Category: Weed Science

Join Emily and Nevin as they discuss the differences between Integrated Weed Management and Integrated Pest management within Weed Science.

This transcript has been edited for clarity.

0:19 Hi everyone, and welcome to another episode of Farm Sci-Ed, the show where we go into the science and education behind farming. I’m Emily Stine, and today we’re continuing the conversation in IPM in different disciplines. Today we’re talking to Nevin about integrated weed management and how it relates to integrated pest management. Nevin, can you describe the difference between integrated pest management and integrated weed management?

0:38 Nevin: Yeah, integrated pest management is something that is, is something that was invented, conceived at first by entomologists. And the idea in – in IPM for weeds, or integrated weed management as some might call it, is basically trying to use a multitude of approaches to reduce herbicide use. And so is there a way we can create different weed control strategies, uhm – such as cultural, mechanical, uhm and biological control in order to reduce the number of herbicides that we – that we’re applying. And the the thought on that is that uh reducing herbicide use may reduce cost, for farmers. uh It reduces exposure of herbicides to the applicator, which sometimes those those can be toxic or carry some sort of health risks. uh There’s environmental benefits too, some herbicides are – can leach into groundwater and cause off-target uhm injury to weeds – or uh to plants – desirable plants if applied improperly. And all these things together is a good reason why we should try to reduce herbicide use if we can. But there’s also a lot of benefits of herbicides as well. I mean, generally they’re gonna be easier to integrate into a system, so if we’re looking to uh incorporate tillage or cover crop, that might require farming a different way, uh by buying a new piece of equipment, adjusting some of your farming practices. So it’s a bit easier to integrate herbicides into the system. uhm It it it’s also could be a cost saving to add approaches other than just using other herbicide practices. So, uh it it’s a trade-off, everything in agriculture has a trade-off. But basically, uhm that’s what integrated weed management is in a nutshell. It’s trying to use diverse uhm management approaches in order to reduce the the usage or the need of different herbicides.

2:46 Emily: You’ve previously mentioned something you call “the critical period” when it comes to weed management. Can you expand on that concept?

Nevin: Yeah, so this is sort of something that I think kind of – it is the closest thing we have to what would be considered an “economic threshold” or an “economic injury level” in entomology, when they talk about IPM. So in entomology, I think what they’re trying to do is figure out at what population threshold a certain insect pest is going to cause enough injury that it’s going to be justified to use an insecticide. And if you’re insect population never gets above that threshold, then there would be no reason to uhm apply that that insecticide. And so a lot of entomology or – a lot of IPM practices based on entomology are formed on the idea of y’know, you’re going to be scouting for the pest, you’re going to be tracking the pest throughout the season, you’re going to know what these thresholds are, and and then do a lot of research to establish these thresholds and sort of guide these thresholds. uhm And those strategies in a lot of ways just don’t work for weed science. And so we uhm – we can’t really uhm, scout for a weed, so it’s in the soil – the seed’s in the soil, and it’s going to come up that next year. There are ways to sample the soil, extract that seed uhm, figure out what that seed is, but those are really difficult to do in a timely fashion and is almost always going to be uneconomical. So it it’s very difficult to scout for weeds in an agronomic setting, and uh as far as thresholds go, uhm there is always going to be enough weeds present in the soil to cause economic injury. All of the time.

There’s never going to be a situation that – I wouldn’t say never, I’ve heard stories of of high-value vegetable producers putting something like a soil sterilant on the ground that kills everything. But that’s very expensive and not very practical. But there’s rarely going to be instances where there’s so few weeds that they won’t have an economic injury.

So uhm you can’t really scout, and you just should expect that every year there’s enough weeds to cause economic injury. So then y’know, how do we sort of model or determine when and when not to control weeds? So this idea was proposed called the “critical period of weed control” which is where you do a series of experiments where you do a series of experiments where sort of half the study you control weeds, maybe for the first uh week, and then the second week, and the third week and the fourth week of the field season. So you’re gonna let uh plots be weed-free for a certain number of weeks, and then you stop controlling weeds. So you might have a treatment where you have a one-week weed-free period, and a two week, a three week and a four week. And so the longer those weed-free periods are, the less yield you’re going to lose – that’s pretty simple, that’s pretty easy to understand. On the other end, of that experiment, what you do is you let the weeds appear all season long, and then later on in the season, you start controlling those weeds. And so you’re going to start controlling those weeds let’s say four weeks after they’ve established all season and then five weeks and six weeks. And so, on the front end, you have different weed-free periods, and then on the back end you have different periods of weed control. And when you link those two values together, you can model then “okay, to preserve – let’s say – 95%, 98% of the yield potential with this crop, you need to control weeds from two weeks from planting until four weeks to harvest and early on in the year, we can let weeds grow and then later in the season we can let weeds grow as well.” So that’s going to prevent at any economic yield loss. And so that’s kind of the methods we can do with yield science as far as modeling when, when not to control weeds and so the threshold really doesn’t have to do with the population of weeds, the threshold has to do with the stage of crop production – or, certain stages of crop production that are more susceptible to yield loss.

