# Weed Control in Ornamentals for the Nursery and Landscape
## GTBOP Green & Commercial — July 13, 2023

**Speaker:** Dr. Chris Marble, Associate Professor, Ornamental and Landscape Invasive Weed Management, Mid-Florida Research and Education Center, University of Florida
**Moderator:** Dr. Shimat Joseph, UGA Turfgrass Entomologist
**Duration:** 50:38

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## Introduction

**Shimat Joseph:** So welcome back everyone. So our second speaker is Dr. Chris Marble. Dr. Marble received his PhD from Auburn University in 2013. And he is an associate professor at the University of Florida, Mid-Florida Research and Education Center. His research focuses on developing integrated weed management plans for ornamental plants in nurseries, greenhouses, and landscapes, focusing on more efficient use of herbicides, and how cultural practices impact weed control. Dr. Marble, the floor is yours. Can you get started?

**Chris Marble:** Thank you very much. I appreciate it. And thank you all for joining me and for inviting me to come and present today. Is my screen showing up good? Good. All right. So we're going to be talking about weed control and ornamentals. And I'm going to share some information that regardless of whether you're trying to control weeds and ornamentals in a nursery situation, a production scenario, or in the landscape, these things would be applicable and kind of apply in both scenarios. So we'll talk about application, timing, and then how to develop a program and what you want to think about when you're developing a weed management program in terms of combining a bunch of different things together and not just selecting herbicides, essentially.

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## Why Herbicides Fail: Calibration and Application

**Chris Marble:** Overview, what I'll talk about, I kind of just discussed that, but one thing that I'm going to start out with is the number one reasons why herbicides fail and people get either poor results or they get plant injury, and that is when you're using a herbicide that's actually labeled for the use, of course, but it's poor application practices and not being calibrated. So I'll cover some of that and then also share some tools that we've developed to help people with that. Also talk about improving success with pre and post-emergence herbicides. Some things to look for and some keys to really getting the most bang for your buck out of the herbicide applications. And then developing a weed control program based upon individual considerations. So, weed species and then also the ornamentals in which you're trying to control those weed species.

I'll give some examples of some different rotations and things like that that could be implemented, but I try to, in these types of presentations, not give people, you know, this is the rotation that you can use. Because some of the examples that I'll give, they could be a great option for your situation, or they could be potentially catastrophic for your situation, depending upon your weed species and the ornamental. So I'm going to try to spend quite a bit of time going through, basically how to develop a program for your specific situation, and just kind of give people the tools and the information they need to do that and not give, you know, just cookie-cutter recommendations.

With the common questions, this is probably the most common questions I get, whether I'm talking about nurseries or the landscape is, why didn't the herbicide work? You know, I've been using this herbicide and it's always worked consistently. And then, you know, why am I getting this plant injury? Could this plant injury be attributed to this herbicide application? And a good possibility is that not the right rate was used and that the applicator was not calibrated properly or there was some other kind of misapplication there. And these are just some examples of some cases where someone was calibrated and you had good weed control and good crop safety versus those same plant species and that same herbicide with that rate being off by somewhere between 50 and several hundred percent.

### Calibration Tools and Mixing Calculators

We've been around actually at several different locations in the Southeast. And we were measuring, you know, people's applications to see how close they were to the label rate. And, you know, I'd say most people were getting it pretty good, were there within 10 percent, 20 percent. And that's that's really in a real world situation. That's kind of a perfect application. We're talking about large scale, getting it within 10 percent plus or minus. But in some cases, that rate might have been exorbitantly high or low, you know, anywhere from a quarter of the rate that they were actually trying to apply. And so in those cases, that herbicide is going to fail and it's not going to provide weed control results.

So these are some of the tools that we've developed to help people with some of this in terms of mixing things properly and staying calibrated and things. We have, for people that are growing in large containers, I don't necessarily recommend this too much. It's kind of still difficult to do, but in terms of applying and treating individual pots, so if someone had, say, 50-gallon, I have growers that, you know, grow in 100-gallon pots, and they want to treat those individually. And so we have some ways to kind of calculate that out to where you're staying calibrated there. We also have some calibration checks where you can do it for liquids or granules in a bunch of different units. And then these are herbicide calculators in terms of mixing. So for granules, you know, what's the size of the area that you're treating, what's the product that you're using, how much you actually need. And then the same for liquid and spray applied. You can put in the size of your tank, the size of the area that you're treating, the length of the production beds and things like that. And then they'll tell you how much to mix, you know, per tank based upon the output of your sprayer. And those can be useful for, you know, whether you're treating turfgrass or ornamentals in the landscape or nursery. But these are available for free download. And I'll talk about our website at the end of the presentation and where some of these resources can be found.

This is just another example of stuff that I see, you know, all the time, just misapplications where, you know, you have very high rate, you know, one side of the container, no herbicide on the other. But this, I just put this in there to just address that with all these different herbicides that I'll talk about today and then the performance and the safety that you'll get with a lot of these, that's based upon someone following the label and getting it at the proper rate. So if it's not the proper rate, all bets are off.

