Blue top
Common names: Blue top, Billy goat weed Scientific name: Ageratum houstonianum
Native to: South America Family: Asteraceae Habit: Herb growing to 1 metre tall. Leaves: Noticeable hairy with toothed margins.
Flowers: Dense clusters at the top of the branches. Blue to purple in colour. Flowers year round.
Control measures: Small plants are easily hand pulled. Bigger infestations can be mown, or whipper snipped before seeding. Chemical control works well with Glyphosate or Dicamba. Once established Blue top is not easy to eradicate.
Blue top loves wet areas and is doing very well with the current rain. Its not so much a problem in household gardens as mowing keeps it from spreading. However, along roadside and within rural properties it can be a big problem. Once bigger plants are pushed over, usually by flood water, the stems root to ground and form a matting. This completely suppresses growth of other species. In these conditions the base becomes almost woody and hard to pull out. When pulled out they can easy break or come away with a large clump of soil.
For more information
Weeds of the Sunshine Coast page 20, 2nd edition.
https://weeds.brisbane.qld.gov.au/weeds/blue-billygoat-weed
By Michelle Newall
