Artemisia biennis
(biennial wormwood)

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.

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.

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).

 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.

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.

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).

Medicinal, pharmaceutical

• Traditional/folklore

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.

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).

23/03/2015 Original text:

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