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## Pre-emergent Herbicide Timing

**Chris Marble:** So herbicide timing, of course, for pre-emergent herbicides, you've got to have those out before your target weed germinates. In a nursery situation, that's typically going to be, you know, at potting, waiting several days for those plants to be watered in and then for the herbicide to be applied. And then in a landscape situation, it will be, you know, after the depends upon the plant species, but for woody ornamentals and things, soon after they're planted, they're tolerant of a wide range of pre-emergent herbicides. But the key is to make sure that that soil is settled, whether they're just being planted, you know, in a container or the landscape. Because where injury can occur, especially with some root inhibiting herbicides and things like that, is if those roots are exposed to those pre-emergent herbicides.

But then in terms of an application schedule, in terms of how many times you would have to apply during a year, you know, in a production situation in a nursery, that's really the only tool that they have are pre-emergent herbicides. They can't go in and spot spray, you know, small containers. So they're going to be applying, you know, approximately every 8 to 12 weeks to keep that weed pressure down. Whereas in a landscape situation, you can go much longer. You know, some people don't even use pre-emergent herbicides and they just spot treat with post-emergent herbicides. And I'll cover that a lot towards the end of the presentation as well in terms of ways to reduce the total amount of herbicides that you're actually using there. But essentially, you know, the timing is going to vary based upon a lot of factors in terms of the weather, the time of year, the herbicide that you're using, et cetera, et cetera.

### Avoiding Plant Injury During Application

This is another important aspect of herbicide timing. So this is all with pre-emergent herbicides, especially those that are going to be applied over the top of ornamentals. So you want to try to avoid during times of tender new growth. That's when plants are going to be most susceptible is during bud swell and development. And when you have very young foliage on those plants. And then also another thing to consider, especially this time of year, when temperatures are really increasing, your chances of injury with these herbicides is going to increase. So there's a lot of plants, you know, that are on, you know, specific herbicide labels and you wouldn't get any injury, but then, you know, in the hot part of, you know, someone's treating in the middle of the day and you have a lot of swelling buds or tender new growth, you can get injury in those cases. Those plants typically recover pretty quickly from that. But if those plants are about to go for sale, that's still not a very good thing that they could have to be delayed and you have to keep them until they recover from that. And in the landscape situation, of course, they're going to upset the clients.

### SureGuard Holly Trial: New Growth vs. Hardened Foliage

This is a good representation of that. So this is a holly, and this is a study that we treated. This was a long time ago, but it's a good photo. And this is an over-the-top application of a herbicide called SureGuard, which is *flumioxazin*. And that herbicide is not labeled for over-the-top use. So please don't apply SureGuard over the top of, especially broadly, ornamental plants. But this was an experiment, and so we were applying SureGuard over the top of plants and also doing directed applications, and we were looking at safety. But this was an interesting thing occurred, and so this is what we saw. So if you look at this holly here, the newest growth on those was severely affected. And so that's what you would expect from SureGuard. It can have a kind of a post-emergence effect to it as well. But then this older hardened foliage, you had no injury on it at all. And so it's a good example of what can happen, you know, maybe on a much lower scale, but with some of these other pre-emergent herbicides and things that plants, once those leaves are fully expanded and they're matured and kind of hardened off, they become less susceptible to injury, whereas that new growth is much more susceptible.

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## Post-emergence Herbicide Timing

**Chris Marble:** And so post-emergence herbicide timing, you know, in a production scenario, it should just be preventative. So you want to mostly focus on sanitation, pre-emergence herbicide use, and then controlling those escapes in the non-crop areas with post-emergence herbicides. But in the landscape, they're going to be a necessity in most cases, unless you have a high tolerance for weeds. But to keep high managed areas, highly managed landscapes, you're typically going to have to have, you know, post-emergence herbicides regardless of your pre-emergence program. And so we'll get into a lot of the different options that you have there. But that timing, you know, it's going to vary based upon basically you're just trying to manage those escapes, treat those weeds when they're small before they go to seed and the problem gets worse.

### Environmental Factors Affecting Efficacy

So some environmental considerations with post-emergence herbicides. Regardless of what herbicide that you're talking about, they're going to be most effective on small, actively growing weeds. And so that's really the most important part of timing with post-emergence herbicides is, trying to get those out when those weeds are still small and actively growing before they get large. Your efficacy is going to be reduced. You're going to have to use higher rates of herbicides, possibly multiple applications to get control of the same weed species. And then also, once they go into the flowering and vegetative state and they're producing seeds, you're increasing that weed seed bank. And so you'll have a problem for a while to come from that.

But the performance can be reduced under certain conditions. So, and this is, again, very herbicide dependent, but cloudy overcast for several days after an application can delay or reduce the effects of herbicides and reduce your efficacy. And so applications early in the morning, you know, during a clear sunny day, they'll likely be more effective than later in the day. For those of you that have route based businesses, that can be pretty hard to do. You're usually treating and managing pests, you know, all day long. So that's not as critical, but that is something where if you're not seeing the same performance that you've had in the past or you do an application and you just don't get good control, the first thing a lot of people suspect is herbicide resistance. And that definitely can be a concern, but keeping good records of your applications and when that went out, what were the weather conditions, all those different things can help you to diagnose these problems and correct it going forward.

