Lessons from Weed Seed Control in Australia with Dr. Michael Walsh

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WSU Small Grains website
The University of Western Australia
Weed science research at WSU
Australian professor shares herbicide resistance knowledge during WSU visit

Contact information:
For questions or comments, contact Dr. Michael Walsh at michael.walsh@uwa.edu.au.

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Episode Transcription


Drew Lyon: Hello, welcome to the WSU Wheat Beat podcast. I’m your host, Drew Lyon, and I want to thank you for joining me as we explore the world of small grains production and research at Washington State University. In each episode, I speak with researchers from WSU and the USDA-ARS to provide you with insights into the latest research on wheat and barley production.

If you enjoy the WSU Wheat Beat podcast, do us a favor and subscribe on iTunes or your favorite podcast app and leave us a review so others can find the show too.


My guest today is Dr. Michael Walsh. Michael is an associate professor with the University of Western Australia. He has spent 30 years working on the development of alternative weed control techniques–in particular, the research and development of harvest weed seed control systems. He is currently in the U.S. on a Fulbright scholarship, assisting with research on the use of these systems and U.S. crop production systems.

Hello, Michael.

Dr. Michael Walsh: Hi, Drew. How are you?

Drew Lyon: I’m doing well in this wintery wonderland of Pullman, Washington. I hope it’s a little warmer where you are.

Dr. Michael Walsh: It’s a balmy 70 degrees here in Texas today so it’s definitely very nice.

Drew Lyon: Oh, very good. So you’re over here helping U.S. researchers incorporate harvest weed seed control systems and research them and their use in our systems here in the U.S. But how do you see harvest weed seed control systems in general fitting in to our integrated weed management programs?

Dr. Michael Walsh: Yeah, I think the fit for harvest weed seed control here in the U.S. is very similar to the fit in Australia. So in Australia the systems were developed as an end of season approach to the targeting weed seed production. And so the idea is that you would use something at the end of the season during harvest to kill the weed seeds as they pass through the combine and prevent those weed seeds from entering the soil seed bank. So it’s a preventative weed seed control practice.

And it will be a very similar use pattern here in the U.S. so that the end of the growing season, particularly with herbicide resistance now, there’s lots of weeds that are surviving through to maturity and so there’s lots of weed seeds present on those weed plants at crop harvest. So there is an opportunity here in the U.S. to target that weed seed production to again have a similar impact on inputs into the weed seed bank.

Drew Lyon: Okay. And I know you’ve been here to the Pacific Northwest a few times and the systems we are kind of developing–wheat production systems of Australia–and probably will move over fairly well here to this part of the world. But you’ve of been in the Midwest looking at corn and soybeans. How do you see them working in those systems?

Dr. Michael Walsh: Yeah. So that’s exactly right, Drew. The systems were developed in Australia with a focus on targeting annual ryegrass in wheat production-based cropping programs. And so they have been evolved and they do pretty well for those types of systems. And it’s there’s a lot of similarities between wheat production in Australia and wheat production of the Pacific Northwest.

Corn and soybeans is a completely different scenario. It’s a–it’s a different harvest time in terms of the time of the year–harvesting in much cooler, typically moister conditions. It’s different, particularly for corn, there’s different header used. So there’s a different potential for weed seed collection and there are different species as well. So that’s some of the big key differences that I think are going to impact the efficacy of harvest weed control systems here in the U.S. in those particular production systems.

Drew Lyon: So when you were here a few weeks ago, we learned that there’s actually quite a few more of these mill systems out there than I thought there were. So growers are starting to adopt them. How long do you think it will take them to start seeing the effect of using these harvest weed seed control methods, particularly the mill-type systems on combines?

Dr. Michael Walsh: Yeah, that was it was a really big surprise, Drew, when we learned about the level of adoption of one of the mill systems. It was encouraging, very pleasing, and good to see that there is such an extensive or significant interest in the use of harvest weed seed control, and in particular, the mill systems. There is obviously some cautionary tales around their use though, of course–they’re not going to provide an instant result because they are targeting the seed bank inputs.

And so the overall fix are very much dependent on just what the size of the weed seed bank is. If you–if you use a mill system or harvest weed seed control system during harvest one year, but you have a very big or very large weed seed bank then you might not see an impact for three or maybe four years.

However, if you’ve got a fairly controlled seed bank level, then you can actually see the results within the first year of use. So it all very much depends on what the size of the weed seed bank is for the species that we’re dealing with.

Drew Lyon: Okay. And also probably a little bit of how much seed is actually left in the head at harvest time. So are you–are you collecting or destroying 90% of the seed, which I think is fairly common with your major weeds in Australia, or is it more like 40 or 50%?

Dr. Michael Walsh: That’s a very good point, Drew. So, we have to keep an eye on the level of seed retention. Seed retention refers to the amount of seed–of total seed production by a weed plant that’s retained at a height that ensures that it gets collected by the combine. So if that seed retention level is high, say 80 to 90%, then you’re more likely to see a big impact fairly quickly on your subsequent seed–sorry, subsequent weed numbers. But similar to the seed bank input, if the seed retention level is low, say 40 to 50%, then it will potentially be a few years before you see an impact on the weed population.

