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Bulletin 421

Winter Annual Weed Control with Herbicides in Turfgrasses

B. J. Johnson and T. R. Murphy

Winter annual weeds are found in most turfgrasses throughout Georgia and the southeastern U.S. during the winter and early spring. Not only on golf courses, they are also found in home lawns, athletic fields, industrial sites, and other turfgrass areas. Mild winter temperatures favor germination and rapid growth of these annuals. The presence of weeds detracts from the aesthetic value and usually results in an undesirable turf. Most winter annuals initiate germination in early fall and growth continues until late spring to early summer. If not controlled, winter annual weeds will delay the spring transition of desirable warm-season turfgrasses (Johnson 1977a, 1982a).

Herbicides can be applied as preemergence (Grant, Cooper, and Webster 1990; Johnson 1975, 1977a, 1982a) or postemergence (Ebdon and Jagschitz 1982; Johnson 1977b, 1982a, 1982b, 1987; McCarty 1991) treatments for the control of winter annuals. Preemergence herbicides when used, must be applied prior to weed seed germination and emergence. Therefore, application time is important in obtaining optimum weed control (Johnson 1975). In this study, annual bluegrass (Poa annua L.) control was higher when benefin was applied in September at Lawrenceville and October at Griffin than when applied in July or August at either location. These results indicate that July and August treatments were too early at both locations and October treatment was too late at Lawrenceville for optimum annual bluegrass control.

Before selecting the preemergence herbicide, it is important to know what weed species are in the turfgrass area. When benefin at 3.0 lb ai/acre was applied in the fall, >80% control was obtained for annual bluegrass, henbit (Lamium amplexicaule L.), common chickweed [Stellaria media (L.) Cyrillo], and corn speedwell (Veronica arvensis L.), but control was <70% for hop clover (Trifolium agrarium L.), parsley-piert (Alchemillamicrocarpa Bossier Reuter), and lawn burweed [Soliva pterosperma (Juss.) Less.] (Johnson 1977a). In the same study, oxadiazon at 4.0 lb ai/acre controlled parsley-piert, hop clover, annual bluegrass, and corn speedwell, but not lawn burweed, henbit, or common chickweed. Grant, Cooper, and Webster (1990) reported that tank-mixes of preemergence herbicides applied in the fall controlled more common weed species in the southeastern United States than when a single herbicide was applied alone. Isoxaben applied alone at 0.75 lb ai/acre provided >80% control of seven to 10 different weed species, while oryzalin applied alone at 2.0 lb ai/acre controlled only annual bluegrass and henbit. When the herbicides were tank-mixed and applied as a single application, control was >70% for all ten species. They reported similar results from tank-mixes of isoxaben with pendimethalin. Therefore, the effectiveness of preemergence herbicides on winter annuals depends on time of application, weed species, and whether the herbicide was applied alone or tank-mixed with other herbicides.

Preemergence herbicides applied in the fall can delay green-up (spring transition) of common bermudagrass (Cynodon dactylon [L.] Pers.) the following March and April (Johnson 1977a). The amount of delay in green-up, however, often depends on herbicide used. Benefin applied at 3.0 lb ai/acre delayed green-up by 34% by late March and 28% by mid-April. The turfgrass recovered from the treatment, however, by mid-May. In contrast, butralin at 6.0 lb ai/acre delayed green-up of common bermudagrass only 15% by late March, while the green-up in plots treated with oxadiazon at 4.0 lb ai/acre was not affected.

The timing of postemergence herbicides can also affect bermudagrass green-up in the spring. In most instances, combinations of 2,4-D with mecoprop and dicamba, or with dicamba injured bermudagrass more when applied to semi-dormant turf in March than to dormant turf in January or February (Johnson 1980).

The 2,4-D and herbicide mixtures that contain 2,4-D have traditionally been used to control most broadleaf weeds in turfgrasses. When these herbicides are used, however, the two- or three-way combinations will usually control weeds more consistently than 2,4-D alone (Johnson 1977b). For example, one application of 2,4-D (1.0 lb ai/acre) controlled common chickweed 43%, compared to 91% from 2,4-D plus mecoprop plus dicamba (0.66 + 0.33 + 0.08 lb ai/acre), and 100% from 2,4-D plus dicamba (1.0 + 0.5 lb ai/acre) (Johnson 1977b). A wider range of weed species can also be controlled from the two- and three-way combinations applied in multiple applications, compared with a single application. One application with 2,4-D plus mecoprop plus dicamba (1.0 + 0.5 + 0.1 lb ai/acre) failed to control henbit, parsley-piert, and corn speedwell effectively, while the control was excellent when 1.0 + 0.5 + 0.1 lb ai/acre was applied in each of two applications (Johnson 1977b, 1982b, 1987).

The consistency of postemergence herbicides in controlling winter annuals often is related to time of application. McCarty (1993) reported that postemergence herbicides applied in December effectively controlled small weeds, as opposed to the poor control when treatments were delayed until March or April. In an earlier study in Georgia (Johnson 1980), two- and three-way herbicide combinations tended to control corn speedwell, hop clover, and parsley-piert better when applied in January or February than when applied in March.

Triclopyr has good to excellent activity on broadleaf winter annuals (Jagschitz 1980; Johnson 1982b, 1987). Triclopyr, however, severely injured a mixture of red fescue (Festuca rubra L.), Kentucky bluegrass (Poa pratensis L.), and colonial bentgrass (Agrostis tenuis sibth.), and delayed spring green-up of common bermudagrass. Therefore, the successful use of herbicides depends greatly on turfgrass tolerance. The herbicide has little value if it controls weeds and causes undesirable turfgrass injury.

It has been several years since preemergence and postemergence herbicides have been evaluated on winter annual weeds in Georgia (Johnson 1982b, 1987). Additionally, several herbicides have been introduced during this time period. Therefore, preemergence and postemergence herbicide experiments were conducted to determine the effects of these herbicides on weed control and on tolerance of common bermudagrass turf.
 

