Absinth Wormwood – invasive species that may come to western Nebraska | TheFencePost.com
Kristi Paul and Gary Stone
Sheridan County weed superintendent and Extension educator, Panhandle R&E Center, Scottsbluff, Neb.

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Absinth Wormwood – invasive species that may come to western Nebraska

Early Detection and Rapid Response (EDRR) is a concept to identify potential invasive species prior to or just as the invasive is becoming established. An integrated pest management plan can be developed to manage, contain and eradicate the invasive species before it can spread further, avoiding costly, long-term control efforts.

Absinth wormwood, a perennial forb that has been identified in parts of Nebraska, is considered either a state or local noxious weed in North Dakota, South Dakota and Colorado. Absinth Wormwood is also known as American or common wormwood, mugwort, wormwood sage, absinth sage. Its scientific name is Artemisia absinthium L., of the family Asteraceae (Sunflower).

Originally from Europe, northern Asia and northern Africa, Absinth wormwood was first reported in North America in the 1840s. It is now found in the Northeast, Midwest and Great Plains of the U.S. and Canada.

Absinth wormwood is an herbaceous perennial forb. It reproduces and spreads primarily from seed and short roots. It is a prolific seed producer, and seeds can remain viable in the soil up to four years.

Seeds can germinate from late spring through early fall. Rosettes form the first year of growth. Plants resume growth in April and May of the second year and flower in July and August. Seeds mature in early fall. The plant dies back in the fall, resumes growth the following spring from new buds and shoots.

Absinth wormwood has a taproot and may have 20 or more erect woody stems. Mature plants may reach a height up to 5 feet. Leaves are light to olive green in color, large and dissected up to 3 inches long. Stems and leaves are covered with fine silky hairs, which give a grayish color to the plant. Inconspicuous flowers are small and dull yellow in appearance, each producing a single seed. Seed is scattered by water, wind, animals and hay.

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HOW IT SPREADS

Absinth wormwood was intentionally introduced into the U.S. as an herb in gardens for social and medicinal purposes. By the 1840s, the plant had spread west and north across North America. Absinth wormwood will establish quickly in disturbed areas and over-grazed sites. It can out-compete desirable forbs and grasses in pastures and rangeland, reducing biodiversity. It can be found in both dry and moist soils.

Most new sites of absinth wormwood can be attributed to imported hay from out of the state that was contaminated with absinth wormwood seed. When purchasing hay or forage, check to see if it is certified as weed-free forage. This can prevent costly problems later on if you have to start managing a weed or weeds you did not have before.

Absinth wormwood appears on roadsides, and quickly invades farmsteads where infested hay has been fed, stacked or stored. It has little or no forage value for livestock. Unless there is no other forage available, horses do not graze absinth wormwood. If they are forced to eat it, all parts of the plant are toxic. While sheep can graze the plant, horses should not.

It will taint the milk of cattle that graze it. It can reduce the amount of forage available for grazing. Its pollen can be a source for allergies and asthma in humans. Absinth wormwood leaves have been used as an herb for the sage flavor, the oil in vermouth, and antiseptic liniments.

At least 10 different locations in different parts of Sheridan County have absinth wormwood growing where hay has been fed or piled.

In one instance, Sheridan County Weed Superintendent Kristi Paul was asked to identify a weed growing in a calving lot, from a photo sent to her from a Sheridan County landowner. Her first question to the landowner was, "Did you purchase some hay from out of state?" The answer was yes and it turns out a load of hay must have been infested with absinth wormwood seed.

MANAGEMENT

Prevention is a good control option. Having well-established grasses and forbs on a maintained pasture or rangeland with proper grazing and rotational grazing techniques can go a long way to prevent its establishment.

Be proactive. If purchasing hay or forage, ask if it is certified weed free. More information on weed-free forage is found at http://neweedfree.org/. Nebraska, South Dakota and Wyoming support weed-free forage.

Burning is not considered a good management option; the infestations may not be reduced and may actually increase. Mowing multiple times throughout the growing season may prevent seed production, but will not eliminate the established plants.

There are numerous chemical treatment options available to manage Absinth wormwood. Products containing clopyralid, dicamba, Picloram, glyphosate and 2,4-D have been shown to work. Be sure to select a product that is labeled for the site. Read, understand and follow all label instructions when using any pesticide.