6:55 Emily: So in your mind, should integrated weed management be focused on preserving yield, or eliminating weeds?

Nevin: That’s a good question. And uh, one of the problems with the critical period of weed control is it it’s focused on preserving yield; so that’s an economic benefit. But you’re producing all of those weed seeds, and so those weeds that you decide you can let grow for these periods, especially on the tail end, are going to produce more seeds. And so they will be contributing more weed seeds in the soil, which might create more problems in the future and it also sort of ignores all the other problems with weeds. And so we have direct costs of weeds, which is generally competition and yield loss, but there’s also indirect costs of weeds.

So, we have potential for weeds to contaminate: weed seeds to contaminate grain that we’re harvesting, or lower quality, and those may not be factored into this equation, so we might say that if you left y’know, weeds until the end of the season, you’re not having that much yield loss, but you also might be sucking a bunch of palmer amaranth seed, let’s say into your combine, which is then gonna create problems. Weeds can also be hosts for insects and pathogens, and so that model also doesn’t really take into account those issues. And so for – although the critical period of weed control is a way to model when or when not to control weeds, in a lot of ways it’s a bit too simplistic.

Additionally, this idea of waiting until y’know, two or three weeks into a season to control weeds, uhm while that may work, it ignores how a lot of our herbicides are used. And generally, in weed science, the best time to apply herbicides are going to be before the weeds ever germinate – or at least before they emerge from the soil. And so we can put on soil-active herbicides early in the year, to prevent weeds from emerging from the soil and it’s easier, generally to control a weed before they emerge, they’re gonna have less yield impact because they never actually come out of the soil, and these models sort of ignore that. And so, for a large part, this critical period idea ignores some of these issues and is simplistic for what farmers actually need to do.

9:01 Emily: So then how does integrated weed management differ from resistance management?

Nevin: So, uh one of – one of the problems with integrated weed management is that the idea is that you’re trying to reduce pesticide use – or, herbicide use. So, okay, if you throw in a cover crop, and you do this sort of tillage strategy, and maybe you plant your crop a little earlier or a little later or at a higher density, you can reduce your reliance on herbicides. And what that generally means is that you’re going to be using less herbicides. And not less herbicide, but less number of herbicides.

So, a farmer might be using let’s say, in a corn field, four to five active ingredients sometimes, so different types of chemicals to control weeds. And so with this integrated weed management does if it’s successful at reducing herbicide use, what that means is you’re going to reduce it down to two or one herbicide. And a big one that would be reduced, especially since – the the herbicide that would be then the herbicide of choice, especially after the introduction of herbicide resistant crops through transgenic technologies and gene insertion would be glyphosate. And so what you’re doing now is you’re reducing the need for these other herbicides, and you can just get by with one herbicide, let’s say, or two herbicides in large part, that means glyphosate. So what that does then is it puts a tremendous amount of selection pressure on the weeds to evolve resistance to glyphosate. And so, sometimes what integrated weed management does is it makes it – it reduces your number of herbicides you’re using so that one herbicide or two herbicides that are left are more likely to get resistance developed. And that’s a problem.

And so, in the long term, thinking about all these different strategies, you know, is the goal to reduce herbicide practices, or is the goal to preserve all these different tools? So as soon as we have resistance developed to a certain herbicide, that herbicide might not be able to be used again in that field for a very long time, potentially forever, because of those resistances development. And so, integrated weed management also seems to reflect that as well. And so, resistance management, which is a different idea, is you use whatever tools are available to spread out that selection pressure so it’s not just focused on a single herbicide. Or it’s going to be focused on several herbicides.

So the idea of herbicide resistance management is you are going to use cover crops, you are going to use y’know, tillage where appropriate, you are gonna use cultural practices, but that’s in addition to applying any – as many herbicides that are useful. And trying not to rely on a single chemical or a few chemicals a year, year after year after year. That way, you’re spreading off the selection pressure and the idea is, basically, the more diverse your management practices are, the harder it is for a particular weed species to adapt to that and become very difficult to manage year after year after year.

12:05 Emily: Do you think integrated weed management is sustainable?