### Stressed Weeds and Mowing Impacts

So some other environmental conditions, weeds that are stressed, they're going to be harder to control. You want those weeds to be actually healthy and actively growing for the herbicides to perform the best. For, you know, for the systemic herbicides, they have to move in that plant. That plant needs to be actively growing for those to be translocated as well as they can be. And then stress weeds are going to have reduced photosynthesis. Herbicide movement can be limited. And so another thing too, I'll talk about these other factors. So drought, of course, that's a stress, very hot or very cold weather. But mowing is a big issue and it's not pertaining to ornamentals. But mowing sooner before or after cultivation can really reduce or impact efficacy. So, you know, you can cut a, you have a large weed and it goes through and gets mowed. You know, you might cut off 80, 90% of that weed kind of goes into a semi-state of stress. And then, that herbicide is not going to be effective or you already made the application and its mode or weeded it after that application and doesn't have time to translocate down and give you thorough control. So that's another thing to consider also.

### Ranking Factors That Impact Post-emergence Performance

So ranking factors and impact post-performance. So the rate and efficacy of the herbicide is really the most important thing. You know, if the herbicide doesn't work on that weed, you know, optimal environmental conditions aren't really going to affect that. And then the size of the weed, that's very important and impacts efficacy a lot. And then the environmental conditions like the temperature and the relative humidity at the time of application. And then after that, I have the adjuvant. And so that's probably dependent. Some herbicides have to have adjuvants or surfactants to work. But, you know, you see a lot of claims on different surfactants and adjuvants and spreader stickers. And, well, those are all different types of adjuvants. But you see a lot of claims on a lot of those. But they're not miracle workers. They can improve control, but if that herbicide is not effective on that weed species, it doesn't really matter what surfactant that you used on it, it's not going to work. But some products do have to have certain ones, so that's all label dependent. And then time of day would be probably one of the more least important factors in a lot of cases. So that ties into what we were talking about previously.

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## Importance of Developing a Program, Not Just Products

**Chris Marble:** And so importance of developing a program. So oftentimes people, you know, they just have different herbicides and they might choose a few herbicides that they like and they use them in a bunch of different scenarios. But you want to program, I say you want to program and not products. You don't want to just have herbicides. Different herbicides that you use, you know, you're managing weeds in landscape beds and Snapshot is your herbicide for that. That's a good herbicide and it might be useful, but you don't want to just have, you know, you want to have multiple options, combining that with cultural controls and things like that to develop a program.

And so what a program is, is basically a schedule of herbicide applications that's planned, but it's also flexible, depending upon the control that you got, the environmental considerations, and the weed species that you have. Also consider with these pre-emergent herbicides that with all these different options that I'll discuss, you might get one, but in a lot of cases you get two or three applications per year. So I hear people talking about, you know, they have this pre-emergent herbicide that they're using in landscape beds, and that's the only one they use, and they apply it, you know, multiple times per year. But in a lot of cases, you only can apply those things two or three times legally according to that label, or to stay within that label rate, that total label rate. That's important, and so that limits, you know, the herbicides that you can use. But I'll talk about some different rotation options and timings. But again, none of this works for everyone. But I'll try to give you the tools to develop one for your own program, for your own situation.

### Herbicide Rotation and Resistance Prevention

Selecting herbicides. If you have a good rotation and a good herbicide plan, you're going to get better weed control, better plant tolerance, and then also reduce the chances of resistance development. In this picture, I like to include it on a lot of slides because it's a great example of this. So this crabgrass is not resistant, but in this particular case, this nursery had been battling bittercress for a long time and they were doing a lot of hand weeding because the herbicides that they were using before did not control bittercress and so they switched and they found Gallery, *isoxaben*, which is very effective on bittercress and we even control bittercress post-emergence if it's pretty small but it provides great pre-emergence control bittercress so they switched to Gallery, started using that over and over again, and they weren't rotating to something that would control grassy species, 'cause Gallery's only really effective on broadleaves. And so then they had grass issues that took over and became a major concern, as you can see in this photo here. So no one herbicide is going to control all the weeds and, you know, the weed that is not controlled is going to eventually take over. And they don't increase linearly. I say they increase exponentially in terms of their population and how many seeds they can produce. And they can do it really fast, too.

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## Three Steps to Choosing Herbicides

**Chris Marble:** So how do you choose herbicides for your situation? So three steps. One, you know, what's labeled or what is safe for the plants that you're having to treat around for the ornamentals? Two, what are the weeds that you're targeting? And then three, you know, putting those together so that you have a plan for the year based upon the number of applications that you need.