MATERIALS AND METHODS

Winter annual weed control experiments were conducted on Kentucky bluegrass at Butternut Creek Golf Course, Blairsville, Georgia, and on dormant common bermudagrass at Beaver Lake Golf and Country Club, Gay, Georgia. Table 1 gives the nomenclature of herbicides used in all experiments. The experiments include the postemergence weed control activity from preemergence herbicides at Blairsville during 1990 and 1992 and preemergence and postemergence herbicide evaluations at Gay during 1993 and 1994. Table 2 gives treatment dates, location of experiments, and turfgrass species within each experiment.

Table 1. Nomenclature of Herbicides
Name
Common Trade a Formulation Chemical Company
Benefin Balan 2.5G N-butyl-N-ethyl-2,6-dinitro-4- DowElanco
(trifluoromethyl)benzenamine
Benefin 
+ oryzalin 
XL 1 + 1G benefin given above;
oryzalin = 4-(dipropyl- DowElanco
amino)-3,5-dinitro-
benzenesulfonamide
Benefin +
trituralin
Team 1.3 + 0.7G benefin given above; DowElanco 
trifluralin = 2,6-dinitro-
N,N-dipropyl-4-(trifluoro-
methyl)benzenamine
Bensulide
+ oxadiazon 
Goosegrass/Crabgrass Control 5.25 +
1.13%
bensulide = 0,0-bis(1- O.M. Scott & Sons
methylethyl) S-[2-[(phenyl-
sulfonyl)amino]ethyl]phos-
phorodithioate;
oxadiazon = 3-[2,4-dichloro-5-
(1-methylethoxy)phenyl]-5-(1,1-
dimethylethyl)-1,3-4-oxadiazol-2-(3H)-one
Butralin EXP 30910A
EXP 31068A
5G 4-(1,1-dimethylethyl)-N-(1- Rhone
Poulenc
methylpropyl)-2,6-dinitro-
benzenamine
Clopyralid XRM3972 3AS 3,6-dichloro-2-pyridinecar- DowElanco
boxylic acid
Diclofop Illoxan 3EC (±)-2-[(2,4-dichlorophenoxy)- Agr EVO
phenoxy]propanoic acid
Dithiopyr Dimension 1EC S,S-dimethyl 2-(difluoro- Monsanto
methyl)-4-(2-methylpropyl)-
6-(trifluoromethyl)-3,5-
pyridinedicarbothioate
Fenoxaprop Acclaim 1EC (±)-2[4-[(6-chloro-2- Agr EVO
benzoxazolyl)oxy]phenoxy]
propanoic acid
Flazasulfuron ASC 67040 10WP, 25DF 1-(4,6-dimethoxypyrimidin- ISK Biotech
2-yl)-3-[(3-trifluoromethyl-
pyridin-2-yl)
Fluoroxypyr XRM 5316 1.5 EC [(4-amino-3,5-dichloro-6- DowElanco
fluoro-2-pyridinyl)oxy]
acetic acid
Imazaquin Image 1.5 AS 2-[4,5-dihydro-4-methyl- American Cyanamid
4-(1-methylethyl)-5-oxo-
1H-imidazol-2-yl]-3-quino-
linecarboxylic acid
Isoxaben Gallery 75DF N-[3-(1-ethyl)-1-methyl- DowElanco
propyl)-5-isoxazolyl]-2,6-
dimethoxybenzamide
MCPA
+mecoprop
+ dicamba
Chipco Three 2.67
+1.28
+ 0.3 EC
MCPA = (4-chloro-2-methyl- Rhone Poulenc 
phenoxy)acetic acid; 
mecoprop = (+)-2-(4-chloro-
2-methylphenoxy)propanoic acid;
dicamba = 3,6-dichloro-2-
methoxybenzoic acid
Metsulfuron DMC  60WD methyl methyl 2-[[[[4-methoxy- O.M. Scott & Sons
6-methyl-1,3,5-triazin-2-yl]-
amino]carbonyl]amino]
sulfonyl]benzoate
Metolachlor Pennant 7.8 EC 2-chloro-N-(2-ethyl-6- CIBA
methylphenyl)-N-(2-methoxy-
1-methylethyl)acetamide
MON 120051 Manage 50 WP methyl-5-[[(4,6-dimethoxy-2- Monsanto
pyrimidinyl)amino]carbonyl-
aminosulfonyl]-3-chloro-1-
methyl-1-H-pyrazol-4-carboxylate
Oryzalin Surflan 4AS 4-(dipropylamino)-3,5-dinitro- DowElanco
benzenesulfonamide
Oxadiazon Ronstar 2G given above Rhone Poulenc
Oxadiazon + benefin Regalstar 1+.5(38% N) given above Regal Chemical
Pendimethalin PRE-M Turfweed grass control 60 WDG N-(1-ethylpropyl)-3,4-dimethyl - Lesco
O M.Scott & Sons
2,6-dinitrobenzenamine
Prodiamine Barricade 65 WDG N3,N3-di-n-propyl-2,4-dinitro Sandoz
-6-(trifluoromethyl)-m-phenylene-
diamine
Quizalofop  Assure II 0.88 EC (±)-2-[4-[(6-chloro-2-quinoxa- Dupont
linyl)oxy]phenoxy]propanoic
acid
Simazine Princep 4L 6-chloro-N,N'-diethyl-1,3,5- CIBA
triazine-2,4-diamine
Triclopyr
+ clopyralid
Confront 2.25+.75 EC triclopyr = [(3,5,6-trichloro-2- Dow Elanco
pyridinyl)oxy]acetic acid;
clopyralid given above
Triclopyr
+ clopyralid
+ isoxaben
Confront
+ Gallery
2.25
+.75 EC
+ 75 DF
Given above DowElanco
2,4-D
+ dichlorprop
Chipco 
Weedone
amine
1.88
+1.82 EC
2,4-D = (2,4-dichlorophenoxy) Rhone
Poulenc
acetic acid; dichlorprop = 
(±)-2-(2,4-dichlorophenoxy)
propanoic acid
2,4-D
+ mecoprop
+ dicamba
Trimec
Classic
2.03
+1.08
+ .21 EC
given above PBI
Gorden
a. A given herbicide may have more than one trade name, and the one used is from the company furnishing the chemicals.
 