Nevin: So that really depends on what you mean by “sustainable.” And uh that’s that’s a tricky term. Y’know, I like to think of sustainable meaning “is this practice gonna be something that farmers can keep doing for thirty years?” y’know – “can they keep using that?” And one of the problems, like I said, with integrated weed management, is you tend to narrow the number of herbicides you use and that’s going to place a big burden on those weeds to become resistant to that. And so in some points, I would say it’s probably not the best strategy. Using herbicide resistance management, where you are using a diversity of herbicides, along with multiple approaches, to really broaden that selection pressure probably is the best management practices for some folks. Although, it’s very complicated to implement that, because it’s very complex. And how do we take a very diverse herbicide management program, that may be costly because you’re using multiple herbicides, multiple cultural approaches, and then you have to add in other practices – your fertility, and disease, insect management, uhm it just gets to be actually quite complicated. But in some ways, I feel like integrated weed management or IPM for weeds; this idea of narrowing down the use of herbicides, over time may not be the best strategy.

13:24 Emily: Well folks, there you have it. Today we talked to Dr. Nevin Lawrence about integrated weed management and how it differs from integrated pest management within weed science. Join us next time as we talk to Bob about how integrated pest management relates to plant pathology, and we continue our exploration into integrated pest management. Find us on twitter @TheFarmSciEd or visit our website at farmsci-ed.com for transcripts and other episodes. Have a good one!

Join Emily and Nevin as they discuss the details about the data collected for Nevin’s palmer amaranth and dry edible bean studies.

This transcript has been edited for clarity.

0:19 Emily: Hi everyone, and welcome to Farm Sci-Ed, the show where we go into the science and education behind farming. I’m Emily Stine and today we’re talking to Dr. Nevin Lawrence, weed scientist, about the data he collects as part of his palmer projects. So sit back, relax and let’s go find out what data nevin collects.

So Nevin, what kind of data do you collect for your palmer studies and how do you go about collecting it?

Nevin: I guess we could classify the data in two different ways. We take weed control data and we take crop performance or crop yield data and we kind of think about that in two separate separate ways. So we have the, “what is the effect of the treatment on the weed population?” and then “hat is the corresponding effect of that particular weed population as controlled or not controlled by that treatment on on the crop?” And so we divide that into two – two different groups for uh weed control data throughout the year.

Maybe every two weeks we take a visual assessment of uh how good the weed control is and the way that we we do that is we always have a non-treated check plot, um and that’s a plot where we don’t do anything. And so our normal plot size for a dry edible bean study is 30 feet long and then uh usually four to six rows and we’re on 22 inch rows so that’s either seven and a third foot or that’s 11 feet and how wide the rows are but within that those treatments, we have one that we didn’t do anything and that one will usually have no dry bean yield because the weeds completely uh took over and the crops dead and non-existent. uh And so we have a yield of zero in those plots, but we also have weeds which are seven feet tall and that’s sort of our baseline of what happens if we do nothing and then when we take this visual assessment throughout the season, we kind of compare the other other plots to that one. So we we do this on a scale of zero to 100 and then we know what zero is and then if we have a really good treatment that we’re pretty sure is going to control all the weeds in in the study design we we keep it there and that’s what we call the the weed free check and that’s going to be 100 control of the weed.

But sometimes we don’t have that option especially in these minor and specialty crops we just don’t have good herbicide options a lot of times. And so we’ll have another treatment where we will go through and have to hand weed weekly which is which is gonna be a lot of work, but we’ll physically remove the weeds all use – all season long and so that way we have a known zero percent control and a known 100 control that we can use to compare the weed – the weed control data.

Additionally, besides in that visual control which which is helpful but it’s it’s not hard data, there’s a little bit of bias in that, is we will we’ll also go through and physically count how many weeds are within each plot and we do that depending on the study. It depends on how much area we’ll count, but we usually use what we call a quadrat which is a square, rectangle piece of pvc pipe or metal and those are various sizes and we’ll we’ll stick that in the plot and we’ll generally this is a rule of thumb – that it’s sort of just arbitrary – we try to count at least a square meter per plot of plants to get that population. So we’ll count how many weeds there are, and we’ll also count what the breakdown is of species.

That’s important because if we have a a weed control plot that fails early in the year, uh or it fails to control the weeds earlier in the year, we’re going to have a lot of early to emerge weeds in that plot so kochia, lambsquarter, those are the earlier weeds to emerge and that’s going to prevent later to emerge weeds from ever emerging because there’s there’s are going to be quite a bit of competition and presence of weeds in that plot. So what we can oftentimes see is if we’re looking let’s say, at palmer amaranth control, some of our worst performing plots actually won’t have any palmer in them but not because they controlled the palmer, it’s just because there was so much early to emerge weeds in them and so these counts are important to see not only what the density of weeds are but what species are coming up and when.

