Pacific Pests, Pathogens and Weeds - Online edition

Pacific Pests, Pathogens, Weeds & Pesticides

Goatweed (451)

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  • Widespread. Asia, Africa, North, South and Central America, Caribbean, Europe (restricted), Oceania. In most Pacific islands.
  • Invasive annual of natural habitats: grasslands, forests, wetlands, banks of water courses, coastal dunes, as well as pastures, plantations, orchards, wastelands and roadsides, forming extensive swathes of the weed, especially in moist, fertile, disturbed soils. Impacts biodiversity, poisonous to humans, and a host of plant pathogens.
  • Erect, branching, 0.5-1 m high. Stems, hairy, soft, becoming woody with age. Leaves, oval, broader at base, up to 7.5 cm long, smell of male goat when crushed. Flowerheads, in branches, flat-topped clusters at top of the stems. Each with 30-50 white, light blue or violet flowers. Fruits, small, brown and 1-seeded. Plants have shallow fibrous roots
  • Spread: contaminant of seeds of other species; on clothes, machinery and vehicles; trade in medicinal plants and ornamentals.
  • Biosecurity: seed is available on the internet.
  • Biocontrol: Little known.
  • Cultural control: hand weed or plough and disc (before plants set seeds); flood fallow (if practical); vehicle hygiene.
  • Chemical control: in Australia (and Fiji): glyphosate. In Fiji, also 2,4-D.
Common Name

Goatweed; it is also known as billygoat weed (or billy goat weed, even billy-goat weed), tropic ageratum, blue flowered groundsel.

Scientific Name

Ageratum conyzoides; previously, known by a large number of different names in the genera Ageratum, Cacalia and Eupatorium. It is also said to be Ageratum conyzoides subspecies conyzoides. It is a member of the Asteraceae.

A similar species, Ageratum houstonianum, is recorded in the Pacific islands (Fiji, French Polynesia, New Caledonia, Papua New Guinea).

AUTHORS Grahame Jackson, Aradhana Deesh & Mani Mua
Adapted from Billygoat weed (Ageratum conyzoides) (2018) Weeds of SE Qld and Northern NSW. Lucidcentral. (; and additional information from CABI (2019) Ageratum conyzoides (billy goat weed). Invasive Species Compendium. ( Photos 1,2,5&10,11 Sheldon Navie, Queensland, Australia. Photo 4 Minghong Photo of Ageratum conyzoides. Photos 8&9 Forest & Kim Starr. Starr Environmental, 

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, in association with the Pacific Community and Koronivia Research Station, Ministry of Agriculture, Fiji.

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