Arkansas Turfgrass Association – The TurfZone Show Host with Matt Bertucci
TurfZone: Before we start talking about crabgrass control, first tell us your background and your position.
MB: Sure. I’m a newly hired research scientist at the University of Arkansas. As a research scientist, I’m not quite faculty, not quite a post-doc, I fall between there, but I have my own research program and I’m responsible for weed and vegetation management and turf, pastures, roadsides and specialty crops, so it’s a real big grab-bag of responsibilities. I like to think I’m pretty well prepared for it. My background – I got a Ph.D. in horticultural weed science at NC State. I was studying weed control in watermelons, so I learned about vegetable production systems, and I have to tell you, turf is pretty far different from the vegetable production. But you learn all the fundamentals of weed science, you learn different management strategies and I think it’s something that I’m really excited to take on.
TZ: I know our turfgrass managers are going to be very interested to hear your insight about crabgrass. Tell us how do we recognize crabgrass, and why don’t we want to see it in our turf?
MB: I think a podcast is a kind of difficult format to help people with weed identification. The fact of the matter is, proper weed ID is most easily achieved with experience. If you’ve seen crabgrass over and over, it starts to become familiar, where you can pick it out a mile away. It’s really undesirable because it’s got big, coarse leaf blades and it has a paler color than usually our desired cool season or warm season grasses. One thing you can look for if you’re holding the grass up from the leaf blade, if you pull back toward the stem, you should be able to observe a membranous ligule (that’s the little organ right between the leaf blade and leaf stem.) If you’ve got large crabgrass that’s going to be hairy all along the leaf blade and the stem and along the sheath. While smooth crabgrass, it’s a little bit difference, wouldn’t have those pubescences (hairs). Crabgrass is a summer annual, that means it completes its life cycle in one year as an annual weed species. Typically with our annuals, we really want to prevent annual weeds from setting seed at all. If you happen to see large crabgrass or smooth crabgrass flowering, it has a very characteristic inflorescence. It has racemes that digitate, they look like fingers protruding from the stem, in an alternating pattern and that actually is the way that it got its Latin name, digitaria sanguinalis in the case of large crabgrass. Or digitaria ischaemum for smooth crabgrass. So that’s something that you can remember. If you ever see those flowers, first thing, you should try to keep those out of your property because you do not want annual weeds setting seed. But if you’ve ever seen those flowers it’s something that can really easily be recognized.
TZ: Now that we know how to recognize and why we don’t want crabgrass, let’s talk about preemergence herbicide. When and how should turfgrass managers use those herbicides for crabgrass?
MB: As I mentioned before, large crabgrass is a summer annual weed species, so that means it’s emerging when the soil temperatures get in the mid-50s to 60 degrees Fahrenheit, then it will germinate from seed and it will start growing vegetatively over the summer, then go through its life cycle over that summer season. With a preemergent herbicide, the objective is to target that weed as it’s germinating from seed. That means that we need to put out our preemergent herbicides before the soil temperatures reach that time, so that would be late in the winter/early in the spring that we can achieve those preemergent weed control strategies. In Arkansas you’re looking at late February/early March. Depending on the residual activity there are different preemergent herbicides, so if you have a really busy schedule, you might try to put it out as early as February, but again, the closest you can get it to the emergence or germination, that’s when you’ve got your longest residual activity after the application. Typically what we’ve considered the ideal timing would be late February or early March.
TZ: So we’ve obviously already applied our preemergence, but why might we need postemergence? Is it difficult to control all crabgrass with preemergent herbicides?
MB: There’s several reasons why a preemergent herbicide application might not have worked. You might have put out your preemergent herbicides and you come back to the site and there’s crabgrass that’s rearing its head. It’s coming up through your turf and you’re probably thinking “This didn’t work at all, this product’s no good.” In extreme cases people want to say that they’ve got herbicide resistance or herbicide resistant crabgrass species and realistically it’s more likely that certain issues, and they’re very common issues, have come up. So if a preemergent fails, you might take a look at the pattern. A lot of times if you go in kind of like a detective and you look for clues as to what could have gone wrong, you might get an idea what the issue was.
