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August 2014

Invasive Watch: Absinth Wormwood

What to Look For
Absinth wormwood, also known as absinthium or common wormwood, is a herbaceous perennial plant that can grow up to 5 feet tall under favorable conditions. It closely resembles sagebrush in both appearance and odor. The plant regrows from soil level each spring, is woody at the base and has many branching stems. Leaves are light to olive green, between 2 and 5 inches long, and will give off a strong sagelike odor when crushed. Both the stems and the leaves are commonly covered with silky gray hairs, especially when the plant is younger. Flowering occurs from early summer to early fall, when numerous pale yellow, tubular flowers develop in the axils of the leaves.

Absinth wormwood reproduces primarily by small, easily scattered seeds but also can spread by its lateral roots. A single plant is capable of producing 50,000 seeds per stem, and plants generally are viable for three to four years. Seeds are dispersed in a variety of ways, including wind, animals, in hay and on equipment. Seedlings emerge from late spring to early fall, with rosettes forming by the end of the first growing season.

Where It’s Found.
Absinth wormwood is established across the United States. It invades open and disturbed sites with well-drained soils such as pastures, rangelands, roadsides, cropland, stream banks, prairies and old fields. The plant is native to Europe and Asia and it was first introduced into the United States in the mid-1800s. It grows naturally on uncultivated, arid ground, on rocky slopes and at the edge of footpaths and fields.

Once established, absinth wormwood can reduce available forage for wildlife and livestock in native and managed rangelands and pastures, as well as inhibit the growth of other desirable plants such as grasses. It can be very difficult to remove.

How to Treat It.
To effectively treat absinth wormwood, apply Milestone® specialty herbicide at 6 to 7 ounces per acre before it is 12 inches tall. Another option is Capstone® specialty herbicide at 7 to 8 pints per acre. Always refer to product labels for complete directions.