Windmillgrass is a major weed in agricultural systems in northern Australia, and it has now become more common in southern Australia. Because little information is available on the biology of this weed species in southern Australia, studies were conducted to investigate plant development and seed biology. Under irrigated field conditions in South Australia, windmillgrass required 748 to 786 growing degree days from emergence to mature seed production. Freshly harvested seed had low dormancy with 16% to 40% germination. Seeds required light exposure for germination and less than 2% germination was observed in complete darkness. Seed could germinate over a wide temperature range (10 to 40 C) with maximum germination at 20 to 25 C. At 25 to 30 C, 50% germination occurred within 27.3 to 45.5 h, and the predicted base temperature for germination of the two populations investigated ranged from 9.2 to 11.2 C. The sodium chloride concentration and osmotic potential required to inhibit germination by 50% were 51 to 73 mM and -0.27 MPa, respectively. Seedling emergence was completely inhibited by burial of seed, which is consistent with its absolute requirement for light exposure to begin germination. Under field conditions, there was no clear effect of burial depth on seed viability in the first 2 yr with average rainfall, and seeds were completely nonviable after 12 mo. However, in the third year, with low spring—summer rainfall, buried seeds (37% viability after 14 mo) persisted longer than those left on the soil surface (6% viability after 14 mo). This study provides important information on plant development and seed biology of windmillgrass that will contribute to the development of a management program for this weed species in southern Australia.

Nomenclature: Windmillgrass, Chloris truncata R. Br.