Amaranthus: Emerging weeds of cotton systems in Australia?

Abstract

Cotton growers in Australia face significant challenges eradicating weeds from the cotton cropping system. Poor weed management can cause up to 90% yield loss in cotton due to competition with the crop for nutrients and water. Amaranthus species continue to be a problem for the cotton crop in Queensland and NSW. Studies are not available on the ecology and biology of these species in Australia, so a Ph.D. research project has been initiated on major problem (or potential problem) weeds - Amaranthus hybridus, A. powellii, A. mitchilli, A. retroflexus and A. viridis. These are the most widespread, troublesome, and economically damaging agronomic weeds of genus Amaranthus in Australia. Numerous factors have enabled these species to become dominant and difficult-to-control weeds. These factors include rapid growth rate, high fecundity, genetic diversity, and ability to tolerate adverse conditions. Further, several species in the genus have become major pests in the USA by evolving resistance to glyphosate. The research currently underway will address the knowledge gaps in the biology and ecology of Amaranthus species in Australia. The project includes field experiments and laboratory studies to better understand weed biology relevant for the development of effective control tactics for these emerging weed species. Obtaining information on dormancy patterns as well as the persistence of weed seed banks under current management systems would allow cotton growers to make informed decisions about their weed management programs. In addition, information on the phenology of these weed species along with their seed production would be useful for decision-support systems helping managers select the best management strategies and, thereby, improving their control. Seeds of different populations of the three species will be collected and screened with glyphosate. If resistant biotypes are found, studies will be conducted to determine the mechanism of resistance. A brief overview of experiments conducted and planned for research on these species will be presented. inhibitors to successful management, will be discussed.