In the United States, there has been an increase in the use of bermudagrass for athletic fields and municipalities due to improved recuperative potential during summer, better cold-tolerant cultivars, and the need to reduce management budgets. This increase has occurred more so farther north and into the transitional climate zone, while areas in the southern US continue to have a high percentage of bermudagrass athletic fields. The transition-zone growing season is short and has less heat units than areas farther south. This may alter herbicide options for managers farther north compared to the southern areas since they have less time to recover from herbicide induced injury. Also the severe damage, loss of turf vigor, and reduction in the turfgrass canopy on highly trafficked areas limits herbicide options even more and makes weed management more difficult.
The most substantial limitation to weed management on trafficked turf is the loss of residual herbicides. Residual herbicides are the “backbone” of most weed management programs because they prevent germination or establishment of seedling weeds for several months during the growing season. But they also inhibit rooting of creeping stolons and prevent seeding or sprigging of damaged areas. These issues related to turf establishment into trafficked turf increase dependence on herbicides that have no or short-lived residual in the soil.
Pre-emergent annual bluegrass herbicides: If you are overseeding bermudagrass areas in the fall, this section of the weed management plan is not applicable to your program. For minimum-wear areas and depending on region, you may begin applying preemergence herbicides for annual bluegrass (Poa annua) in late august to October before air temperatures drop below 70F consistently, but timing may be dependent on seasonal play. For trafficked fields, we recommend waiting until the last game of the fall sports season before applying annual bluegrass herbicides to prevent any further injury or stress on the field. Two suitable herbicides for this application are simazine (Princep Liquid) or flumioxazin (Sureguard). These herbicides can control young annual bluegrass plants that have already germinated and suppress germination for the rest of the fall and winter season. They also can control many winter annual broadleaves as well. If you are in a more southern region of the US, you may already have populations of annual bluegrass resistant to herbicides like simazine or atrazine. These Deep South areas also seldom have completely dormant bermudagrass suitable for flumioxazin or nonselective herbicides like glyphosate. Flumioxazin will turn semi-dormant bermudagrass completely brown but does not delay green-up the following spring.
If winter color is not important, it may be an option for bermudagrass control in the Deep South just as it is in areas further north. Root inhibitors like indaziflam (Specticle FLO) or prodiamine (Barricade) control annual bluegrass, but they can cause problems with bermudagrass recovery in highly trafficked areas the following spring. We only recommend using them in areas that are out-of-play or have very low traffic requirements, but these may be the only viable options for managers farther south who have resistant annual bluegrass populations. In multiplex facilities, these herbicides are great options for areas between fields or general areas that have proven over time to receive little wear. By applying more economical root inhibitors in zones that get minimal traffic, budget can be freed for more costly postemergence herbicides or shoot inhibiting preemergence herbicides on wear areas.
Post-emergent annual bluegrass herbicides: When bermudagrass is mostly dormant, you can apply non-selective herbicides like glyphosate (Roundup, Glypro, etc.) or glufosinate (Finale). Simazine or flumioxazin will also offer post control of annual bluegrass. Glyphosate may be used in combination with oxadiazon (Ronstar FLO), simazine, flumioxazin, or other residual herbicides in January or early February, depending on region, to give residual crabgrass control into the late spring/early summer. Glyphosate + simazine will improve winter annual broadleaf control but simazine will not offer much for crabgrass and goosegrass in the coming season.
If no green leaves are evident above brown turf and digging in the canopy produces no more than 10 partially green leaves under hand, the area can be considered fully dormant for the purpose of nonselective herbicide treatment. As more and more green leaves break the surface, the glyphosate rate must be lowered from a high of 40 fl oz/A down to as low as 12 fl oz/A. If more than 5% of the turf has green leaves on the surface, prolonged delay in greenup can be expected, even with the lower rate. For selective options we recommend using foramsulfuron (Revolver), trifloxysulfuron (Monument), rimsulfuron plus metsulfuron (Negate), or flazasulfuron (Katana). All herbicides except foramsulfuron require nonionic surfactant (NIS) at 0.25% V/V (e.g. 0.25% V/V in a 10 gal tank equals 0.025 gallons (gal) or 3.2 fluid ounces (fl. oz.), while foramsulfuron requires methylated seed oil (MSO) at 1 % V/V and ammonium sulfate (AMS) at 1.5 lbs/A. These more aggressive adjuvants recommended on the Revolver label can also improve efficacy of trifloxysulfuron, rimsulfuron plus metsulfuron, and flazasulfuron. Pronamide (Kerb) is another herbicide that can be integrated into annual bluegrass control programs to delay or prevent resistance development. Among the selective herbicides listed above, all are safe to bermudagrass but try to avoid spraying during early greenup (0-50%) as some discoloration and stunting may occur.