### Pre-emergence Options Color-Coded by Mode of Action

Here's basically a pretty thorough list of all the different pre-emergence herbicide options that you have for use in ornamental plants. And these are all color-coded by mode of action. So I developed this so that people could look and see which herbicides are really similar in terms of the modes of action. The ones that have two colors on the same product, those are combination products where you have two different herbicides that have been combined there. But we have a lot of herbicides from our group three, our mitosis inhibitors, that's represented by yellow. And then we also have a lot of PPO inhibitors, which is represented by orange. But those are a lot of the herbicides that we have for use in ornamentals. So when you're developing a program, you want to make sure that you're rotating through these different modes of action. You're not using the same products every application, you know, multiple years in a row or the same mode of action, not just the same herbicide.

### The 2017 Southeast Pest Control Guide

So this is probably the best resource that I know of for in terms of a compilation of a bunch of pest control guides and things. It has information on weeds, insects, and then also diseases. But it's the 2017 Southeast Pest Control Guide. And so we have efficacy charts in there. We have safety charts in there. But it's available for download for free or you can order a copy from I think it's North Carolina State. And it's only I think it's $20 for a hard copy of it if you want it. But it's probably the best resource with a compilation of all that different information there. And so that's going to be kind of what I use for these examples that I'll show here.

### Step 1 Example: Labeled Options for Container-Grown Gardenia

So the step one, figuring out what herbicides that you can use. In this example, let's say that we need a year-long rotation for a container-grown gardenia. And so we look at gardenia, and this is from that guide. We have all of our pre-emergence herbicides, and then we have all the different products that are labeled for use on that, represented by an FC, whether it's field or container. And so with gardenia, you can look at that and you see all of your different options and we'll narrow it down to just granulars. We'll say that we're going to develop a program and the only thing we can apply is granular. But these are our different granular products here. These are all labeled for use, you know, over the top in gardenia to control different weeds. So we have a lot of different labeled options. So the next step is to figure out, you know, which ones are going to be most effective for the weed species that we're dealing with.

### Grouping Herbicides by Mode of Action

So let's take those different herbicides and let's group them because, you know, you look at a list like this. So, you know, how did you go through picking, you know, which herbicide to use? So that's where this kind of comes into handy where you look at basically the modes of action of those and you want to kind of group them by that. Here's all of our 14 plus three combinations. You know, five different herbicides have the same mode of action. Some of the active ingredients are a little bit different, but they all perform, you know, pretty much similarly. We have a couple of group threes, one group 29, which is represented by *indaziflam*. Then we have some isoxaben combinations. Those are all products that contain isoxaben, which is the Gallery, essentially, but they contain an isoxaben plus, you know, another herbicide. Those are all group 23 or group 21 plus three combinations. Then we have one 15 plus three and then some group 14s, or it's just group 14 by itself. So the reason to think of it like this is you wouldn't want to pick, you know, a rotation with two or three options from the same combination because you may be controlling the same spectrum of weeds. And, you know, you can lead to resistance development as well.

### Step 2: Targeting Primary and Secondary Weed Species

So determining what weeds you need to target, at least in the nursery industry and in the southeast, I'll say that there's two seasons. There's spurge season and bittercress season. And that's by our primaries here. But really what you want to do when you're thinking about this is, you know, you have your herbicides that are safe for your, you know, your potential site. And the next thing is to look and see, OK, what is my primary weed species that I'm dealing with at this time of year, whether it's spring, summer, fall or winter? And then you've got to pick a herbicide that's effective, especially for that primary weed species. But then you're also going to have some secondary species that are problematic at the same time or possibly a little bit before or later. And so you want to make sure that that herbicide is effective for your primary species, but is also at least okay on the secondary species.

So you could go back to that guide, the 2017 pest management guide, and you could look up, so say we spotted spurge was our primary issue, and so we look, and then myself and Jeff Derr and Joe Neal rank these based upon their labels and also our data. And we have whether they're good, fair or poor, you know, for these different herbicides. And so you would want to look and then for your primary species, you'd want something that's good that has a G. There, that will be, you know, that's your most important plant or your most important weed to control because it's your primary weed species. And so we look and we narrow that list down. And so these are all ranked as good for spurge and they're also labeled in gardenia.

And so let's say that our secondary species was eclipta. And so for that secondary species, it's not as bad, you know, it's kind of a problem, but it definitely isn't, you know, taking over like spurge was. So in this case, we want something that's at least fair or good, you know, a G or F based upon these particular charts. And so then we narrow our list down further. And so all these options here, they're good for, they're great on spurge. They're, you know, pretty good on eclipta and they're labeled for use in gardenia. So these would be good options, you know, in that warm time of the year when spurge and eclipta are issues. So that will be, you know, where you would place these in a rotation.

