Clint Waltz and Patrick McCullough, Turfgrass Specialist and Weed Specialist, University of Georgia
Annual bluegrass – Robert Vidéki, Doronicum Kft., Bugwood.org
Annual bluegrass (Poa annua L.) is a troublesome winter annual weed in residential turf. Compared to most turfgrasses, annual bluegrass has a lighter green color, coarser leaf texture, and produces unsightly seedheads.
Annual bluegrass seed germinates throughout the late-summer and early-fall once soil temperatures drop below 70° F. Seedlings grow and mature in fall, overwinter in a vegetative state, and produce seed in spring. A second germination can occur in late-winter as soil temperatures rise and the days become longer.
Annual bluegrass is a prolific seed producer and individual plants may produce hundreds of viable seed, even when closely mowed. Annual bluegrass flowers over several months in spring and produces seed that may remain dormant in soil for years before germinating. Annual bluegrass often dies from summer stresses but may survive in protected sites that receive irrigation. Controlling annual bluegrass in mid- to late-spring in residential lawns can be difficult.
Annual bluegrass can produce seeds even when closely mowed. Image – John Kaminiski
Control in bermudagrass and zoysiagrass
Up until mid-February (when the bermudagrass was fully dormant) applying a glyphosate containing product (e.g. Roundup) was an option for postemergence annual bluegrass control. Even then, care must be taken not to “overdose” the weed and harm the bermudagrass. Applicators commonly over-spray the weed with glyphosate and some herbicide moves deep into the bermudagrass canopy where it contacts green bermudagrass stolons near the ground. Any green part of the plant in the bermudagrass can absorb the glyphosate which can damage the plant.
It is now too late and risky to consider spraying glyphosate to control annual bluegrass in dormant bermudagrass. While bermudagrass may still look “completely” dormant it is starting to greenup and the application of glyphosate during greenup can damage the turf. Do not apply glyphosate to dormant grass of any type other than bermudagrass since other grasses never really go completely dormant and may be damaged by the herbicide.
There are a few selective herbicidal options to control annual bluegrass at this point in the season. In bermudagrass and zoysiagrass, if the annual bluegrass population is bad enough the best option is treating with either Revolver (foramsulfuron) or Monument (trifloxysulfuron).
Control in centipedegrass and St. Augustinegrass
Neither of these herbicides is labeled for use on centipedegrass or St. Augustinegrass. In centipedegrass and St. Augustinegrass, atrazine containing products are an option but large annual bluegrass grass plants are difficult to control with a single application.
The weed is an annual cool-season grassy weed that will die-out in a couple months as temperatures warm. For now, having patience and tolerance maybe the best option. Plan for next winter and spring. Begin with good turfgrass cultivation this summer. For example:
Deep and infrequent irrigation encourages turfgrass root development which improves the ability of the lawngrass to compete with weeds.
• Identify and alleviate soil compaction since annual bluegrass prefers compacted soils. For rapid recovery and improved vigor, core aerifications should be performed during the active growth period of warm-season turfgrasses.
• Mow the lawn at the appropriate height for the grass species. Lower mowing heights may stress turf and reduce its ability to compete with annual bluegrass. For proper mowing height recommendations, visit www.GeorgiaTurf.com
• Lastly, begin a preemergence herbicide program in late-summer to help control the seed that were deposited this season.
Landscapers can help homeowners with controlling annual bluegrass now and planning a healthier lawn to prevent annual bluegrass next year.
Wild Garlic Identification and Control In Home Lawns
Drs. Jialin Yu and Patrick McCullough, UGA
Wild garlic (Allium vineale L.) is a common weed in most turf areas throughout Georgia. It emerges from underground bulbs in late fall and grows through the winter and spring months. Wild garlic is a winter perennial plant that declines in early summer. This weed species is highly objectionable because it grows faster than cool-season turfgrasses after mowing and causes unsightly clumps in dormant warm-season turfgrasses during winter. Wild garlic has a similar appearance to wild onion (Allium canadense L.) but they are easily distinguishable by their leaves. Wild garlic has round hollow leaves and while wild onion has solid flat leaves.
Wild garlic bulbs – Photo by Jialin Yu
Mowing is not effective for controlling wild garlic because bulbs or bulblets in the soil will continue to sprout and grow. In addition, the bulbs can remain viable in the soil for years before emergence. Mowing, however, can weaken the plants and help prevent the production of seeds.
Chemical control is similar for wild garlic and wild onion. Preemergence herbicides do not provide effective control. Multiple applications of postemergence herbicides over more than one season are typically required to control wild garlic. Wild garlic has slender and waxy leaves, which may reduce herbicide uptake. In Georgia, herbicides should be timed during winter or early spring before the formation of bulbs.
Synthetic auxin herbicides are typically the best herbicides to use in tall fescue lawns for wild garlic control. 2,4-D alone or in three-way mixtures with dicamba and mecoprop (Trimec, Triplet, Weed B Gone, etc.) effectively control wild garlic. These herbicides are safe in warm-season grasses during active growth but should not be applied during the spring green-up. Reduced rates are recommended when spraying to sensitive turfgrasses including centipedegrass and St. Augustinegrass. Using PowerZone or SpeedZone, which include carfentrazone and three-way synthetic auxin herbicides, may improve wild garlic control in cold winter. However, turfgrass tolerance to these products may vary and temporary turfgrass yellowing may occur on certain turfgrass varieties.
Postemergence control may also be achieved with ALS-inhibitor herbicides. Imazaquin (Image) controls wild garlic on warm-season turfgrasses but should not be used during spring greenup or on newly planted or sprigged lawns. Imazaquin will severely injure fescue and ryegrass.