Table 2. Annual Weed Control Experiments, Locations, and Treatment Dates
Experiment Location Turfgrass Treatments
Postemergence from preemergence herbicides Butternut Creek Golf Course
Blairsville, Georgia
Kentucky bluegrass 1990: March 5
1992: March 2
Preemergence herbicides Beaver Lake Golf Course
Gay, Georgia
Common bermudagrass  1992: September 11
1993: September 13
Postemergence herbicides Beaver Lake Golf Course 
Gay, Georgia
Common bermudagrass 1993: January 27
1994: February 14

Postemergence weed control activity from preemergence herbicides.

Preemergence herbicides were applied to Kentucky bluegrass turf at Blairsville on March 5, 1990 and March 2, 1992 for subsequent evaluations of crabgrass control. Early spring evaluation of these plots revealed that some preemergence herbicides exhibited postemergence activity on corn speedwell and chickweed (common chickweed and mouseear chickweed [C. vulgatum L.]) (Table 3). Therefore, control ratings for these winter annual weeds were recorded April 4, 1990, and May 4, 1992. At time of ratings, the cover of weeds in untreated plots was 35% and 11% corn speedwell cover in 1990 and 1992, respectively, and 25% chickweed spp. cover in 1990.
 

Table 3. Performance of Preemergence Herbicides on Postemergence Weed Control In Kentucky Bluegrass,
Butternut Creek Golf Course, Blairsville, Georgia.
Treatmentsa
Weed controlb
Corn Speedwell Checkweed
Herbicide Formulation Rate
lb ai/acre
1990 1992 1990
%
Untreated - - 0 0 0
Dithiopyr 1 EC  0.25 60 100 35
0.5 59 100 74
Isoxaben 75 DF 0.75 78 - 92
Prodiamine 65 WDG 0.75 51 78 54
Pendimethalin 60 WDG 3.0 44 100 58
Oxyfluorfen
+ oryzalin
2 + 1G 2.0 + 1.0
3.0 + 1.5
6.0 + 3.0
--- 20
45
88
-
-
-
LSD @ 0.05 18 21 15
a. Herbicides were applied for preemergence crabgrass control on March 5, 1990 and March 2, 1992.
b. Weed control ratings were made April 4, 1990 and May 4, 1992 and based on 0 = no control and 100 = complete control.
 

Preemergence weed control.

Preemergence herbicides at rates given in tables 4 and 5 were applied to common bermudagrass on September 11, 1992 and September 13, 1993 at Gay, Georgia. Treatments were made to different plots each year. Weed control ratings from 1992 treatments were made in March and ratings from 1993 treatments were made in March and April 1994. The later ratings in 1994 were necessary because colder temperatures in January 1994 slowed weed emergence and growth. The lowest temperature during January 1994 was 6oF and there were 15 days when the temperature was less than 30oF. In contrast, the lowest temperature during January 1993 was 26oF, and the temperature was less than 30oF for only five days.
 

Table 4. Effects of Fall-Applied Preemergence Herbicides on Winter Annuals in Dormant Common Bermudagrass, Beaver Lake Golf Course, Gay, Georgia, 1992-1993
Treatments a
Weed controlb
Annual bluegrass  Lawn burweed Purple cudweed
Herbicide Rate
lb ai/acre
Mar 9 Mar 30 Mar 9 Mar 30 Mar 9 Mar 30
%
Untreated - 0 0 0 0 0 0
Oxadiazon 3.0 96 97 29 31 40 42
4.0 100 100 17 28 42 45
Butralin 5.0 81 95 7 0 15 0
Isoxaben 0.75 0 0 100 98 61 74
Oryzalin 1.5 100 98 20 9 0 0
2.0 100 100 0 0 8 3
Dithiopyr 0.25 83 83 0 0 0 1
1.0 97 98 0 0 14 0
Benefin 3.0 100 100 0 0 32 18
Metolachlor 2.0 0 0 14 25 17 20
4.0 23 0 0 0 46 32
Prodiamine 0.75 100 95 0 0 51 25
1.0 88 83 26 12 25 25
Pendimethalin 3.0 79 74 0 0 47 43
Simazine 2.0 52 22 39 25 100 100
Oxyflourden
+ oryzalin 
2.0 + 1.0 100 100 73 62 70 66
Benefin
+ oryzalin
2.0 + 2.0 100 100 73 62 70 66
Benefin
+ trifluralin
2.6 + 1.4 100 100 17 0 54 40
Oxadiazon
+ benefin
2.0 + 1.0 100 93 0 0 62 62
LSD P = 0.05 30 24 21 22 25 22
a. Herbicides were applied September 11, 1992. Oxyfluorfen plus oryzalin, benefin plus oryzalin, benefin plus trifluralin, and oxadiazon plus benefin were applied as single products.
b. Weed control ratings were based on 0 = no control and 100 = complete control.
 