### Step 3: Building a Year-Round Rotation

And so the third step is basically just combining all those together through the year to figure that out. So we covered the priorities and how to kind of pick those and go through everything. But you just want to pick your best options and then make sure that you're saving those applications for when you need them. You know, if you get two applications of FreeHand a year and you really like it for spurge, you wouldn't want to put it in the winter when spurge isn't really an issue. You want to place them maybe in the spring and then one, you know, late summer, something like that, so that you get the best advantage out of that herbicide for your weed. But this could be like a for a three or about a 16, 20, 24 week rotation here are more like 24 to 30 week rotation where you have three different products here. They're all safe on gardenia and they all control spurge and eclipta. And then, you know, for your cool season, you might have a different group of herbicides that you've also determined to be safe. They're good on, you know, your cool season weed spectrum like bittercress or annual bluegrass or oxalis, and they're effective for those. And so you kind of combine all those together and figure out your program for the year.

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## Year-Round Nursery Rotation Plan

**Chris Marble:** In landscape, you know, you might just have one application, two applications that you can make. In the nursery situation, you know, you're making an application every 8 to 10 weeks, and so you'd have to have more options put together to develop your program for the year.

This would be a plan for the year for this would be like a nursery situation. You've got your months of the year up here, your primary species, and then all of your herbicide options based upon the ones that are safe and labeled for your plants. And so, you know, early February, you know, you've got a 3 plus 21, then you follow that with a 14 plus 3, then you come with a group 29, then a group 3 plus 15, on and on down the line, so that you're not repeating the same mode of action too many times, and you're controlling all those weeds in that spectrum when those weeds are most problematic.

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## Research: Pre-emergent + Post-emergent vs. Post-Only Programs

**Chris Marble:** And then, you know, in a landscape, you know, people might say, you know, I don't like to use any pre-emergence herbicides or it's too much trouble to go in and make a pre-emergence application. Or I've gotten this before, too, where people will say, you know, why are you recommending people use pre-emergence herbicide? I thought you always talked about reducing herbicide applications. I can just go and manage them by spot spraying, you know, Roundup or Finale or something like that. And the reason I say I'm kind of a proponent of pre-emergent herbicides in certain situations is that we've done a lot of research on this, and this is results from one of the trials that we did.

And so basically what we wanted to look at is for someone that's managing weeds in the landscape situation, if they wanted to keep weed pressure to optimal level, let's say 15 to 20%, you know, how many follow-up post applications of just Roundup or glyphosate, could they eliminate if they incorporated pre-emergent herbicides? And so this is a study that we did where we had Ranger, Finale, and Reward. Ranger was our glyphosate product. Finale is glufosinate, and then Reward is diquat. But those are all post-emergent herbicides. And then we combine them with either Specticle or SureGuard. And those are two pretty long-lasting pre-emergent herbicides that are labeled for use in landscape planting beds. And then we compared them to just Ranger or glyphosate by itself.

And so this is the average control that we got over the course of 12 weeks. And the way that we did this was we went out every two weeks and we did our ratings, our weed control ratings. And then if those ratings were, you know, if our weed control rating was basically below 80%, we would go back in and spot treat like someone would do in a landscape situation. And so then over time, after we got to about, I think, and the data that I have here is for maybe four months, I believe. But then we looked and we saw the average number of basically retreatments that we had to make.

And so when we included these pre-emergent herbicides, like especially if we started out with glyphosate or Finale, and we included Specticle or SureGuard, we were only making one or two follow-up applications after that. If we just used Ranger or glyphosate by itself, we were having to go in basically every month or more than every month to go back in and spot treat because that weed pressure was up. And so we ended up using a lot more herbicide by just using, you know, a post-only program. With Reward, the diquat, we had to make three follow-up applications is that's because we didn't get, you know, optimal control with that first initial post-emergence treatment. Because it's, all things considered, it's not as effective as Finale and definitely not as effective as glyphosate as a post-emergence herbicide.

### Cost Savings and Herbicide Reduction Results

And so this is the total cost expected over 12 months. And then this is the pounds on the ground, or basically the total amount of herbicide active ingredient that was applied. And so this is the estimated potential savings for the total cost over 12 months. When we included basically these different combinations, we were reducing total costs by anywhere from 3% or up to 30% reducing our costs by 30%. And then if you look at the amount of herbicide that we eliminated, we were reducing the amount of herbicide that we actually had to use by somewhere between 40% and 60%. We were really reducing the amount of herbicide that we needed to use to get that, still get that good optimal weed control by including, you know, a pre-emergent herbicide into the mix. They can offer advantage, you know, in certain situations, especially if the primary weed species that you're dealing with are annuals that are spreading from seed. Perennials, it's a different story.

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## Application Interval Considerations

**Chris Marble:** Application interval, it's going to depend upon a lot of things. The season, your location, you know, down here in Florida, you know, people are going to have to use it more than they would, you know, a lot further north because we don't really get a winter or a break, you know, production practices and then things like cultural practices like irrigation, mowing heights, stuff like that is going to affect it as well. Rainfall also, you know, higher the rainfall typically the higher the weed growth especially for a lot of species. And then on a production situation, eight to 12 weeks, eight to 10 weeks on average, could push it up to 12 weeks. Then in the landscape, you know, maybe two or three applications per year, and you're going to get pretty good results from that.