Metsulfuron (Manor, Blade, others) effectively controls a wide number of broadleaf weeds and wild garlic. Metsulfuron can be applied to tolerant warm-season turfgrasses including bermudagrass, centipedegrass, St. Augustine, and zoysiagrass. However, applications may temporarily inhibit greenup of centipedegrass and other species during spring transition. Metsulfuron should not be used in lawns with desirable bahiagrass populations. Woody ornamentals should not be planted in treated areas within one year following the metsulfuron application.
Glyphosate may effectively control wild garlic in dormant bermudagrass. To avoid injuring desired turfgrasses that are not completely dormant, spot treatments should be used on sensitive turfgrasses.
Table 1. Postemergence herbicides for wild garlic control.
Chinese privet (also called privet) is an invasive weed that escaped from cultivation. It is often found in landscapes and around old homesites, edges of fields and in low areas. According to Dr David Dickens, UGA Extension Forester, this time of the year, a foliar treatment is a good option to control privet.
Basal treatments of privet (spraying the stems) can be difficult because of the large number of branches. Dr Dicken’s says that dormant-season foliar sprays with 3-5% glyphosate provide effective control. Concentrations greater than 5% are not economical.
Take care to keep the spray off the foliage and young green bark of desirable plants. Since many plants are dormant at this time of year, there should be less effect on non-target plants.
Privet seeds are only viable for one year so in areas where they continues to germinate, the seeds are being introduced by birds or other means.
Climbing fern – Chris Evans, Illinois Wildlife Action Plan, Bugwood.org
UGA Extension Forester, Dave Moorhead, points out that this 3 – 5 % glyphosate spray will also work in controlling another invasive weed – climbing fern.
The turfgrass industry is officially losing Illoxan (diclofop-methyl) and Embark (mefluidide) in 2015. These are two important tools in weed control programs with no comparable replacements. The loss of these materials has significant implications for resistance management, seedhead control, and efficiently managing high quality turfgrass.
Goosegrass – John D. Byrd, Mississippi State University, Bugwood.org
Illoxan (diclofop-methyl)
Bayer will not be reregistering Illoxan. Unfortunately, the return on Illoxan sales was not worth the expenses of reregistration for the company. Illoxan is a postemergence herbicide used for goosegrass control in bermudagrass golf courses. This herbicide is one of the most effective chemistries for controlling goosegrass in greens, tees, fairways, and roughs. More importantly, Illoxan is the only ACCase inhibitor used in bermudagrass turf and the loss of this mechanism of action may have significant consequences for resistance management. Goosegrass resistance to ALS inhibitor herbicides, specifically foramsulfuron (Revolver), is becoming more widespread throughout the Southern U.S. Turf managers also have restrictions on MSMA use on golf courses that limit the ability to effectively control goosegrass and other weeds.
Illoxan is an excellent herbicide for controlling goosegrass at most growth stages in bermudagrass and also offered an alternative mechanism of action in resistance management programs. The implications of losing Illoxan in golf course management will emphasize the need for investments in good preemergence herbicides for goosegrass control. Dinitroanilines (DNAs) like prodiamine (Barricade, others) and pendimethalin (Pendulum, others) have potential to control goosegrass but results are often erratic. Resistance to DNA herbicides has also developed in goosegrass populations and alternative chemistries may be needed for effective control. From our research at UGA, Ronstar (oxadiazon) and Specticle (indaziflam) have consistently been the best preemergence herbicides for controlling goosegrass in bermudagrass turf. Other herbicides such as Dismiss (sulfentrazone), Sureguard (flumioxazin), and Tower (dimethenamid) have potential to control goosegrass but our results have been inconsistent over years.
With the loss of Illoxan, bermudagrass managers will only have Revolver (foramsulfuron), Tribute Total (foramsulfuron + thiencarbazone + halosulfuron) and Dismiss (sulfentrazone) available for postemergence goosegrass control. While these herbicides may control immature goosegrass, single applications often do not control tillered plants. Revolver and Tribute Total are both ALS inhibitors and will not effectively control mature goosegrass or resistant biotypes.
Turf managers may also explore the use of MSMA + Sencor (metribuzin) for goosegrass control but these treatments can be very injurious to bermudagrass in summer and may require sequential applications. Moreover, superintendents in Georgia are limited to one application of MSMA per year, not to exceed 25% of the total golf course. Turfgrass managers must understand that losing Illoxan may limit their ability to control goosegrass and may have serious repercussions in resistance management programs.
Embark (mefluidide)
Embark is a growth regulator primarily used for annual bluegrass seedhead control in turfgrass management. Earlier this year there was controversy around the future manufacturing of mefluidide, the active ingredient in Embark, and if this product would be available after 2015. PBI Gordon explored opportunities inside and outside of the U.S. to have mefluidide manufactured and formulated to make new Embark products. The opportunity to make new material was very costly for the company and PBI Gordon has decided not to pursue this investment. The Embark 2S product will be pulled completely, and there will be new Embark T & O 0.2L (essentially a dilution of the 2S) released until the current supply is gone. Once the existing inventory has been sold, Embark will no longer be available from PBI Gordon.
Embark is a growth regulator that has a long history of use in turfgrass and roadside management. Embark is the only seedhead inhibiting growth regulator available for use in warm and cool-season turfgrasses. Turfgrass managers primarily use this chemistry for seedhead control on annual bluegrass, tall fescue, bermudagrass, and other turfgrass species. Proxy (ethephon) is the other seedhead inhibitor available for turfgrass. It is labeled only for cool-season grasses but may be applied to certain zoysiagrass varieties. Proxy causes leaf chlorosis, stand thinning, and quality reductions in bermudagrass, seashore paspalum, and other warm-season species. Other PGRs like Primo (trinexapac-ethyl) or Trimmit (pacloburazol) may provide partial seedhead control but are generally less effective than Embark and Proxy.