Table 5. Effect of Fall-Applied Preemergence Herbicides on Annual Bluegrass Control in Dormant Common Bermudagrass, Beaver Lake Golf Course, Gay, Georgia, 1993-94.
Treatments a
Annual bluegrass control b
Herbicides Rate 
lb ai/acre
April 4
%
Untreated - 0
Oxadiazon 3.0 100
4.0 100
Butralin 5.0 81
Isoxaben 0.75 42
1.0 64
Oryzalin 1.5 100
2.0 100
Dithiopyr 0.25 89
0.5 100
1.0 97
Benefin 3.0 94
Metolachlor 2.0 0
4.0 0
Prodiamine 0.75 100
1.0 100
Pendimethalin 3.0 94
Simazine 2.0 89
Oxyfluorfen
+ oryzalin 
2.0
+1.0
100
Benefin
+ oryzalin
1.5
+1.5
100
Benefin
+ trifluralin
2.0
+1.0
97
Oxadiazon
+ benefin
2.0
+1.0
100
LSD P = 0.05 - 22
a. Herbicides were applied September 13, 1993. Oxyfluorfen plus oryzalin, benefin plus oryzalin, benefin plus trifluralin, and oxadiazon plus benefin were applied as single products.
b. Weed control ratings were made on 0 = no control and 100 = complete control.
 

Weeds evaluated were annual bluegrass, lawn burweed, and purple cudweed (Graphalium purpureum L.) in 1993 and annual bluegrass, corn speedwell, chickweed (common and mouseear), and knawel (Scleranthus annuus L.) in 1994. When final ratings were made, weed cover in 1993 was 26% for purple cudweed, 36% for annual bluegrass, and 38% for lawn burweed. The cover of weeds in 1994 was 36% for annual bluegrass, 8% for knawel, 5% for chickweed, and 2% for corn speedwell.
 

Postemergence weed control.

Postemergence herbicides at rates given in tables 6 and 7 were applied for weed control in dormant common bermudagrass at Gay, Georgia on January 27, 1993 and February 14, 1994. A nonionic surfactant was added at 0.5% v/v with flazasulfuron, quizalofop, 2,4-D plus mecoprop plus dicamba, MON 120051, and imazaquin. Treatments were applied to different plots each year. Weed control ratings were made in March 1993 and in March and April 1994. Weeds and population of weeds evaluated when final ratings were made consisted of 46% annual bluegrass, 38% lawn burweed, 12% innocene (Hedyotis procumbens [Walt. ex Gmel.] Fosb.), and 4% corn speedwell in 1993. The population of weeds in 1994 was 30% annual bluegrass, 13% chickweed, 13% knawel, and 4% innocene.
 

General information.

Experiments were conducted on golf course fairways at Blairsville and Gay, Georgia. Kentucky bluegrass at Blairsville and common bermudagrass at Gay were managed similarly to the surrounding turf. None of the experimental sites were fertilized or irrigated. Both turfgrasses were mowed at weekly intervals to a height of 0.5 to 0.75 inch, while actively growing. Clippings were returned in all experiments. Neither grass was mowed during the winter after Kentucky bluegrass growth stopped and common bermudagrass was dormant.

Winter weed control and turfgrass density ratings were visually estimated at various times from March through May. Winter weed control ratings were based on difference in cover of weeds in treated and untreated plots, where 0 = no control and 100 = complete control. On this scale, >90 = excellent control, 80 to 89 = good control, 70 to 79 = fair control, and <79 = poor control. Crabgrass emergence ratings were made from the fall preemergence experiment on the following May 25. The ratings were based on 0 = no crabgrass present and 5 = heavy population. Turfgrass density ratings were based on 1 to 10, where 1 = no turfgrass and 10 = uniform complete dense cover.

Herbicide treatments in all experiments were arranged in a randomized complete block design with four replications. Analysis of variance procedure of SAS was used to analyze the data (SAS Institute, Inc. 1982). Treatment means were separated by LSD at P = 0.05 level. Data were analyzed and presented by year, as herbicide treatments and weed species varied between years.

RESULTS AND DISCUSSION

Weed Control

Postemergence control from preemergence herbicides.

Corn speedwell and chickweed spp. were controlled with several preemergence herbicides applied in early March in Kentucky bluegrass (table 3). Dithiopyr at <0.5 lb ai/acre and pendimethalin at 3.0 lb ai/acre completely controlled corn speedwell in 1992, but the control was poor (<60%) in 1990. Prodiamine at 0.75 lb ai/acre resulted in fair (78%) control for corn speedwell in 1992, but the control was poor (51%) in 1990. Dithiopyr at 0.5 lb ai/acre resulted in fair (74%) chickweed spp. control, but control was poor (<58%) in plots treated with pendimethalin or prodiamine. Oxyfluorfen plus oryzalin at 6.0 + 3.0 lb ai/acre resulted in good (88%) corn speedwell control, but the control was poor (<45%) when the herbicides were applied at lower rates. The higher corn speedwell control from the herbicide in 1992 was probably related to smaller weeds at the time of treatment in 1992. Isoxaben at 0.75 lb ai/acre was the only herbicide that controlled >78% of corn speedwell and chickweed in both years. There was little or no postemergence activity on either corn speedwell or chickweed from oxadiazon, benefin, benefin plus oryzalin, trifluralin plus benefin, metolachlor, oryzalin, oxadiazon plus benefin, or bensulide plus oxadiazon (data not given).

These results indicate that most preemergence herbicides applied for crabgrass control in late winter have little or no postemergence activity on winter annuals. Therefore, if postemergence activity is desired on emerged weeds at the time preemergence crabgrass herbicides are applied, it would be desirable to tank-mix a postemergence herbicide with preemergence herbicide and apply as a single application (Johnson 1983).
 

Preemergence weed control.

All preemergence herbicides applied on September 11, 1992 controlled at least 80% annual bluegrass the following March, with the exceptions of isoxaben, metolachlor, pendimethalin, and simazine (table 4). The control with simazine at 2.0 lb ai/acre was poor (52%) when rated on March 9. Annual bluegrass control was excellent (>90%) with simazine in earlier studies (Johnson 1977b, 1982a). The poor control in the present study was probably related to 11.6 inches of rainfall in November 1992. This was 7.5 inches above normal. Pendimethalin resulted in fair (74%) annual bluegrass control by late March.

