Blue Billygoat Weed Biology Ageratum conyzoides Family: Asteraceae (Daisy family).
Common names: Billygoat weed, Blue bonnet, Bluetop, Goatweed.
Confused with: Billygoat weed and blue billygoat weed (A. houstonianum) are very similar and readily confused. Billygoat weed is more common in northern Queensland.
Description:Seedlings – cotyledons leaves are circular to egg shape, 3 mm long by 3.5 mm wide.
Early leaves – are broadly egg-shaped, with lightly serrated margins. The serrations are widely spaced, rounded and shallow. Later leaves have obviously serrated margins and clearly defined veins.
Leaves – are egg shaped to triangular, arranged in opposite pairs along the stems. Leaves are 10 – 100 mm long and 10 - 60 mm wide, borne on stems 5 – 50 mm long. Leaves are mid-green and lightly hairy.
Mature plants – an erect annual or short-lived perennial plant 30 – 100 cm high with hairy stems.
Flowers – are 4 – 5 mm across, pale lavender blue to white. They occur in fluffy clusters on the end of erect or slightly drooping stems.
Fruit – seeds 1 - 3 mm in length, black and topped by a fluffy pappus of 5 white hairs, 1.5 - 3 mm in length which assists the seeds in wind dispersal.
Lifecycle/Biology: An annual or short-lived perennial plant which emerges and flowers year round.
Ecology: Occur on a wide variety of soil types.
The problem: Billygoat weed is a major weed of cropping in northern Queensland and a common weed of pastures and disturbed areas.
Distribution: Occurs New South Wales north coast, Queensland and the Northern Territory. It is most common in northern Queensland and the Northern territory. It is a major weed in the Burdekin region.
Origin: An introduced species from tropical America.
Reference: Crop Weeds of Northern Australia, p. 104 - 105.
Compiled by: Graham Charles
