Annual, spreading by seed, it is not a grass as the common name might suggest, but is a member of the Polygonaceae Family. It is usually found on arable land, but in a new garden or where soil has been imported, it can appear in the garden. The wirey branched stems have 'knots' at leaf joints which are swollen with a covering silvery scale. The lance-shaped leaves have a short stalk. Sap can be irritant to the skin.
Flowers from August to November - a cluster of small pink and white flowers in the angle between leaf and stem.
Height - up to 60 cm, but on open ground it is usually prostrate, scrambling over the surface.
Hoe or hand pull, tough branching tap-root, but easily pulled up. Apply mulch to newly cultivated beds to prevent germination.
Weedkillers to use:-
Dichlobenil prevents emergence of seedlings among established woody plants, for up to one year.
Paraquat, Diquat kill on contact.

See also Common Knotgrass and Northern Knotgrass which have similar growth habits and flowers. Redshank is related but has flower spikes

Follow these links for further details on Weeds, Weed Removal and Weed Prevention.