Integrated Pest Management, Weed Science

Episode 3: Introduction to Palmer Amaranth Study

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, for more information and for transcripts of this video. Have a good one!