So it really is very much dependent on both how much is in the seed bank but also just how much seed you’re actually targeting during the harvest operation.

Drew Lyon: Okay, there’s a number of different harvest weed seed control systems utilized in Australia. How have these systems affected or how are they affecting Australian growers and the way they go about farming?

Dr. Michael Walsh: Yeah, so, at the moment there’s six different systems and they vary in how they target the chaff fraction during harvest. The chaff fraction is where the weed seeds exit the combine during a typical harvest operation where the combine has been set up appropriately. And so these systems have all been developed to target that chaff fraction to control the weed seeds that are present.

They range in the way that they treat the chaff and that influences the adoption, if you like. So some of the simple approaches of then just concentrating the chaff material into windrows, either to leave it there in situ and do nothing; whereas other systems have been a bare cut, collecting material in carts or part of a baling operation.

So the range of options vary in terms of the, I guess, sophistication, if you like–and cost of initial setup. So something like a chaff lining system, very easy to set one of those systems up–just few hundred dollars, compared to an impact mill system which costs several thousands of dollars to purchase and install. They’re sort of the two spectrums of options for managing chaff during the harvest.

And so then becomes really very much a matter of preference for the growers. Which system do they want to try initially? And then after those initial few years of use, which system are they then prepared to graduate to ongoing use?

Drew Lyon: And what’s your current estimates on adoption of harvest weed seed control methods in Australia?

Dr. Michael Walsh: Yeah, so the current estimate based on a survey in 2019 is that 70% of Australian growers are using some form of harvest weed seed control. At the moment, they’re mostly using the relatively simple forms of harvest weed seed control, so they’re concentrating residues during harvest and then by burning those residues or leaving them in situ. Yeah, that overall very high level of adoption, which indicates to us as researchers that harvest weed seed control now is an accepted practice and that growers recognize the opportunity to use this weed control treatment at crop harvest to help manage their weed management.

Drew Lyon: Okay, you’ve spent a little time here in eastern Washington and seeing our systems and some of our unique geography. What are your thoughts on harvest weed seed control and how effective it might be here versus what you know in Australia?

Dr. Michael Walsh: Yeah, I think, well, there’s definitely some geographical challenges with the sloping hills. I mean that’s a challenge during harvest operation anyway. But I guess in that context, anything that affects the operation of the combine does affect your ability to target weed seeds during harvest. So, growers have obviously been dealing with that for a long period of time in the Pacific Northwest and they know about the combine setup, so they should be aware of how to make sure that the weed seeds are exiting in the chaff fraction. There’s obviously some systems that are just not going to work in that region. So things like chaff carts or burning operations are not really going to be an option for that region. So you’re either looking at chaff-only systems, so chaff lining, chaff tramlining, or the impact systems–impact systems that are going to be more suited to that environment in particular.

And I think that given the similarities that we talked about, targeting cereal—targeting grass weeds, and cereal crops, there should be some good learnings from Australia that the growers in that region can adopt.

Drew Lyon: Alright. So what’s next on your agenda as a Fulbright scholar in the States and then when do you get back to Australia?

Dr. Michael Walsh: Well, yeah, next on the agenda, I’ve been looking at opportunities during cotton harvest. That’s a completely different scenario. It’s a different type of harvesting system. So it’s been kind of fun playing around with those cotton pickers and cotton strippers just to see what happens during harvest to the weeds that are present. And then I guess also looking at all the other alternate technology–weed control technology research that’s underway here in the U.S.

There’s some pretty exciting stuff going on and hoping to take some of some of those opportunities back to Australia with me.

Drew Lyon: Oh perfect. Well, that’s what these international collaborations are about–sharing new ideas and hopefully making both collaborators better off in the end.

Dr. Michael Walsh: Yeah, that’s exactly right, Drew. There’s a lot of learning that goes on when we start sharing our ideas and visiting different locations and seeing how those ideas are being implemented.

Drew Lyon: Alright, Michael, I have appreciated our collaborations and your visits here in the Pacific Northwest. I wish you the best in what remains of your time in the U.S. and hope to learn more about what you’ve learned when you get back to Australia.

Dr. Michael Walsh: Thanks, Drew. And yeah, I look forward to continuing our research efforts.

Drew Lyon: As I do too. Thanks, Michael.

Dr. Michael Walsh: Thanks, Drew.

Drew Lyon: Thanks for joining us and listening to the WSU Wheat Beat podcast. If you like what you hear don’t forget to subscribe and leave a review on iTunes or your favorite podcast app. If you have questions or topics, you’d like to hear on future episodes, please email me at drew.lyon — that’s lyon@wsu.edu — (drew.lyon@wsu.edu). You can find us online at smallgrains.wsu.edu and on Facebook and Twitter @WSUSmallGrains. The WSU Wheat Beat podcast is a production of CAHNRS Communications and the College of Agricultural, Human and Natural Resource Sciences at Washington State University.

I’m Drew Lyon, we’ll see you next time.


The views, thoughts, and opinions expressed by guests of this podcast are their own and does not imply Washington State University’s endorsement.