Germination ecology of hairy fleabane (Conyza bonariensis) and its implications for weed management

Hairy fleabane [Conyza bonariensis(L.) Cronquist] is a problematic weed in Australian no-till cropping systems. Consequently, a study was conducted to examine the effect of temperature, light, salt stress, osmotic stress, burial depth, and sorghum crop residue on germination and emergence in two populations (C and W: collected from chick pea [Cicer arietinumL.] and wheat [Triticum aestivumL.] fields, respectively) ofC. bonariensis. Both populations were able to germinate over a wide range of alternating day/night temperatures (15/5 to 35/25 C); however, the C population had optimum (and similar) germination over the range of 20/10 and 30/20 C, while the W population showed maximum germination at 25/15 C. A negative relationship was observed between osmotic potential and germination, with 31% and 14% germination of the C and W populations at -0.6 MPa, respectively. These observations suggest that population C was more tolerant to higher osmotic potentials than population W. Seeds of both populations germinated when exposed to a wide range of sodium chloride levels (NaCl, 0 to 200 mM); however, beyond 200 mM NaCl, no germination was observed in either population. Maximum germination of the C (70%) and W (41%) populations was observed on the soil surface with no emergence from a burial depth of 1 cm. The application of sorghum residue at an amount of 6,000 kg ha(-1)reduced emergence of the C and W populations by 55% and 58%, respectively, compared with the no-residue treatment. Knowledge gained from this study suggests that the following strategies could be used for more efficacious management ofC. bonariensis: (1) a shallow-tillage operation to bury weed seeds in conventional tillage systems, and (2) retention of sorghum residue on the soil surface in no-till systems.