Timely Weed Management Considerations for Corn and Soybean

Welcome. This webinar is part of a series presented by the Agonomic Crops Team from Auburn University in Alabama Cooperative Extension System. The series is brought to you by Optima Fields, [music] helping producers make smarter datadriven decisions on the farm. We're glad you're here and hope you leave with practical researchbased knowledge you can put to work this growing season and beyond. Hello everyone. My name is David Russell. I'm an extension specialist with Auburn University and Alabama Extension. Today I'd like to talk to you about the topic of weed management in corn and soybean. And to start off, I'd like to start with the topic that I begin with a lot of my growers discussing and that's just how important the timeliness is whenever we're talking weed control, right? Generally speaking, for rorowcrop agriculture, we hear the phrase control weeds when they're small and actively growing. Um, and to also start off and preface this conversation, I want to acknowledge that in an integrated pest management approach, there are multiple methods of weed control, not just herbicide. uh we we do have mechanical uh options, the the physical removal through tillage or other means or crop rotation. Um but the large majority of weed management decisions does come down to herbicide uh use. And so we're going to talk about a lot of those today. Um and even though we stress the importance of timeliness in weed management, there are um the primary primary points of precision agriculture in weed management and that's uh the importance of the right place, the right rate and the right time when it comes to weed management. And I know the weather patterns are are often difficult to pin down uh and predict. Um just take the last couple years from 23 24 and 2025. Um even even this year in 2026 for example, we go from uh extremely wet spring last year um to extremely dry this year. And planning is all over the board. Um, we've gone from really wet fields to uh very um overgrown fields and it's hard to be timely in a lot of situations like this. But when growers are able to get into the field, um we're going to talk about those pre-emergence um applications, those burndown applications prior to the crop ever getting into the ground. uh and then those applications for corn and soybean once the crop uh is planted and emerged. Um so it's often difficult to wait on conditions to dry up like the one you see on the left right there and it's often difficult to tackle uh a weed population like the one you see on the right. So knowing your fields uh is important. No one knows your fields and the history of those weed populations better than you do as a producer. Um, but when you are considering what's been there in the past and what is expected to emerge this year, we do typically have pre-emergence options. And I'll just start with soybean, right? These are residuals and post-emergence herbicide options as an overall weed management program in soybean. So we start with after burndown and the fields are clean the crop is in we usually start with something like a dual magnum or those esmatoll products or uh the zigua type applications or fierce type applications that are a pre-emergence that includes peroxy sulfoam or met tank mix of metriusen um is really good for an extended level of weed control and just overlapping those active ingredients uh to extend the life of that that we control application. And then depending on your traded crop, whether you've got Enlist, those E3 beans or extend flex technology, uh you've got the option obviously in enlist to go with the 24D choline, liberty ultra or glyphosate or mixtures thereof. And then obviously with Extend Flex, we've got the the dicama based technology there. Um and then you know those obviously are available to us depending on that traded crop once the crop is up and emerged at that appropriate growth stage. And then depending on the weed pressure or the expected weed pressure, right? We usually would recommend some additional type residual application that goes out in that first or second postemergence treatment. So that's just kind of an overall general recommendation for um pre-post applications in in soybean. Um and as we begin 2026, I want to remind everyone that we now have dicama back labeled for southern states and that's in three different products. Striacenia and tavium. I'm not going to go through all the details of Dicama, but there's the EPA registration numbers right there. You can look those up through those appropriate sources to find out the details of those. But what has changed this year from previous years is that the max annual rates have been cut in half from 2 L pounds to no more than one pound acid acid equivalent uh per acre. no more than two applications over the top of a dicama tolerant cotton and soybeans. Um there are temperature-based limits this year for those date for those cut offs rather than the date cut offs that we've had in the past. Um there still exists the mandatory conservation practices just to minimize the drift and reduction in the downwind um damage from offtarget movement. Right? So keep those in mind. Even though we've got dicama back and those post-emergence applications and traded technologies, I don't want to overlook the importance of residuals because what's easier than spraying weeds and killing weeds when they're small and active actively growing is controlling those weeds before they ever become a problem. And so that's where those timely applications of a pre-emergence