Current research efforts at UGA include evaluating seasonal application timing of PGRs to minimize injury and maximize seedhead control on warm-season grasses. We are also evaluating alternatives to Embark, primarily ALS inhibitor herbicides, for seedhead management in bermudagrass turf. Embark is the most popular PGR for annual bluegrass seedhead control in bentgrass greens in Georgia and further research will be needed with Proxy, Proxy + Primo, and other compounds to replace Embark.
Patrick McCullough is an associate professor and extension specialist in turf weed science at the University of Georgia in Griffin.
This weed is Florida betony. It is also called rattlesnake weed.
The publication Controlling Florida Betony in the Landscapegives cultural and chemical controls for this weed in lawns and landscape beds. The authors are Mark Czarnota, Ph.D., and Tim Murphy, Ph.D., Weed Control Specialists. Departments of Horticulture and Crop Science
Click here to see the publication for the following information:
Florida betony (Stachys floridana) (also called rattlesnake weed and hedge nettle) is a problem weed in both turfgrasses and ornamentals.
Figure 2 – Tubers of Florida betony that look like the rattle of a rattlesnake, hence the name “rattlesnake weed.”
Florida betony is a “winter” perennial and, like most plants in the mint (Labiatae) family, has a square stem with opposite leaves. Flowers are usually pink and have the classic mint-like structure (Figure 1). Unlike its relatives, it has the unique characteristic of producing tubers that look like the rattles (buttons) of a rattlesnake, hence the name “rattlesnake weed” (Figure 2).
Contrary to its name, both annual (live for one season) and perennial (live for many seasons) populations of annual bluegrass may be found in turf. Annual bluegrass may out-compete other turf species during late fall and early spring. Annual bluegrass often dies from summer stresses but may survive if irrigated – especially the perennial biotypes
Postemergence Control (See Table 3)
Annual bluegrass may be selectively controlled with postemergence herbicides (Table 3).
Landscapers managing warm-season grasses have more options for selective postemergence annual bluegrass control than cool-season grasses.
Flazasulfuron (Katana), foramsulfuron (Revolver, Tribute Total), rimsulfuron (TranXit), and trifloxysufluron (Monument) are labeled for bermudagrass and zoyiagrass non-residential commercial lawns and other sites. Flazasulfuron and rimsulfuron are also labeled for use in centipedegrass. Efficacy of these herbicides generally increases under warm temperatures in spring compared to winter and non-ionic surfactants may enhance efficacy.
Pronamide (Kerb) is a restricted use herbicide for annual bluegrass control in non-residential bermudagrass, centipedegrass, St. Augustinegrass, seashore paspalum, and zoysiagrass. Pronamide is root-absorbed and must be watered in following applications. Pronamide efficacy is generally slower than most sulfonylureas and activity for annual bluegrass control may take approximately four to six weeks.
Atrazine (Aatrex, Bonus S, others) and simazine (Princep, WynStar, others) may also be applied to bermudagrass, centipedegrass, St. Augustinegrass, and zoysiagrass for selective postemergence annual bluegrass control. These herbicides often provide erratic control of annual bluegrass but may control other grassy and broadleaf weeds. Actively-growing bermudagrass is sensitive to atrazine and applications are recommended only during the late fall and winter months.
Dormant bermudagrass may be treated with nonselective herbicides, such as glyphosate (Roundup, Touchdown, others), glufosinate (Finale), and diquat (Reward). These herbicides will injure or kill existing vegetation, including annual bluegrass and managers should only spray at peak dormancy when no green turfgrass foliage is observable. Nonselective herbicides should only be applied to completely dormant bermudagrass and applications during early spring may delay greenup with significant turf injury.
Flumioxazin (Sureguard) is a new herbicide for pre- and postemergence annual bluegrass control but applications are limited to dormant bermudagrass only. Flumioxazin use after greenup or on other species are not recommended due to excessive injury potential.
Selective annual bluegrass control options in cool-season lawns are limited.
Ethofumesate (Prograss) controls established annual bluegrass in perennial ryegrass, tall fescue and dormant bermudagrass (see the current edition of the Georgia Pest Management Handbook). Two or three ethofumesate applications may be applied in late fall at three- to four-week intervals. Annual bluegrass control may be seen that fall, but control is usually observed the following spring. Annual bluegrass control with ethofumesate may vary greatly over years depending on environmental conditions.
Amicarbazone (Xonerate) is a new Photosystem II inhibitor, similar to triazine herbicides, but may be used in tall fescue lawns and other cool-season grasses. Applications of amicarbazone in Georgia are limited to springtime only to minimize injury to cool-season grasses. Warm-season turf is very tolerant to amicarbazone and may be treated at any seasonal timing.
Bispyribac-sodium (Velocity) has shown potential for selective annual bluegrass control in tall fescue and perennial ryegrass lawns. However, this herbicide is currently registered for creeping bentgrass and perennial ryegrass on golf courses and sod farms only. Spot treatments of nonselective herbicides are generally the most effective treatment regimen for annual bluegrass control in cool-season grasses.
Table 3. Efficacy of postemergence herbicides for annual bluegrass control in turfgrass.
Common Name
Trade Name (Examples)
Efficacy
amicarbazone
Xonerate
F-G
atrazine
Aatrex, others
E
bispyribac-sodium
Velocity
F-G
flazasulfuron
Katana
G-E
flumioxazin
Sureguard
F-G
foramsulfuron
Revolver
E
glufosinate
Finale
E
glyphosate
Roundup, others
E
imazaquin
Image
P-F
metribuzin
Sencor
G
pronamide
Kerb
E
rimsulfuron
Tranxit
E
simazine
Princep, others
G-E
thiencarbazone + foramsulfuron + halosulfuron
Tribute Total
G-E
trifloxysulfuron
Monument
E
E = Excellent (90 to 100%), G = Good (80 to 89%), F = Fair (70 to 79%), P = Poor (<70%).
