Weed Control Issues for Prickly Lettuce, Russian Thistle, and Others with Ian Burke

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


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Episode Transcription:

[ Music ]

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 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 podcasting app and leave us a review while you’re there so others can find the show too.

[ Music ]

Drew Lyon: My guest today is Ian Burke. Ian is a professor in wheat 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 weeds in the environment. Ian teaches the undergraduate courses in wheat science and cropping systems. Hello, Ian.

Ian Burke: Hello, Drew.

Drew Lyon: So, what are some of the weed control issues you’ve been dealing with these last few months?

Ian Burke: What– I’m always amazed that I get to go back to prickly lettuce, which is one of the first weeds I began to work with here in the Pacific Northwest, and now 13 years on. And, I still get a lot of questions about prickly lettuce. It’s a persistent weed. And, it’s difficult to control in just about every environment. And, that’s one that we’re seeing continually being just a nuisance.

Drew Lyon: I know anywhere you drive in eastern Washington, the road sides are just loaded with prickly lettuce. What makes prickly lettuce such a tough weed to control?

Ian Burke: It’s pretty adaptable. In fact, in my travels in the world, I’ve managed to take a picture of prickly lettuce in every country I’ve visited. It’s just ubiquitous. It’s just everywhere. It’s a native of the eastern Mediterranean. So, think countries like Turkey and Greece. In fact, we think that prickly lettuce is the progenitor to cultivated lettuce. So, even though they’re considered separate species now, there’s a little bit of prickly lettuce in every lettuce we eat. Prickly lettuce can be a facultative winter annual. It can come up in the fall, and in a mild winter, overwinter, and set seed in the spring. It appears to germinate all spring, and into the early summer. And, produce some amount of seed. The seed is wind-borne, and can move great distances. I know I’ve had prickly lettuce appear in my gutter, many feet off the ground. And, I know there was no prickly lettuce around my house setting seed, because I’m a weed scientist, and I manage that stuff. [ Drew chuckles ] And so, it’s just a– it’s got a set of attributes that make it a particularly difficult thing to manage.

Drew Lyon: I think I’ve noticed, just walking around fields this spring, that there’s prickly lettuce of all sizes. So, obviously some of it came up last fall. Some of it this winter. Some of it’s just coming up, which poses a bit of a control issue, because the amount of herbicide you might need to control that thing that came up in the fall is different than what you might need for the spring, and–

Ian Burke: Indeed.

Drew Lyon: So, what have you found to be some of the most effective approaches for managing prickly lettuce in wheat and other systems?

Ian Burke: So, I always try and remind growers that it has a different name. It’s also called the compass plant. Particularly here now in late spring, you can see prickly lettuce germinate, and it germinates bolting. So, when it germinates before the equinox, it usually forms a rosette. And, it looks like every other little aster plant, weed, that we see in the field. You know? The leaves are laying on the ground essentially. And, when it germinates well after the equinox, it’s bolting already when it comes out of the ground. The day length triggers that bolting. And, if you look at it carefully, you’ll notice that the leaves are not held flat, or facing up. They’re actually turned 90 degrees to the stem, and they orient themselves north and south. So that the leaves are actually pointing north and south. We call it the compass plant because of that. And so, there are a number of herbicides that are pretty effective for managing prickly lettuce if you’re using herbicides. But, you have to understand that if you’re just using a set of nozzles that point the spray straight down at the ground, you’re trying to get the spray droplets to stick to the sides of the leaves. And so, I usually recommend growers, if they have a prickly lettuce issue, switch nozzles out, and use something that has some angle to it, or angle their boom in some way. And, they have to recognize that the leaves of the prickly lettuce are being held in a way that the spray droplets just aren’t getting on them.

Drew Lyon: Okay. Intersting.

