The ecology of fleabane ('Conyza' spp.)

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.