Australian Herbicide Resistance Initiative (AHRI)

Hit em hard, early?

Hit em hard, early?

Below is the output from a RIM run we developed here at AHRI to demonstrate how the Ryegrass Integrated Management (RIM) computer model can be used to put theories to the test. Have your own theory? Click here to contact us or follow the link below.


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by Peter Newman



This rotation was suggested by agronomist Paul Lavis from Corowa in southern NSW. Growers in this area are successfully managing ryegrass by hitting the seed bank hard for three years with RR Canola : Barley (crop topped) : RR Canola then reverting to the Canola : Wheat : Wheat rotation. Paul says that it works well but he is very concerned about the pressure on glyphosate with this strategy, and rightfully so. So the question, can we add enough weed control to look after glyphosate?


Let’s set it up:
  • Corowa, high rainfall, southern NSW
  • No resistance to glyphosate or the pre-emergent herbicides
  • If we hit the ryegrass hard for three years in a row then revert to Canola : Wheat : Wheat rotation how long does it last?
  • Can we do this and look after glyphosate at the same time



The first thing to notice is that there is money to be made with high yielding crops. Naturally, with gross margins like this, these growers are keen to keep the paddock in crop.



C:B:C:W:W:C:W:W herbicides only v adding croptop barley and burn wheat stubble


Screenshot 1



Can we add anything to make this rotation more sustainable and minimise the risk of destroying glyphosate?


Plus narrow windrow burning of canola V Harrington seed destructor (HSD) every year
Screenshot 2


The strategy used by NSW grain growers will work in the short term and make plenty of money but it is sure to break glyphosate. The RIM runs that we have done show how we can add more weed management to a rotation to get the seed bank to zero, but there is still a lot of glyphosate in the system. An even better system would involve less glyphosate and a seed bank of zero, perhaps this could be fodder for future RIM runs.


RIM is a great tool to compare some weed control strategies using computer simulation before making the changes on farm. RIM simulates the ryegrass seedbank based on years of research data to give realistic results.



Download RIM for free and give it a try.


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Some of the assumptions used in this simulation were:
  • High rainfall zone of Australia
  • Yields. Wheat 4 t/ha; Canola 2 t/ha. Barley 4.5 t/ha
  • Herbicide control %. Trifluralin (or trifluralin + avadex) 80%; Propyzamide 90%; Sakura 90%; Glyphosate 99%, croptop barley with glyphosate 95% seed set control
  • Whole paddock burn, HSD or Narrow windrow burn – removed 70% of ryegrass seed in crop


The picture below shows some of the assumptions used for these scenarios. All of these assumptions can be adjusted to suit a particular farm.


Lavis RIM assumptions