Four more weeds develop resistance in Australia

Prior to the recent confirmation of glyphosate resistance in awnless barnyard grass (Echinochloa colona) in northern New South Wales (Australia), only annual ryegrass (Lolium rigidum) had been confirmed resistant to glyphosate in Australia. A report dated 21 June 2007 showed in some tests with barnyard grass seeds and their progeny from a paddock sample from Belatta (NSW), 3 weeks after treatment, an almost total plant kill in non resistant weeds and high survival rates in glyphosate-resistant populations. Four more weeds have been identified as at risk of developing resistance to glyphosate: wild oat (Avena fatua and Avena ludoviciana), sowthistle (Sonchus oleraceus) flaxleaf fleabane (Conyza bonariensis) and liverseed grass (Urochloa panicoides). Some of the weeds at risk of developing resistance  Three common factors determined the high risk category for these weeds:
  • Each produce large quantities of seed, resulting in large populations;
  • They have a history of herbicide resistance somewhere in the world;
  • They occur in minimum tillage


    Least possible soil disturbance for preparing a seedbed by reducing cultivation and avoiding the use of a plow. It can involve direct drilling, broadcasting into existing stubbles or adopting a strategy of reduced tillage. The main benefits are to reduce tillage energy consumption, to conserve moisture and soil structure, to reduce disturbance of soil organisms and to retain plant cover to minimize erosion.

    Authoritative On-line References and Resources

    The European Conservation Agriculture Federation (ECAF) promotes best soil management practices based on minimal soil disturbance by reduced tillage.
    or no-till


    Also known as conservation tillage or zero tillage is a way of growing crops from year to year without disturbing the soil through tillage ie cultivating the soil usually with tractor-drawn implements.

    Authoritative On-line References and Resources  A portal for on-line information about no-till farming.
    farming systems where they are exposed to multiple applications of glyphosate.
The risk assessment was conducted as part of the Northern Glyphosate Resistance Project, by members of Weeds CRC, NSW Department of Primary Industries and Queensland Department of Primary Industries and Fisheries.  Researchers emphasise the importance of using good herbicide practice and early identification of low levels of herbicide resistance right across Australia. According to Mr Andrew Storrie (from NSW DPI) "Barnyard grass is a highly competitive weed of summer crops and fallows".  Where glyphosate resistance is suspected in awnless barnyard grass, a summer fallow using residual herbicides and paraquat should be considered in the rotation." According to Dr Steve Walker (Queensland DPI), glyphosate alone is only effective on very small flaxleaf fleabane plants. "Our research has shown that as flaxleaf fleabane matures, control was reduced from 88 per cent kill for weeds five centimetres diameter to a very poor 13 per cent kill for weeds 10cm diameter or larger." A number of tank mixes including glyphosate were found to provide better control or the use of a double knock, such as glyphosate followed by paraquat (eg Gramoxone ®) or a mix of paraquat and diquat (eg Spray.Seed ®) was also effective. Both researchers emphasise that using different herbicide mode-of-action groups is essential if herbicide resistance is to be kept to a minimum. "Continual use of any one herbicide group increases the potential for the development of herbicide resistance, resulting in reduced control options," said Dr Walker, "A mixture of cultural and herbicide control methods should be employed to maximise the opportunity to prevent seed-set and to reduce the weed seed bank." Note: SpraySeed ® is a branded product containing paraquat and diquat, both active substances are from the same chemical (bipyridium) family, Gramoxone® is a branded product containing paraquat.