So we take these several times throughout the year um you know, probably three to five times we’ll we’ll do a weed count and just to kind of give some perspective on that you know a weed-free plot as i said earlier that’s going to have zero weeds in it, but the non-treated one can have hundreds, um sometimes even thousands we’ve seen weeds within a square meter, so it’s it’s pretty difficult to actually do that. You’re – you’re gonna be spending um 30 minutes on on one plot just on your hands and knees counting those weeds. uh Towards the end of the year we’ll also take biomass in those plots as well and so what we do with that is from that same quadrat we’ll go in and we’ll – we’ll cut using a knife – a rice knife actually – it’s a knife for hand harvesting rice but we’ll physically cut all the above ground biomass from weeds within that plot and then get then weigh that per species.

Occasionally the other thing we’ll do is we’ll also go in those plots and remove seed heads when they’re mature but before they shatter.
That way we can estimate seed production too. So from a given treatment, which is you know fairly small – you know we’re seven and a half feet by 30 feet at the smallest – we could say this treatment is going to produce or it has the ability to control, you know, this percentage of the weed population but you’re looking at under worst case scenarios, you know, potentially 30 palmer plants per square meter which is quite a bit and those 30 palmer plants each can produce let’s say 50 to 100,000 seeds. and so that can give a – when you extrapolate out to a whole acre, that gives the farmer an idea of what that treatment may or may not do in their field.

Right, as far as crop information that we collect, we we do stand counts throughout the year, so we’ll do stand count at planting and then we’ll – if we have zero yield in some treatments because it completely failed to control the weeds uh by the end of the year, there might not be any dry beans in there. So we can see when that stand was lost. We also take measurements of plant physiology – so how um tall is the lowest leaf, what’s the height of the – the pod height throughout the season and that’s going to be impacted by uh weed presence. So as we have more weeds, the plants going to potentially grow taller and so we’re going to have these these physiological changes and those could have yield impacts as well. So we look at what we call yield components and so, with dry beans that would be the number of pods per plant the number of seeds per pod so in a good dry bean uh plant you’re gonna have five to seven seeds per pod and uh when we have a high weed pressure, that might get reduced to one to three and so that’s a pretty significant yield loss right there.

We also look at test weight or the um the the weight of 100 seeds and so we’ll – we’ll physically take 100 seeds out, count them out 100 and then weigh those for each each treatment. Or we’ll sometimes do a thousand seed weight counts, and what that does too is it tells us we have a larger bean or a smaller bean generally you want a larger bean um but with a lot of wheat competition that the bean actually does become smaller and then finally just yield: how many pounds or how many tons per acre or tons per hectare of dry edible bean yield did we receive in those in those treatments?

8:17 E: Why do you collect so much data?

N: Yeah uh it is a lot of data. And not only is it a lot of data, but all the data we collect uh the majority of it’s probably in the last week of the crop so it’s it’s um it gets pretty busy that time of year. But what we want to do is get a thorough understanding of how the weeds are competing with the crop and what the impacts are.

So for example, um we might measure a yield reduction, but it’s important to know what the mechanism that yield reduction is. Is it because we’re having a smaller test weight? Are we having fewer pods being formed? Are we losing stand? Are we having fewer seeds per pod? All that sort of plays into what why the yield can be reduced and dry bean in particular. And so we’re trying to understand the nature of how that competition is occurring.

The other thing is we know what the end of the season um weed biomass is and density, and so sometimes uh plots that are looking good early in the year, they’re not looking that great at the end they’re not looking much better than some of the treatments been poor all year, but the yield impacts really aren’t that bad. And so what happens, is those plots because we’ve been tracking weed density throughout the year, we know that maybe those weeds didn’t come up until July or maybe even August and we’re harvesting the crop in September. And so although there’s there’s quite a bit of um emergence it was late enough that most of the yield inputs into the crop or the physiological processes that need to occur before yield, have taken place – that have taken place before those those weeds emerge.

And so there’s a lot of things we can do to link that up and that helps us know – um you know if I get a phone call from a dry bean grower that you know “we had a huge escape of of a particular weed, uh you know it’s getting harvest season what do I do?” depending on when those weeds emerged uh we’ll we can – we can inform him that you know if you harvest now there’s not gonna be that tremendous amount of uh yield loss, or we can tell them uh yeah actually um they’ve been growing all season long you’re not going to get much out of there. We also could tell them that hey your your test weight’s going to be a bit lower so you’re going to get dinged uh when you try to sell those beans at the elevator because they’re not as large uh the quality is not as good and so that’s some other components. It’s necessary to know this that we can inform growers of what to do and what to expect from different populations of weeds and what the value of using other treat – certain treatments are compared to other options they may be doing.

10:50 E: Well folks, there you have it. Today we talked to Dr. Nevin Lawrence about the data he collects as part of his palmer amaranth studies, why he collects it, and what he can then infer from that data. Join us next time as we continue examining what goes into the research in plant pathology, entomology, and weed science. Find us on twitter @TheFarmSciEd

or on our website at farmsci-ed.com for transcripts and more information. Have a good one!

