# Weed Control in the Landscape and Nursery
## GTBOP Green & Commercial Series — November 18, 2021

**Speaker:** Dr. Mark Czarnota, Associate Professor of Horticulture, University of Georgia Griffin Campus
**Moderator:** Dr. Shimat Joseph, Turfgrass Entomologist, University of Georgia
**Duration:** 50:05

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## Introduction and Speaker Background

**Shimat Joseph:** Welcome everyone. Today our first speaker is Dr. Mark Czarnota. Dr. Czarnota is an associate professor of horticulture located here at the University of Georgia Griffin campus. He received his master's in weed science from Virginia Tech in 1995 and a PhD in weed science from Cornell University in 2001. His primary responsibility is applied research and extension on weed management in nursery and ornamental plants and also in the landscape. So welcome Dr. Czarnota. The floor is yours. Oh, thanks. Thanks.

**Mark Czarnota:** I appreciate it. And I guess I'm ready to go. I got to share my screen again here, I think. Exactly. There we go. Is it stolen back?

**Shimat Joseph:** Now can you see it? Yes I can see it. Okay we're good to go.

**Mark Czarnota:** And anyway hopefully we don't get the zoom bomb. Hopefully Richie prevented all that. Anyway, I'm going to talk about weed control in the landscape and nursery today. And if you have any questions, let me know. And I was going to tell you, Matt, that I have a history slide of where I came from and what I did. Anyway, the next, let me see. How do I... Does that come through? Yeah. I have two.

**Shimat Joseph:** I don't know.

**Mark Czarnota:** I do. Give me one sec here. I just got to get it. That's fine. Okay, I got two open. That's why. Okay, so let's go. So anyway, this is a brief history. As Shimat said, I got my degrees. I actually went to the University of Delaware for undergrad in '85, Virginia Tech for a master's, Cornell for a PhD. And I worked for three years between my master's and PhD, or from my bachelor's and master's degree. I was at a plant nursery selling trees for about a year and a half, selling landscape plants, and then was at the DuPont chemical company when they were, before they merged with Dow. And I was at their Stine Haskell location just as a lab technician. And, but it was a weed control. It was in the weed science lab.

So anyway, I work for, of course, you mentioned what I do now. And I have a really strange three-way appointment, which is probably going to change again. And then I cover all aspects of weed control and ornamental, small fruits, Christmas trees, and orchard floor management. And I also do a little bit of work. And some of you might see my work I've been doing with the Christmas tree industry. We've been working with how to propagate that. And I've worked on a couple other propagation projects. But the main thrust of why I'm here is weed science.

So I guess I have 45 minutes to go over this talk. I'll go as quick as I can. I got a lot of information to tell you and hopefully you'll gain some weed science knowledge and information on how to control weeds in the landscape and nursery.

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## What Is a Weed? Definitions and Weediness Predictors

**Mark Czarnota:** So before, of course, I deal with weeds and weed control, but the big thing — but if you ever take a weed science class, I don't know how many of you had one, but weeds are, there's a laundry list of what actually a weed is. And we could talk about them being weeds that grow where they're not wanted, a plant out of place. My favorite is a plant whose virtues have not yet been discovered. It might be a chemical in that plant that might save your life or something that we can utilize for other things and as well as food, but other pharmaceutical needs and whatnot. And the biggest reason that I'm here is because their plants out there cause economic loss and we try to make growers as profitable as possible. But there's lots of definitions of that.

If you ever take a weed science class, some of the things you talk about in the first class would be something like — and I've sat through lots and lots of weed control talks and seminars. And so I've been through a lot of these where these people come up with basically mathematical models that try to predict whether a plant's going to become a weed or not. For example, if you import a plant, some type of annual type plant in the U.S., you'll want to know some information about whether or not it's going to be a weed problem. And they always come up with these different categories. And the ones I have here, the six I have here, are ones that always pop up.

And it's the presence of a vegetative reproductive structure. That would be like yellow or purple nutsedge. And I'll show you a picture of it, two of that. Abundant seed production, and that would be a plant like pigweed, if you're familiar with all the problems in South Georgia, where one plant will make 5,000 to 10,000 seeds per plant. It's not unusual. Rapid population establishment where that seed can germinate and grow quickly and go to flower and seed again and spread quickly. Seed dormancy, having seed that are dormant for a long time. Adaptive, if you have both the ability to produce lots of seeds and vegetative parts. And if they can occupy a disturbed site, like in mostly in agricultural situations, you'd think of things like that.

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## Challenging Weed Problems in Nursery Production

**Mark Czarnota:** And some of the problems that I run into — here's a few that I had difficulty trying to control, but this was actually the, in a propagation house in a greenhouse industry, they were growing *Marchantia* growing azaleas and had problem with this weed called *Marchantia*. And excuse me, this weed was, they of course want something they put down on this. And what happens is this will suck up nutrients and water and prevent the azalea plant that's recently been rooted from a rooted cutting to getting up to full size to where they could sell it.

There's a couple things. We found actually a great product that will control this. It was actually a fungicide, someone who was playing around with another weed scientist that, and we started testing it and it looked great. And unfortunately it didn't get registered by the EPA in our country, even though it was a fungicide already labeled Europe. So strange situation, but it had to do with how they wrote the legal up. And it was, they didn't consult with any of the academic people, which could have helped guide them a little bit. And they didn't do that and they kicked it out because of the toxicology problem. But here's something that we really have no, nothing we can really spray on as a herbicide. And you basically have to go back to doing cultural things where you'd have to cut down on watering as much as you can. Times that the plant is watered and try to keep the surface as dry as you can. Can you use some pre-emergent granular herbicides to help keep it beat back a little bit? But this is a difficult problem we can continue to face in some growers and propagate stuff, might be aware of it.

