with scattered stalked glands; corollas of the outer ray flowers about 1 mm long, somewhat tubular; those of the disk flowers bell-shaped, 1–2 mm long, with five triangular teeth. Cypselae (seeds) obovoid to ellipsoid, glabrous, lacking a pappus (bristles), very small (0.2–0.9 mm long), longitudinally 4-5 nerved and light brown.

Distribution

The precise native range of A. biennis is not known, but has been assumed to be the northwestern USA and adjacent areas of southwestern Canada (Thomas, 1961; Cronquist, 1994).

Records of A. biennis in Argentina, Brazil and Russia (Ling, 1995) are thought to be invalid. In addition to this, records in Iran (Nematollahi et al., 2006), India (Sood et al., 2001) and China (Lin et al., 2011) are thought to represent A. tournefortiana.

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

History of Introduction and Spread

Historical records suggest that the species has moved north, south and eastwards across the North American continent with the aid of human activity. Gray (1848) reported A. biennis occurring on river banks from Ohio westwards, indicating that it had already spread through much of the northwestern states by the mid 1800s. By the time of his fifth edition, Gray (1867) noted that the species was moving eastward with the railways and a century later, it was reported as present throughout the northeastern states and in much of eastern Canada (Fernald, 1950). In western Canada it was first reported from northern Saskatchewan and the Northwest Territories in the 1820s (Drummond, 1830; Hooker, 1840), where it may have been native or introduced along early trading routes. By the end of the century, it was recognized as a weed in grain and hayfields of the Great Plains (Fletcher, 1897) and had spread into eastern Canada (Macoun, 1883; Rousseau, 1968).

Introduction of A. biennis into Europe appears to have been accidental, as a contaminant in grain, oilseeds or other factory raw materials. Hegi (1929) stated that the species reached parts of Germany and adjacent countries in the late nineteenth and early twentieth centuries. The species reached other parts of Europe as an introduced casual, occasionally becoming naturalized in some areas as recently as after the Second World War. 

Introductions

Risk of Introduction

As A. biennis becomes more common in North American agricultural crops, the risk of it spreading as a commodity contaminant or hitchhiker increases correspondingly. The production of a large number of tiny seeds which are difficult to detect can enter the trade of transported goods in various ways. Although the small seeds are easy to remove with commodity cleaning techniques when dry, if A. biennis seeds come into contact with moisture, an outer pertinacious slime layer is produced making them sticky even when subsequently dried out (Kreitschitz, 2012).

Habitat

 In some areas A. biennis can completely dominate disturbed habitats, such as fallow fields (Hall and Clements, 1923). A. biennis is associated with early successional habitats with other pioneer plant species.

A. biennis is a species of grasslands, meadows, roadsides, waste places and fallow agricultural fields, as well as crop fields. In non-agricultural situations A. biennis occurs in a wide range of habitats, often characterized by natural or anthropogenic disturbances, including, shores, riparian habitats, salt marshes, mud flats, gravel bars, sloughs, talus slopes, ditches, gardens, roadsides, railway embankments, quarries, field edges and burnt-over areas.

Habitat List

Biology and Ecology

Genetics

Chromosome counts ofn = 9, 2n = 18 have been reported (Powell et al., 1974; Löve and Löve, 1982). Relatively high levels of genetic diversity were found in A. biennis populations in Minnesota and North and South Dakota, USA. This diversity is attributed in part to low levels of genetic exchange amongst populations (Mengistu et al., 2004).

Reproductive Biology

Species in the genus Artemisia are primarily wind pollinated, but may be visited occasionally by pollen eating insects (Knuth, 1908). Cross pollination is inferred to be the rule (Kegode and Christoffers, 2003); but self pollination may occur (Mulligan and Findlay, 1970). Reproduction is solely by prolific seed production with up to a million seeds produced per plant (Stevens, 1932; Mahoney and Kegode, 2004).

Physiology and Phenology

Annual forms will emerge throughout the growing season when conditions are favourable (Mahoney and Kegode, 2004). In North America seedlings tend to emerge from light soils earlier (May) than from heavy soils (late-June), while 70% of emergence occurs in July in all soils (Fronning and Kegode, 2004a, 2004b; Kegode et al., 2007). Mahoney and Kegode (2004) reported seedlings that emerged and had five weeks of growth at a juvenile stage produced seed, whereas seedlings with a shorter juvenile stage did not produce seed or survive the winter. Late emergence can allow seedlings to escape herbicide control (Kegode and Fronning, 2005). Biennial forms develop very slowly in the first year, with growth concentrated in the root and rosette leaves, ensuring sufficient storage capacity for successful overwintering. New growth from the roots in early spring ensures rapid vegetative growth and full flowering and seed production in the second year. Plants compete with crop species for light and can reach the adult stage by the end of the season, producing less biomass in the roots and first leaves and more in the development of the stem and reproductive parts (Mahoney and Kegode, 2004).

Allelopathic effects have been observed in this species, with increasing effect as plants increase in size (Kegode and Ciernia, 2005).

Longevity

A. biennis is an annual or biennial herbaceous plant.

Environmental Requirements

A. biennis is highly adaptable to a range of soils and microclimates in temperate, continental climate zones, provided that adequate moisture is available. The species is photoperiod sensitive, with the result that if day lengths are not optimal at flowering time, plants may either produce a much lower number of seeds than usual, or fail to develop seeds altogether (Jehlik, 1984; Mahoney and Kegode, 2004). Plants, particularly the annual form, are unlikely to survive early frost or cold winters.