herbicide comes into play. And for soybean as shown here in this uh researchbased data that we've collected over multiple years on Alabama ext experiment stations we just show the efficacy of single versus two versus three active ingredients and the importance of overlaying those chemistries. Right? So what we've got here is pre-emergence treatments in soybean and these bars show the effectiveness of broadleaf and grass weed control 8 weeks after treatment. And so you go from left to right with just single active ingredients of dicama and inia or metriusen or esmatollin something like dual magnum. Then you jump up to those two active ingredients like boundary which include esma chlor plus metribusen or those two active ingredients like prefix or or fierce ez the peroxy sulfone and uh the flumioin uh and then you can see the increased efficacy of the fierce MTZ which includes three active ingredients the flioisin peroxyone and metriusin so that that just simply not to pick on one particular particular product. But here's a picture just to show the efficacy from a single application at the time of soybean planting and how effective that is at extending the level of weed control in our crop hopefully to reach soybean canopy without many trips over the top of that crop. Right on the left you've got dual magnum just a single application of esmatanola versus that fierce MTZ which includes three active ingredients on the right. Now a caveat here u always read and follow the label uh rest uh recommendations uh product like fierce MTZ that includes metriusin is a product that is not fitted or suited for all soil conditions or environmental conditions. So please be aware of not only the use rates dependent on soil type but also those plantback restrictions. Metribusen, for example, is one that may hang around a little bit longer in those heavier clay soils or those soils that have higher organic matter. Um, they could have a tendency to carry over a little bit longer and injure that crop or subsequent crops in that area. Um want to touch on just an important one here that we focused on the last couple years in research and that's teaweed or prickly sada or airleaf sada. Typical applications have used uh the esmatoclore or acetalore type chemistries with some effect because that's typically our pre-emergence options in soybeans. But we've found that um it's it's often better to include a different form of chemistry known as the ALS chemistry or the group two um active ingredients for this one. And these are the type populations that we've begun focusing on. These are this is what I would call research quality populations. And this one's tough. It it's un an unassuming weed. It looks very small, a very tender weed, but as this thing emerges early spring, it probably has a tap routt just as long if not longer than the above ground growth that you see above the ground. And so we have gone out for multiple seasons now with a variety of herbicides looking at the efficacy for uh control here. Everything from a PO chemistry to group 15 chemistry all the way to the ALS chemistries. look at look at just looking at what would be effective. And just like our last slide that talked that showed percent weed control, you've got an increased weed control from 0 to 100 there um on that scale. And from left to right, you see an increase in efficacy there out to 36 days after treatment. And basically, statistically speaking, what treatments are above that red line is sort of our quote unquote best treatments for uh um or te-weed as a pre-emergence in soybean. And so those would be Python, Valor, First Rate, Authority Supreme, or or Zigua. All those right there on that upper end to the right seems to be some of our better treatments, which is sort of in line with what previous recommendations have been um in other states. But just it goes to prove that we do have to switch a little bit from the typical uh dual magnum or warrant type pre-emergence applications. Additionally, we did prove that Roundup Power Max or Roundup Power Max with Enlist One proved to be pretty beneficial at slowing down the tee once it was emerged. Here's an example of where the grower sprayed out a boom using just Roundup alone. Uh, and here you can actually see the rows of soybeans when we suppress that weed population. All right. So, just some take-home notes there for the troublesome teeed if you have that on your fields. Uh, secondly is just the importance of using Liberty correctly. Uh, we we now have Liberty Ultra, but we've proven in previous research the importance of droplet size and out sprayer output. So typically with Liberty, you want to use that medium to coarse droplet to get good coverage and increase your your output there. These left and right pictures just show the use of an XR tip, which produces very fine droplets. Often not good enough to get down through that soybean canopy and cover that Palmer pigeed well enough to get good levels of control. You compare that to a 15 and a 20 gallon per acre output left and right using AIXR tips which produces a medium to coarse droplet. And pretty similar here with those TTI tips. Uh left you've got the 15 GPA versus 20 GPA on the right. So increasing that output but using the correct medium to course droplet for good coverage. It it gives us better weed control over overall specifically for those pig weed populations which has been very difficult in for several several years now. Grasses are another concern for us and and I show these two because Italian ryrass in the cool season and goose grass in the warm