So if you see a strip right across your property, and everywhere else there’s good control, but there’s this one strip where crabgrass came through, I think most experienced managers would recognize that “We just didn’t put herbicide there, did we?” That could be that the applicator made a mistake when going through the property. Another possibility, and this is something that I’ve seen on some of the research stations prior to me arriving at the University of Arkansas, but it’s very common for people to continue applying and not realize that they ran out of product, and so a lot of times at the very end of the application, the solution isn’t coming out in the same volume or the product has run out and you end up getting no control. There’s all sorts of reasons why you might not have delivered the product to the site, so be aware that that might have just been a mistake. It’s possible that you didn’t get the proper irrigation or rainfall event. These preemergent herbicides work by preventing or killing the germinating seedling as the germ tube is emerging from that seed so it needs to be in contact with those seeds and if you apply a preemergent herbicide and there’s no rainfall, all of that herbicide is stuck strictly at the surface of the soil. There’s no movement down into the soil profile without some sort of irrigation or rainfall event. That’s what we call an activating rainfall and if you didn’t have an activating rainfall, you can have major breakdowns or major consequences as far as preemergent weed control. Then really, a final scenario is that the preemergent herbicide worked and it did its job, and then it’s just broken down. So different preemergent products have different residual activities, so that means that they last for a certain amount of time and then biochemically or under environmental conditions that chemical breaks down, it doesn’t work forever. So it may be that you put out a low rate of that product and your application called for a sequential preemergent application, but you haven’t gotten around to that yet. So there’s a situation where there was no error, there was no mistake, the herbicide did exactly what it was supposed to, however, crabgrass has begun emerging. If you observe crabgrass emerging, that’s when you can’t rely on preemergent herbicides because by definition you won’t be putting it out before it’s emerged.
TZ: When we have that realization that the crabgrass has emerged, when should we apply postemergent?
MB: I think that’s the good news, right? So if you’ve got a preemergence herbicide that’s failed, there are postemergence control options. I’ve toldyou before that I’ve gotten experience as a vegetable weed scientist. As far as crabgrass control, it was very easy in watermelons because targeting a grass species in a broadleaf crop is very, very easy. They’re very physiologically different. With turfgrass, it can be very similar to the weedy grass species, so we need to be careful about the postemergence products that we select, because we don’t want to accidentally injure the desirable turfgrass species, so really what we need to do is look through the chemicals that are available, we need to think through – which of these will work, which of these are labeled for which uses. But as far as the crabgrass goes, the best thing to do is target those cragbrass plants when they’re small. The smaller the crabgrass is, the more susceptible it is to chemical control. If they get a little bit larger they produce full leaves, then they’ll begin tillering. Tillering is when they have a new shoot emerging that would then bear more inflorescences at the end of the season. As they shift to tillering, they become much more difficult to control and that would require not just postemergence treatments but sequential postemergence treatments. You’re very unlikely to have a successful single application with a postemergence product with a crabgrass that’s begun tillering. As a general rule, if you see that you’ve got emerged crabgrass and you’re thinking you’ll hit it with some postemergence product, the best thing you can do is act quickly, when those crabgrass plants are very small.
TZ: What are some products that turfgrass managers could use and what are the specifics of each of those products?
MB: Turfgrass managers are going to have a lot of different options, it’s really going to be based on what the use is, what the species is for the turfgrass in question. The first product that’s listed on this publication associated with this podcast is Asulam. That’s labeled only for sod farms, and specifically for use in St. Augustinegrass and bermudagrass only. So this has some postemergence activity on crabgrass, but again, only if you’re a sod farmer.
If you move on to Celsius®, that is a three-way mix with thiencarbazone, iodosulfuron and dicamba. That’s got a wide range of activity because it’s got different products in it, but that’s for warm season turf types. What you’re going to expect with crabgrass, it’s going to be the warm season, but Celsius® would be one product.
Now Dithiopyr, that’s under the trade name Dimension®, this is a good product because it’s labeled for preemergent control of crabgrass, but it also has some early post activity, so that’s good news, because if you put it out early and you want to use it for preemergence control, that’s one use, but then also, if you happen to get to a site a little bit late, and you see just very very small germinating crabgrass seedlings, you can actually put out this Dithiopyr treatment and it will achieve a level of control postemergence and also have that continued residual activity similar to preemergence herbicides. So it can kill crabgrass that’s emerged and then also the residual activity will behave similar to a preemergence herbicide. Dithiopyr is a very useful herbicide in that specific scenario where you see small emerged crabgrass.
Another option would be Mesotrione, which goes under several trade names — Lucto™, Slipstream™, Tenacity® — and that offers contact and residual weed control in turf. But be aware that can cause severe injury on actively growing bermudagrass, zoysiagrass, creeping bentgrass and even other turf species. With Mesotrione for postemergence control of crabgrass, that’s saying it has activity on the crabgrass, but really be aware, you need to look at the label, you need to be aware of which turf species it can be safely applied in.