Here's one where I can control plant weeds in the top of the container, but when the weep holes where the seeds come out, it was a difficult situation. You could just spray this with glufosinate or Reward or glyphosate and eliminate this. But I can't put a herbicide in the weep hole. It's just impossible.

And anyway, another one in blackberries where I had purple nutsedge coming through the plastic. Most people try to use the plastic type cover and a purple nutsedge, even if there's been fumigated, will survive the fumigation, the tubers will germinate and easily poke through six mil plastic, you can see here. We really have no label product to control this and blackberry, but we were researching Sandea, which you might know as a SedgeHammer as a possible alternative. And if this is yellow nutsedge, which can do the same thing, I could use Basagran or a few other things to try to help them. But it was another situation where there's so much of an answer.

This is a picture from when I was out in Oregon one time. This would be people managing grafted cuttings where they actually seeded out plants, grafted them to these seedlings, cut out the actual plant they didn't want, allowed the seedling to grow. This would have been an ash of some type. I don't know which one, I can't remember. And of course the weed control is fabulous here. And this would be, there was hand weeding done in here as well as chemical weed control. And you can see it's perfect for, this is where you're going to get the maximum amount of growth on your tree with no interference from any weed problems.

Another situation, this is one just south of me where I live in Pike County. There's a nursery called, it's Mid-Georgia Nursery. And anyway, this is one where they would try to grow, for example, Southern Magnolias. And you try to keep a four to six foot alley where the plants are actually growing and keep that completely weed free and just mow the alleys where the grasses or weeds are. And then try to get as much growth out of these trees as you can and harvest them as quickly as you can. So this is a situation where you'd want to use pre-herbicides to keep the weeds down and you might have to use some post-herbicides in other states where the pre-emergent weed control has failed or stopped working and you just have to do a cleanup application. You see all the situations that you can run into.

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## Weed Identification and Plant Life Cycles

**Mark Czarnota:** But when you're trying to control weeds, one of the most important things I tell people is to try to be able to identify the weed you're trying to control. And here's just a quick picture to try to refresh people or make people aware of this. If you're not too versed on weed control, but for example, we have a picture of yellow nutsedge on the left and another picture of chamberbitter or a leaf flower, a couple of different names for that plant. But it's a *Phyllanthus* species that you'll see in containers. And we have little ones that kind of look like tiny mimosa trees if you're familiar with them. It's another species, but very similar growth pattern and can be a problem in the landscape.

But the yellow nutsedge will be a plant that's a vegetative, coming back from a vegetative structure every year. We'll die back to the ground, come back from a vegetative structure, and then you have chamber bitter, which will be a plant growing from seed, but it's only going to germinate when the soil temperatures are up around — you have to get the soil temperatures above 70 to get it to germinate. And it tends to be a late spring, early summer weed that you start seeing. So if you don't have a pre-emergent herbicide down during that period that's active, then you're not going to control this plant very well. So you have to think about the strategies. And if you know about the history of the weed problems that you've had, you can start thinking about, okay, what I got to do is try to control these. With the yellow nutsedge, you don't have to use post-emergent type herbicide. And that can be limiting depending on where you have the yellow nutsedge growing.

Glyphosate will work really well on it as long as you have the right rates. And you can use a product called Sandea, which I'll show you a list of these as we go forward here. And that'll selectively control it in landscape situations as long as you keep the spray off of most of the landscape ornamentals.

And then on top of that, I'm going to try to hopefully beat into your head that you need to really consider using pre-emergent herbicides, but on particularly annual type plants. But the life cycle of plants are either annual or perennial, and sometimes they fall in that gray area where they're a biannual, where our plant is. It's going to last about 18 months to 24 months, the plant will stick around. It's usually most plants that are biennial are about 18 months from seed to finally when they perish or die and then pass their genes on through the seeds. But annuals, of course, will only do that by seed. Perennials, of course, can do that from seed or vegetative structures. For example, we meet bermudagrass all around and sod. And then with plants like yellow nutsedge, we come in either containerized ornamentals or bald burlap ornamentals or in sod.

And then, but plants like dogfennel, they come from seed. Originally where they blow out like dandelion seed growing, bland in a dandelion field germinate. But once that plant's germinated, it's going to come back as a perennial. We require a very different weed control method to control it. And you'd have to go back to use the selective post-emergent herbicides. And we'll talk about those here in a little bit.

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## Weed Control Methods: Physical Removal

**Mark Czarnota:** As far as the control options, you have physical removal, physical barriers, and chemical weed control. And these are my categories of weed control. I try to simplify it as best I can. And of course, I'm going to talk about each one of these, the first three very briefly, and of course, chemical weed control. I'm going to spend a few minutes on that one.

As far as physical removal, that's just tillage, mainly used in bed preparation and hand removal, can be useful with annual type shallow-rooted plants. That's really, in the fields I work in, that's pretty much all we can do, utilize our own as far as tillage. And the physical removal also would be when encounter, we can use heat or flame. That's used quite a bit in the industry. It used to be a lot more, but the flamethrowers can be used in landscape situations where you can buy propane tanks to burn stuff down.

