The Avondale Heights Community Garden currently has a nasty infestation of this weed. Unfortunately it is difficult to differential between the weed and the native grass until the seed head develops.
Identification page 3 of this document http://www.weeds.gov.au/publications/guidelines/wons/pubs/n-neesiana.pdf
The garden is working to eradicate the week and increase the amount of kangaroo and wallaby grasses on site.