The Ecology of Fleabane (Conyza Spp.)
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The ecology of fleabane (Conyza spp.) Todd Douglas Green B.LandMgmt(Ecological Agriculture) University of Sydney B.Sc (Hons) University of Newcastle A thesis submitted for the degree of Doctor of Philosophy of the University of New England School of Environmental and Rural Science Faculty of Arts and Sciences University of New England October 2010 DECLARATION I certify that the substance of this thesis has not already been submitted for any degree and is not currently being submitted for any other degree or qualification. I certify that any help received in preparing this thesis, and all sources used, have been acknowledged in this thesis. Todd Douglas Green i ACKNOWLEDGEMENTS I would like to acknowledge the Cotton Research Development Corporation (CRDC) and the Cotton Catchment Communities Co-operative Research Centre (Cotton CRC) for funding this research (Project #1.01.54) and thank these entities for offering me an opportunity to undertake a PhD. My supervisory team of Professor Brian Sindel, Dr Jeff Werth and Mr Graham Charles all played a role in getting my research completed and thesis submitted. I thank them all for supporting my journey over the past three years. I am grateful for the detailed reviews and editing by Professor Sindel, his encouragement, knowledge and understanding. I would like to thank Dr Jeff Werth for his promptness in feedback, knowledge and his encouragement. To Mr Graham Charles, I am fortunate to have access to his practical knowledge and thank him for his thorough reviews and encouragement. I would also like to thank general staff members of the University of New England who provided assistance to me personally and for practical elements of my research, namely, Dan Alter, Greg (‘Tractor’) Chamberlain, Mick Faint, George Henderson, Dave Edmonds and Elizabeth Davies. Fellow postgraduates, past and present, have also assisted me in reaching submission through their advice, friendship and encouragement. There have been many health professionals who have assisted in the management of my health and wellbeing throughout my PhD journey. I would like to especially thank Dr Suzanne Robertson (University Medical Centre), who has seen me regularly throughout my entire PhD journey and provided me encouragement and assistance over and above what is expected from a General Practitioner. I also thank Dr Caroline Croft for her assistance, sense of humour and encouragement over many lengthy sessions. Furthermore, several staff members of Community Health (Hunter-New England Area Health Service) have also been critical in managing my health. ii I have enormous appreciation of my parents, Ron and Maureen Green, for their involvement in my PhD journey. I thank them both so much for their encouragement, interest and support. I also thank them for putting up with all my complaining on the telephone and for their love and emotional support which has enabled me to complete my thesis. A special thank you to Darren, for his support, motivation and encouragement, which has been vital in completing this project. I thank Darren for ensuring that I eat properly and have time out. Also, I thank Darren enormously for putting up with my PhD mood swings. iii ABSTRACT Conyza bonariensis (L.) Cronquist, flaxleaf fleabane, originating from South America, is a major emerging weed threat for dry-land cropping systems in Australia. Conyza bonariensis is particularly increasing in importance within the northern cropping region of Australia, is one of the most difficult-to-control weeds in minimum tillage systems, and is tolerant to important herbicides. There is a need to expand the ecological knowledge of C. bonariensis in order to better understand its success in minimum tillage systems and to provide principles for the improved management of this weed. Conyza bonariensis is common in fallows, thereby depleting the soil stored moisture, and has caused a doubling of control costs in certain areas of the northern cropping region. Control costs are likely to further increase due to the weed’s rapid development of herbicide resistance. In addition, C. bonariensis is a problem weed within many field crops, including – cotton, chickpea, lucerne, maize, sorghum, soybean and wheat. Conyza bonariensis competes for water and nutrients, especially in wheat and dry-land sorghum crops. Control of C. bonariensis is greatly dependant on herbicides, thereby increasing the risk of herbicide resistance. There are currently glyphosate resistant populations of C. bonariensis in six countries and there have been reports of differential responses to glyphosate in southern Queensland populations. In this study, ecological aspects of the key life stages of C. bonariensis were investigated, comprising of germination, emergence, growth and development, seed dispersal and seed longevity. All ecological findings were compared with a congeneric species, C. sumatrensis (Retz.) E. Walker (tall fleabane), which is currently not problematic in cropping systems in Australia, despite being present in the region within other ruderal sites (e.g. roadsides), as a way of determining what ecological characteristics in C. bonariensis may be responsible for its increase in the northern region cropping system. Germination was limited by temperature, moisture and light. Seeds of C. bonariensis germinated between 10 and 30 oC, with optimal germination at 25 oC. Conyza bonariensis iv seeds were able to germinate under moisture stress down to -0.8 MPa. Light was essential for germination of C. bonariensis . In a 90% shade environment, C. bonariensis germination was reduced by 80% compared with a full light environment. With adequate temperature, light and moisture, C. bonariensis seeds can germinate within 2 to 3 days. Soil type and stubble levels affected C. bonariensis emergence. Emergence was reduced in heavy black vertosol soil compared with lighter soils. There was no significant difference in emergence with 1.8 t ha -1 of stubble compared with no stubble. Conyza bonariensis can emerge all-year-round, and there are differences in development and fecundity between emergence cohorts. More than 85 000 seeds were produced per plant in the overwintering cohort, which was 40% higher than the spring emerged plants. The root:shoot ratio at the time of stem elongation in overwintered C. bonariensis plants was 60% higher than spring emerged plants. This ecological feature makes the late-autumn cohort more difficult to control. There was a short period of six weeks between stem elongation and seed production in C. bonariensis , and with a slow response to herbicide, this adds to the success of this weed. Conyza bonariensis s eed settling velocity and pappus geometry was affected by humidity. Settling velocity was 0.28 m s -1 at 30% humidity and increased to 0.33 m s -1 at 90% humidity. The pappus bristles of C. bonariensis seeds were closer together in environments of high humidity. Conyza bonariensis seeds were not able to emerge from burial depths of 0.5 cm or greater, although the length of time that the seed remained viable increased with burial depth. Seed longevity at 1 cm burial depth was 37 months and at 10 cm depth, this increased to 80 months. Seeds which enter a minimum tillage system typically remain on or near the soil surface, the preferred germination site for C. bonariensis , therefore adding to the weed’s success in these systems. In comparison with C. sumatrensis , C. bonariensis produced more seed, had a higher relative reproductive effort, developed more rapidly, could germinate in milder temperatures only and had a longer lived seed bank. These ecological findings are likely to account for the greater success of C. bonariensis in minimum tillage cropping systems. The effective long- term management of C. bonariensis requires an integrated approach to weed management, v in which herbicide use is complemented with non-chemical control measures. Through limiting soil disturbance, there will be a reduction in the burial of seed and thereby a more rapid depletion of the seed bank, assuming there is no further addition of seed to the soil seed bank from elsewhere. Where appropriate, cultivation could be used to bury the seeds of C. bonariensis and prevent germination or to perhaps kill overwintering plants with large taproots. Agricultural practices should also aim to maximise competition, including shade, against C. bonariensis . Diligent control is required to prevent seed set, especially for the overwintered plants which are more difficult to control and have a higher seed production. vi TABLE OF CONTENTS DECLARATION ................................................................................................................. i ACKNOWLEDGEMENTS....................................................................................................ii ABSTRACT ......................................................................................................................iv TABLE OF CONTENTS .....................................................................................................vii LIST OF FIGURES .............................................................................................................xi LIST OF TABLES.............................................................................................................xiii APPENDIX .................................................................................................................... xiv Chapter One: Introduction ..................................................................................................1