But anyway, I was talking about heat being utilized in the soil system and of course fire in the landscape type system. I mean, in the forestry system. But anyway, they have all, there's going to be a lot of automation come in certain situations, particularly like vegetable situations. Like this is an auto hoe I took out this past January or February out of the publication I get. And this is a type of situation where you're growing like broccoli, they can scan the surface and they know exactly what the broccoli leaves look like, there's mechanical pickers inside that machine, they won't let us look into it because it's proprietary, and but then you're going to see these type things develop as we move forward in a lot of situations. But we got a long ways to go, but I think as time moves forward, it's going to be a very popular thing because they don't require an insurance policy or 24 hours a day, seven days a week and don't complain about bathroom breaks.

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## Physical Barriers: Fabrics and Mulches

**Mark Czarnota:** As far as physical barriers, all these are, if you really think about these are just a fabric or some type of carrier on the ground to prevent the seed from germinating. And that's the whole goal of these. And there are fabrics, films, layers that smother plant growth. There are many synthetic fabrics that allow, you want these fabrics to allow air and water to pass, but prevent the weed seed from popping through. And there was lots of research done on this in the 90s, they're used to generally in combination with some type of mulch being inorganic mulch like stone or even regular mulch that are organic mulch which I don't recommend. And they can, they're usually about 10 cents a square foot somewhere around that barrier. They prevent weeds from — and weeds often penetrate these which can be a problem. But as long as you keep the UV light off of them, you don't, they can last eight, ten years no problem. Unlike plastics where they, six plastic is for about three years roughly is what we get out in the field until it naturally starts falling apart, in like blueberry situations.

As far as mulches, there's organic and inorganic. And organic mulches would be like pine needles, pine bark, wood chips. And inorganic mulches, inorganic would be like river rock, stone, marble chips, lava rock, so lots of these out on the market. Organic mulch should be composted. Make sure there's no wood in them or very limited, less than 10%. You should see that white wood. That's what you don't want to see. But if it is, it just needs to be composted for several months to get rid of that, to make sure it's not going to affect nitrogen uptake with your plant.

We try to maintain the two to four inch layer of mulch to maintain good weed control. We probably want to do that once or twice a year at least to keep the mulch layer refreshed. And this helps maintain soil temperatures and moisture as well as adds organic matter. But a big thing I used to tell and always remember is you have bare soil, you're going to have weed growth. Try to remember that. You have to get mulch or plant material growing on that.

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## Biological Control

**Mark Czarnota:** So anyway, as far as bio control, there's not that much out there that most of us at the research level. And, but there are some situations where it works well. I do answer questions quite a bit on aquatic weed control, but there's, these are pathogens, insects and grazing animals can be used for weed control, but grass carp are very popular. And if you have a small pond, we'd recommend about eight, 10 grass carp per surface acre. And they do a really good job of controlling stuff over time. A lot of the emergent weeds, a lot of the submerged weeds, and they're pretty good.

And a lot, there are some people I see use geese. And of course, goats, I'll show you a picture of one that I saw. And geese, they run them around in a lot of nursery situations, and they'll eat a lot of those small seedlings, weed seedlings coming up. And then pathogens and insects are hard to develop. They can move the desire of a plant and have a short shelf life. A few marketable products are available.

There was a product that called DeVine that was real popular, that was popular with the citrus growers to control Florida Strangler Vine, worked real well. When it worked so well, it killed everything and they couldn't sell it anymore, but they didn't plan on doing that. But that was one of the reasons that they, like the USDA and the company worked on it together, put much of our investment in it, but it was an organic type of thing, worked real well.

Goats are one, or sheep are one, where this picture I took where they were, this was our ag forest field day, probably six years ago. And anyway, the guy came out from Fort Valley, fenced in an area of kudzu, and this was in about four o'clock in the afternoon. I came back the next morning and this is what it looked like. It'll be a real good situation where you can come in here and chop all this stuff out now and you can use herbicides on regrowth. It would be a good example of a combo combination type attack and control on weeds where you use an organically type situation and also chemical means also.

The biocontrol on the thistle weevil worked really well too. And it was a one where you would actually release this weevil, the thistle weevil eggs around these thistles that are biennial. They would hatch out, produce a little worm. You could see in the second picture. It's right here. And that would actually choke out where all the seeds are developing, prevent a seed or really cause the seed development to not develop so well. And you'd have very limited production of the seed. So you don't get much of the regrowth. So over about a two, three year period, these little weevils can eliminate a lot of this problem. And so it worked as a good example of where bio control worked really well.

We might not see many of these organisms develop in the future, but you'll probably see a lot of their products or mechanisms come to light. I think you'll see a lot of that. The first bioherbicide virus was released back in 2014 for a controlled tropical soda apple. That was a real interesting thing they came out with, but it was a thing out of the University of Florida.

And the first top picture is a picture of my doctorate degree where I worked on — this is actually a root hair, root hair is touching the glass slide and off the slides, there's this root exudate coming off. So it's very similar to a product called Atrazine, which you're familiar with. And that product actually, that plant product is also fairly toxic, but it does a really good job of providing pre-emergent control. And I spent four years of my life working on it. I could tell you a whole lot of information about it, but you'd probably be bored to tears. But anyway, what we were hoping to do though, is take that, the genes that produce, they're able to produce that and put that in another plant like rice and overexpress it. And then maybe get a plant to produce some herbicide. But anyway, there's all kinds of problems with that, but it's a great idea.