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## Landscape-Specific Rotation Planning

**Chris Marble:** And so landscape-specific rotations, these are kind of some things to consider. So one is how many applications do you actually want to make? You might have only time to make one application per year. So where is that going to be most optimal? And then some people, you know, they might do two applications. And so you have some flexibility in terms of when you can apply those. And then in any of their other cases, someone might make, you know, they say, you know, I want to focus on pre-emergent herbicide so that I can reduce my callbacks or my labor or, you know, the weed species that we have. We took over this job and the weeds were out of control. We can't stay on top of it with just our post-emergence program. So we've got to focus on pre-emergence herbicides to get this place back, you know, into shape.

So you want to consider how many applications you want to make. Are pre-emergent herbicides going to be the foundation of your program, or do you want just to be kind of a supplement to your program? And there's not really a wrong way to do that. You know, what's the weed pressure like? What are the weed species that you're dealing with? And then when are those pre-emergent herbicides going to be most advantageous? You know, is it a case where, you know, in the winter you don't have very many issues, but then in the summer, you know, spurge goes crazy or, you know, the only weed that you deal with in the summer is yellow nutsedge. And so you just got to, you're not going to get great control with any pre-emergent herbicide, but you want an option to at least suppress that a little bit. You know, you would apply it maybe later in the year than if you were targeting crabgrass, for instance, which is an early species to come up. So those are just kind of all things to consider. What is my primary goal with these? And what is my primary issue?

### Timing Examples: One, Two, or Three Applications Per Year

Some timing examples for the landscape. I'd say if someone had just one application per year, it's probably going to be best, you know, is that first spring part to give you a head start into the warmer time of the year, somewhere around February to March, at least in the southeast. That's going to vary depending upon where you're at and then also the weather and where you're at. If you had two applications per year, you have some flexibility. I would say still that first application in the early spring is probably the most important. Then if you had a second one, you know, if you had, if you really dealt with weeds really bad during the warm time of the year and they weren't as bad in the winter, you might do, you know, you might not make a fall application. You might apply one in May and June. Say that doveweed is a primary concern. Well, maybe time it for then as opposed to September, October timeframe. And then for that third application or for a fall application, somewhere between August to October, maybe you can push even into November in some cases. It's really going to depend upon the weather, but you want to get it before those cool season weeds start coming up like chickweed and annual bluegrass and all that. And then again, you don't really want to base a lot of these application things upon calendar month, kind of use the calendar as a way to gauge it and plan and start prepping for those applications, but really want to go based upon the weather. That's the most important thing.

### Generic Landscape Rotation Example by Season

So this is kind of a generic rotation example for the landscape. So what you want to do is you've got several options here. I listed three or four different herbicide options that would be effective on particular weed species, and these are all important weeds in Florida. Are going to be different in your scenario. But, you know, you want to look at the early spring, you know, for your first application, what species are you really trying to target? And then make sure you have some options that are going to control all these. So a lot of times it's crabgrass, maybe goosegrass a little bit later after crabgrass. And then some of the other warm season weeds that germinate a little bit earlier. So you want to time it and make sure that you're getting those species. And then if you do a second application in the late spring or early summer, you know, you have things like doveweed, artillery weed, stuff like that, at least in Florida we do. Maybe if you had sedge, you might put Pennant Magnum as that application. Sedge was the primary thing that you were targeting. And then for that fall application, you have more cool season species, possibly still some warm species, warm season species still hanging around that you might have to control like spurge. But you look for those options that are effective on those.

And basically, you've got your applications when you can do them and when you want to do them. Look at your most critical weed species at that time. And try to pick an option that's, you know, controls that weed spectrum at that time of year. You know, don't just choose dimension because it worked great on crabgrass. That doesn't necessarily mean it's going to work great, you know, on a cool season weed spectrum.

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## Post-emergence Alternatives to Glyphosate in Landscape Beds

**Chris Marble:** So post-herbicide options in the landscape beds, this is another thing that I want to talk about just a little bit. And really the, what I know I've talked to a lot of people across, really the U.S. and really the number one standard is glyphosate, just spot spraying with glyphosate. But of course, you know, I don't have to tell all of you that that's becoming a lot less popular. In Florida, you know, it's been banned in certain counties for use on public properties and things. And then I'm also, you know, I've sat in on meetings with HOAs and municipalities and stuff like that where people don't want it used in common areas. So it's becoming, you know, very limited in terms of where people can use it. And so people need alternatives to it.

And then I think even if people don't need alternatives to glyphosate, if your customers and your sites, you know, don't have any problem with it at all and understand the, you know, some of the benefits of glyphosate and things, but it's not a perfect herbicide for sure. And you don't want to rely too heavily on just any one herbicide. That's the reason we have a lot of glyphosate-resistant weeds is because it's probably been overused and not enough people have rotated between different modes of action. So you need alternatives regardless.