Join Emily as she talks to Nevin about what weed competition is and why managing fields for weeds is important.

This transcript has been edited for clarity.

0:21 Emily: Hi everyone, welcome back to Farm Sci-Ed, the show where we go into the science and education behind farming. My name is Emily Stine and today we’ll be talking to Dr. Nevin Lawrence about weed competition and how it relates to his studies as a weed scientist. So sit back, relax, and let’s go find out all about weed competition.

0:43 So Nevin, can you explain what weed competition is?

Nevin: Weed competition is uh simply the negative impacts on fitness to a plant caused by neighboring plants of another species. And this is most easily understood in the – in the terms of crops -with crops being competed against for resources by weeds.

1:07 E: And what is it that weeds compete for?

N: Usually, when we talk about weed competition – uh weeds and crops are competing for water. So especially in – you know – dry land agriculture where you might not have enough water for optimal crop yield, when weeds are using some of that available water in the soil profile, you can have additional shortages to the crop. Nutrients, so fertilizer or just the nutrients that are naturally there in the soil, sunlight, and so you can you can have a tall plant that’s blocking some sunlight from reaching the bottom and that’s going to interfere with the optimal photosynthesis. And then sometimes also space is included in there as well – that they’re they’re running out of space because of the number of weeds in the field for a particular crop.

1:59 E: How early does competition begin?

N: So competition – uh – when we think about it in terms of nutrient or resource competition – so they’re competing for a a resource that has to occur; you have to have a limited resource for for the competition to be to be happening. So if we think about planting a crop – let’s say corn – and you’re going to put in a starter fertilizer, well the corn is not going to be using all of that fertilizer right away. It’s gonna have to get to a certain height before it’s starting to need, let’s say if you’re doing a type of farming where you’re gonna be putting two applications of fertilizer on, there’s gonna be a point earlier on the season where it doesn’t need it yet, based on growth stage, that second fertilizer application.

So there’s there’s enough fertilizer – more than enough for for – let’s say that corn plant in this example, so we can imagine early on the season uh when we’re preparing the seed bed, everything’s just perfect and the the crops just coming up, there’s probably enough sunlight, space, water, and fertilizer for all the plants that are grown in the field – including the weeds. So we wouldn’t think that nutrient competition or resource competition’s occurring right early in the field. But we also do sometimes see yield impacts from early season weeds. But this isn’t generally considered to be caused by resource competitions. Instead it’s caused by something called the “shade avoidance response.”

3:35 E: What is the shade avoidance response?

N: Plants absorb certain wavelengths of light and they reflect other wavelengths of light. The reason why plants are green is because they’re reflecting green lights; they’re not absorbing that green light. And so, when a plant is is hit by sunlight and it it sends off certain wavelengths, neighboring plants can detect the presence of that particular plant based on the reflectance or changes in the way the wavelengths of of light that’s hitting them. So in particular, what happens is plants are able to change – detect changes in what’s called the red to far red ratio.

So red light is the light that we see, far red is uh red light that’s on a wavelength that we we cannot see. And so those changes in red to far red ratio, plants can detect that and those changes occur because of neighboring plants; either the light reflecting from the plant to the soil or to the neighboring – just directly to the neighboring plant. But they can detect that.

So plants can detect the presence of other plants nearby and just the simple act of detecting those other plants nearby, causes what we what we refer to as a “shade avoidance response.” So what they’re trying to do – the plants – is they’re once they know that “okay there’s another species nearby,” is they’re going to try to grow in a way to avoid being shaded.

They don’t want to be the lowest plant in that canopy, so they’re going to try to grow taller and so this is – this is called the shade avoidance response. And what that means is the plants will actually grow taller. We can also see changes in leaf morphology – leaf morphology. So the angle that they uh are going to hold their leaves up and so instead of being – let’s say – flatter, they’re going to be more upright. They might have smaller leaves because they’re putting more resources getting tall and all these changes that occur and not just with crops but also with weed species is in response to neighboring plants. They’re trying to avoid being shaded in the future from competition. uh

And what can happen though when we think about crops is uh when they’re putting these resources into growing taller and potentially smaller leaves, they’re going to be putting less resources into other things. Particularly when we think of a grain crop – so corn, soybeans, dry beans, peas, wheat – these plants which produce grain that’s harvested, less resources are going to go into that grain and so you might have a decrease in yield just because these plant – these weeds are nearby. And these weeds are nearby and this this response can occur when the weeds are very small and at a point where they’re not actually competing for resources yet.

