Herbicide-Resistance in Jointed Goatgrass and Downy Brome with Ian Burke

Contact Information:

Contact Ian Burke by email at icburke@wsu.edu or by phone at 509-335-2858.

View Ian Burke’s contact page.


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Episode Transcription:

[ Music ]

Drew Lyon: Hello, and 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. We have weekly discussions with researchers from WSU and the USDA-ARS to provide you with insights into the latest research on wheat and barley production.

[ Music ]

Drew Lyon: My guest today is Ian Burke. Ian is an associate professor in weed science at Washington State University. His research program is focused on basic aspects of wheat biology and ecology with the goal of integrating such information into practical and economical methods of managing wheat in the environment. Ian teaches the undergraduate courses in weed science and cropping systems. Hello Ian.

Ian Burke: Hi Drew.

Drew Lyon: So, what do we know about herbicide resistance in jointed goatgrass and downy brome?

Ian Burke: We’re learning more every day. When I first began to receive reports about herbicides resistance in downy brome, in particular, it was from Northern Walla Walla Counties. It since expanded to almost the entire production region. We have samples of downy brome that appeared to resist one or more of the group two herbicides that we used to manage it. It’s a growing problem. I think growers are just coming to terms with the amount of money they’re potentially wasting by applying group two herbicides to manage downy brome in these areas. And I anticipate the problem growing rapidly worse. I would say we are on the last few years of this technology. Jointed goatgrass is a little bit different situation. We’ve only had one reported case of group two imazamox or beyond resistance in jointed goatgrass. The grower was very proactive and very collaborative with us, and is working to eliminate the population from his property. So, unless there are other cases out there that we don’t know about, the jointed goatgrass resistance to particularly the imazamox or Beyond is quite limited.

Drew Lyon: So I remember in the 90’s back in Nebraska, telling my growers, “We’ll never be able to selectively take downy brome or jointed goatgrass out of winter wheat.” And then we came out with these group two herbicides that could do it for downy brome and Clearfield wheat so we can take goatgrass. But it looks like that technology, getting to the end of that, we might have to go back to how we used to manage it before we had those. So, what do we learn about the biology of downy brome that might help us do a little better job of that going forward?

Ian Burke:  We’ve been working in my lab to understand vernalization traits as wells as seed dormancy traits in downy brome, and we’re learning a lot. Downy brome is the consummate avoider. So it comes up a little after the winter wheat in the fall and completes its lifecycle well before the wheat begins to head in the spring. And we know that, for instance, it appears that we have brome that really doesn’t need vernalization down in the southern part of the state, and we have brome that needs more vernalization in the northern part of the state, and we suspect that it has the ability to adapt to a change in climate and continue to avoid our inputs to manage it. The stuff that doesn’t need vernalization is a really special case where, I think, in the spring it’s physiologically tolerant to the herbicides we’re applying because it’s such an advanced plan. When it comes to dormancy traits, you know, the conventional thinking among the weed scientists that I’ve interacted with is that the seed doesn’t last very long in the soil. That if we manage the seed bank well, and ostensibly this group two herbicide was supposed to allow us to that. That we would manage downy brome to extinction. And certainly that hasn’t happened. So, what I suspect we have here is a really complex set of seed dormancy scenarios combined with much longer seed longevity in the seed bank than we anticipated. And we need to begin to understand how to rotate out of wheat and deploy some more effective strategies for managing downy brome.

Drew Lyon: So downy brome, little less so of goatgrass, but most of them tend to be more of a problem in our winter wheat fallow areas, or low rainfall areas. So, what options do we have for rotational crops and other management practices in that environment which is fairly difficult environment to be controlling these winter annual grasses?