Pre-emergent crabgrass/goosegrass herbicides: During spring, we typically see large and smooth crabgrass emergence from March – May with goosegrass emerging a few weeks after crabgrass. We recommend applying your pre-emergent herbicide from February to mid-April depending on location by using natural indicators or growing degree day (GDD) models. Turf managers from the transition zone to the Deep South can typically start applying preemergence herbicides for crabgrass between full bloom and full wilt of daffodils, between bud set and full bloom of dogwoods, and/or between full bloom and 50% bloom drop of Forsythia. A GDD model with base temperature of 55 F will prompt applications before reaching 70 units. This means every time your daily average of high and low temperatures is over 55 F, you accumulate GDD units and add them to a running total while ignoring any negative values. You will then need to apply your pre-emergent herbicide before an area reaches 70 GDD units at base 55 F. January 1 each year is a suitable time to start tracking base-55 GDD units.
A great preemergence herbicide option for trafficked bermudagrass areas is oxadiazon (Ronstar FLO or G). If you apply before greenup, you can use sprayable formulations, but after significant greenup has occurred, it is recommended to use granular formulations to reduce injury. Sprayable formulations of oxadiazon are more economical and offer better coverage than equivalent rates of granular formulations. Oxadiazon does not inhibit root growth of stolons or new sprigs, so it makes recovery of worn or winter-damaged areas much easier and faster. Flumioxazin can also be used in a similar manner but is available only as a spray formulation that cannot be used on actively growing bermudagrass and requires a short interval between spraying and sprigging. Thus, flumioxazin must be applied to dormant turf and will not last as long as oxadiazon.
If we normally see 4 months of residual goosegrass control from a high-label rate of oxadiazon, we will get about 3 to 3.5 months from the 12 oz/A rate of flumioxazin. The advantage of flumioxazin compared to oxadiazon is cost savings and postemergence annual bluegrass control. For a cheaper alternative to the shoot inhibitors, root-inhibiting herbicides like indaziflam, prodiamine, or dithiopyr (Dimension) can be used at half rates repeatedly in areas of the field that are out-of-play or get very low traffic/wear and are not at risk of winterkill.
Post-emergent crabgrass/goosegrass herbicides: The ideal herbicide for crabgrass and goosegrass control in highly trafficked bermudagrass will cause little injury or growth delay to desired turf. Since MSMA is no longer an option in athletic fields, our best approach is to catch the weeds when they have less than 3-tillers and treat with theincarbazone plus foramsulfuron plus halosulfuron (Tribute Total) or foramsulfuron. If weeds are over 3 tillers, quinclorac (Drive XLR8, Quinclorac 75DF) can be used at 0.75 lb active ingredient per acre for crabgrass control and topramezone (Pylex) at 0.15 fl oz/A + metribuzin (Sencor) at 4 oz/A can be used for goosegrass. The topramezone plus metribuzin programs were developed for Virginia, so areas farther south may need higher rates of topramezone (0.25 to 0.5 fl oz/A) to be effective on goosegrass.