Isoxaben (0.75 lb ai/acre) was the only preemergence herbicide applied in September 1992 that effectively controlled lawn burweed (>98%) when ratings were made the following March (table 4). Oxyfluorfen plus oryzalin (2.0 + 1.0 lb ai/acre) provided fair (73%) control when rated March 9, but the control was reduced to an unacceptable level (62%) by March 30.

Of the 14 herbicide treatments applied September 1992, only isoxaben (74%) and simazine (100%) controlled purple cudweed when ratings were made on March 30 (table 4). Purple cudweed control with oxyfluorfen plus oryzalin was 70% in early March, but reduced to 66% by late March. Lawn burweed control with oxyfluorfen plus oryzalin was similar to that observed for purple cudweed.

All preemergence herbicides applied on September 13, 1993 resulted in good to excellent (>81%) annual bluegrass control the following April (table 5). Poor control with isoxaben and metolachlor during 1993 (table 4) and 1994 indicates that these herbicides have minimal activity on annual bluegrass.

Corn speedwell, knawel, and chickweed were present in the test area. The populations were variable, however, and prevented reliable control ratings. The 1994 test area was selected the previous year because it contained a uniform stand of several winter weeds. There was evidence that lateral movement occurred with some herbicides across plots during 1994, which may account for variation in weed population. Rainfall was 1.8 inches the six weeks following the September treatments in 1993. The highest rainfall at any date during this period was <0.5 inch. A total of 4.3 inches, however, occurred within a seven-day period at six to seven weeks after herbicide treatments. The lateral movement of the herbicides probably occurred during this period. Most preemergence herbicides applied in the fall effectively controlled annual bluegrass, but not lawn burweed or purple cudweed. In 1993, isoxaben controlled both broadleaf weeds, while simazine controlled only purple cudweed.

It was observed that dithiopyr applied at 1.0 lb ai/acre in the fall was the only treatment where crabgrass had not emerged by late May during 1993 and 1994 (data not given). Some of the other herbicides controlled crabgrass by this date during one year, but not in the other years. These results suggest that preemergence herbicides applied in the fall have some activity on crabgrass the following spring. Additional information is needed, however, to determine how much activity is present from the various herbicides.
 

Postemergence weed control.

Flazasulfuron at rates of >0.04 lb ai/acre was the only herbicide applied in January 1993 that provided good to excellent (>87%) annual bluegrass control (table 6). The control with flazasulfuron at 0.02 lb ai/acre was fair (72%) when rated on March 9, but the control was reduced to 45% by March 30. Control was effective throughout March when the rate of flazasulfuron was increased to 0.04 lb ai/acre. Imazaquin at 0.5 lb ai/acre provided fair control of annual bluegrass (<79%) in early March, but reduced to an unacceptable level (<57%) by late March.
 

Table 6.Effects of Postemergence Herbicides on Winter Annuals in Dormant Common Bermudagrass, Beaver Lake Golf Course, Gay, Georgia, 1993.
Treatmentsa
Weed controlb
Annual bluegrass Lawn burweed Innocene Corn
Speedwell
Herbicide Rate
lb ai/acre
Mar 9 Mar 30 Mar 9 Mar 30 Mar 30 Mar 30
%
Untreated - 0 0 0 0 0 0
Flazasulfuron 0.02 72 45 100 100 93 0
0.04 86 94 100 100 100 0
0.09 82 87 100 100 100 0
Fenoxaprop 0.25 0 4 9 48 91 0
Diclofop 1.0 11 0 11 15 21 0
Quizalofop 0.04 14 0 6 44 36 0
0.08 66 20 0 0 0 0
Metsulfuron 0.009 0 0 100 100 100 62
0.018 1 0 98 100 100 62
0.0376 0 0 99 100 100 44
Clopyralid 0.25 0 0 77 80 93 5
0.5 0 0 67 78 100 30
Fluoroxypyr 0.25 0 0 59 100 85 0
0.5 0 0 95 100 82 67
Triclopyr 0.75+0.25 0 77 93 100 75
1.5+0.5 0 0 85 100 100 100
Triclopyr + clopyralid + isoxaben 0.75+0.25+0.75 0 0 89 97 100 100
2,4-D + mecoprop + dicamba 1.0+0.5+0.1 0 0 83 99 100 75
2.0+1.0+0.2 0 0 99 100 100 87
MON 120051 0.06 0 0 100 90 19 0
Imazaquin 0.38 76 41 100 98 93 0
0.5 79 57 100 98 100 0
MCPA + mecoprop + dicamba 1.42+0.68+0.16 0 0 77 100 100 42
2,4-D + dichlorprop 0.94+0.91 0 0 28 100 100 67
LSD P = 0.05 14 19 14 18 8 18
a. Herbicides were applied January 27, 1993. Triclopyr plus clopyralid, 2,4-D plus mecoprop plus dicamba, MCPA plus mecoprop plus dicamba, and 2,4-D plus dichlorprop were applied as single products. A nonionic surfactant was added to flazasulfuron, quizalofop, MON 120051, imazaquin, and 2,4-D plus mecoprop plus dicamba.
b. Weed control ratings were based on 0 = no control and 100 = complete control.
 

All postemergence herbicides applied in January 1993 effectively controlled (>78%) lawn burweed, except fenoxaprop, diclofop, and quizalofop (table 6). The control, however, by late March was not as good with clopyralid (<80%) as when treated with flazasulfuron (100%), metsulfuron (100%), fluroxypyr (100%), MCPA or 2,4-D plus mecoprop plus dicamba (100%), and 2,4-D plus dichlorprop (100%).

All postemergence herbicides controlled innocene >75%, except diclofop, quizalofop, and MON 120051 (table 6). In contrast, the combination of triclopyr plus clopyralid, alone or with isoxaben, and 2,4-D plus mecoprop plus dicamba were the only herbicides that controlled >75% corn speedwell at the same date. In earlier studies (Johnson 1977b, 1987), corn speedwell control was generally improved when a second application was made at a two-week interval. Since most of the postemergence herbicides included in the present study have not been previously evaluated in Georgia, it is not known whether a second application would improve weed control.