This will be a picture of the thistle that we were released in 1990 and what it looked like in 96. These pictures off of Dr. Bunn and I can see what's working with this in the nineties. And it worked quite well. And usually when you work with grown-up pasture people, you might get a bush hog to be the best means of weed control. And this is something that would work real well, I think, for people, particularly on these invasive type weeds like thistle. It was a weed we brought in and imported it. It became a problem. And, of course, cattle don't like to eat it.

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## Chemical Weed Control: Impact of Major Herbicides

**Mark Czarnota:** So our chemical weed control now, I'm going to talk a bit about this and hopefully I'll get you something before that. Hopefully you'll learn something from this.

But anyway, the chemical weed control is usually, it's sometimes the last alternative. And it's usually combined with other control measures for controlling weed. The products are safe when used properly, most of them have been around for longer than 50 years. They are easy to use and save hours of labor. And there's some products that really have huge impacts on food production. But 2,4-D, atrazine, and glyphosate, they've changed the world forever as far as production. And most people don't know, 2,4-D is still, I think, number one produced herbicide in the world. It goes back and forth between glyphosate and 2,4-D.

But anyway, 2,4-D, it works real well in row crops that are grass crops, kills broadleaves for you. And there's a lot of plants that are getting transformed to be able to handle 2,4-D applications over the top of them. So, for example, if you can put a 2,4-D resistant gene in soybeans and kill off plants that might be resistant to glyphosate. So, we're doing a lot of that type of stuff now, but these three products have impacted our abilities to produce our food and allow people to do other things in life, be doctors, lawyers, economics people, entertainers. Otherwise, they'd be out pulling weeds in the field. And I don't like doing that.

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## Pre-Emergent vs. Post-Emergent Herbicides

**Mark Czarnota:** Now, hopefully you can listen to this. This is where you might gain some really good information. But of the herbicides that are out there, there's pre-emergent herbicides and post-emergent herbicides. Those are the main two categories we have. And pre-emergent herbicides are applied to bare soil mulch before germination seeds. They need water to move or activate the soils into the seed germination zone, which means you want to put these products on before the seeds come up. So I'd recommend January, February for most people around here in Georgia. And then you need a rain event of about a half inch to an inch to move the product into the first quarter inch of the soil you hope, because most of these products are really watering solid. And then you'll get about at least 8 to 12 weeks weed control where it will interact with any germinating seeds that prevent them from becoming an issue.

Most emerging herbicides are applied anytime after the seeds have germinated and they need a certain period of dryness after the application. For example, a product like glyphosate or Roundup, you might be very familiar with. You'd apply that, spray that on a plant leaf or a plant, it would dry and then be absorbed into the plant. With glyphosate it's a phloem-loaded product which moves around the entire plant system, which is, we don't have very many of those. And it would control the plant by cutting down the production of three amino acids. And that would be the two differences.

But some herbicides actually work, can work as a pre and post-emergent herbicide. But there's plenty like glyphosate, which only is a post-emergent herbicide. And if you spray it on the ground, it's inactivated immediately because it falls to the soil particles and come off until it falls off as carbon, hydrogen, and oxygen.

This is just a quick shot of what most of the seeds that germinate, we have a seed bank, anything less than about a quarter inch of soil, most of those seeds are in what we call seed bank. Anything above quarter inch in this plant that could be actively germinate and grow. Most of the pre-emergent herbicides you apply and when we get a rate of that, they move or migrate in that top quarter inch of the soil where the germinating seeds, where the hypocotyl usually comes out first and then the radicle comes out. And then they can get absorbed on either the hypocotyl or the radicle and absorb a couple of herbicide molecules. And then those herbicides cause usually problems. There's some biopathway that inhibit the plant from growing well and allow the other plants to grow, canopy over, and eventually these plants will die because they just can't grow. It's what you hope. Sometimes they can linger for quite a while.

As far as the pre and post-emergent herbicides, we have selective and non-selective herbicides. Selective herbicides control a certain group of plants that are safe like 2,4-D and then a non-selective group like Roundup where they control everything they come in contact with. So you should remember that.

And then just some examples of ones like we got Preen, which is a pre-emergent herbicide. There's a couple of different versions of it. The regular Preen was just trifluralin. Preen Southern, which you might be familiar with, has dithiopyr, which I think is one of the most underused herbicide, pre-emergent herbicides on the market. And then we got, of course, Roundup, which is the post-emergent herbicide Roundup, which has gained a lot of notoriety because of some of the court cases. And then we have one called SedgeHammer or ProSedge, if you're familiar with those, which can kill nutsedge that's emerged, but it can also have some pre-emergent weed control on even nutsedge and a lot of annual weeds coming from seed.

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## Herbicide Formulations

**Mark Czarnota:** But anyway, the formulations of herbicides are made to be applied as dry, as granular. So they either put the herbicide on a granular and it's usually on a piece of, it's either kaolinitic clay or it's on biodeck, which is newspaper, or it's meant to be formulated and applied with water as a carrier most of the time or as a liquid. So you can either create, the formulations are created to be applied dry as a granular, be a sprayable or a use of water as a carrier. And sprayables can be a concentrate that's either a liquid or a dry. So either one of those could be, you know, it just depends on chemical manufacturer and what's the best way to formulate that product is what I can tell you.

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## Trade Names, Active Ingredients, and Cost Savings

**Mark Czarnota:** And then just as an example, the trade name would be Roundup. The active ingredient would be glyphosate, the full chemical name. If you want to know exactly how to draw a molecule, you would use that chemical name. And then you could learn a lot about that molecule's charge and activity and whatnot by knowing that. But what I'm most interested myself in is the active ingredient or common chemical name. If that product tells me it's glyphosate and I know the formulation, I always look on there and tell you how many pounds per gallon. If it's a four-pound gallon, I know exactly how much to put out. I get decent weed control most of the way, and I can make that information.