Both quinclorac and topramezone may injure bermudagrass for up to 2 weeks and both require MSO adjuvant at 0.5 to 1% by volume. Speedzone has controlled small and medium size goosegrass in research trials, but requires using the highest labeled rates (2 qt/A) with multiple applications. These rates may injure bermudagrass and the 14-day interval found effective in research trials is off label. Labeled monthly treatments are less effective for goosegrass control but still of utility. When using topramezone in bermudagrass, there are a few things to note: 1) some bermudagrass cultivars like common bermudagrasses, ‘Patriot’ and ‘NorthBridge’ are typically more sensitive than hybrid varieties like ‘Tifway’; 2) using just topramezone at 0.25 to 0.5 oz/A and 0.5% MSO will cause severe white discoloration but typically not more than 2 weeks of delayed growth; 3) adding chelated iron (Sprint 330) can slightly speed the recovery; 4) adding triclopyr (Turflon Ester) at 4 oz/A will eliminate white discoloration but increases delayed growth to 3 weeks; 5) our program of 0.15 oz topramezone + 4 oz/A metribuzin has decreased injury duration for some cultivars like Tifway but increased injury of Patriot in one trial; 6) recent reports by Dr. Bert McCarty, Clemson University, suggest rapid irrigation immediately after topramezone treatment can reduce bermudagrass injury. These topramezone programs are all effective on 3-5 tiller goosegrass and sometimes work well on much large plants.
Post-emergent herbicides for broadleaf weed control: In bermudagrass, broadleaf weeds can be controlled during dormancy with nonselective herbicides like glyphosate or with selective options when turf is actively growing. Most three- and four-way combo products that contain 2,4-D, dicamba, MCPP, triclopyr, carfentrazone, etc. (Speedzone, Trimec, etc.) can control common broadleaf weed species, but struggle on more hard-to-control weeds like Virginia buttonweed, ground ivy, and prostrate knotweed. Also products that contain 2,4-D or triclopyr can injure bermudagrass especially during greenup in the spring, so using the “southern” versions of these products for example Trimec Southern may be a safer option. The top recommended products for common and hard-to-control weeds in trafficked bermudagrass would be products containing metsulfuron (MSM Turf) or sulfosulfuron (Certainty), and they both require 0.25% V/V of NIS. Sulfosulfuron can also be used for grass and sedge control as well. Quinclorac is another herbicide that can effectively control both broadleaves and grass weed species. Newer products like thiencarbazone + dicamba + iodosulfuron (Celsius), penoxsulam + sulfentrazone + 2.4-D + dicamba (Avenue South), and halauxafin + florasulam (Relzar) may improve turf safety and broaden weed control spectrum.
Post-emergent herbicides for sedge and kyllinga control: There are multiple herbicide options for sedge and Kyllinga spp. control and these options also change depending on the species such as purple or yellow nutsedge. Some of the better options for bermudagrass turf include trifloxysulfuron, sulfosulfuron, and imazosulfuron (Celero). Other options include halosulfuron (Sedgehammer) and sulfentrazone (Dismiss). Trifloxysulfuron and sulfosulfuron have the broadest spectrum sedge and Kyllinga control, which includes purple and yellow nutsedge and also different Kyllinga species, but will require repeat applications for purple nutsedge and Kyllinga species. Imazosulfuron, halosulfuron, and sulfentrazone are effective on both yellow nutsedge and green Kyllinga. All three will require repeat applications to control Kyllinga species effectively. All herbicides except sulfentrazone require 0.25% NIS at application. Trifloxysulfuron and sulfosulfuron also have activity on other grass and broadleaf weeds as well. Only halosulfuron, imazosulfuron, and sulfentrazone can be used in both cool-season and warm-season turf.
Remember to avoid root inhibiting preemergence herbicides (indaziflam, prodiamine, and dithiopyr) on highly trafficked areas but zone treat them where possible. Always read the product label before application to prevent any costly or damaging mistakes. Read the label and confirm if a product does or does not need a surfactant/adjuvant and is legal to use in the region and site desired. Failure to use surfactants can cause a significant drop in weed control for some herbicides. Always check the weather and don’t apply herbicides if rainfall is imminent. Most herbicides need at least 4 hours drying time for best absorption into plants. We also recommend not mowing your treatment area for at least 2 days before and 2 days after application, and preferably 3 days before and after. Treat young weeds to improve effectiveness. Be mindful of the time required for certain herbicides to work effectively and schedule field use accordingly.
By John Brewer is a graduate research assistant, and Shawn Askew, PhD, is an associate professor and turf weed specialist, at Virginia Tech.