Annual bluegrass (Poa annua L.) is a problem winter annual weed. Contrary to its name, both annual (live for one season) and perennial (live for many seasons) populations of annual bluegrass may be found in turf.
Annual bluegrass seed germinates in late summer/early fall once soil temperatures fall below 70° F. Annual bluegrass may out-compete other turf species during late fall and early spring. Annual bluegrass often dies from summer stresses but may survive if irrigated – especially the perennial biotypes.
Cultural Control of Annual Bluegrass
Irrigate deeply and infrequently to encourage turfgrass root development and improve the ability of turf to compete with annual bluegrass. Overwatering, especially in shady areas, may encourage annual bluegrass invasion.
Avoid soil compaction. Core aerate during active turf growth to encourage quick recovery. For cool-season grasses, time aerfications before annual bluegrass germinates.
Reduce nitrogen fertilization during peak annual bluegrass germination and periods of vigorous growth. Fertilizing dormant turfgrasses when annual bluegrass is actively growing may make infestations worse.
Use the proper mowing height, frequency, and equipment for your turfgrass (Table 1). Raise the turf mowing height during peak annual bluegrass germination.
Mow turfgrass frequently during periods of vigorous growth to prevent scalping. Returning clippings recycles nutrients to the soil but clippings may need to be removed when annual bluegrass is producing seedheads to reduce the spread of viable seed.
Prevention Using Pre-emergence Herbicides (See Table 2)
Preemergence herbicides may prevent annual bluegrass establishment from seed. However, preemergence herbicides will not eradicate established plants and will not effectively control perennial biotypes of annual bluegrass from spreading vegetatively. Application timing of preemergence herbicides for annual bluegrass control is very important. Herbicides must be applied in late summer/early fall before annual bluegrass germination. A second application can be applied in winter to control later germinating plants. Fall applied preemergence herbicides should not be used if reseeding or resodding is needed to repair areas of damaged turf within several months after herbicide applications.
Several preemergence herbicides used for summer annual weed control will effectively control annual bluegrass in fall and winter (Table 2). Fall applications of herbicides such as bensulide (Betasan), dithiopyr (Dimension), flumioxazin (Sureguard), oxadiazon (Ronstar, Starfighter), pendimethalin (Pendulum, others), and prodiamine (Barricade, others) may effectively control annual bluegrass. Indaziflam (Specticle) provides excellent preemergence control of annual bluegrass and also provides early-postemergence control as well. Indaziflam is only labeled in warm-season turfgrasses but may provide greater application timing flexibility than dinitroaniline herbicides in fall.
Combination herbicide products are also available which may improve efficacy of applications. These products include oxadiazon plus bensulide (Anderson’s Crab and Goose), oxadiazon plus prodiamine (Regalstar), and benefin plus oryzalin (Team 2G or Team Pro). Many preemergence herbicides are available under a wide variety of trade names and formulations and turf mangers should carefully read label directions before applications.
Atrazine (Aatrex, Purge, others) and simazine (Princep, WynStar, others) are labeled for centipedegrass, zoysiagrass, St. Augustinegrass and bermudagrass. Atrazine can be applied to actively growing and dormant centipedegrass or St. Augustinegrass but bermudagrass can be injured if treated while actively growing. Both herbicides have excellent preemergence activity on annual bluegrass but soil residual is generally shorter (four to six weeks) compared to aforementioned herbicides. Several atrazine products are restricted use pesticides and turf managers should check labels for further information before use.
Mesotrione (Tenacity) is labeled for use in centipedegrass, perennial ryegrass, St. Augustinegrass (sod production only), tall fescue, and dormant bermudagrass (Table 2). Mesotrione may be applied during establishment of these grasses (except bermudagrass) and effectively controls annual broadleaf and grassy weeds. Preemergence applications of mesotrione control or suppress annual bluegrass but postemergence use is ineffective for control of established plants. Mesotrione may be applied in tank-mixtures with atrazine or simazine on centipedegrass to improve efficacy of applications.
Most preemergence herbicides will provide similar initial efficacy if applied before annual bluegrass germination and sufficient rain or irrigation is received. Preemergence herbicides require incorporation from irrigation or rainfall so that weeds may absorb the applied material. In order to effectively control annual bluegrass, preemergence herbicides must be concentrated in the soil seedbank. Retention on leaf tissue can be avoided by irrigating turf immediately after application for effective soil incorporation and herbicide activation.
Preemergence herbicide applications on non-irrigated sites have less potential for residual control, compared to irrigated turf, from product loss, poor soil incorporation, and failure to activate the herbicide. Practitioners should return clippings on non-irrigated sites to help move potential herbicides remaining on leaf tissue to the soil. If clippings are collected as part of routine maintenance, practitioners should consider returning clippings until at least half to one inch of rainfall is received. Granular products may also be applied to non-irrigated sites for better soil incorporation than liquid formulations. Granular products may be easier to handle and apply with less equipment necessary than sprayable formulations. Granular herbicides should be applied when morning dew is no longer present to avoid interference from leaf tissue.
Managing Herbicide Resistance
Repeated use of one herbicide chemistry may control annual bluegrass but resistance may develop. Herbicide resistance is the survival of a segment of the population of weeds following a herbicide dosage lethal to the normal population. Resistance occurs from repeated use of the same herbicide or mode of action over years and may be a concern with annual bluegrass.
Triazine herbicides, atrazine and simazine, have been repeatedly used for years due to the wide spectrum of weeds controlled as pre- or postemergence treatments in warm-season grasses. Resistance in weed populations has been reported with these herbicides which may contribute to inconsistent efficacy for annual bluegrass control in turf. Resistance to sulfonylureas has been reported in numerous weed species and repeated use in turfgrasses may also contribute to resistance in annual bluegrass populations.