And so what can happen in a farmer’s field, for example, is you might control the weeds when they’re very small so they emerge uh you’re you’re – through tillage or through an herbicide application – you’re gonna, you’re gonna kill all those weed species off. But they’re present for just long enough to alter the red to far red ratio reaching the crops. And that might trigger the shade avoidance response and lead to decreases in yield or yield potential even without any resource competition taking place.

7:10 E: Can you explain how the shade avoidance response ties into your research?

N: Yeah, uh so we we just, we’ve got a couple projects we’re looking at this. But one of them is – uh – we just finished, actually it’s it’s currently being prepared for publication uh from a former grad student – Clint Bierman and uh what we’re looking for is how long you need to keep the crop weed free to preserve maximum yield. And this is a long time old concept in weed science. It’s been done for a long time, and so what you do is you’ll start weeding a plot with with a hoe; you won’t use any herbicides and so it’s a very time consuming experiment.

But you’ll you’ll keep out of the plot for the whole season and then you might start – in this case it was dry beans – so when the dry beans hit the first trifoliate, so the first set of trifoliate leaves that come up will start weeding then. So we’re allowing a few weeks of weeds to be present and the next time we might start at the sixth trifoliate. And so what we see is as you let weed competition go on longer and longer and longer the yield goes down and that’s not very surprising.

But one thing that we did with this experiment is um in half the plots we had the same amount of weed-free periods so we’re removing these weeds by hand throughout the season for different lengths of time, but for half the plots they received what we call a soil active herbicide treatment at planting and so this was a a pre-crop emergence. So before the crop emerged, we put down an herbicide that’s active in the soil and it controls weeds after they germinate. And so that’s when the roots first emerge from the seed. But before those plants emerge from the soil, and so those plants never actually come out of the soil – those weeds never come out of the soil.

And when we compare the the weed free – so the whole season we we controlled all the weeds through hoeing when there was a uh the soil active herbicide applied, which only provided weed control for about the first four weeks of the year. That yielded higher than when we came in every – let’s say uh two to three times a week – and and controlled the weeds. And so we were literally going out there with a hoe three times a week, The plants never – the weeds never got taller than a quarter inch but just that small amount of weed emergence that would happen, let’s say between a Monday and a Wednesday, was enough to get a decrease in the yield.

Now it’s not a large amount, it might have been five percent of the yield that we we got from the season long weed free with the pre-emergent herbicide, but what we’re seeing is: having this herbicide that controls weeds while they’re germinating applied at planting actually provides some yield benefits just because of the shade avoidance response. So we’re preventing through the use of herbicides – um weeds – our crops from responding to the these changes in light quality um caused by the weeds being present.

And so that’s one example is that we’re actually seeing the use of soil active herbicides applied before crops emerge as preserving yield season long even when we remove all the weeds and the other treatments. And and this this is gets related to some other products we have. So um one of the things we’re doing right now in dry edible beans, uh again with our my graduate student Joshua Miranda is we have um we have – most herbicide – most programs in dry edible
beans you apply these soil active herbicides at planting, they wear off after about four to six weeks, and then uh you’ll apply – you’ll – once the weeds come up, you’ll apply an application of herbicides that control weeds that are that are emerged.

And these treatments, because of herbicide resistance no longer controlling uh one weed in particular – palmer amaranth – in our area, so we have to – what else can we do? So what we’re doing now is we’re applying these same herbicides that are applied at planting but we’re applying them – let’s say three to four weeks after the crop emerges. And so we’re overlapping these residual herbicides and so the goal is to never let that herbicide that’s applied at planting dissipate in the field where it’s no longer providing control. And so we have this overlapping residual herbicide that’s active in the soil and we can extend that control from four to six weeks at planting to maybe um six to eight, maybe even ten weeks after planting. And so what that means, is we’re preventing the weeds from ever coming up in in the soil. And that means we’re we’re probably not having actual crop competition when we use these post-emergent herbicides but uh that control weeds that already emerged, but those treatments may not be preventing the shade avoidance response.

And not only in dry beans but I’ve – I’ve personally – there’s a number of corn products out which are, have a high amount of activity in the soil and products like Acuron, Resicor, there’s a few others as well – I’m not trying to be particular in any herbicide brand – but but those herbicides, you apply them – uh let’s say at planting of corn – and then you can apply them at V4, the fourth collar stage on corn, and and basically you’re you’re you’re keeping that crop weed free all the way up until uh pretty late in the season without ever having to control emerging weeds. And so uh this is just another argument for why these soil active herbicides may be quite a bit better than herbicides that control weeds after they emerge, because we are not only preventing competition but we might be preventing the shade avoidance response as well.