I used to get a lot of questions on — I was on this glyphosate product that works real well, and it's half the cost of regular Roundup. It works great, and I tell people to use it. But if you can arm yourself to start looking at what the active ingredient is, you can save a lot of money. I guess is what I'm trying to get across, because it's just the same way with like designer clothes and things like that. Once the product comes off patent, a lot of people start to make it and it's the same product and just in a different container for the same uses that you might be utilizing before. So that's something to keep track of.

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## Herbicide Modes of Action

**Mark Czarnota:** As far as the modes of action, it's real important for some people to understand this because you cannot understand how the product is, realize it, maybe the safety of it to you and whatnot. But for example, glyphosate, it inhibits what we call the EPSP synthase pathway, which is production of three amino acids. So it's tryptophan, phenylalanine, and tyrosine. You might not know about that pathway or the amino acids, but the important thing to remember is those amino acids, we have to eat those to get those. We don't have that pathway in our body. And this is what makes glyphosate so, one of the reasons it's so non-toxic to us in the environment, because no animals have that pathway. So it works on a pathway that's not even in our bodies.

And then as far as the mechanisms by which plants detoxify these herbicides, that's sometimes called a mode of action too. And for example, a lot of people want to know why 2,4-D is not, it doesn't hurt grasses. And it's mainly because there's several ways plants actually detoxify that herbicide. But there's this one called NIH shift, which basically means that the plant has an enzyme system that can gobble up that 2,4-D molecule and change where the actual chlorine groups are on the molecule and inactivate it. That's what the grasses do. One of the ways the grasses deactivate that herbicide. So it's quite fascinating.

But what I understand these modes of action, like I mentioned, is how to use the herbicides, better understanding of how they perform, diagnosis of herbicide injury, make you sound like you know what you're doing in public. You can explain this information to the public and try to make them less scared of it.

### Dinitroaniline Herbicides

**Mark Czarnota:** Some of the ones that you might really be understand or help you to understand is the herbicides would be the dinitroaniline herbicides. You might be from everything because they're colored. They're either orange or yellow. And Treflan, which would be one, pendimethalin, Surflan, benefin, and Barricade would be ones that are in this mode of action. And they cause what we call microtubule disruption. And that's actually when the cells go to divide in a plant, the chromosomes go to two different, they'll divide and then they'll get pulled two different ends of the cells. And those organs that pull the chromosomes apart and make them equal on both sides of the cell are called microtubules. This herbicide binds onto there and prevents them from happening and or messes this whole system up and plant can't lay what's called cell plate down and make another cell basically. And that's why you see this club rooting on the left on the corn that you see, and this happens a lot in growers fields that they put somebody in a previous crop put too high of a rate of one of these herbicides down and this can cause big problems.

But anyway, they're mainly used as pre-emergent herbicides to the backbone of the ornamental industry still. And they can also change ploidy numbers. They have to spray a high rate on the plant and try to get ploidy number to change. If you're a breeder and can change chromosome number basically, because the plants can't, the chromosomes will get doubled a lot of times because the cells will pull apart and that cell that becomes stuffed, you can get a different plant to come off of that if you grow tissue culture or it can even come out of some different shoots sometimes. But it's interesting.

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## Pre-Emergent Herbicides for Landscape and Nursery

**Mark Czarnota:** These are all the herbicides that are available to the landscape industry, these are all the pre's that are available and I could talk and bully to death about all these but I'm not going to do that. And anyway, Surflan is one you might be familiar with, this one has come off — it didn't come off the market, the last plant that manufactured it actually blew up. It's unavailable to the growers today or it's what you can find on the market, so you can get — it's pretty much gone.

A couple you might want to know is Dimension is one of the ones that's one of the least utilized herbicides, needs to be utilized more in the landscape and turf industry because you can spray this in most turfgrasses on most landscape situations, pretty much all the broad woody ornamentals, there are even some perennials and annuals you can use this product on. It works very well. And I'm very impressed with it.

Broadstar or flumioxazin is one that's really good. As far as it comes in, this is granular formulation. There are also a sprayable formulation called SureGuard. And then Marengo and Specticle is a indaziflam. This is probably one of those best products I've tested, but it's mainly for just the woody ornamentals, established woody ornamentals. But you can get upwards of 16 weeks of pre-emergent weed control out of this product.

And of course, isoxaben is a great product if you do sprays, but if you spray this, you can spray it with a product called Pennant and get really safe weed control on very young material and lots of perennials and annuals. So anyway, but these are all pre-emergent herbicides and pretty much all of them are available for use of container or shield-grown ornamentals or landscape uses.

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## Post-Emergent and Selective Herbicides

**Mark Czarnota:** And these are post-emergent herbicides, just as I switch gears, these are the ones that are available for the post-emergent control where you can use them. And you can see for non-selective herbicides, we have Reward, Finale, Glyphosate, Roundup, Goal, and Scythe. And the only one of these products that's actually systemic and will move around and plant and kill it is Glyphosate. So it's a real important herbicide for us.

The grass herbicides, you might be familiar. These are just products, grass products, these burn down emerged grasses, and they cause control of the grass. And so they work real well, controlling emerged grasses. And then as far as selective weed control, we hardly have anything. So that's why it's so important to control things pre-emergingly from seed.

