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Australian Herbicide Resistance Initiative (AHRI)

How do weeds resist glyphosate?

Tag Archives | mechanisms

Weeds sample in glass

Australian Herbicide Resistance Initiative (AHRI)

How do weeds resist glyphosate?

If you ever find yourself in the situation where you are catering for a group of people, and you are wondering how much food to prepare, the best thing to do is to prepare a little extra, just in case. The last thing that you want to do is run out. Believe it or not, this is how some weeds resist glyphosate. They make an extra-large batch of the enzyme that glyphosate binds to, just in case. This way, if the weed is sprayed with glyphosate that inhibits some of the enzyme, there is still enough left for the plant…

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Man touching a plant

Australian Herbicide Resistance Initiative (AHRI)

AHRI Mythbusters – can 2,4-D induce resistance in ryegrass?

What if you accidently sprayed the wrong herbicide? Agronomists of yester-year developed a handy trick. They found that if they accidently sprayed an oat crop with Hoegrass® (diclofop-methyl), they could stop crop damage in its tracks if they quickly applied 2,4-D. The grand question is…does it actually work? The ‘myth’ says yes. What does the science say? The AHRI Mythbusters team got the answer! In this latest AHRI research, Dr Heping Han and others found that when they pre-treated ryegrass with 2,4-D amine it became resistant to Hoegrass®. This is likely due to 2,4-D causing a spike in P450 activity…

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Researcher looking at samples

Australian Herbicide Resistance Initiative (AHRI)

How do P450 enzymes cause resistance?

What is a P450? Is it a car from the 70’s that fits a 44 gallon drum in the boot? No, that would be a P76. A P450 is an enzyme that eats herbicides. In fact, there are literally hundreds of P450 enzymes and some of them can chew on some herbicides, resulting in enhanced herbicide metabolism (metabolic resistance). We are now seeing an increased effort around the world to better understand metabolic resistance involving P450 enzymes. In 2005, Dr Paul Neve showed that ryegrass could quickly develop resistance after being sprayed with low doses of Hoegrass® (diclofop). Some recent…

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Glasshouse with plants

Australian Herbicide Resistance Initiative (AHRI)

Too cold for glyphosate resistance

Most of us are a bit slow out of bed on a cold morning and take a little while to get moving. Weeds are no different. Some glyphosate resistant weeds become less resistant in cool weather. One of the mechanisms of resistance to glyphosate is to reduce the movement of the chemical through the plant (known as translocation). Researcher Dr Martin Vila-Aiub and others from AHRI tested annual ryegrass and Johnsongrass with this resistance mechanism. They found that the plants were much less resistant to glyphosate when the plants were grown in cool conditions. The good news? If you know…

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Wild Oat

Australian Herbicide Resistance Initiative (AHRI)

Why do Wild Oats evolve resistance slowly?

Why is it that we can often kill wild oats (black oats) with grass sprays but the ryegrass in the same paddock evolved resistance to these herbicides years ago? The answer is in the genes. Ryegrass is like we humans – it must cross pollinate to reproduce and it has two copies of each gene (diploid). Wild oat is more like wheat – it mostly self-pollinates (88 to 100% self-pollination) and it has six copies of every gene (hexaploid). A single gene mutation can cause ryegrass to be resistant to a grass herbicide but it will have only a minor…

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