Opportunities to reduce weed management costs
OPPORTUNITIES exist for grain growers in Australia's southern cropping region to more effectively manage weeds in retained stubble systems, according to new research conducted by the CSIRO and funded by the Grains Research and Development Corporation (GRDC). CSIRO Senior Research Scientist (Farming Systems) Dr Rick Llewellyn says the new study has highlighted just how costly weed management has become and where there are opportunities to reduce further cost increases. Presenting at a meeting of farming systems groups involved in the GRDC's southern “stubble initiative”, Dr Llewellyn said data collected through a study of 600 grain growers' weed management practices showed that while there has been recent rapid uptake of some key IWM practices across the southern cropping region (South Australia, Victoria, Tasmania and southern and central New South Wales) there were still many areas where adoption remains low despite the herbicide resistance threat. “The data shows very large differences between regions for practices like harvest weed seed control, crop topping and double knockdown which reflects past differences in the levels of herbicide resistance, but we're now seeing resistance issues becoming much more important in all cropping regions,” Dr Llewellyn said. “Many southern farmers have not yet faced the same herbicide resistance crisis that has come about in Western Australia or cropping-intensive parts of the medium rainfall zone, such as the Mid North of SA, but now there's the chance to make earlier use of some of the practices that have been refined through farmer experience to extend the life of important herbicides, not just control resistant weeds once herbicides are lost. “Where an integrated weed management practice can be introduced relatively cheaply we're seeing that growers are very willing to take up the practice and narrow windrow burning is an example of that.” While ryegrass remains the most commonly resistant weed, changing weed dynamics in the southern cropping region mean that long-term strategies are increasingly needed for control of other grass weeds as well, according to Dr Llewellyn. “Brome grass in particular is really increasing in its spread and importance in much of the region. Recent studies have shown how brome has risen up the charts in terms of costs to growers and implications compared to a decade or two ago. “Ryegrass has received a lot of the attention in Australia in the past but we're now working with the University of Adelaide weeds team to look at the most economic long-term strategies of managing brome which has become the driver grass weed for a lot of our cropping land – it's a weed for which there aren't a lot of herbicide options and harvest weed seed control methods aren't always highly effective. And what herbicides options there are, are being placed under a lot of pressure. “There is a requirement of farmers to carefully manage the herbicide options they have over time. We're aiming to help farmers and advisers take a longer-term seedbank and resistance risk view, by considering when they should use these herbicides to get the biggest bang for their buck and not use them up too quickly, as well as looking at the longer-term value of introducing new weed management practices.” Dr Llewellyn said the latest study had also shown that summer weeds were likely to be now causing more crop yield loss than winter weeds. “This is partly because, despite the challenges, growers are continuing to keep winter weed densities in crop quite low, partly because summer weeds are becoming increasingly difficult and costly to control and partly because stored moisture is so often of very high value to crop production. “Even though about two thirds of land for cropping in the southern region may receive a herbicide treatment for summer weeds and about a third of growers use at least some cultivation for summer weed control, we are still seeing high total costs to yields from summer weeds. “It's a part of the farming system that is increasingly costly and is in need of more management options, particularly as new herbicide resistant or herbicide tolerant summer weeds become more important,” Dr Llewellyn said. • Details: www.grdc.com.au/resources/IWMhub.
CSIRO Senior Research Scientist (Farming Systems) Dr Rick Llewellyn says a new study has highlighted just how costly weed management has become and where there are opportunities to reduce further cost increases. Photo: C. Sullivan.