But we have Basagran and product Image, which is still, you can find it difficult to find, but those two products used to be used to control yellow nutsedge and purple nutsedge. Basagran controlled yellow, Image controlled purple. And that's the main reason we had those products. They do control some other weeds. And then of course, when SedgeHammer came out of ProSedge, that pretty much eliminated the need for Basagran and Image. But that controls yellow nutsedge and purple nutsedge fairly well in turfgrass situations. That also is post-directed application in the landscape situation. And so is Certainty. It's like that also.

And then of course, Garlon is utilized. I put this one in here because it's in the Brush-B-Gon products that a lot of people had a hold of for controlling brush. You can paint this product on a stem like an oak or a pine that's coming up in your landscape bed and it'll keep it from emerging and just cut it off and you don't have to dig it out.

And then that's pretty much all we have.

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## Combination Granular Herbicides

**Mark Czarnota:** As far as the combo herbicides, these are granular herbicides you might be familiar with, but these products are used as pre-emergent herbicide. Some of them have a product called oxyfluorfen in it, and this product naturally will prevent when the seeds germinate, if it's not beyond the two to three leaf stage, you can use these products to have oxyfluorfen in it that will prevent or burn down the germinated weeds and also have a good pre-emergent herbicide like, for example, an OH2 and pendimethalin. And they give you a good eight to ten weeks of weed control in that container. And these are mainly used by container growers. Most of these could be used in the landscape, but most of the sales are container people.

And the most popular one is probably for a long time, Snapshot. And it's because of safety, as isoxaben and trifluralin, it's very safe in use and a lot of plant material. But these are great products. And you utilize all these products, too, I should tell you, from 100 to 200 pounds per acre.

But anyway, a lot of people ask me about annual and perennial weed control. But of those products, I just listed, Cancel, Snapshot, XL, FreeHand, Treflan are very good but I would highly recommend Snapshot, XL, and FreeHand are three, they're really good. The only problem is XL has a oryzalin that's going to be around once, once all the stock is used up.

As I mentioned about Surflan, hopefully AMVAC is going to make some agreement with China to try to come back. That's basically where we're going to head. And the earliest will be available, it'll be late 23 now. That's not going to happen anytime next year.

And then alternatives for Surflan would be Pennant Magnum. I would use it from 20 to 42 ounces per acre. And you can do up to 67.2 ounces per year. And it's a re-entry interval of 24 hours. And you can tank mix it with Simazine or Gallery for really good broad-spectrum weed control.

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## Recommended Products: Marengo, BroadStar, SureGuard

**Mark Czarnota:** Anyway, I'm going to skip. So I'm going to try to fly through this year, but the new herbicides that are out there, Marengo came out about three years ago now. And a lot of people still don't know about it, but you can use it in landscape. And if you're growing ornamentals in either containers or in the ground, that is a product you need to try. And any share of a landscape situation, I'd highly recommend.

But also Broadstar is another great one, which is a granular form, but you can buy. The sprayable form is called SureGuard. And then, of course, I always spray the Snapshot, FreeHand, I mentioned to you about the safe weed control. Safety, desirable plants can get fairly decent weed control.

And just a slide, you can see Marengo 16 weeks after treatment, a pecan study I had out, how great it works. The only thing that would be problems here, if you had nutsedge, it would not control nutsedge and that Marengo would fall apart.

Just some sprays you might be interested in, Gallery, of course with Surflan, if you can still get it, Barricade, Pendulum, Marengo, and SureGuard, they can stand all by themselves. And be a great product and get weed control from 10 to somewhere between 12 and 16 weeks, even in South Georgia.

Just a picture of a slide. When you're using pre-emergent herbicides, this would be just when I was looking at a product called Tower and I'd put weeds in the pot. It was a sabal palm. We control, you could imagine weeding out an acre of ornamentals like this. It's going to cost you about $1,200 to $1,600 an acre to pull weeds out of one gallon pots on an acre. And I can easily do a weed control for less than $200. You don't have to do that about three or four times a year, which would, if you had hand weed, you'd do that probably two or three times a year, which you'd go bankrupt trying to keep yourself in business.

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## Best Practices and Common Application Errors

**Mark Czarnota:** Just good things to remember is good weed control doesn't happen by accident and will not last and takes time. You never get 100% weed control with a single application on pre or post herbicide. You're always going to have to go do some hand weeding or some post-directed applications of herbicides. But you need to think about what you're trying to control and have some plan that you're trying to attack stuff.

And this time of year is great because you get a reset. We'll get a frost to kill all the annual weeds. And that gives you a little time to adjust, get some herbicides if you need them or make a plan of getting some mulch down and using it maybe some herbicides in combination to try to get rid of some problematic weeds. I mean, you know that there's, for example, if you have a lot of chamber bitters, like I showed you a picture of, you could get a pre-emergent herbicide like Dimension or Marengo down during that timeframe. So if you put it down, maybe an application in January, February, and again in April, May, you're going to have pretty good weed control of those problematic weeds.

I'd love to have a selected post-emergent herbicide for every weed we have, see it and treat it, but that's not reality. But currently the best way to control weeds is with pre-herbicides. And then granules do provide poor control of the sprays, but are much safer. And people often ask me why do they have so many different formulations? But the granulars will fall through the canopy of the plant, hit the ground. And then when you get a rain event, they ooze out from those granulars and then give you weed control. But sprays come in contact right with the plant, which increases the possibilities of damage. But sprays are always cheaper to get the same amount of active ingredients just because the fact that most granulars are 2% active, but sprays can be, the bottle you get, can it be upwards of 90% active.

