A Herbicide Resistance Guru. Helping growers combat herbicide resistance is what I do!
Joined May 2016
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322 Photos and videos
Jun 14
Wild oat seedlings arrived in perfect condition for resistance testing. Grower testing Achieve, Axial, Atlantis & Hussar. Will have answer in 4 weeks.
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More info that keeping atrazine & clethodim separated avoids antagonism. Here on DIM resistant ryegrass. The benefit of the 10 min split indicates chemical antagonism as it's unlikely there would be any biological effect in such a short time. SOA and 1% Hasten used. @WeedSmartAU
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May 27
Something you don’t see often in ryegrass. Resistance to Paraquat at 1.2 and 2 L but not resistant to Glyphosate at 1 L.
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May 24
Variation in DIM resistance in ryegrass. Higher clethodim rates can work. Adding Factor often better. From 500 comparisons of clethodim resistant ryegrass, in 40% of cases, the addition of 180g Factor provided greater control. We can test this with the Quick-Test.
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May 21
I’ve been asked to repost some previous work as it’s timely for the current season.
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Peter Boutsalis retweeted
22 May 2023
Ryegrass surviving label rates of Clethodim Glyphosate a concern.
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Peter Boutsalis retweeted
17 May 2023
Plants arriving in perfect condition for resistance Quick- Testing.
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Peter Boutsalis retweeted
22 Jun 2021
Combination of Clethodim Roundup Ready Performance Liquid on ryegrass resistant to Dims, Glyphosate or both. Photo is of 12 populations. Each pot is a single population. The location of each pot in each tray is the same population.
Ryegrass from WA, SA, Vic and NSW chosen.
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Peter Boutsalis retweeted
17 Aug 2021
Plant Science Consulting tested Clethodim plus Atrazine as a tank-mix vs Clethodim followed by Atrazine spray immediately after on susceptible and Dim-resistant ryegrass. Used Hasten and SOA. Significantly better activity on resistant ryegrass when NOT tank-mixed.
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Peter Boutsalis retweeted
3 Nov 2021
Our replicated pot trials identified that tank-mixing Clethodim Atrazine was antagonist vs. Clethodim alone or separating the mixes. The longer the separation the greater the control. We included 3 DIM-resistant and 1 susceptible ryegrass in the study. @WeedSmartAU
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Feb 25
I don't think I have to explain the below too much for this ryegrass from 2025 season. This is what over reliance on herbicides can create, an absolute monster! Not much in-crop control. Perhaps Liberty? Heavy reliance on PRE and EPE plus crop topping/ Seed Terminator needed.
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Peter Boutsalis retweeted
10 Dec 2025
Thankyou to @WeedSmartAU & @grassrootsag for including me. We need to be clever to stay ahead of weeds and resistance and keep our key herbicides working effectively. I took home some good points from the other presenters, great to have access to this info!
10 Dec 2025
A big thank to our presenters @CropDoctor54 @PBoutsalis @becsta1984 & attendees for today’s @WeedSmartAU webinar.
Clethodim is critical for ryegrass but warrants effort to stay effective. Peter, CD & Bec provided some key insights. Check the website for a recorded version.
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8 Dec 2025
We have a mystery wild oat sample to test for herbicide resistance. It arrived in a black post bag. The tracking Nr & barcode didn’t work. I called Australia Post & the only details they had was that it was sent on 27 Nov from Sydney. If the sender is on X can they contact me.
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Peter Boutsalis retweeted
2 Dec 2025
Declining clethodim efficacy in canola & pulse-based rotations can be addressed with increased diversity. Join Greg Condon & Chris Davey talking to @becsta1984 & @PBoutsalis to discuss strategies to slow clethodim resistance.
🎧 Register buff.ly/aX4tKhD
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8 Nov 2025
Seed volume (part 3). The more seed sent the less important dormancy is as don't have to wait for the majority of seed to break dormancy. More seed = quicker turnaround in testing. Germination of crop topped seed can be low or zero -> no resistance result @WeedSmartAU
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8 Nov 2025
Pre-emergent testing (part 2 of 2) however is more difficult. Have to wait for seed to start breaking dormancy, occurs when the temp's cool in autumn and not before. Frustrating for you and us. The results are however relevant for the next 5 or so years. Seed volume (part 3)...
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8 Nov 2025
Ryegrass dormancy- the reality.. Most ryegrass is highly dormant after maturity, protection against false starts from summer rainfall. We have tricks to germinate seed in artificial media thereby completing timely post-emergent testing. Pre-emergent testing ... (part 1 of 2)
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8 Nov 2025
Options available to control this ryegrass. Even the clethodim resistant ryegrass is heavily stunted, indicated by the 'R' rating. Plenty options in pulses on GM canola coupled with a strategic pre-em herbicides. Value in testing...
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8 Nov 2025
Example of a herbicide resistance report on ryegrass. Initial testing showed strong Group 1 and 2 resistance. We've responded by testing higher DIM rates. Sometimes these are fully effective. What value would you put on this information ...
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