Climate

Latitude/Altitude Ranges

Notes on Natural Enemies

Very little is known about herbivores attacking A. biennis. A number of fungi were reported on A. biennis in North America, including: Albugo tragopogonis [Pustula tragopogonis], Leptosphaeria pyrenopezizoides, Ophiobolus claviger, O. fulgidus, O. tanaceti, Peronospora artemisiae-biennis [Paraperonospora artemisiae-biennis], P. leptosperma [Paraperonospora leptosperma], Puccinia atrofusca, P. universalis and Thanatephorus cucumeris (Farlow, 1884; Brenckle, 1917, 1918; Bisby et al., 1938; Shoemaker, 1976; Frank, 1981; Kegode and Darbyshire, 2013).

Means of Movement and Dispersal

Natural Dispersal

Although the production of sticky slime may assist dispersal under some conditions, this is likely only a secondary factor in seed dispersal (Kegode and Darbyshire, 2013). Natural vectors may include water, wind and animals.

Vector Transmission

Animals may assist in dispersal of seeds, either by seed caching or the adherence of sticky seed to body parts. When A. biennis seed comes into contact with moisture an outer pertinacious slime layer is produced making them sticky even when subsequently dried out (Kreitschitz, 2012).

Accidental Introduction

Introduction of A. biennis into Europe appears to have been accidental, as a contaminant in grain, oilseeds or other factory raw materials. The small size and potential stickiness of seeds contribute to the likelihood of contamination of traded goods and packing.

Impact Summary

Economic Impact

The economic impact of A. biennis is largely due to the yield loss and weed management associated with agricultural crops which it infests. Stevens (1950) suggested that as a biennial species, A. biennis would be largely controlled in agricultural fields by annual cultivation, however, a shift to annual growth habit is now seen in most agricultural ecosystems (Kegode and Darbyshire, 2013). Increased occurrence of A. biennis in cropping systems appears to be related to a combination of factors that include selection of annual forms (Kegode and Christoffers, 2003) and increased practice of conservation tillage (Blackshaw et al., 2006). In addition, A. biennis is a significant weed in some regions of North America due to factors, which include, increasing bean acreage, misidentification as common ragweed, limited herbicide options providing control, and extended seedling emergence period (Kegode and Christoffers, 2003).

Environmental Impact

Impact on Biodiversity

A. biennis is alleopathic and will inhibit the growth of other plants. This enables it to outcompete native species reducing biodiversity.

Threatened Species

Social Impact

As a plant which causes hay fever, social impact occurs when human health is affected by airborne pollen. However, A. biennis is usually not the most problematical species contributing allergenic pollen to the air but may contribute to asthma.

Risk and Impact Factors

• Invasive in its native range
• Proved invasive outside its native range
• Abundant in its native range
• Highly adaptable to different environments
• Is a habitat generalist
• Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
• Pioneering in disturbed areas
• Benefits from human association (i.e. it is a human commensal)
• Fast growing
• Has propagules that can remain viable for more than one year

• Ecosystem change/ habitat alteration
• Negatively impacts agriculture
• Negatively impacts human health
• Damages animal/plant products

• Allelopathic
• Competition - monopolizing resources
• Competition - shading

• Highly likely to be transported internationally accidentally
• Difficult/costly to control

Uses

Social Benefit

Essential oils in A. biennis have both antibacterial and antifungal properties and have been used in traditional medicines in North America (Lopez-Lutz et al., 2008).

Similarities to Other Species/Conditions

The glabrous foliage and annual/biennial growth habit distinguishes A. biennis from other similar and common weeds such as common ragweed (Ambrosia artemisiifolia), common wormwood (Artemisia absinthium) and many other Artemisia species. It particularly resembles the annual weedy species Artemisia annua, but the leaves of this species are more finely dissected and the mature flower heads are nodding on distinct pedicels.

Morphological similarities to both A. tournefortiana and A. magellanica have been noted and may be considered as conspecific.

Prevention and Control

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Control

Cultural Control and Sanitary Measures

Some control of infestations can be accomplished by pulling or mowing several times before seed heads mature (Blatchley, 1912; Pammel et al., 1913) and tillage is one of the most effective control methods (Lewis, 2012).

Chemical Control

Tolerance to several classes of herbicides and to other human manipulations has allowed this species to thrive in crop habitats and to expand its range (Johnson et al., 2004). In North America, A. biennis is increasing primarily in soyabean and dry bean cultivation because of its tolerance to many of the herbicides applied to these crops (Kegode and Christoffers, 2003). Tolerance was confirmed for several ALS (acetolactate synthase) inhibitors, dinitroanalines, HPPD (hydroxyphenylpyruvate dioxygenase) inhibitors, PPO (protoporphyrinogen oxidase) inhibitors, acetamides, and some growth regulators (e.g. bromoxynil and fluoxypyr) (Kegode et al., 2007).

Good to excellent (81-100%) pre-emergence control can be achieved with flumetsulam, flumioxazin, isoxaflutole, metribuzin and sulfentrazone (Kegode, 2000; Fronning and Kegode, 2004a, 2004b; Kegode et al., 2007). Flumetsulam is one of the few ALS-inhibiting herbicides that can control A. biennis. Post-emergence control must be initiated when seedlings are less than 8 cm in height to achieve greater than 80% control (Fronning and Kegode, 2004a; Kegode and Fronning, 2005). Atrazine, bentazon, clopyralid, dicamba, glufosinate, glyphosate, MCPA, and 2,4-D can provide 80% control. As a result of indeterminate emergence, greater than 90% control can be achieved with split applications of bentazon or glyphosate but required application rates will depend on the size of the young plants (Kegode and Fronning, 2005).

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Contributors

23/03/2015 Original text:

Stephen Darbyshire and Ardath Francis, Agriculture and Agri-Food, Canada

Distribution Maps