13:03 E: Thanks Nevin. Well folks, today we talked to Dr. Nevin Lawrence about weed competition and the shade avoidance response and how those two concepts tie into his research here at the Panhandle Extension and Research Center in Scottsbluff. Join us next time, as we continue to look at Nevin and the other researchers’ projects over the course of the growing season. Be sure to like this video, comment below, and subscribe for more updates. Find us on Twitter @theFarmSciEd
and visit our website at farmsci-ed.com for transcripts and other information about this program. Have a good one!

Join Emily discussing with Dr. Nevin Lawrence his work on palmer amaranth in dry edible beans.

This transcript has been edited slightly for clarity and grammar.

00:18 Emily: Hi everyone! Welcome to Farm Sci-Ed. My name is Emily Stine and today we’ll be talking to Dr. Nevin Lawrence, weed scientist at the Panhandle Research and Extension Center about his project working on palmer amaranth – a weed – and dry edible beans. So sit back, relax, and let’s go talk to Nevin.

00:35 Nevin: Hi, I’m Nevin Lawrence, weed scientist at the University of Nebraska Panhandle Research and Extension Center in Scottsbluff, Nebraska and I’m a weed scientist that works on many of the specialty crops and minor crops grown in Nebraska: dry edible beans, sunflowers, potatoes, alfalfa, sugar beets.

One of the major problems that we’re seeing now in the panhandle of Nebraska is palmer amaranth. And especially in dry edible beans, this is becoming a major issue for for farmers. Palmer amaranth is a troublesome weed across much of the United States. It’s in the news quite a bit; if you’re any way involved in production agriculture,
it’s something you’re probably aware of. But for Scottsbluff, Nebraska – for western Nebraska – it’s a fairly recent weed. When I first began my position here in 2016, not a lot of the farmers actually had heard of it, nor were they dealing with it. But just a few years later, it had expanded past Nebraska into Wyoming and it’s it’s now a growing issue in our area.

1:52 Palmer amaranth is a pigweed. It’s very similar to red root pigweed, which is the more common traditional weed out in the area, but there’s some key differences. One of them is palmer amaranth has a wider germination window than red root pigweed or the other pigweeds. So it emerges earlier in the season and it could be a problem throughout the production season. Along with that earlier emergence, it’s also more competitive: it grows faster, it grows larger, it tends to have more of an impact on on crop yield. Additionally, it produces far greater number of seeds than other pigweed species. In our research we’ve done, we’ve seen up to two-, three-hundred thousand seeds produced per plant. As you get more plants that number goes down, but a pretty consistent number we’re seeing is a hundred thousand seeds per square yard or square meter. It’s a pretty consistent number amount of weed seeds that can be produced from from palmer amaranth.

But kind of more of the issue why this is a problem, is there’s just not a lot of options to control palmer amaranth and that’s because our farmers rely quite a bit on herbicide options to control it. And palmer amaranth compared to other pigweed species, such as red root pigweed, prostrate pigweed, tumble pigweed, tends to have far more cases of herbicide resistance – similar to a water hemp – but both those species can have quite a number of herbicide resistance cases. And in the minor and specialty crops within the panhandle of Nebraska, sugar beets, dry edible beans, alfalfa, sunflower, we don’t really have that many herbicide options to begin with. So when resistance does show up in in the case of dry edible beans – this is why we’re mostly concerned with ALS resistance or group two resistance – when that resistance shows up within palmer amaranth, we run out of options very fast.

Not only do we we have issues with running out of herbicide options within the minor and specialty crops, but when we do rotate to a major crop like corn, for instance, many of the options that are available throughout the rest of the country aren’t really available in our area. And the reason for that, is rotation restrictions. Our soils are low in organic matter, very sandy, high pH, and a lot of herbicides tend to stick around longer than they would in other regions additionally because those herbicides are sticking around and we’re rotating these specialty crops. Some of our crops, such as dry beans and sugar beets are very sensitive to herbicides that can be used in corn and soybeans and so we can’t use those in our rotation. So we have just less options in general than a lot of the country and we end up having not many options to control palmer amaranth, both in in the dry beans and other minor and specialty crops but also in in the corn.

4:17 So I’ve been working on palmer amaranth as my major – one of my major focuses of my position since I since I’ve been here in the Scottsbluff or the Panhandle Research and Extension Center, I’ve done work in almost all the all the crops that we grow in the region. But in the past, in dry beans in particular, we’ve we’ve looked at some of the traditional herbicide options. So a traditional program here for weed control in the panhandle of Nebraska would be either using a pre-emergent herbicide – something like Prowl and Outlook – applied at planting or after planting, or you could use a PPI herbicide where you’re going to be applying something like Eptam and Sonolan in the soil, you’re going to be tilling that in to incorporate that before planting. And then both those programs if they need to, they’re going to follow it up with a post-emergence of something like Raptor and Basagram. Raptor is a group 2 herbicide, ALS inhibiting herbicide and Basagram doesn’t really work well on palmer amaranth to begin with.