season I think are some of our more troublesome species that we're dealing with. Um in previous research we have found um and made the recommendations that if you're going after these grasses don't mix those oxins like 24D or dicama with clefodm or roundup just use the cleftm alone or roundup alone if grasses is are are majority of your problem. Do we have resistance? Yes. uh primarily glyphosate resistance across the state and the southeast and those mapping efforts and resistance testing uh is still underway. We know that cleftm is sort of suspect. It's hit or miss here or there, but I think I tend to think that's more of a application issue or a timing or an environmental factor that you may see reduced levels of control. Germoxone um tends to be the go-to where we have glyphosate resistant populations. But understand that if we have these big established clumps of these Italian bio Italian ryrass biioypes which have pretty large underground biomass um it's hard to get rid of those in just one shot of Grimoxone. So what we are recommending if you have a population like this is paraquat applied uh with some of those group five chemistries like metriusen or atrizine ahead of corn or paraquat and metriusen ahead of soybean or mixtures of paraquat and cauteran or diuron ahead of cotton and and what that tends to do is try not to be too technical here, but it almost slows down the burn. Um, you know, with parakquad alone, you see that initial fast flash burn on the grasses or target weeds. When you combine these, it almost gives us a more thorough burn to help control especially those glyphosate resistant populations. Uh, and we certainly don't want to get in a case like this where corn is planted and emerged and we've still got those troublesome grass populations out there. Once we get in a case like this, we really only have a steadfast cue to slow down any escape grasses when our corn is emerged. And um it's sort of hit or miss at best as far as we control with that one. Um, not to pick on any certain herbicide, but this is just kind of the list of options that we have pre or early post-emergence applications in corn for both broadleaf and grass control. And we've evaluated a variety of these in previous experiments. And one that I want to touch on just because it's important across the board, uh, is the control of morning glory species in corn. We all know how troublesome this can be, especially as we get later in the season and corn uh reaches maturity and begins to dry down. Once the ground level sees sunlight, as the corn is uh defoliated or begins to dry down, that's when those morning glory vines start um climbing up those corn stalks. And so we what we wanted to do is look at the efficacy of some of our uh bleacher herbicides which we know some of these have good morning glory and even grass activity but in a layby type application. The goal here is just to help us get further into the growing season further or closer to harvest uh and get good weed control but not yet not injure the crop. In other words, have a layby type application like the picture that you see here in the previous slide from my colleague Dr. Eric Prosco. Um that could be applied either this way or through drop nozzles to get that herbicide between the row under the canopy. And so what we found is that uh you know in in multiple trials now we've run this over multiple years just evaluating the effectiveness of morning glory control between these four bleacher herbicides that we have available to us is that impact or the tramm product um proves to be a little bit better than balance flex or kalisto or lauis uh in our systems specifically for morning glory control and I emphasize that specifically for morning glory control because you can see the differences in weed control. On the left you've got the non-treated check. This is where we spray nothing at all. Um the middle picture there is a Kalisto 3 ounces of Kalisto and obviously the morning glory is controlled pretty well but what is left is that sickle pod. And what probably happened in this case is that sickle pod had gotten a little bit too big for that rate of of kalisto to slow down. So we got poor control there. But did a fair job on the morning glories. And then obviously you can see the the level of good weed control for both species there using impact. And what that does overlaying residuals and relying on that first and maybe even second shot of atrizine as well just to extend the level of weed control all the way to harvest. And so what we've done if is try to break that down and give you a price per acre there of what a typical program would look like for morning lure control in in corn. Um, and it kind of proves what other researchers have found as well as far as targeting morning glory species and other broad leaves and grass weeds in corn. So, that's a quick overview of what we have to offer and the research that we've done here lately uh throughout Alabama uh and Auburn University. If you have any questions, feel free to reach out to me for corn and soybean weed management recommendations at dpr000013 auburn.edu or give us a call or find out other information on our website. Thanks. That's all for today's session. Thank you for joining us and a special thank you to Optima Fields for organizing and producing the webinar series. For more resources [music] from Auburn University and the Alabama Cooperative Extension Agonomic Crops Team, please visit our website at aces.edu or [music] reach out to your local extension office. We look forward to you joining us again next time.