Ian Burke: So it’s a different– sort of a different approach to thinking about the problem. If you do have to reach into the herbicide toolbox, you know, to name a few trade names, there’s Huskie, and the new Talinor. And, depending upon what system you’re in, you know, some of the growth-regulating herbicides appear to be effective. There are pockets of 2,4-D resistance out there. And, where we see 2,4-D resistance occur, it’s usually in a system where growers have been using glyphosate plus 2,4-D in a fallow situation, or they’ve been using low does of 2,4-D in fallow– or in CRP ground. And, that’s just selected for a localized biotype, but that doesn’t really respond to the prickly lettuce. And, in those instances, you want to make sure you deplete the seed bank, and stay on top of it. The nice thing about prickly lettuce is, in just a few short seasons, you can really deplete the seed bank quite quickly. Most of the stuff that falls as seed germinates pretty quickly, within that season. So, if you’re successful for three or four seasons, you can usually see that the biotypes change over.

Drew Lyon: Okay. And, if I recall, prickly lettuce, along with Russian thistle, are two of the weeds where resistance to the ALS inhibitor, Glean– well, develop very quickly. So, it all seems to be capable of developing– you mentioned 2,4-D, but also the ALS inhibitors. So, that’s another issue we have with that. But, these current products, Huskie, Talinor, still pretty effective on them?

Ian Burke: Appear to be pretty effective. I’ve also had decent luck with Sharpen and some of the other PPO inhibitors. But, you do have to– again, you have to make sure you have good contact, particularly when you’re using something like Sharpen. You’ve got to make sure you cover those leaves, because it’s contact high herbicide, and it doesn’t translocate. And so, if you’re using those, if you’re not thinking critically about how to cover those leaves up with droplets, you’re likely to see a, just not a good outcome with a herbicide input. Prickly lettuce also appears to be pretty well adaptable to reduced or minimum tillage systems. When you introduce tillage, I typically see prickly lettuce sort of fall away. It just sone’t seem to respond to tillage as much. You mentioned those chlorsulfuron, Group 2 herbicides. The ALS inhibitors. And, it’s another first of ours, the PNW was actually the first to document and discover ALS resistance, and it was in prickly lettuce. And, it was actually pretty close to Pullman. It was just down in Lewiston that that first biotype was discovered. So, prickly lettuce has been around for a long time. It’s been adapting to many of our inputs for a long time, and will likely continue to do so.

Drew Lyon: So, you mentioned this, how the plant changes architecture, I guess. Rosette if it comes up prior to the equinox, or the solstice. So, prior to– what is it? Well, we go to March 21st, or whenever that is. If it comes up before that, it tends to be a rosette. After that, tends to– so, that also might explain why maybe you have differences in control. Because it’s probably easier to cover that rosette than those plants that are now standing up and bolting.

Ian Burke: Yes. And, that’s not something I’ve ever tested in field work, but intuitively, it appears to me that the bolting habit where the leaves are not held up for receipt of that herbicide spray, that just appears to be a critical factor. And, make sure you get good coverage. You just got to be cognizant of what the plant looks like. And, you could say the same thing about Russian thistle, with its tiny little leaves, you know. You want to make sure you cover that plant really well. And so, droplet contact to the leaves is really critical. And, whatever you can do to maximize that will likely help a lot, and should likely give you a good outcome.

Drew Lyon: Could explain maybe why Roundup might be not real effective if you’re using low rates, and big droplets. It might not be the best approach to a plant like prickly lettuce.

Ian Burke: Prickly lettuce has another interesting attribute. It actually has among the highest quality rubber in the plant kingdom. We did a little bit of work early in my career here at Washington State University. And, although we never figured out how to milk the prickly lettuce for the rubber, we were able to find that it had very high quality rubber. I’ve observed that glyphosate doesn’t work very well on many species that have a latex and rubber in their sap.

Drew Lyon: Okay.

Ian Burke: And, that could include some of the morning glories, for example, in the Southeast. Not the kind of morning glory we have here. So, the — whenever you see that white sap, I typically tend to associate that with a reduced efficacy of glyphosate. And, you want to add something in to the tank to control the prickly lettuce in addition to the glyphosate. When you’re using glyphosate plus 2,4-D, and the prickly lettuce is evolving, or has evolved 2,4-D resistance, that also can manifest itself in this weird, hardened-off prickly lettuce that now doesn’t respond anymore to systemic herbicides. And so, what we’ll see is a prickly lettuce that has swollen stems. The leaves appear malformed, but it’s all still green. And, over time they do eventually recover and produce new shoots and eventually seed. So, they’re using moisture in that fallow situation. So, when you see glyphosate and 2,4-D fail, probably because the 2,4-D has antagonized what little glyphosate activity there was, you need to go back with a contact-type herbicide instead of attempting to use more glyphosate in that situation. So, there’s a — there’s some idiosyncrasies attributed to the biology that the prickly lettuce rubber and latex, the shape and how it forms its leaves. Took a little bit of thought to just think of ways to approach– to manage it.

