Dame's rocket (Hesperis matronalis L.)
Dame’s rocket was originally introduced to North America as an ornamental plant and has since escaped cultivation. It has become invasive in parts of Sublette County, particularly in the Bondurant area, where it establishes in disturbed sites, roadsides, and riparian corridors.
Dame’s rocket is a biennial or short-lived perennial forb with an aggressive root system and prolific seed production, allowing it to form dense stands quickly. In its first year, it develops a basal rosette from a taproot. In subsequent years, it produces an erect flowering stem that typically grows 2–4 feet tall and may branch near the top.
Basal leaves are elongated with toothed margins and fine hairs. Stem leaves are arranged alternately, lance-shaped, toothed, and arise directly from the stem without petioles. All leaves have a prominent, light green midvein.
Flowering occurs from late spring to early summer. Flowers are borne in showy, loose clusters at the ends of branches. Individual flowers are ¾ to 1 inch across and have four petals arranged in a cross shape, characteristic of the mustard family. Flower color ranges from purple to pink or white.
Seeds develop in elongated pods (2–5 inches long) that split open lengthwise when mature. Stalks with dried, split seed pods may persist late into the season, even after the plant has died or gone dormant.
Quick ID Guide
Life Cycle:
• Biennial or short-lived perennial
• First-year rosette
• Second-year flowering stem
Height:
• 2–4 feet tall
Stems:
• Erect
• May branch near the top
• Slightly hairy
Leaves:
• Alternate
• Lance-shaped
• Toothed margins
• Prominent light green midvein
• Basal leaves with fine hairs
Flowers (Late Spring–Early Summer):
• Purple, pink, or white
• Four petals• ¾–1 inch wide
• Loose terminal clusters
Seeds:
• Long, narrow pods (2–5 inches)
• Split open at maturity
• Pods may persist after the plant dies
Management Options
Prevention and cultural control strategies should be emphasized whenever possible. There are currently no approved biological control agents for dame’s rocket.
Because dame’s rocket has a taproot, small infestations can be effectively managed by hand pulling or digging, ensuring the entire root is removed. Plants are easiest to control before seed production.
Repeated mowing after bolting and before seed production can prevent seed development. Mowing approximately two weeks after an herbicide application can improve control by helping to kill the root and prevent seed production. Do not mow once seeds are present.
Clipping flower heads before seeds mature is also effective. Cut flowers may be used ornamentally, but all plant material should be bagged and disposed of in the trash to prevent seed spread.
Large infestations may require herbicide treatment. Spring applications targeting rosettes or early bolting plants are recommended. Always read and follow herbicide label directions before application. Contact Sublette County Weed & Pest for assistance with product selection, rates, and timing.
