Pacific Pests, Pathogens and Weeds - Online edition

Pacific Pests, Pathogens, Weeds & Pesticides

Knobweed (497)

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  • Worldwide distribution (except Africa). In Australia, Federated States of Micronesia, French Polynesia, Guam, Palau, Samoa, Solomon Islands.
  • Forms dense thickets in open forests, forest margins and clearings, fallows, pastures, wastelands, roadsides, along streams. Replaces native species in open eucalypt forests and rainforests, and overgrazed pastures or those with poor nutrition. Produces abundant ‘seed’.
  • Up to 2.5m, branching square stems, becoming woody. Leaves opposite, widely spaced, with serrated margins, and minty smell. Groups of flowers, white, in small clusters up to 25mm, in upper leaf axils. Individually, white, minute, round, surrounded by a tube of green leaf-like structures (calyx), turning brown and containing the fruit, which divides into four, forming the ‘seeds’. Ripe seedheads rattle.
  • Spread: ‘seeds’ in water, attached to animals, clothing, in mud on vehicles, and in seed consignments.
  • Biosecurity: check seed of pasture species.
  • Biocontrol: none.
  • Cultural control: hand-weed or slash infestations, making sure crown is removed to avoid resprouting; monitor and treat regrowth with herbicide. Apply fertilizer to promote rapid growth of pasture species. Clean machinery/vehicles.
  • Chemical control: 2,4-D, glyphosate.
Common Name

Knobweed. It is also known as false ironwort, wild-hops.

Scientific Name

Hyptis capitata; previously, it was known as Hyptis rhomboidea. It is a member of the Lamiaceae.

AUTHOR Grahame Jackson
Information from PIER (2013) Hyptis capitata Jacq., Lamiaceae. Pacific Island Ecosystems at Risk (PIER), Institute of Pacific Islands Forestry. (; and CABI (2019) Hyptis suaveolens (pignut). Invasive Species Compendium. (; and DAF (2020) Knobweed Hyptis capitatia. Queensland Government. (; and Conran J (2021) Hyptis capitata Jacq. Knobweed. WeedsAustralia - Profiles. Centre for Invasive Species Solutions, Department of Agriculture, Weeds and the Environment. Australian Government. (; and from Ken Fern (2019) Hyptis capitata. Useful tropical plants. ( Photo 3 Vinayaraj Hyptis capitata. ( Photo 4 M Fagg, Australian Plant Image Index (

Produced with support from the Australian Centre for International Agricultural Research under project HORT/2016/185: Responding to emerging pest and disease threats to horticulture in the Pacific islands, implemented by the University of Queensland and the Secretariat of the Pacific Community.

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