Preemergence chemistries, such as the dinitroanalines, (benefin, oryzalin, pendamethalin and prodiamine) may have resistance among weed populations from repeated use over years. Turf managers should rotate preemergence herbicides from dinitroanilines to other modes of action to minimize resistance in annual bluegrass populations. Herbicides to consider in rotation programs from dinitroanilines would include indaziflam, ethofumesate, or oxadiazon. These chemistries offer a different mode of action than dinitroanilines but cost, label restrictions, and turfgrass tolerance may be limiting factors for using these products. Combination herbicides are also available, such as oxadiazon + prodiamine (Regalstar) and oxadiazon + bensulide (Anderson’s Crab and Goose), with more than one mode of action that effectively control annual bluegrass in turf.
Table 1. Mowing requirements for commercial turfgrasses.
Mowing Requirements for Turfgrasses
Species
Mower Type
Height (inches)
Frequency (days)
Bermudagrass
Common
Rotary/reel
1 to 2
5 to 7
Hybrid
Rotary/reel
0.5 to 1.5
3 to 4
Centipedegrass
Rotary
1 to 2
5 to 10
Perennial Ryegrass
Rotary/reel
0.5 to 2
3 to 7
St. Augustinegrass
Rotary
2 to 3
5 to 7
Tall Fescue
Rotary
3
5 to 7
Zoysiagrass
Reel
0.5 to 2
3 to 7
Table 2. Efficacy of preemergence herbicides for annual bluegrass control in commercial turfgrasses.
Common Name
Trade Name (Examples)
Efficacy
atrazine
Aatrex, various
E
benefin
Balan, others
E
bensulide
Betasan, others
F
dithiopyr
Dimension
G
ethofumesate
Prograss
G-E
flumioxazin
Sureguard
G
indaziflam
Specticle
E
mesotrione
Tenacity
F
oryzalin
Surflan, others
G
oxadiazon
Ronstar, others
G
pendimethalin
Pendulum, others
G
prodiamine
Barricade, others
E
pronamide
Kerb
E
simazine
Princep, others
E
E = Excellent (90 to 100%), G = Good (80 to 89%), F = Fair (70 to 79%), P = Poor (<70%).
Patrick McCullough, Extension Weed Specialist, University of Georgia
Annual bluegrass, Joseph M. DiTomaso, University of California – Davis, Bugwood.org
Annual bluegrass (Poa annua L.) is a problematic winter annual weed. Compared to most turfgrasses, annual bluegrass has a lighter green color, coarser leaf texture, and produces unsightly seedheads. Contrary to its name, both annual (live for one season) and perennial (live for many seasons) populations of annual bluegrass may be found in turf. Perennial plants are more prevalent on closely mowed turf that receives frequent irrigation and high nitrogen fertilization. These populations are more prevalent in shady or highly trafficked areas with compacted soil. Annual plants are more upright in growth and produce more seed than lower-growing perennial types.
Annual bluegrass seed germinates in late summer/early fall once soil temperatures fall below 70° F. Seedlings grow and mature in fall, overwinter in a vegetative state, and produce seed in spring. Annual bluegrass is a prolific seed producer and individual plants may produce hundreds of viable seed, even when closely mowed. Annual bluegrass flowers over several months in spring and produces seed that may remain dormant in soil for years before germinating. Annual bluegrass grows well under short day lengths and cool conditions, and may out-compete other turf species during late fall and early spring. Annual bluegrass often dies from summer stresses but may survive if irrigated and pests are adequately controlled, especially for perennial biotypes.
Cultural Control
Several cultural practices can be utilized to control annual bluegrass. Deep and infrequent irrigation encourages turfgrass root development which improves the ability of desired grasses to compete with annual bluegrass in mixed stands. Withholding water until desirable turfgrass species exhibit initial drought stress symptoms can help reduce soil moisture for potential annual bluegrass infestations. Overwatering, especially in shady areas, may predispose the site to annual bluegrass invasion.
Practices that promote soil compaction should be avoided to promote turfgrass growth and competition with annual bluegrass populations. Core aerifications should be conducted during active turf growth and favorable periods for quick recovery. Voids left in turf with exposed soil following aerifications may permit annual bluegrass invasion during periods of peak germination. For cool-season grasses, fall aerfications should be timed before annual bluegrass germinates. Warm-season grasses should have enough time to recover from summer aerifications to promote dense, high quality turf prior to annual bluegrass germination in fall.
Nitrogen fertilization should be reduced during peak annual bluegrass germination and periods of vigorous growth. High nitrogen at these times encourages annual bluegrass spread and survival in to winter and spring. Fertilizing dormant turfgrasses when annual bluegrass is actively growing may also exacerbate infestations and should be avoided.
Mowing height, frequency, and equipment requirements vary among turfgrass species and practitioners should maintain turf under appropriate regimes for successful long-term culture (Table 1). Raising the mowing height during peak annual bluegrass germination may encourage turf competition to reduce potential infestations. Lower mowing heights may predispose turf to stress and reduce competition with annual bluegrass populations. Turfgrass should also be mowed frequently during periods of vigorous growth to prevent scalping. Scalping thins out turf and may enable weeds, such as annual bluegrass, to establish. While returning clippings is recommended to recycle nutrients to the soil, removal of clippings may be useful when annual bluegrass is present and producing seedheads. Removal of clippings at this time will reduce the spread of viable seed.