Flazasulfuron was the only herbicide that controlled >80% annual bluegrass during both years (tables 6 and 7). To obtain this level of weed control, flazasulfuron must be applied at rates >0.04 lb ai/acre. The results with flazasulfuron in 1994 were similar to 1993. Annual bluegrass control with imazaquin at 0.5 lb ai/acre, however, was higher in 1994 than in the previous year.
 

Table 7. Effect of Postemergence Herbicides on Winter Annuals in Dormant Common Bermudagrass, Beaver Lake Golf Course, Gay, Georgia, 1994.
Treatmentsa
Annual bluegrass Chickweed Knawel Innocene Corn speedwell
Herbicide Rate April 4 April 4 April 4 March 21 April
lb ai/acre --------------------------------------------------%--------------------------------------------------
Untreated 0 0 0 0 0
Flazasulfuron 0.02 0 86 94 0 0
0.04 92 100 1400 100 70
0.09 80 100 90 100 73
Fenoxaprop 0.25 32 31 70 0 0
Diclofop 1.0  42 70 0 0 19
Quizalofop 0.04 0 37 0 0 27
50 0 9 0 0
Metsulfuron 0.009  17 100 100 100 0
0.018 0 100 100 100 16
0.0376 45 100 100 100 75
Clopyralid 0.25 0 55 25 100 0
0.5  0 51 0 100 0
Fluoroxypyr 0.25 0 90 100 80 19
0.5  0 100 100 100 86
Triclopyr
+ clopyralid 0.75+0.25 0 78 92 100 0
1.5+0.5 0 100 100 100 84
Triclopyr + clopyralid
+ isoxaben 0.75+0.25+0.75 0 100 96 100 89
2,4-D + mecoprop
+ dicamba 1.0+0.5+0.1 0 100 100 100 100
2.0+1.0+0.2 0 100 100 100 100
MON 120051 0.06 0 96 70 0 11
Imazaquin 0.38  42 100 86 100 41
0.5  89 100 100 100 65
MCPA + mecoprop
+ dicamba 1.42+0.68+0.16 0 100 86 100 54
2,4-D + dichlorprop 0.94+0.91 0 86 94 77 48
LSD P = 0.05 21 18 10 7 20
a. Herbicides were applied February 14, 1994. Triclopyr plus clopyralid, 2,4-D plus mecoprop plus dicamba, MCPA plus mecoprop plus dicamba, and 2,4-D plus dichlorprop were applied as single products. A nonionic surfactant was added to Flazasulfuron, quizalofop, MON 120051, imazaquin, and 2,4-D plus mecoprop plus dicamba.
b. Weed control ratings were based on 0 = no control and 100 = complete control.
 

Flazasulfuron at 0.04 lb ai/acre was the only postemergence herbicide that controlled >70% of all five weed species (annual bluegrass, chickweed, knawel, innocene, and corn speedwell included in the test area) (table 7). Imazaquin at 0.5 lb ai/acre resulted in good to excellent control of all species except corn speedwell. The control was similar among the combinations of triclopyr plus clopyralid alone (1.5 + 0.5 lb ai/acre), or with isoxaben (0.75 lb ai/acre), 2,4-D plus mecoprop plus dicamba (1.0 + 0.5 + 0.1 lb ai/acre), metsulfuron (0.0376 lb ai/acre) and fluoroxpyr (0.5 lb ai/acre) for all weed species except annual bluegrass. Corn speedwell control was poor (<70%) when the rate for triclopyr plus clopyralid was reduced to 0.75 + 0.25 lb ai/acre, fluoroxypr reduced to 0.25 lb ai/acre, and metsulfuron reduced to <0.018 lb ai/acre. Combinations of MCPA plus mecoprop plus dicamba and 2,4-D plus dichloroprop controlled chickweed, knawel, and innocene, but not annual bluegrass or corn speedwell.

The activity of fenoxaprop, diclofop, clopyralid, quizalofop, and MON 120051 was not as good for a wide range of weed species as was flazasulfuron, metsulfuron, fluoroxypyr, triclopyr plus clopyralid, 2,4-D plus mecoprop plus dicamba, imazaquin, MCPA plus mecoprop plus dicamba, and 2,4-D plus dichlorprop (table 7). MON 120051 controlled only two species (chickweed and knawel), while clopyralid (innocene), diclofop (chickweed), and fenoxaprop (knawel) controlled only one species. Quizalofop did not control any of the weed species (<50%).

These results indicate that flazasulfuron has fair to excellent activity on annual bluegrass and most broadleaf weeds included in this study. The broadleaf weeds include lawn burweed, chickweed, innocene, and knawel. Corn speedwell control with flazasulfuron at 0.04 lb ai/acre was >70% control in one of two years. Metsulfuron controlled all broadleaf weeds effectively, except for corn speedwell. Generally, 2,4-D plus mecoprop plus dicamba at 1.0 + 0.5 + 0.1 lb ai/acre over the two-year period was as effective as any other herbicide for winter annual broadleaf weed control.

Turfgrass tolerance.
 

The density of common bermudagrass was significantly lower in April 1993 in plots treated with metolachlor at 4.0 lb ai/acre in September 1992, when compared with untreated turfgrass (table 8). The delay in green-up with metolachlor from September treatment agrees with that reported from a late February treatment in an earlier study (Johnson and Murphy 1993). There were no other observed differences from preemergence herbicides at the April 20 ratings.
 

