Australian Herbicide Resistance Initiative (AHRI)

Blog: AHRI insight

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 radish flower

Australian Herbicide Resistance Initiative (AHRI)

Is there a fitness penalty in Group B resistant weeds?

When we talk about the fitness of weeds, it’s not about how fast they can run a marathon. We are talking about how well they grow and how many viable seeds they produce. Weeds with fitness penalties just don’t grow and reproduce as well as they should, even in the absence of herbicides. Are there fitness penalties for Group B (e.g. Glean®; ALS inhibitor) resistant wild radish? Visiting researcher, Mei Li, along with other AHRI researchers, set out to answer this question. Unfortunately, the answer is NO! Wild radish, with four different target-site ALS mutations, were equally as fit as…

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Plants in flowerpots

Australian Herbicide Resistance Initiative (AHRI)

The rate debate

Many a late night has been spent over a glass of red at weeds conferences around the world debating whether high or low herbicide rates lead to faster resistance evolution. All weed scientists have an opinion on this issue, some of which are held very tightly. To some extent, the debate is still raging because the answer is not straight forward. The answer is both. As you can imagine, both sides of the debate are claiming victory! What we do know is that low herbicide rates have been documented to lead to rapid resistance evolution to Hoegrass®, Roundup® and Sakura®…

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Nature landscape of grass trees and sky

Australian Herbicide Resistance Initiative (AHRI)

Think outside the drum

If herbicides alone were the answer to all of our weed problems we would have eradicated crop weeds years ago. Most of us now realise that to achieve true weed control success we need to add non-herbicide tools into the mix. It doesn’t matter which weed, which crop, or which country we are talking about, the benefits of good cultural practices apply everywhere. Some excellent long term Canadian research has confirmed how important it is to combine good cultural practices with herbicide use. The Agri-Food Canada trials show that after nine years of full herbicide rate, high barley seeding rate,…

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Man touching a plant

Australian Herbicide Resistance Initiative (AHRI)

How to break glyphosate

To break a herbicide such as glyphosate takes considerable effort. The Americans have broken glyphosate in a big way due to overuse, and Brazil and Argentina are not far behind. As an indication of the scale of the problem, in Arkansas last year over half of the cotton crops were hand weeded before harvest. How did they achieve this amazing feat? In a nutshell, they universally adopted Roundup Ready crops and abandoned almost all other forms of weed control for about a decade. The USA now has the unenviable title of the world’s biggest herbicide resistance problem. You may well…

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Truck transporting vehicles for agriculture

Australian Herbicide Resistance Initiative (AHRI)

Weed Destructor integrated into harvester

The Harrington Seed Destructor (HSD) is on the verge of taking the step that most grain growers would like to see. The majority of Australian grain growers who have seen the HSD are very positive about the concept of destroying weed seeds as they exit the harvester. It seems crazy that we would spread the weed seeds back over the field (so we have something to spray next year!). However, many growers have commented that they are reluctant to tow such a machine behind their harvester. Agricultural engineers from the University of South Australia in collaboration with AHRI, are taking…

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Older man giving speech

Australian Herbicide Resistance Initiative (AHRI)

Do Monsanto have the next big thing?

Imagine if some technology came along that made glyphosate kill glyphosate resistant weeds. If this did happen, what would we do with this technology? BioDirectTM (aka RNAi) is a new concept from Monsanto that could do just that. It could be the next big thing for the herbicide industry. The ‘i’ in RNAi stands for ‘interference’. RNA is essentially a small piece of genetic code that all living things use to carry out a specific function within a cell, including coding enzymes that plants need to survive. One way of killing the plant is to spray a herbicide that stops…

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