Chemical Control
Preemergence Control
Preemergence herbicides may prevent annual bluegrass seed germination. However, preemergence herbicides will not eradicate established plants and will not effectively control perennial biotypes of annual bluegrass from spreading vegetatively. Application timing of preemergence herbicides for annual bluegrass control is very important. Herbicides must be applied in late summer/early fall before annual bluegrass germination. A second application can be applied in winter to control later germinating plants. Fall applied preemergence herbicides should not be used if reseeding or resodding is needed to repair areas of damaged turf within several months after herbicide applications.
Several preemergence herbicides used for summer annual weed control will effectively control annual bluegrass in fall and winter (Table 2). Fall applications of herbicides such as bensulide (Betasan), dithiopyr (Dimension), flumioxazin (Sureguard), oxadiazon (Ronstar, Starfighter), pendimethalin (Pendulum, others), and prodiamine (Barricade, others) may effectively control annual bluegrass. Indaziflam (Specticle) provides excellent preemergence control of annual bluegrass and also provides early-postemergence control as well. Indaziflam is only labeled in warm-season turfgrasses but may provide greater application timing flexibility than dinitroaniline herbicides in fall.
Combination herbicide products are also available which may improve efficacy of applications. These products include oxadiazon plus bensulide (Anderson’s Crab and Goose), oxadiazon plus prodiamine (Regalstar), and benefin plus oryzalin (Team 2G or Team Pro). Many preemergence herbicides are available under a wide variety of trade names and formulations and turf mangers should carefully read label directions before applications.
Atrazine (Aatrex, Purge, others) and simazine (Princep, WynStar, others) are labeled for centipedegrass, zoysiagrass, St. Augustinegrass and bermudagrass. Atrazine can be applied to actively growing and dormant centipedegrass or St. Augustinegrass but bermudagrass can be injured if treated while actively growing. Both herbicides have excellent preemergence activity on annual bluegrass but soil residual is generally shorter (four to six weeks) compared to aforementioned herbicides. Several atrazine products are restricted use pesticides and turf managers should check labels for further information before use.
Mesotrione (Tenacity) is labeled for use in centipedegrass, perennial ryegrass, St. Augustinegrass (sod production only), tall fescue, and dormant bermudagrass (Table 2). Mesotrione may be applied during establishment of these grasses (except bermudagrass) and effectively controls annual broadleaf and grassy weeds. Preemergence applications of mesotrione control or suppress annual bluegrass but postemergence use is ineffective for control of established plants. Mesotrione may be applied in tank-mixtures with atrazine or simazine on centipedegrass to improve efficacy of applications.
Most preemergence herbicides will provide similar initial efficacy if applied before annual bluegrass germination and sufficient rain or irrigation is received. Preemergence herbicides require incorporation from irrigation or rainfall so that weeds may absorb the applied material. In order to effectively control annual bluegrass, preemergence herbicides must be concentrated in the soil seedbank. Retention on leaf tissue can be avoided by irrigating turf immediately after application for effective soil incorporation and herbicide activation.
Preemergence herbicide applications on non-irrigated sites have less potential for residual control, compared to irrigated turf, from product loss, poor soil incorporation, and failure to activate the herbicide. Practitioners should return clippings on non-irrigated sites to help move potential herbicides remaining on leaf tissue to the soil. If clippings are collected as part of routine maintenance, practitioners should consider returning clippings until at least half to one inch of rainfall is received. Granular products may also be applied to non-irrigated sites for better soil incorporation than liquid formulations. Granular products may be easier to handle and apply with less equipment necessary than sprayable formulations. Granular herbicides should be applied when morning dew is no longer present to avoid interference from leaf tissue.
Postemergence Control
Annual bluegrass may be selectively controlled with postemergence herbicides (Table 3). Practitioners managing warm-season grasses have more options for selective postemergence annual bluegrass control than cool-season grasses. Flazasulfuron (Katana), foramsulfuron (Revolver, Tribute Total), rimsulfuron (TranXit), and trifloxysufluron (Monument) are labeled for bermudagrass and zoyiagrass non-residential commercial lawns and other sites. Flazasulfuron and rimsulfuron are also labeled for use in centipedegrass. Efficacy of these herbicides generally increases under warm temperatures in spring compared to winter and non-ionic surfactants may enhance efficacy.
Pronamide (Kerb) is a restricted use herbicide for annual bluegrass control in non-residential bermudagrass, centipedegrass, St. Augustinegrass, seashore paspalum, and zoysiagrass. Pronamide is root-absorbed and must be watered in following applications. Pronamide efficacy is generally slower than most sulfonylureas and activity for annual bluegrass control may take approximately four to six weeks.
Atrazine (Aatrex, Bonus S, others) and simazine (Princep, WynStar, others) may also be applied to bermudagrass, centipedegrass, St. Augustinegrass, and zoysiagrass for selective postemergence annual bluegrass control. These herbicides often provide erratic control of annual bluegrass but may control other grassy and broadleaf weeds. Actively-growing bermudagrass is sensitive to atrazine and applications are recommended only during the late fall and winter months.
Dormant bermudagrass may be treated with nonselective herbicides, such as glyphosate (Roundup, Touchdown, others), glufosinate (Finale), and diquat (Reward). These herbicides will injure or kill existing vegetation, including annual bluegrass and managers should only spray at peak dormancy when no green turfgrass foliage is observable. Nonselective herbicides should only be applied to completely dormant bermudagrass and applications during early spring may delay greenup with significant turf injury. Flumioxazin (Sureguard) is a new herbicide for pre- and postemergence annual bluegrass control but applications are limited to dormant bermudagrass only. Flumioxazin use after greenup or on other species are not recommended due to excessive injury potential.