Table 8.Effects of Fall-Applied Preemergence Herbicide on Common Bermudagrass the Following Spring, Beaver Lake Golf Course, Gay, Georgia, 1993-94
Turfgrass densityb
Treatmentsa 1993 1994
Herbicide Rate April 20 May 25 April 4 May 23
lb ai/acre 1 to 10
Untreated - 3.8 5.5 3.8 3.8
Oxadiazon 3.0 3.4 4.9 5.0 4.7
4.0 4.2 5.1 4.6 4.1
Butralin 5.0 3.7 5.1 3.9 3.7
Isoxaben 0.75 3.0 4.6 4.6 3.6
1.0 3.8 4.7 5.1 4.5
Oryzalin 1.5 4.2 5.6 4.5 4.5
2.0 3.1 4.4 4.1 4.7
Dithiopyr 0.25 3.1 4.3 4.4 4.1
0.5 3.9 4.8 4.3 3.6
1.0 3.5 4.5 4.8 4.3
Benefin 3.0 3.1 4.0 4.1 3.7
Metolachlor 2.0 3.1 4.3 3.8 3.8
4.0 2.8 4.4 3.5 3.7
Prodiamine 0.75 4.1 5.0 4.5 3.8
1.0 3.4 4.7 4.8 4.0
Pendimethalin 3.0 3.0 4.0 4.1 4.7
Simazine 2.0 4.3 5.0 4.9 4.4
Oxyfluorfen
+ oryzalin 2.0 + 1.0 3.9 5.2 3.9 4.0
Benefin
+ oryzalin 2.0 + 2.0 3.3 4.8 4.0 3.9
Benefin
+ trifluralin 2.6 + 1.4 3.6 4.3 4.6 4.0
Oxadiazon
+ benefin 2.0 + 1.0 4.2 5.9 5.1 4.8
LSD P = 0.05 0.9 0.9 0.9 0.7
a. Herbicides were applied September 11, 1992 and September 13, 1993. Oxyfluorfen plus oryzalin, benefin plus oryzalin, benefin plus trifluralin, and oxadiazon plus benefin were applied as single products.
b. Turfgrass density ratings were based on 1 to 10, where 1 = no turfgrass and 10 = complete uniform dense cover.
 

When common bermudagrass density ratings were made May 25, 1993, there were several preemergence herbicides applied in September 1992 that delayed turfgrass growth (table 8). Oryzalin at 1.5 lb ai/acre did not affect the spring growth of common bermudagrass at any time during the spring of 1993. With oryzalin at 2.0 lb ai/acre, however, the growth was less than in plots not treated or treated at 1.5 lb ai/acre. In an earlier study (Johnson 1994), oryzalin applied at 3.0 lb ai/acre in late February delayed growth of `Tifway' bermudagrass (C. transvaalensis Burtt-Davy x C. dactylon [L.] Pers.) during April and May. Common bermudagrass in the present study was delayed when treated in September 1992 with dithiopyr, benefin, metolachlor, pendimethalin, and benefin plus trifluralin. During this period, the growth was not delayed when treated with oxadiazon, butralin, isoxaben, prodiamine, simazine, oxyfluorfen plus oryzalin, benefin plus oryzalin, and oxadiazon plus benefin.

None of the preemergence herbicides applied in September 1993 delayed turfgrass growth when ratings were made in April or May 1994 (table 8). These results indicate that preemergence herbicides may affect turfgrass green-up in the spring differently across years. Therefore, selection should be made not only for weed control, but also for turfgrass tolerance.

Postemergence herbicides applied in January 1993 and February 1994 generally did not delay spring green-up and reduced density of common bermudagrass very little when ratings were made in April and May (table 9). Two exceptions were observed in 1993, as the density was lower in plots treated with triclopyr plus clopyralid alone or with isoxaben. Triclopyr plus clopyralid applied at 0.75 + 0.25 lb ai/acre did not delay bermudagrass growth, but the growth was delayed when the rate was increased to 1.5 + 0.5 lb ai/acre. Common bermudagrass growth on April 20 was delayed when isoxaben (0.75 lb ai/acre) was tank-mixed with the lower triclopyr plus clopyralid (0.75 + 0.25 lb ai/acre) rate, but the turfgrass fully recovered by May 25. Three exceptions were observed in 1994, as the density was lower in plots treated with fluoroxypyr at 0.5 lb ai/acre, triclopyr plus clopyralid at 1.5 + 0.5 lb ai/acre, and 2,4-D plus mecoprop plus dicamba at 2.0 + 1.0 + 0.2 lb ai/acre than in untreated plots when ratings were made in April. None of these herbicides, however, delayed turfgrass growth in April when applied at normal rates (fluoroxypyr at 0.25 lb ai/acre, triclopyr plus clopyralid at 0.75 + 0.25 lb ai/acre, and 2,4-D plus mecoprop plus dicamba at 1.0 + 0.5 + 0.1 lb ai/acre). Turfgrass growth affected by herbicides in April completely recovered by late May. Of the postemergence herbicides, only triclopyr plus clopyralid applied at 1.5 + 0.5 lb ai/acre reduced turfgrass growth both years. Therefore, the use of most postemergence herbicides for winter weed control did not affect early spring growth of common bermudagrass.
 

