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Cover Story
New and Updated Herbicides for Turfgrass Weed Control
Jay McCurdy, Associate Professor and Turfgrass Extension Specialist, Mississippi State University
Amy Wilber, Extension Associate, Mississippi State University
There are a number of new and novel herbicides on the market. Here, we share our experiences and insights on their role in modern turfgrass management. At Mississippi State University, we conduct roughly 40 replicated trials per year, targeting a variety of turfgrass weeds in all major warm-season grasses. The more hands-on experience we get with new herbicides (especially during the early development phase), the better we can advise stakeholders on how to use them. That’s why we work with and advise industry colleagues on new products for our unique challenges here in the southeast.
Our research often focuses on controlling “driver” weed species—common weeds such as crabgrass, goosegrass, doveweed, Virginia buttonweed, Poa annua, chickweed, nutsedges, Kyllinga species, and dallisgrass. These are the weeds that turf managers in any southern state must contend with.
Let’s discuss some of the newest herbicides introduced over the last couple of years. These products offer exciting advancements and opportunities to improve current weed management strategies.
New Herbicides for Turfgrass Management
Allstar (2,4-D, quinclorac, triclopyr, and sulfentrazone): This product is uniquely well positioned for crabgrass and broadleaf weed control in the cool-season market where it is labeled for use in most cool-season turfgrass species. It is also labeled for use in bermudagrass and zoysiagrass, though some injury to stressed turf should be expected. At the highest use rate of eight pints per acre, this product delivers the equivalent quinclorac rate of a full rate of Drive XLR8, which is normally sufficient to control young crabgrass.
Arkon and Vexis (pyrimisulfan): Both are products containing pyrimisulfan, an ALS-inhibiting herbicide. Arkon is a liquid formulation that is touted as being stable in water mixture for a longer period than most other ALS-inhibiting herbicides—a notable quality for LCOs who mix a backpack sprayer then spray over consecutive days; Vexis is the granular, which has been commercialized slightly longer. We’ve been working with this active ingredient since early-development. Arkon and Vexis both control sedges (including yellow and purple nutsedge and various Kyllinga species) and certain broadleaf weed species. Pyrimisulfan has some pre- and early-post emergence activity on crabgrass but likely insufficient for standalone use. Like other ALS-inhibiting herbicides, its activity is slow to manifest (two to three weeks after application) and requires actively growing, immature weed species in order to be effective.
Pyrimisulfan has broad tolerance across most turfgrass species, but the labels for Vexis are slightly more restrictive. Tolerant species include established cool-season species like Kentucky bluegrass, fine fescues, tall fescue, perennial ryegrass, creeping bentgrass (only Arkon, including on tees and greens); and established warm-season turfgrasses like bermudagrass, bahiagrass, buffalograss, centipedegrass, kikuyugrass, seashore paspalum, St. Augustinegrass, and zoysiagrass. Because of its slow activity, we’ve observed a few keys to its use:
• apply during periods of active growth, without growth limiters like drought and temperature stress
• root absorption appears to be required for Vexis, so we assume Arkon to be similar
• irrigate or apply when moderate rainfall can be expected
Aethon (pyrimisulfan and penoxsulam): Another pyrimisulfan product, but this time it is formulated with penoxsulam. Both have some unique capabilities. We’ve worked with penoxsulam before as Sapphire or on a granular carrier—penoxsulam-alone has a little residual activity and has often been included in homeowner mixtures because it is safe across a broad spectrum of grasses and controls things like white clover and English lawn daisy (driver weeds in many cool-season and west-coast markets). Aethon is for warm-season species only, including bermudagrass (common or hybrid), buffalograss, centipedegrass, kikuyugrass, seashore paspalum, and St. Augustinegrass. Its market share is uniquely on sedges with the added benefit of controlling certain broadleaf species. We’ve compared it with industry standards on yellow nutsedge, and it competes. Like Arkon, it has the benefit of being fairly tank-steady—that is, you can likely mix it and spray it over several days without decreased herbicide efficacy.
Celsius XTRA (thiencarbazone, iodosulfuron, halosulfuron): while not entirely new, it is new enough to mention. One of the industry standards for sedge control has long been halosulfuron. Celsius XTRA controls most sedge species equal to halosulfuron alone while controlling a broad spectrum of broadleaf weeds. Thiencarbazone, one of the key active ingredients in Tribute Total, is uniquely fast acting (relatively speaking) compared with most other ALS-inhibitors, and iodosulfuron is analogous to metsulfuron, though it is active in much lower concentrations—hence added safety around young oak trees. Celsius XTRA controls most major warm-season broadleaf weeds (ex. dollarweed, doveweed, buttonweed). It still requires two applications to control anything but immature seedlings. Celsius XTRA is labelled for use in bermudagrass, centipedegrass, St. Augustinegrass, and zoysiagrass. Both it and the OG formulation will kill carpetgrass, so beware if you’re in coastal or low-lying areas of the southeast, and don’t simply assume that all you have is centipede or St. Augustine.