Selective annual bluegrass control options in cool-season lawns are limited. Ethofumesate (Prograss) has controls established annual bluegrass in perennial ryegrass, tall fescue, and dormant bermudagrass (Table 5). Two or three ethofumesate applications may be applied in late fall at three to four week intervals. Annual bluegrass control may be seen that fall, but control is usually observed the following spring. Annual bluegrass control with ethofumesate may vary greatly over years depending on environmental conditions. Amicarbazone (Xonerate) is a new Photosystem II inhibitor, similar to triazine herbicides, but may be used in tall fescue lawns and other cool-season grasses. Applications of amicarbazone in Georgia are limited to springtime only to minimize injury to cool-season grasses. Warm-season turf is very tolerant to amicarbazone and may be treated at any seasonal timing.
Bispyribac-sodium (Velocity) has shown potential for selective annual bluegrass control in tall fescue and perennial ryegrass lawns. However, this herbicide is currently registered for creeping bentgrass and perennial ryegrass on golf courses and sod farms only. Spot treatments of nonselective herbicides are generally the most effective treatment regime for annual bluegrass control in cool-season grasses.
Managing Herbicide Resistance
Annual bluegrass is a genetically diverse species and various biotypes present in turf may have differential responses to herbicides. Repeated use of one herbicide chemistry may effectively control annual bluegrass but resistance may develop in local populations if herbicides with different modes of action are not incorporated in to management regimes. Herbicide resistance is the survival of a segment of the population of weeds following a herbicide dosage lethal to the normal population. Resistance occurs from repeated use of the same herbicide or mode of action over years and may be a concern with problematic annual weeds, such as annual bluegrass.
Triazine herbicides, atrazine and simazine, have been repeatedly used for years due to the wide spectrum of weeds controlled as pre- or postemergence treatments in warm-season grasses. Resistance in weed populations has been reported with these herbicides which may contribute to inconsistent efficacy for annual bluegrass control in turf. Resistance to sulfonylureas has been reported in weed populations in agronomic crops and repeated use in turfgrasses may also contribute to resistance in annual bluegrass populations.
Preemergence chemistries, such as the dinitroanalines, may have resistance among weed populations from repeated use over years. Turf managers should rotate preemergence herbicides from mitotic inhibitors to other modes of action to minimize resistance in annual bluegrass populations. Herbicides to consider in rotation programs from dinitroanilines would include indaziflam, ethofumesate, or oxadiazon. These chemistries offer a different mode of action than dinitroanilines but cost, label restrictions, and turfgrass tolerance may be limiting factors for using these products. Combination herbicides are also available, such as oxadiazon + prodiamine (Regalstar), oxadiazon + bensulide (Anderson’s Crab and Goose), and prodiamine + sulfentrazone (Echelon), with more than one mode of action that effectively control annual bluegrass in turf.
Table 1. Mowing requirements for commercial turfgrasses.
Mowing Requirements for Turfgrasses
Species
Mower Type
Height (inches)
Frequency (days)
Bermudagrass
Common
Rotary/reel
1 to 2
5 to 7
Hybrid
Rotary/reel
0.5 to 1.5
3 to 4
Centipedegrass
Rotary
1 to 2
5 to 10
Perennial Ryegrass
Rotary/reel
0.5 to 2
3 to 7
St. Augustinegrass
Rotary
2 to 3
5 to 7
Tall Fescue
Rotary
3
5 to 7
Zoysiagrass
Reel
0.5 to 2
3 to 7
Table 2. Efficacy of preemergence herbicides for annual bluegrass control in commercial turfgrasses.
Common Name
Trade Name (Examples)
Efficacy
atrazine
Aatrex, various
E
benefin
Balan, others
E
bensulide
Betasan, others
F
dithiopyr
Dimension
G
ethofumesate
Prograss
G-E
flumioxazin
Sureguard
G
indaziflam
Specticle
E
mesotrione
Tenacity
F
oryzalin
Surflan, others
G
oxadiazon
Ronstar, others
G
pendimethalin
Pendulum, others
G
prodiamine
Barricade, others
E
pronamide
Kerb
E
simazine
Princep, others
E
E = Excellent (90 to 100%), G = Good (80 to 89%), F = Fair (70 to 79%), P = Poor (<70%).
Table 3. Efficacy of postemergence herbicides for annual bluegrass control in turfgrass.
Common Name
Trade Name (Examples)
Efficacy
amicarbazone
Xonerate
F-G
atrazine
Aatrex, others
E
bispyribac-sodium
Velocity
F-G
flazasulfuron
Katana
G-E
flumioxazin
Sureguard
F-G
foramsulfuron
Revolver
E
glufosinate
Finale
E
glyphosate
Roundup, others
E
imazaquin
Image
P-F
metribuzin
Sencor
G
pronamide
Kerb
E
rimsulfuron
Tranxit
E
simazine
Princep, others
G-E
thiencarbazone + foramsulfuron + halosulfuron
Tribute Total
G-E
trifloxysulfuron
Monument
E
E = Excellent (90 to 100%), G = Good (80 to 89%), F = Fair (70 to 79%), P = Poor (<70%).
Purple nutsedge in flower, Mark CzarnotaLeaf tips of Yellow and Purple Nutsedge. Notice the differences in leaf tips. Purple Nutsedge has a keel shape, and yellow nutsedge is pinched. Mark Czarnota
Information supplied by Patrick McCullough, UGA Extension Weed Scientist and the publication Weed Control in Home Lawns
Purple nutsedge – Forest and Kim Starr, Starr Environmental, Bugwood.org
Hot and humid weather contributes to certain weeds in lawns – particularly sedges! Sedges come in many types – nutsedges, annual and perennial sedges and kyllinga. Identification of the sedge is the first step (though exact id of sedges can be difficult!) See this site if you need help with identification. Another great resource for weed identification is the UGA publication Weeds of Southern Turf.
Once you identify the sedge; select control methods based on this identification and the weeds biology – annual/perennial, warm/cool season, etc.