Table 9.Effects of Mid-Winter-Applied Postemergence Herbicides on Common Bermudagrass the Following Spring, Beaver Lake Golf Course, Gay, Gergia, 1993-94.
Turfgrass densityb
Treatmentsa
1993 1994
Herbicide Rate April 23 May 25 April 4 April 20 May 23
lb ai/acre 1 to 10
Untreated - 2.7 4.1 2.5 3.3 3.2
Flazasulfuron 0.02 3.8  4.6 3.8 3.6 3.4
0.04 3.2 4.6 4.3 3.5 3.4
0.09 3.5 4.2 3.6 3.9 3.9
Fenoxaprop 0.25 3.0 4.4 2.8 3.1 3.0
Diclofop  1.0 2.5 3.7 3.1 3.0 2.4
Quizalofop 0.04 2.5 3.8 2.8 3.6 2.8
0.08 2.8 4.0 3.0 3.0 2.4
Metsulfuron 0.009 3.0 4.1 4.1 4.2 4.2
0.018 3.7 4.2 4.0 3.8 3.7
0.0376 3.3 4.3 4.1 4.0 4.2
Clopyralid 0.25 2.2 4.3 3.8 3.9 3.0
0.5 2.3 4.2 3.3 3.2 2.8
Fluoroxypyr 0.25 2.4 4.0 2.7 2.9 3.3
0.5  2.0 4.0 1.1 1.7 3.1
Triclopyr
+ clopyralid 0.75 + 0.25 2.3 3.9 1.6 2.7 2.9
1.5 = 0.5 1.3 3.1 1.2 1.9 3.0
Triclopyr + clopyralid 
+ isoxaben 0.75 + 0.25 + 0.75 1.7 3.9 1.5 2.7 3.3
2,4-D + mecoprop
+ dicamba 1.0 + 0.5 + 0.1 2.9 4.2 2.0 2.9 3.0
2.0 + 1.0 + 0.2 2.5 4.1 1.2 1.7 2.1
MON 120051 0.06 3.1 4.1 3.5 3.8 3.6
Imazaquin 0.38 3.5 4.3 3.4 4.2 4.4
0.5 3.3 4.4 1.5 3.3 3.6
MCPA + mecoprop
+ dicamba 1.42 + 0.68 + 0.16  3.1  4.4 2.8 3.9 3.4
2,4-D + dichlorprop 0.94 + 0.91  3.0  4.4 2.6 3.4 3.3
LSD P = 0.05 0.9 0.6 1.1 0.8 1.1
a. Herbicides were applied January 27, 1993. Triclopyr plus clopyralid, 2,4-D plus mecoprop plus dicamba, MCPA plus mecoprop plus dicamba, and 2,4-D plus dichlorprop were applied as single products. A nonionic surfactant was added to flazasulfuron, quizalofop, MON 120051, imazaquin, and 2,4-D plus mecoprop plus dicamba.
b. Turfgrass density ratings were based on 1 to 10, where 1 = no turfgrass and 10 = complete uniform dense cover
 


SUMMARY AND CONCLUSIONS


Herbicides were applied for evaluation of preemergence and postemergence control of winter annuals in turfgrasses in Georgia. The major findings are as follows:

1.Although exceptions may occur, preemergence herbicides applied in late winter for crabgrass and goosegrass control, generally will not control emerged winter annuals.

2.Annual bluegrass control ranged from fair to excellent when oxadiazon, butralin, oryzalin, dithiopyr, benefin, prodiamine, pendimethalin, oxyfluorfen plus oryzalin, benefin plus oryzalin, benefin plus trifluralin, and oxadiazon plus benefin were applied in September. The control from simazine was poor in one of two years. Neither isoxaben nor metolachlor provided annual bluegrass control.

3.By late March 1993, isoxaben was the only preemergence herbicide that controlled lawn burweed (98%), while simazine (100%) and isoxaben (74%) were the only herbicides that controlled purple cudweed.

4.Flazasulfuron was the only postemergence herbicide that controlled annual bluegrass consistently during 1993 and 1994.

5.Combinations of 2,4-D plus mecoprop plus dicamba at 1.0 + 0.5 + 0.1 lb ai/acre controlled all broadleaf weeds as effectively as any other postemergence herbicide.
 


REFERENCES

Ebdon, J. S. and J. A. Jagschitz. 1982. Chemical control of spurge and other broadleaf weeds in turfgrass. Proc. Northeast. Weed Sci. Soc. 36:307-313.

Grant, D. L., R. B. Cooper, and H. L. Webster. 1990. Isoxaben for broad-spectrum weed control in warm-season turf. Proc. South. Weed Sci. Soc. 43:145-152.

Jagschitz, J. A. 1980. Broadleaf weed control in turfgrass with herbicides. Proc. Northeast. Weed Sci. Soc. 34:357-363.

Johnson, B. J. 1975. Dates of herbicide application for weed control in bermudagrass. Weed Sci. 23:110-115.

Johnson, B. J. 1977a. Preemergence winter weed control in dormant bermudagrass turf. Agron. J. 69:573-576.

Johnson, B. J. 1977b. Controlling winter annuals with herbicides. Georgia Agric.Res. Bull. 206.

Johnson, B. J. 1980. Postemergence winter weed control in bermudagrass (Cynodon dactylon turf. Weed Sci. 28:385-392.

Johnson, B. J. 1982a. Simazine formulation treatments on control of winter weeds in bermudagrass turf. Agron. J. 74:881-886.

Johnson, B. J. 1982b. Postemergence herbicide control of winter weeds in dormant bermudagrass turf. Georgia Agric. Res. Rep. 389.

Johnson, B. J. 1983. Response of weeds in bermudagrass (Cynodon dactylon) turf to tank-mixed herbicides. Weed Sci. 31:883-888.

Johnson, B. J. 1987. Postemergence herbicide activity on broadleaf winter weeds, wild garlic, and bermudagrass turf. Georgia Agric. Res. Bull. 359.

Johnson, B. J. 1994. Response of Tifway bermudagrass and tall fescue turfgrasses to preemergence herbicides. J. Env. Hort. 12:19-23.

Johnson, B. J. and T. R. Murphy. 1993. Summer weed control with herbicides in turf- grasses. Georgia Agric. Res. Bull. 411.

McCarty, L. B. 1991. Metsulfuron and prostrate spurge control in bermudagrass. Proc. South. Weed Sci. Soc. 44:180.

McCarty, L.B. 1993. Winter weed control. Landscape Management 32(12):26,35,38. SAS Institute. 1982. SAS Users' Guide. Cary, NC.
 
 

ACKNOWLEDGMENTS

The authors thank Louis Henderson, Butternut Creek Golf Course, Blairsville, and J. C. Patel, Beaver Lake Golf and Country Club, Gay, Georgia for their cooperation. The authors also gratefully acknowledge the technical assistance of W. Olson, M. Gilmer, and T. Dinkins.