Absinth (Artemisia absinthium)
By Brandon Barungan and Charles Geddes
Artemisia absinthium is a large herbaceous perennial introduced from Europe and now grows in all provinces. Usually occurring on the edges of fields, dense enough populations will encroach pasture. It also goes by absinthe, absinth, and wormwood. Originally cultivated for the sage-like flavor, medicinal properties, and psychedelic effects, it's become a naturalized weed with the potential to taint milk and grain.
According to the 2017 Alberta Weed Survey, absinth is the 110th most abundant weed in annual crops. However, due to its growth habit, it is more suited to invade perennial crops and pasture land. In Alberta, the relative abundance of this weed species has decreased from the 62nd most abundant weed species in annual crops between 1987-1989 and 91st in 2001 to 110th in 2017.
At maturity, absinth can have 20 or more grooved stalks, and stand 5 feet tall. The stems are woody near the base, and branch slightly near the top. The leaves appear in a spiral pattern and are deeply lobed: when crushed, they smell strongly of sage. Where moisture is readily available, plants are greener. In drier environments, they have more fine hairs, and the plants are gray colored. These plants produce small, yellow flowers in branching, droopy clusters.
Flowering in July, absinth is able to produce upwards of 50,000 seeds per stem from August until winter. These small seeds can be spread by wind, water, animals, or by human activities via hay, soil, or equipment. Absinth is sensitive to moisture, and growth and seed production are heavily impacted by drought. Most seedlings emerge in early spring but some emerge as late as autumn, as long as it is warm enough and there is enough moisture available. Seedlings are poor competitors but establish themselves easily on exposed soil, and form rosettes to overwinter at the end of the season. In the spring, they resume growth and reach 30cm in height by June. Flower stalks grow in July and are mature by late August. Most growth dies off in the winter and then emerges again from the base in the spring, amid the dead stalks.
Absinth produces tens to hundreds of thousands of seeds per plant. Seedlings establish quickly on disturbed soil, such as land that has been overgrazed or exposed to heavy machinery. They are poor competitors, however, and perennial grasses will help prevent invasion. Mowing can also reduce seed production, though it does not usually kill the plant. Tilling can eradicate large stands of more mature seedlings but rosettes can persist following soil disturbance.
Mature plants may continue to grow, as their root bases are very resilient. When pulling, make sure to remove the whole root. Rosettes and buds close to the soil surface are also susceptible to repeated spring burning. Young plants, around 12 inches tall (May), can be controlled with aminopyralid, clopyralid, dicamba, picloram, or glyphosate (consult your provincial Guide to Crop Protection. Spraying from June to August helps prevent spring growth. 2,4-D ester, applied once or twice in the fall and once in the spring can provide almost complete control.
Absinth wormwood identification and control 2019. King County. [Online].
DiTomaso, J.M., Brooks, M.L., Allen, E.B., Minich, R., Rice, P.M., Guy, B.K. 2006. Control of Invasive Weeds with Prescribed Burning. Weed Technology. 20: 535-548
Leeson, J.Y., Hall, L., Neeser, C., Tidemann, B., Harker, K.N. 2017. Alberta Weed Survey of Annual Crops in 2017. Agriculture and Agri-Food Canada
Maw, M.G., Thomas, A.G., Stahevitch, A. 1984. The Biology of Canadian Weeds 66. Artemisia absinthium L. Canada Journal of Plant Science. 65: 389-400
Washington State Noxious Weed Control Board. (2008). Absinth Wormwood: Options for control [Pamphlet]. Davenport, WA, USA: Lincoln County Noxious Weed Control Board.