Prevention and Control of Herbicide Resistant Weeds in Australia

Abstract

Herbicide resistance has now developed in several monocot and dicot weed species in southern Australia. Of these, annual ryegrass (Lolium rigidum) has developed resistance to most of the selective herbicides available for its control and, therefore, has had the biggest impact on farm profitability. The seed-bank of ryegrass is relatively short-lived and can be depleted to low levels by effective management in the pasture phase. However, it is much more difficult to manage resistant populations of this weed under continuous cropping. Consequently, there has been a dramatic rise in the use of alternative herbicide groups, such as the dinitroanilines to which resistance is still uncommon. Innovative techniques such as capture of weed seeds during the harvesting operation and preventing seed-set of weeds in crops by the application of non-selective herbicides (e.g. paraquat after anthesis of ryegrass) are also being adopted by some farmers. So far, dicot weeds have only evolved resistance to the ALS inhibiting herbicides and can, therefore, still be managed effectively with several other herbicides. There is a growing appreciation in the farming community of the need to reduce reliance on selective herbicides and, instead, employ a wider range of weed control methods to delay the onset of herbicide resistance in weed populations.