Post-emergence herbicide controls for sedges
Leaf tips of Yellow and Purple Nutsedge. Notice the differences in leaf tips. Purple Nutsedge has a keel shape, and yellow nutsedge is pinched. Mark Czarnota
flazasulfuron – Katana (25 WG) is a selective herbicide for control of annual and perennial grasses, sedges and broadleaf weeds in bermudagrass, zoysiagrass and certain other warm season grasses. Flazasulfuron has postemergence and some preemergence activity and may be used on golf courses (fairways, roughs and tees) and the following non-residential turf areas: industrial parks, tank farms, sod farms, seed farms, cemeteries, professionally managed college and professional sport fields and commercial lawns for control of cool season grasses and weeds from tolerant grasses. The maximum yearly application rate is 9.0 oz. per acres. Use only on labeled turfgrasses or severe injury may result. Do not apply to newly seeded, sodded or sprigged turfgrass until well established. Allow at least 2 weeks from the last application to the time of overseeding when applied at 1.5 oz per acre. Allow 4 weeks for rates above 1.5 oz
halosulfuron – Sedgehammer (75DF) is a selective herbicide for postemergence control of sedges such as purple and yellow nutsedge in established lawns. Sedgehammer may be applied to most major warm- and cool-season turfgrasses. For best results, apply 2/3 to 1 1/3 ounces of product per acre after nutsedge has reached the three to eight leaf stage of growth. A second treatment may be required six to 10 weeks after the initial treatment. Use the lower rate in light infestations and the higher rate in heavy infestations. No more than four applications can be made with the total use rate not exceeding 5 1/3 ounces of product per acre per season. Use 0.25% v/v of a nonionic surfactant (1 quart per 100 gallons of spray solution) for broadcast applications. Use only high quality nonionic surfactants that contain at least 80% active ingredient.
imazaquin – Image (1.5 lbs/gallon) is labeled for use only in established bermudagrass, centipedegrass, St. Augustinegrass and zoysiagrass. All other turfgrasses can be severely injured by imazaquin. This herbicide is primarily used for the postemergence control of annual sedges, yellow nutsedge, purple nutsedge and wild garlic. Imazaquin will also control numerous winter annual weeds and sandbur.
Green kyllinga – Rebekah D. Wallace, University of Georgia, Bugwood.org
sulfentrazone — Dismiss (4 lbs/gallon) is a postemergence herbicide labeled for most major warm- and cool-season turfgrasses. Use lower rates on cool-season turfgrass than warm-season turf due to injury concerns. Dismiss controls annual and perennial sedges, broadleaf weeds and suppresses goosegrass.Dismiss may be used on seeded, sodded or sprigged turfgrasses that are well established. Applications of Dismiss can be initiated following the second mowing provided the turfgrass has developed into a uniform stand with a good root system. Turfgrass injury could result from application of this product on turfgrass that is not well established or has been weakened by stresses such as unfavorable weather conditions, disease, chemical or mechanical damage. Dismiss may cause temporary discoloration to St. Augustinegrass and zoysiagrass.
Sulfentrazone is also found in the combination products Surge and Q4. Surge contains sulfentrazone, 2,4-D, dicamba and MCPP and effectively controls annual, biennial and perennial broadleaf weeds. Surge may be applied to dormant bermudagrass, zoysiagrass and bahiagrass but do not apply during spring green-up or in the fall during the transition period between active growth and dormancy. Q4 contains sulfenetrazone, quinclorac, 2,4-D and dicamba for broadleaf weed, crabgrass and nutsedge control. For best results, add 0.25 lb of active ingredient per acre of quinclorac (Drive) and 0.06 to 0.19 lb of active ingredient per acre of sulfentrazone (Dismiss) for crabgrass and nutsedge control, respectively.
sulfosulfuron — Certainty (75DF) is labeled for bermudagrass, St. Augustinegrass, zoysiagrass and centipedegrass. Certainty selectively controls sedges, kyllingas and tall fescue. A second application of 0.75 to 1.25 ounces per acre may be made four to 10 weeks after initial treatment, if needed. Some chlorosis or stunting of the desirable turf may occur following application. Use of a nonionic surfactant is required. Certainty suppresses annual bluegrass and controls or suppresses roughstalk bluegrass.
trifloxysulfuron-sodium – Monument (75 DG) is labeled for established bermudagrass and zoysiagrass. Monument is not recommended for use on other turfgrass species. Controls nutsedge(s), green kyllinga, annual bluegrass, tall fescue, torpedograss and certain broadleaf weeds. Not labeled for use on home lawns. Add a nonionic surfactant at 0.25 to 0.5% v/v to the spray mix. Avoid mowing for 1 to 2 days before and after application. For nutsedge repeat the application at 4 to 6 weeks if regrowth is observed. DO NOT overseed bermudagrass with cool-season turfgrasses for 3 weeks after application.
Cultural practices to control sedges
The first line of defense against weeds is to follow cultural practices that promote vigorous turfgrass growth and development. Weeds do not easily invade turfgrasses that are properly fertilized and watered and that are mowed at the correct height and frequency. Weeds appear primarily in bare or thin areas of the turfgrass, which may be due in part to one or more of the following:
Use of non-adapted turfgrasses.
Improper fertilization (too much or too little, wrong application date or N-P-K ratio).
Improper watering (too much or too little).
Improper mowing procedures (cutting height is too low or too high, or the turfgrass is not mowed at correct time intervals).
Failure to control diseases and insects.
Excessive amounts of thatch.
Visit www.GeorgiaTurf.com for additional information on turfgrass maintenance practices. The impact of proper cultural practices on a lawn weed control program cannot be overemphasized. Properly maintained turfgrasses are more competitive with weeds than turfgrasses that do not receive good cultural practices. The use of herbicides without following approved cultural practices will not result in a high quality, weed-free lawn.
