Caltrop also known as bindii is a summer growing annual plant that has a high level of drought tolerance.
Caltrop germinates in late spring and summer after rains, rapidly growing, producing a deep root system and yellow flowers within 3 weeks.
Multiple germinations occur within the season so more than 1 spray during the season may be necessary.
Source: Prime Fact 723, November 2009, Tribulus: Caltrop and Yellowvine, NSW Department of Primary Industry