Drew Lyon: OK. Do you see any new technologies come along to help us battle weeds like prickly lettuce and other weeds in fallow?

Ian Burke: I do. I’ve had the opportunity to work with what I would call a weed-sensing sprayer here last season, and we intend to expand that work here in the coming season. And, the weed-sensing sprayer- you know, there’s multiple companies that sell technology like that where the sensor head can detect that there’s something green in the field, and activate the nozzle to spray. And, that fundamentally transforms what you can do to– and, the herbicide technologies you can deploy in fallow, if you’re dealing with prickly lettuce in fallow. And so, I encourage growers to take a look at those available technologies. What it really finally does is, it changes the equation on the cost per acre. And, typically a grower would only need to spray 20% of the acre if they could use this sort of technology. That would be the typical use. And so, you– instead of spraying 100% at X rate, they could spray 20% at maybe a more elevated rate, or with a number of other active ingredients in the tank to facilitate better control. And, that would be economically easy to achieve, because you’re not treating the entire acre. You’re treating a very small portion of it. And so, those sort of technologies, I think, will help us with weeds like prickly lettuce and Russian thistle, where we’ve been sort of relying on incrementally increasing our rates of a couple of relatively inexpensive herbicides. And now, maybe these new technologies might help us.

Drew Lyon: Yeah. Sounds like a really interesting technology that may really help us get out of this situation we’re starting to run into with glyphosate resistance, particularly in some of our fallow situations. What about a weed that I hear a lot about? I think a lot of growers probably read about it in their popular press magazines. Palmar amaranth and waterhemp seem to be taking over the country. Are they in Washington yet? And, if they aren’t are they likely to come here, you think?

Ian Burke:To my knowledge, they’re not in Washington yet. And, I hope it stays that way. Palmar amaranth is pretty well adapted to the environment that would be present in the Columbia Basin. It’s a native of New Mexico and Arizona. And, it evolved to grow in those really dry environments. And, when it’s spread into relatively more moist environments, areas like Georgia in the mid-South, this is a plant that will grow two inches a day, given ideal conditions. And so, we have very nearly ideal conditions for its growth in the Basin. And, it would be very damaging to crop rotations that would include potato, onion, corn. Those are rotations that are pretty susceptible to something like a palmer amaranth. And, it’s really expensive to manage. And, it really makes a lot of seed. So, in many ways it’s nearly intractable where it does occur. It does really fundamentally change the cropping systems where it’s become resistant to glyphosate, and infests areas, like, where they grow cotton and peanut. So, to my knowledge, it’s not here. We definitely need to keep it that way. If it’s ever discovered here, I think that we need to make a strenuous effort to eradicate it. I think it’s in the process of being listed as a noxious weed in this state, and it definitely should be. The benefit of having it not present is that it really helps our seed industry out quite a bit, because there’s a growing interest in making sure that the seed that’s planted across the United States, like corn– you know, we grow a lot of corn for seed here in this state. That that corn seed is clean of any weed seed, including things like– particularly palmar amaranth.

Drew Lyon: Right

Ian Burke: So, being able to say that we don’t have it is a real benefit to our industry.

Drew Lyon: Okay. So, not a problem yet. Could be in the Basin, but probably because of its warm season nature, probably not going to be a major weed problem in our winter wheat-growing areas?

Ian Burke: I don’t anticipate it being a real issue in the summer fallow areas. And, you know, redroot pigweed is here in the PNW, in the high rainfall zone. And, in certain areas of the intermediate rainfall zone. And, wherever redroot pigweed can survive, palmar amaranth can. But, redroot pigweed is a shadow of what it can do in more temperate climates.

Drew Lyon: Yes. Alright. Well, appreciate you coming in today to share what you’ve been thinking about and working on here Thanks, Ian.

Ian Burke: Thanks Drew.

[ Music ]

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 podcasting 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.

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