### Glufosinate (Finale/Cheetah) as an Alternative

The most common alternative is glufosinate. That's sold as Finale or Cheetah. Liberty is the crop version of that. But it's pretty similar to glyphosate in terms of it's a post-emergence, broad-spectrum herbicide. It has activity on broadleaves, grasses, and sedges, but it is primarily contact action. So you don't get the same post-emergence control as you typically would with glyphosate.

### Non-Selective Alternatives: Desiccant-Type Herbicides

But we've looked at a lot of other non-selective alternatives that are out there that can be applied, you know, in a similar manner to glyphosate as a spot treatment. You know, there's things that have been around for a while, like Scythe or Reward or diquat, but then there's a lot of other products. You're seeing more of these. And look at the herbicide names, not necessarily the trade names, because a lot of these are sold under multiple different trade names, but things like Axxe, Finalsan, FireWorxx. There's a bunch of different plant oils that are out there, but a lot of these different products, they all have different signal words. That's something to pay attention to because they have differing degrees of acute toxicity. A lot of these can be pretty caustic to your eyes and skin. So people have to wear different PPE than they would with just glyphosate or some of the other pesticides that they might be used to applying.

But then another thing that comes up with school boards and things like that is that they want only organic options to be used. So some of these are OMRI certified and they could technically be used on organic foods and things like that, USDA organic. But these are all certified as organic. Some of these options are. So if that was important, you know, you could look and pick some organically labeled options there.

So these things, all of them are fairly similar in that they work very fast. They primarily work as desiccants. And you see symptoms very quickly. And the burn down can be remarkable. You know, you can apply some of these on a hot day. And 30 minutes later, you know that you treated that weed. And it's already starting to desiccate.

### Acetic Acid Trial: Burndown and Recovery Results

And so these pictures we're taking, this is an acetic acid product. This was all taken at two weeks after treatment. You have a high degree of burn down on crabgrass, garden spurge, and then also bittercress. But then if you go out to four weeks, this is the problem that you see with some of these products is, is that because they're not translocated, if you don't get good coverage or if that weed is pretty large, like in this case, these weeds were pretty large when we treated them, they can recover from that. And so oftentimes you're going to have to make a follow-up application with these herbicides. So now bittercress, I will point out that we did get 100% control of those post-emergence, but what you see here is seed germination. Those are all bittercress seed that are being germinated. But with spurge and crabgrass and those larger plants where it's difficult when you have a weed that's up, it's really difficult to get thorough coverage because you're hitting the top part of the weed and it's not going down to the bottom there.

Here's how some of them perform. This is four weeks after treatment. This is a visual injury rating. So all of them, you know, 60 to 90% or so. We have glyphosate here that we used as a control. So all of them, you know, most of them perform pretty well on these three weed species, crabgrass, spurge, and oxalis. But then if you get to eight weeks, this is the control that we saw. And so they drop, you know, dramatically as those weeds recover. And so you need a follow-up application for that. And if you do a follow-up application, even though it's large weeds, this is another study that we did where we did two applications. And in that case, that's when you can get really good control. You treat, you have some regrowth and then you do another treatment. And of course, that increases costs and things like that. But with a lot of these, you have to get at least two applications to get control similar to glyphosate with annual. These were oxalis is technically perennial, but for annual species, they're small perennials. With large perennials, all bets are off and it's going to be multiple, multiple, multiple applications to get the same control as a systemic post-emergence herbicide.

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## Selective Post-emergence Options for Landscape Beds

**Chris Marble:** Then lastly, I'll just share this. So these are some selective alternatives that can be used and labeled for use in landscape beds. So I have on here, you know, the trade name of all the different options and then the active ingredient, and then whether they control broadleaf grasses or sedge. We have a lot of products that will control grasses and then several that will give you really good control of much said species. Broad leaves are the difficult options. And so these are all, or a lot of these can be applied over the top too for certain ornamental species. The exceptions to those are the ones that are highlighted here.

### Graminicides: Underutilized Grass-Selective Herbicides

So these are the graminicides, *sethoxydim*, *clethodim*, *fluazifop*, and *fenoxaprop*. Whereas things like Basagran, Lontrel, Certainty, Scepter, they might have 20 to 30 different ornamentals on the label where they can be applied over the top. Those grass herbicides, Segment, Envoy, Fusilade, Acclaim, they can be applied over the top of hundreds of different ornamental plants. They only affect grasses, true grasses. So some of them can even be applied in things like liriope and mondo grass and stuff like that. But they're great options. I think that they're probably underutilized. People will rather try to go in and spot treat a grass around a rose and potentially damage that rose with glyphosate as opposed to utilizing one of these options. And I think they're really useful tools in some cases and very safe to most broadleaf ornamental plants.

### Basagran, Lontrel, Certainty, and Scepter

So Basagran, you know, that's been around for a while, used in turfgrass a lot. It'll control some broadleaves, but mostly used as a sedge product. Lontrel is *clopyralid*, so that can be used in turfgrass, but you can use it in planting beds. And it's really good on any weeds that are in the Asteraceae family, and then also for legumes. So things like your beggar weeds and stuff like that, it's a really good option. And Certainty, I also kind of consider it a sedge product, but it will control some broadleaf and grass weeds. It has things like Asian jasmine, liriope, certain junipers. Those are all on the label as it can be applied as an over-the-top application. So it's useful in some ground cover situations. And then Scepter, it is the same way. Just some different things to consider and possibly add to your toolbox, depending upon your needs.