Some errors I see: no rain after pre-herbicide applications, rained after post-herbicide applications, poorly calibrated equipment, poor choices in herbicides, and using a pre-herbicide after most of those weeds have germinated. Most pre-herbicides aren't going to give you control with that.

And then if you're doing field applications, I do two to four applications a year. If you're doing container weed control, you're going to have to do about four to six applications a year. With pre-herbicides, try to use at least two different products. But if you use the combo herbicides, this really is a problem. And make sure you have a rain event after you put a pre-herbicide on. When you get in that May, April, May area here in Georgia, sometimes we don't get any rain. And you put a pre-herbicide down and you don't get any range within 72 hours, you're going to start losing weed control with that product.

And then also two to four inch layer of mulch, like I mentioned, is a great pre-emergent herbicide. In a case situations, once the plants can be, herbicides or applications should be rare at that point. But you can just come back and do just manually pull the weeds out or do a post-directed application or even paint a product like glyphosate on a blackberry or something to get rid of it. Those are things that you can do to get rid of stuff.

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## Glyphosate Application and Safety Data

**Mark Czarnota:** And then anyway, as far as only spray glyphosate on a live growing plant material, you don't apply glyphosate solution to the trunk of base of thin bark trees and the herbicide applications need to be dry, need to dry before rain, otherwise it's not going to work well. And glyphosate, remember, is the only broad spectrum herbicide.

And this is just a slide here of all where you can get the actual MSDS sheets or the safety data sheets, SDS sheets, they call them now. And then, or the labels, but this, the CDMS.net probably has 80% of all the pesticides you might come in contact with. Otherwise, you're going to have to get contact a manufacturer's website to find it if you want to get it.

---

## Herbicide Fate, Half-Lives, and Organic Options

**Mark Czarnota:** And then a lot of people want to know where herbicides go when they break down, but most of them actually bond to, they're absorbed by the clay or organic matter and hang out until they break down. That's usually what happens to them. And if you're interested in seeing how long they, the half-life of them, which is how long it takes to go if we extract the soil to see the original amount to half of what we put out — a lot of people might be interested in this. Glyphosate takes about 50 days to break to get about half of what you put down to go. And then you probably need two or three half-lives until you can't get it. And you couldn't extract it anymore. But 2,4-D is about 10. Post herbicides about five. And glufosinate might be, right, whether it's only about seven days. It breaks down very quickly.

So on the organic products that are out there, they're all burned down products. And the last time I checked, which is less than a year ago, there was acetic acid, all the these, one, two, three, four, five, six, seven, eight, burned down type products that are either oils or acids. And then you also pre-emergent, the only pre-emergent herbicide we have is corn gluten, put it down at about 2,000 pounds an acre, which obviously is not useful here, but it could be useful if you're working out in Iowa where they produce a lot of corn.

---

## Glyphosate: Formulations, Safety Research, and Damage Symptoms

**Mark Czarnota:** And then glyphosate, lots of new formulations that keep coming out, if it's a four-pound gallon or the 41% active, you use it between a quarter of a 10% solution, but 2% kill almost everything. If you're wicking it on, you want to use 25 to 50% and then stuff. She can use a 50 or a hundred percent solution to kill weeds.

And then I don't, I'm going to go, I'm not going to go through this, but let's say basically came under scrutiny and it's still a problem. There's lots of lawsuits out there has settled with them. I think, but, a lot of people asked me if glyphosate is safe. They found out there was, in 2017, the Journal of the National Cancer Institute reviewed glyphosate of 44,932 licensed applicators of glyphosate, North Carolina, Iowa, 5,779 indicate incidents of cancer were out of these 44,000 were noted, but it's no different than the national average background actually of people getting cancer. So there's really no association between glyphosate and any solid tumor or lymphoid malignancies overall is what they concluded. And a lot of people ask me, is glyphosate safe? It's a registered product. It goes under heavy scrutiny from the US EPA and European EPA for human toxicity, environmental impact. And if used correctly, the evidence is that glyphosate is not likely to cause issues with us.

So anyway, if you're interested in that, and if you spray continually like glyphosate on the base of crape myrtles, it's kind of damaging. We call it bud blasting. And if you have glyphosate mixed in your tank, there's a picture of hydrangea below guys showing you the difference in the bud. But this will be an example of the guy above, holding it, this would be a sublethal dose, plant still comes out, looks terrible and people want to ask me how long is it going to take for that plant to come out. The picture of the crape myrtle on the left, it needs to be torn out, replanted. The picture of the hydrangea on the bottom, if you prune that back, it'd probably come back in probably two months.

---

## Adjuvants and Stump Control

**Mark Czarnota:** And then anyway, the surfactants, just make sure if you have to use a surfactant or an adjuvant is what the umbrella is, that you use it. You can decrease activity from 20 to 40% if you're not using an adjuvant when you need to.

And then people often ask about stump control. Don't forget you can apply glyphosate as a paint, selectively apply it so you don't have to spray it. And keep it away, but you could paint glyphosate on a, for example, or a triclopyr on a piece of, and that'll kill that plant. 90% of the time, that thing's not even going to re-bud. If it re-buds, it's not going to be happy.

