Blue Billygoat Weed

Description:

Blue billygoat weed (aka floss flower, bluemink, blueweed, pussy foot, Mexican paintbrush) is an environmental weed, and is an invasive species in Australia, but is native to Central America and adjacent parts of Mexico. Often found in grazing country, Ageratum houstonianum is toxic to grazing animals, causing liver lesions. Usually an invader of disturbed sites, degraded pastures, roadsides and neglected areas.

Habitat:

Spotted at a clearing at Lake Manchester, a freshwater reservoir west of Brisbane. It is located in Brisbane Forest Park, an area of dense native bushland and subtropical rainforest. I often see this species in cleared areas which have grass and are mowed, but don't see it in any great numbers in native bushland areas. Perhaps that is how this weed spreads, transported by machinery like tractors and mowing equipment?

Notes:

Why is this weed associated with billygoats? Perhaps because the weed is toxic but billygoats can eat anything?