Ian Burke: Historically it’s been the competitiveness of the wheat that’s really been to our benefit. So wheat germinates and emerges in those fallow systems. We will plant August or early September and get it a stand well before the downy brome will begin to germinate in October and November. So the wheat is pretty resilient to the competition. You know and it occur I’ve seen instances where I had significant densities of brome cause from yield loss. For the most part, it’s likely just an annoyance that fix about of the canopy and interferes with the harvest. That said, if it doesn’t merge with the wheat, it can be a significant damage. Often as much as 90 percent yield loss on the same holds true for jointed goatgrass. But it all comes up with that wheat. Then it will cause some injury. Rotational crops that appear to be viable include, of course, there’s always this spring wheat rotation where you are able to manage those winter annuals in the winter. Of course there’s a yield loss associated with that as well. More promising in my opinion is a rotation to winter pea. Winter pea forms a pretty early dense canopy, and the jointed goatgrass and downy brome to a less extent don’t appear to compete as well with it. And we have different herbicide technologies that we can deploy there. And then there’s always winter canola which is a little bit higher risk to get established and through the winter, but could potentially provide additional technologies for herbicides there as well. Either case, winter pea, winter canola, or another broadleaf crop in my view is a more viable option, and it should be something growers at least try become familiar with to use in the future so that they can have that option when they need to.

Drew Lyon: One of the new technologies I’m starting to hear a little bit about is coAXium wheat where it’s got resistance to ACCA’s group one, ACCA’s inhibitor, herbicide group one herbicide. Do you think that will play a role in trying to control some of these weeds that we can no longer seem to control so well with group two, or the LAS inhibitors?

Ian Burke: I have mix feelings about that technology. You know, historically we used the old product called Holon to control downy brome. In fact, it was one of the first herbicides introduced for the management of downy brome that actually had some selectivity. I know there might be a few that still remember it. It’s an old group one ACCA’s inhibitor. And so if that technology was used in a grower’s operation for quite a few years then the likelihood that they exist on your property, and ACCA’s resistance to downy brome is potentially high. Dan Ball, the former weed scientist down at Penilton documented ACCA’s resistance to downy brome in Oregon so we know it can happen. It was resistant to Holon. We also have those broadleaf crops I just mentioned where we can use the ACCA’s inhibiting herbicides and achieve the same selectivity. So, I think growers should view that technology as maybe a time extension tool to give you a couple of extra seasons a week where you might need it. We know that ACCA’s mode of action is highly susceptible to resistance development, and it’s nothing more than a stop dep. So, growers should be prepared to diversify through crop rotation and deployment of those technologies rather than maybe picking of one of these herbicide-resistant weed systems to the ACCA’s inhibitors.

Drew Lyon: And it’s kind of unfortunate that we’re getting this after we’ve kind of burned through the group two; it would have been nice to have the other rotate between the other two while they are both still effective. But at this stage, I tend to agree it by extending the inevitable, and these other more ecological, more management strategies might be what we’re going to have to go back to here.

Ian Burke: One of the things we know about herbicides resistance is that, based on some really good recent research, mixing two different herbicides mode of action that both have the same activity on the same weed is a good resistance management strategy rather than rotation of herbicide modes of action. And the really frustration thing about that bit of data is that, the group two herbicides don’t mix well with the group one herbicides. And so we’re really stuck even with these new technologies coming along like coAXium wheat rotating tool to broadleaf that group one herbicide has to go in the tank by itself. So we can’t take advantage of that new knowledge in managing this herbicide resistant weeds. And I agree if having both of these technologies would’ve been better, but they’re still not compatible.

Drew Lyon: Okay. Well, herbicide resistance and these winter annual grassy weeds aren’t going away. And I look forward to hearing more about weed control efforts and the work you’re doing in the future episode of the week beat podcast. Thanks for joining me today Ian.

Ian Burke:  Thanks, Drew.

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Drew Lyon: Thanks for listening to the WSU Wheat Beat podcast. If you have questions for us, that you’d like to hear addressed on future episodes, please email me at drew.lyon@wsu.edu. You can find us online at smallgrains.wsu.edu. You can also find us on social media on Facebook and Twitter @WSUSmallGrains. Subscribe to this show through iTunes or your favorite podcasting app. The WSU Wheat Beat podcast is a production of CAHNRS Communications in the College of Agricultural Human and Natural Resource Sciences at Washington State University. I’m Drew Lyon; we’ll see you next week.

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