---

## Emerging Technologies

**Mark Czarnota:** And, but there's lots of new stuff going on. And impregnated mulches were released back in 2012 with gly... They actually have Surflan on, you can buy them, and I've seen them available at Home Depot on Lowe's. There's going to be better herbicide formulations, vehicles for slow release herbicides. Our common target is targeting weeds with herbicides. That I could see being a big issue. There's laser machines out now. And I showed you a picture of the mechanical picker.

And that's all I have. I'm sorry I lost you. I would have been a little bit slower. But anyway, does anybody have any questions?

**Shimat Joseph:** Do you have time? I'd be happy to answer.

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## Questions and Answers

**Shimat Joseph:** Thank you so much, Mark. Is it, anybody has any questions, please, you can use the Q&A box and type it there. And I can ask. It looks like we have a question.

### Torpedograss Control

**Shimat Joseph:** So this is from Robert, asking, having a difficult time with torpedograss, what would you recommend to control?

**Mark Czarnota:** Okay. I guess you had, I guess I can repeat the question. Guy has trouble with torpedograss. Oh, that's a great question. And I have an answer for you. I don't know what it's growing in, but there's a product actually called Drive that works really well on torpedograss. And you, Drive is not labeled yet for use in overtop ornamentals, but we're working on a label for that or that we're, I don't know where it got to, but we actually got it for weed control in blueberries and blackberry, but it does control torpedograss very well. And I don't know if that would be an option for you. I don't know where it's growing in turfgrass or in ornamentals.

But I've done some studies with it at the university here. The product Drive, quinclorac, you would have known. It's fairly safe on most woody type ornamentals. But again, it's not labeled. You'd have to do experiments yourself to decide. It wouldn't be a label application. You'd have to just try it out and see how it works and then hopefully we get a label for it.

### Virginia Buttonweed Control

**Shimat Joseph:** We have time for one more question. I think the other question that popped up is a control of Virginia buttonweed in turfgrass. Do you have any other conditions?

**Mark Czarnota:** Yeah, buttonweed, I don't do turfgrass, buttonweed, weed control, most of the time you can use — it depends on the turfgrass variety, but you can use atrazine or there's a couple other of the products like Revolver or Manor or Monument. They have some activity on that plant. It's a very difficult plant to control in turfgrass. And even if you get it creeping into the landscape bed, which often happens, it can be difficult.

But, you know, in turfgrass, atrazine is probably the cheapest way to go. If you do probably two applications of a quart per acre each time, if you use the four pound gallon. But anyway, Patrick would be McCullough, Dr. McCullough, or I call him Patrick or he can call him Pat too, I'm sure. But he does turfgrass weed control, but that's a big perennial problem. And that's a plant too that sometimes over winters, as we get global warming, you know, a lot of these plants that sometimes aren't, are just annuals are starting to be perennial because they're not getting killed back. And that's one I'm saying starting to make it through South Georgia winters. But atrazine, again, for turfgrass would be probably the cheapest route if you've got Bermuda or zoysia or turfgrass that atrazine can help.

### Bermudagrass Control in Ornamentals

**Shimat Joseph:** I will take one more question. So this is from, what is your recommendation for selective control of bermudagrass in ornamentals?

**Mark Czarnota:** Okay, that's another great question. When you, anytime you have bermudagrass creeping into your ornamentals, I really tell people probably the best product that, that I, that's out there currently that gives you the best activity — but there really isn't much difference between all the grass herbicides — it would be the clethodim or the Envoy product. That one works really well and it'll beat back the bermudagrass probably for a, old for you, you probably get three, four months before you have to do a retreat.

And basically, for example, if you have junipers and bermudagrass creeping into it, that's a really good option to do that. You just spray that band where the bermudagrass is meeting with junipers and it'll do a good job of keeping that back. But any of them work okay. We would have Segment, Envoy, Fusilade, which would be DX, and you can buy that as GraspiGuard also. Those three products all work fairly well. But clethodim probably gives you about 10%, 15% better activity, if I had to tell you that, from what I've seen.

But Glyphosate works really well if you get the rates high enough. But of course, you can't use that selectively like you can't in the grass herbicide. So if you spray that over top, [laughing] you're not going to be happy. It'll kill both the bermudagrass and any desirable plant that you want. But that's a great question. That's often a big question, I guess.

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## Closing

**Shimat Joseph:** Yeah, Mark, it looks like we have more questions popping in, but I would say we need to wind up now for the next speaker.

**Mark Czarnota:** All right, I'm sorry. I'm sorry it dropped me. I'm on a satellite at home. I'm on a satellite at home, Shimat, so sometimes that happens. And I'm going to update my computer this weekend. Yeah. So I have a much better video card. So anyway, that's good. Thanks for having me. Hopefully, thank you so much.

**Shimat Joseph:** Thank you so much for the presentation today. Okay.

**Mark Czarnota:** Okay. And they can give them my email and I could try to answer their questions if they want to. I guess you'll give them that.

**Rich Braman:** Nice. Right. Yeah, we can do that. Anyone who didn't get a chance to have their question passed to Mark, if you go ahead and follow up with him in email and we can pass that out today at the end. Just go ahead and do that.

**Shimat Joseph:** So we give day—

**Rich Braman:** Thanks for help Richie too, I appreciate that. You bet. All right folks, we're going to go ahead and jump to break now for just a little bit under five minutes. Thank you Mark, have a good day.

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*Transcript processed for UGA Center for Urban Agriculture / GTBOP Archives*
*Source: Corrected SRT (Stage 1) — GTBOP_Transcript_2021-11-18_WeedControl.srt (786 blocks)*
