July 2013

Invasive Watch: Absinth Wormwood (Artemisia absinthium)

Absinth wormwood is a herbaceous perennial that is capable of growing up to 5 feet tall and 2 feet wide. Woody at the base, with many branching stems, it is covered with light- to olive-green leaves that are 2 to 5 inches long, which give off a strong sage like odor when crushed. Stems and leaves are commonly covered with silky gray hairs, especially when the plant is younger.

The plant regrows from soil level each spring. In late fall, the above-ground portion of the plant generally dies back. Then, each spring, the crown of the plant produces buds that generate new shoots. It also can reproduce by seedlings, which emerge from late spring to early fall. Rosettes form by the end of the first growing season. Flowering occurs in midsummer, when the plant’s numerous flower heads develop many tubular yellow flowers on the axils of the leaves.

Seedlings produce several small leaves close to the soil surface that may go unnoticed in areas with good grass cover. Seeds are small and easily scattered by wind, water, animals, hay and equipment. Each stem can produce up to 50,000 seeds, which generally are viable for three to four years.

Absinth wormwood typically invades open and disturbed sites such as pastures, rangelands, crop land, stream banks, prairies and fields. The plant is native to Europe and was introduced into the United States in the mid-1800s.

Follow these herbicide recommendations.
Several herbicides have proven effective on this species. For best results, spray the foliage and stems of actively growing plants before they reach 12 inches tall. An application of 3.0 to 3.3 ounces of Opensight or 6 to 7 fluid ounces of Milestone® specialty herbicide per acre will provide control. Another proven option is a treatment of Capstone® specialty herbicide applied at 7 to 8 pints per acre.

For fall treatments, first mow in early to midsummer to promote active regrowth in the fall. Adding a surfactant helps ensure coverage of the fine hairs covering the plant. Whichever herbicide treatment is selected, remove the plant’s old duff by fire to achieve the best results.