Crew (dithiopyr and isoxaben): this granular product has been around for about two years, but for various reasons has never had a big launch party—blame COVID? These two active ingredients are no strangers. Dithiopyr is a reliable preemergence herbicide that has both grass and some broadleaf activity. Isoxaben adds a broader spectrum of broadleaves controlled. Since it’s a granular, this is an especially attractive product for ornamental beds and adjacent lawns.
Prodoxaben 3.7 SC (prodiamine and isoxaben): seeing a trend yet? This combination revisits two older chemistries in a liquid formulation (Gemini 3.7 SC was a similar formulation several years back). Prodiamine is still our go-to for preemergence crabgrass control—it may lack the Poa annua and goosegrass control of the likes of oxadiazon, flumioxazin, and indaziflam, but it’s the standard for crabgrass. And isoxaben broadens the spectrum for broadleaf weeds.
StriCore (pethoxamid) is a new (to turf) active ingredient. Its mode of action is similar to other group 15 herbicides like dimethenamid and metolachlor in that it is thought to inhibit very long chain fatty acid synthesis. The product is labelled for preemergence application alone and in tank mixture with other preemergence herbicides across a wide variety of turfgrasses, including cool-season species like creeping-bentgrass, fine and tall fescue, perennial ryegrass, and Kentucky bluegrass, and it is labelled for use on warm-season species like bahiagrass, bermudagrass, buffalograss, carpetgrass, centipedegrass, kikuyugrass, seashore paspalum, and zoysiagrass. It is labelled to control or suppress a range of annual weed species, with goosegrass being one it can hang its hat on. It really shines when tank mixed with other actives like indaziflam or prodiamine, particularly for the major annual grasses like Poa annua, crabgrass, and goosegrass. It has an 8-week seeding interval for those trying to integrate its use into overseeded scenarios.
Southpaw (sulfosulfuron, metsulfuron, dicamba): we’ve worked with Nufarm for at least five years on Southpaw. At one time, there were three individual companies pursuing a similar mixture of the same active ingredients. We know this three-way combination works—in fact, it has become one of our standards for buttonweed and yellow/purple nutsedge control. From what we understand, formulating ALS-inhibitors together or with auxin chemistry (like dicamba) is a major challenge. Certainty (sulfosulfuron) has always been an interesting sedge and broadleaf material. Applied alone, sulfosulfuron has slightly inferior nutsedge activity relative to halosulfuron; but sulfosulfuron has a little grass activity on the likes of young crabgrass and Poa annua, as well as bahiagrass suppression/control. Add in dicamba and metsulfuron, and it shines for broadleaf control. Southpaw is labelled for use on warm-season turfgrass only—bermudagrass, centipedegrass, St. Augustinegrass, and zoysiagrass. It will kill carpetgrass and maim bahiagrass (not sure anything really kills it), so again, use caution in mixed stands.
GameOn (fluroxypyr, halauxifen, 2,4-D) is an auxin mixture for nonresidential turf only. GameOn includes the choline formulation of 2,4-D, which has reduced volatility compared to traditional 2,4-D formulations and improves its safety around trees and ornamentals. Like other auxin mixtures, weed injury appears within a few days. GameOn has also shown season-long broadleaf weed control in golf course native areas following application in mid-spring. GameOn is labelled for cool-season turfgrass species like bentgrass, fescues, and perennial ryegrass as well as bermudagrass and zoysiagrass. GameOn should not be applied to turf maintained at less than half an inch.
Surepyc IQ (sulfentrazone and imazaquin): this is a novel combination of two established active ingredients. Imazaquin and sulfentrazone both control nutsedge and various Kyllinga species, but also control assorted broadleaf weeds, including doveweed.
SureGuard EZ (flumioxazin): this is a new formulation of the previous SureGuard SC. Like the previous version, use this in dormant bermudagrass for postemergence and late-preemergence Poa annua control. Apply in combination with your favorite nonselective herbicide (ex. glyphosate). Selectively apply around landscape ornamentals.
StayGuard (flumioxazin): the active ingredient flumioxazin has been around a while (notably as SureGuard in turf), but its formulation on a granular prill has long proven to be a white whale.