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## UF Mid-Florida REC Resources and Contact Information

**Chris Marble:** Getting ready to close out the presentation, but I'll share this. This is the Mid-Florida Research and Education Center. That's my faculty page. And so I've got a list of a lot of the publications that I've done. And then also that herbicide calibration chart, that's all on this page. We have several weed identification resources on there. It's a weed ID by flower color, a little thing that you can go and search for weed species. And then we also have a couple of guides on how to use weed or plant identification apps. Because there's a lot of great apps out there, but you've got to be able to take a good picture for them to work. We looked at all the free versions of all of them, and we kind of show you how to use those to get the best results and the most accurate results from each of those different plan outs. But that's something you can check out. My email address is down there, too. I'd be happy to share this presentation with anyone and help in any way that I can for any kind of weed control issues. There's the rest of my contact information. And with that, I'll close it down and try to answer any questions anyone has.

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## Questions and Answers

**Shimat Joseph:** Thank you so much, Chris. This is a wonderful presentation. Thanks. This is time for question and answers. Any questions you might have, please use the Q&A box here and type it in. And we have about five minutes. For like a minute or so for people to think about the questions. Sure. Yeah, I'll wait for a couple more minutes and there is no questions. I think that's very good.

**Chris Marble:** Yeah, there's a comment saying very thorough, so I either did a thorough job or everyone's asleep, one or the other. It's a very thorough job. Yeah, it's either thorough or everybody does it all.

**Shimat Joseph:** It looks like your talk was really comprehensive. Now there's no questions there.

### Signal Words and PPE Requirements

**Shimat Joseph:** So there's one question about a quick review of the signal words.

**Chris Marble:** Yeah, so there's caution, which is the lowest level. And then there's the warning, which is upper. And then the danger poison is the most dangerous signal word. And those can all be based upon several different routes of toxicity, whether it's skin exposure, eye exposure, et cetera, et cetera. But so it's something to consider for sure with any pesticide. In Florida, we have laws like where people can use only caution label products. You know, for certain licenses, they can get a limited license and use caution label products to non-turf areas and landscapes. So they have to look at that in terms of their specific options that they can use. But for everyone, it's important to consider, but, you know, just from a safety standpoint, but then also the PPE that has to be supplied to the employees or to have on site. As those caution labels go up, you're typically going to be required to have a lot more PPE and then they become restricted use and stuff like that. So there's stricter label or record-keeping requirements on those restricted use products as well.

### Wind Drift and Reducing Spray Drift

**Shimat Joseph:** One more question about wind drift. So wind drift can sometimes be problematic when spraying herbicides. So what is the maximum wind speed recommended?

**Chris Marble:** Yeah, so it's going to be different depending upon the herbicide. Typically, most of them are going to recommend, you know, not when wind speeds are below 5 miles an hour. You know, that's optimal for things. But, you know, some of them will allow it to go up to higher wind speeds. It's real difficult in a real-world situation, and it's going to be variable. You can't just go outside and tell that it's going to be constantly five miles per hour while you're treating or whatever. But some things to reduce drift. Physical drift like you're talking about from wind, coarser nozzles so that those water particles are larger and they fall easier. The worst things you can do is have high pressure and a real fine nozzle tip where you have just real fine water particles that are just going everywhere. So coarse particles and lower your sprayer pressure and that's going to do a lot, you know, in terms of reducing drift.

### Marengo for Nursery Gravel Areas

**Shimat Joseph:** Great. We have one more question and I will call this the last question, okay, for this interest of time. So is the Marengo sprayed over your gravel roads a good way to control weeds throughout the year at a nursery operation?

**Chris Marble:** Yes, the easy answer to that is yes, but Marengo, and *indaziflam* in the landscape side of things is called Specticle, same herbicide, but different uses. But that's probably that and SureGuard are probably the two herbicides that I recommend the most for non-crop use in nursery operations. Marengo is probably the most broad spectrum option. You can't go over the top of ornamentals with at least the spray version, but it's a pretty broad spectrum herbicide. It's a great option for gravel areas and things or to treat prior to putting plants onto a gravel production space. Yeah, that's a good option. You could rotate Marengo and possibly something like SureGuard. SureGuard, and then if you had sedge, you know, maybe something like Pennant Magnum or Tower or something like that, so that you're using different modes of action. But it's a good, really good herbicide for those, for that use case.

**Shimat Joseph:** Thanks. Thank you so much, Chris. And really appreciate your talks. I'm sure we learned a lot today. Thank you.

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*Transcript processed for UGA Center for Urban Agriculture / GTBOP Archives*
*Source: Corrected SRT (Stage 1) — GTBOP_Transcript_2023-07-13_WeedControlOrnamentals.srt (618 blocks)*
