Integrated Pest Management, Weed Science

Episode 11: Weed Sampling

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

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