And so, those post options just don’t really work in our research. In previous work, we’ve compared basically what’s better between those pre- and those PPI options and we found pretty consistently that the PPI herbicides – likely due to the the tillage that involved with the incorporation of those herbicides – can get quite a bit more control throughout the season. Sometimes it’s enough control that you don’t even need to apply that post-emergent herbicide and so those are some just kind of basic studies we’ve done. We’ve also looked at a micro-rate program that was developed by the North Dakota State University, where several different post options were applied at reduced rates at multiple intervals throughout the season and see if that compared, well to the conventional options. Now that program contains a herbicide called Reflex. Reflex is a great option for palmer amaranth and we we found that using the micro rate program, we’re reducing rates, making multiple applications, just really didn’t see any benefits compared to just a full labeled rate of the Reflex. Unfortunately, after that trial was completed and we got the results, the Reflex label was not renewed for our area due to herbicide carryover concerns to corn, and it’s not really an option anymore. So at the moment in the Panhandle of Nebraska, we don’t have any post-emergent herbicide options to control palmer amaranth. There – there are none. They don’t work well and all we have is these soil applied herbicides applied at planting generally.

6:41 And so what I’ll be talking about this season on Farm Sci-Ed is some of our ongoing research this summer, where we’re trying to control palmer amaranth with these limited options. The the first thing that we’re doing this year to kind of better understand palmer amaranth is we’re doing an interference study, where we are allowing different densities of palmer amaranth to grow with dry edible beans all season long and the idea for that is to provide farmers a great visual tool to know what the yield impacts are if if they have some palmer amaranth escape. And so we can say, “if the density is x number plants per per yard of row or per foot of row, this is the corresponding yield reduction that you can expect” and that helps us justify further grant opportunities for future research. But it also provides farmers an idea of what the the palmer amaranth induced yield loss would be and also what the seed production could possibly be in contributing to that soil seed bank the next year. That’s the first study we’ll be talking about. The second one this year, is the evaluation of split applications of Outlook. So Outlook is labeled for both a pre-application – so planted at or before the dry beans come up – and also as a post application. Outlook will not control palmer amaranth that’s already emerged, but it will prevent palmer amaranth from emerging. So what we can do is apply Outlook at planting, and then do a second application a few weeks later and try to get some residual coverage of palmer amaranth for several weeks. And so we may be able to expand a pre-emergent application which might provide control for – let’s say four to five weeks, maybe even six weeks and really extend that to six to eight to nine to ten weeks depending if all the conditions work out and that’s really our best option right now moving forward.

Additionally, there are other dry edible bean herbicides that are similar to Outlook: Dual II Magnum or Dual Magnum is one of them (Esmacholiclor) and that product is labeled pre-, but it doesn’t have that post emergence option labeled currently. So we’re evaluating that right now to see maybe is that something that could have a label expansion and be used similar to Outlook. And so we’re evaluating multiple group 15 herbicides – also Warrant and Zidua – to see if they could have potential usage in dry edible beans to expand our options for palmer control. Another study we’re doing this year is we’re just going to be screening a whole bunch of soybean herbicides to see which ones may or may not have tolerance to dry edible beans for palmer amaranth control, because there tends to be better options in soybeans than there are in dry edible beans. There may be some overlap, and there may not. We’re also doing quite a bit of research on cover crops and so we have both a trial looking at winter planted cover crops, which is not often an option in our area because by the time corn is harvested, we don’t have time to get the winter crop in. But it’s it’s worked in other areas, so we’re evaluating that. And then we’re also looking at a spring planted cover crop which is not a very common strategy in a lot of the country but there’s potential that we can get a cover crop planted in about March area and there might be enough time before dry edible bean planting to get suppression of palmer amaranth. And so we’re looking at those programs, and seeing how we can incorporate the cover crop with herbicide programs to have a nice broad slate of options for control palmer amaranth. And then finally we’re also looking at what options in corn work best for control palmer amaranth and bring more modes of action, more herbicide diversity into the program and still allow rotation that next year in the dry edible beans and that’s more of not necessarily a research project – we’re not going to be discovering anything new – but it’s an extension project that hopefully will provide farmers with some options where they can see what works, compare prices, compare how it looks in different field trials, and make an informed decision.

10:23 Emily: Well folks, there you have it. Today we talked to Dr. Nevin Lawrence about his palmer amaranth and dry edible bean studies and discussed the different studies he’s doing – specifically looking at how weed density influences plant growth and different herbicide options for weed management and dry edible beans. Don’t forget to like this video, and subscribe to our channel for more science and education behind farming. And leave a comment if there’s something you found interesting in this video! Be sure to visit us at our website at FarmSci-Ed.com, for more information and for transcripts of this video. Have a good one!