Continuing, we have MSMA, that’s good for postemergence control of crabgrass, but again it’s only labeled for use in sod farms or in golf courses, so with MSMA, that’s not going to be for home lawns and you really need to make sure (and I’m going to reiterate this every time) you need to be familiar with the label use and the restrictions stipulated by those labels.
A new product that people should be aware of is Pinoxaden. This is a product under the trade name Manuscript®. This is a new Group 1 herbicide and it was released for control of torpedograss, I only saw it with a 24C label. Now it’s got the full registration for bermudagrass, zoysiagrass and St. Augustinegrass for sod producers. So growers should be aware that Pinoxaden is a new active that can be used in this capacity and it will have good control of crabgrass.
Really one that people probably would have expected to start on, I’ve just been going alphabetically, people would have expected me to start on for postemergence control of crabgrass, is Quinclorac*. That’s under the trade name Drive®, Drive® XLR8, and then also many others. That’s really the staple postemergence product. It can be used in many different environments. But be aware that St. Augustinegrass, centipedegrass or bahiagrass, those are sensitive to Quinclorac* and they’ll likely be injured by applications. You’ll probably see there’s a lot of different products that include Quinclorac and that are labeled for use for postemergence control of crabgrass. That could include something like Q4, SquareOne®, Solitare®. Those are all combinations of Quinclorac or quinclorac + sulfentrazone + 2,4-D + dicamba or any other combination of those products and quinclorac. But just be aware that quinclorac is the only one that really is doing any of that postemergent control of crabgrass. Those additional actives are helping with other weed species, but quinclorac is the one doing the lifting in these mixtures.
Now wrapping them up there’s Topramezone, that’s under the trade name Pylex™. That’s similar to mesotrione, it’s got that bleaching characteristic. That’s got postemergence control of crabgrass. The difference is that Topramezone is labeled for use in creeping bentgrass and that is not allowed for mesotrione.
Lastly, there’s Sethoxydim, under the trade name Segment®. That’s got broad spectrum control of annual and perennial grass weeds, but be aware, Sethoxydim is only labeled for use in centipedegrass and fine fescue. We call those the grass killers or the germinicides, that class of chemicals that Sethoxydim belongs to, so with the exception of centipedegrass or fine fescue, Sethoxydim can be very harmful to your turfgrass species. Again be very careful and make sure you’re familiar with the uses and restrictions of these products.
TZ: Sounds like we have a lot of options, as long as we’re aware of our turfgrass variety and label instructions. It seems like there are some good choices for turfgrass managers to handle their crabgrass. Wrapping up, what are the most important things to remember about controlling crabgrass?
MB: Things that I would recommend to remember – we started out by explaining some of the mistakes that may have been made. So why your preemergence herbicide application failed. Maybe your sprayer wasn’t properly calibrated, maybe you didn’t measure out the proper amount of product and you accidentally ran out during the application. The key is you just need to make sure you don’t make that same mistake twice. So I think that’s just a real easy way to make sure – it’s always great to learn from your mistakes. If you’ve seen something that’s failed, amend and change your behavior to make sure that you don’t make that same mistake again.
If you’re in the situation that you’re looking at crabgrass that has come up and you don’t have any preemergents to rely on anymore because you’ve got emerged crabgrass, be sure that you’re targeting these crabgrass plants when they’re small. The postemergence herbicides have greater success, they have greater activity on small crabgrass plants rather than fully mature, or tillering, crabgrass plants. There’s different postemergence products that have labeled use in different scenarios – for sod only or for golf course only or only for these specific turfgrass species. That’s something that you really need to make sure you’re being careful not to harm your turf. As much as we want to keep these crabgrass plants from growing, setting seed in our property and coming back next year, we also don’t want to injure the turf by applying some sort of postemergence products. One way to avoid that is to make sure we are following the label instructions, and then also exercise some caution on high-heat days in the summer. So we’re putting out these postemergence products that could be warmer in the year. If you’re getting temperatures above 85 degrees Fahrenheit, and you put out a surfactant with these postemergent products, as is usually required by the label, you could see some turf injury. If you have any opportunity to put it off for a cooler day, that might be a good idea to try not to harm your turf. Because you don’t want to do any damage while we’re trying to keep those weeds out. The last thing, I try to remind everyone of this, the label is the law. So you’re responsible to be familiar with this government issued herbicide label. You’re responsible to make all of your applications in accordance with that. And it has a lot of information that’s useful for all managers. So by all means, please make sure you familiarize yourself with the intended use of this product and that you’re following directions for use.
TZ: Great information. Thank you so much, Matt, for joining us and sharing your expertise.READ THE ISSUE