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Cultural and chemical management practices are needed to maintain a high quality turfgrass. One of these practices is to control weeds that germinate and emerge at various times during the year. McCarty and Colvin (1990) reported that effective weed control begins with proper management practices that encourage a dense, thriving turf. They concluded that a healthy turf shades the soil and prevents sunlight penetration to weed seed and seedlings. Therefore, a thick, dense turf produces competition to emerging seedlings and minimizes the physical space available for weeds to become established.
Crabgrass (Digitaria spp.) and goosegrass (Eleusineindica [L.] Gaertn.) are problem summer annual weeds on home lawns, golf courses, athletic fields, parks, and other turfgrass areas. Although proper fertility levels will reduce crabgrass densities (Johnson and Bowyer, 1982; Johnson and Carrow, 1993; Murray et al. 1983), it is still necessary, in most instances, to control weeds with herbicides. Herbicide selection depends on weeds present in the area and the ability of the herbicide to consistently control weeds throughout the growing season.
Although preemergence herbicides have activity on crabgrass and goosegrass (Bhowmik and Bingham, 1990; Dernoeden and Davis, 1985; Dernoeden and Krouse, 1991; Johnson and Murphy, 1987; 1989; 1993; Sawyer and Jagschitz, 1987; Watschke et al. 1988; Watschke and Hamilton, 1990; Webster et al. 1986), the selection of the herbicide as well as the rate of application is important for consistent control. Oxadiazon applied at 4.0 lb ai/acre (all herbicide rates are presented as pounds active ingredient per acre) controlled goosegrass better than any other preemergence herbicide (Johnson and Murphy, 1993). However, when oxadiazon rate was reduced to 3.0 lb/acre, goosegrass control was reduced to levels similar to other preemergence herbicides (Johnson and Murphy, 1987, 1989).
The performance of preemergence herbicides often depends on the length of the growing season. Preemergence herbicides applied for crabgrass control in Georgia and the southeastern United States must perform effectively for approximately six to seven months. However, the length of the growing season for this weed in the northeast United States is four to five months. Therefore, the efficacy of preemergence herbicides and the application rate in the northeast is often different compared to the southeast. For example, in Georgia, the normal use rate for pendimethalin is 3.0 lb/acre compared to 1.5 lb/acre in the northeast. When pendimethalin was applied to cool-season grasses at 1.5 lb/acre, crabgrass control was >82% in Rhode Island (Sawyer and Jagschitz, 1987), Pennsylvania (Watschke et al., 1988), and Massachusetts (Bhowmik and Bingham, 1990). However, crabgrass control in Georgia when pendimethalin was applied at 3.0 lb/acre to common bermudagrass [Cynodon dactylon (L.) Pers.] varied from 64 to 87% in seven experiments from 1986 through 1991(Johnson and Murphy, 1987, 1989; 1993). Another example in the response between geographical location occurred with dithiopyr. Crabgrass control ranged from >90% in Maryland (Dernoeden and Krouse, 1991) and Pennsylvania (Watschke and Hamilton, 1990), to 51 to 95% in Georgia (Johnson and Murphy, 1989; 1993) with dithiopyr at 0.5 lb/acre. In general, crabgrass control was similar when prodiamine was applied at 0.75 lb/acre in Georgia (75-98%) (Johnson and Murphy, 1989; 1993) and at 0.5 lb/acre in the northeast (80-93%) (Dernoeden and Davis, 1988; Dernoeden and Krouse, 1991; Watschke and Hamilton, 1990). To improve the consistency of weed control with herbicides in Georgia, sequential applications of preemergence and postemergence herbicides were made in an earlier study (Johnson, 1993). In this experiment, large crabgrass [D. Sanguinalis (L.) Scop.] control in common bermudagrass was greater (94%) in plots treated with oxadiazon at 1.0 lb/acre on February 24 and followed by MSMA at 2.0 lb/acre on May 11, 1992, than when either herbicide was applied alone at the same respective dates (20 to 60%). Similar results were observed from sequential applications of pendimethalin at 1.0 lb/acre and MSMA at 2.0 lb/acre (Johnson, 1993).
Goosegrass control in common bermudagrass was greater
during 1991 (84%) and 1992 (96%) from sequential applications of dithiopyr
at 0.38 lb/acre (February 27, 1991 and April 1, 1992) and MSMA plus metribuzin
at 2.0 + 0.125 lb/acre (June 3, 1991 and June 24, 1992) than when either
herbicide was applied alone (Johnson, 1993) (Figure 2). There was no advantage
from sequential oxadiazon and MSMA plus metribuzin treatments on goosegrass
control when oxadiazon was applied at 2.0 lb/acre in 1991 and 4.0 lb/acre
in 1992, or when diclofop at 1.0 lb/acre was applied postemergence in June
either year.
Tank-mixed combinations of preemergence and postemergence
herbicides applied to emerged large crabgrass and goosegrass, generally
did not provide effective control (Johnson 1994a). An exception occurred
in two of three experiments when dithiopyr (0.25 lb/acre) plus MSMA (2.0
lb/acre) was applied mid-May, and controlled large crabgrass better than
the herbicides applied alone (Figure 3). Quinclorac effectively controlled
large crabgrass and there was no increase in control when tank-mixed with
pendimethalin or dithiopyr (Johnson, 1994a). Tank-mixture of various preemergence
and postemergence herbicides did not control goosegrass as effectively
as the same herbicides applied sequentially (Johnson, 1993; 1994a).
Herbicides are used extensively in Georgia to control
large crabgrass and goosegrass in turfgrasses, and there is a need for
preemergence herbicides to be more consistent in weed control throughout
the growing season. Therefore, efficacy experiments were conducted to determine
the effect of rate, formulation, and application frequency of preemergence
herbicide on large crabgrass and goosegrass control and the tolerance of
turfgrasses to these herbicides.
MATERIAL AND METHODS
General information. Herbicides were evaluated from 1991 through 1994 for preemergence large crabgrass and goosegrass control in turfgrasses. The nomenclature ofherbicides and companies furnishing the herbicides are given in table 1. Location of experiments and dates of treatment are shown in table 2.
Table 1. Nomenclature of Herbicides
| Name | ||||
| Common | Trade | Chemical | Company | |
| Benefin + oryzalin | XL | benefin = N-butyl-N-ethyl-2,6-dinitro-4-(trifluoromethyl)-benzenamine;
oryzalin = 4-(dipropylamino)-3,5-dinitrobenzene-sulonamide |
DowElanco | |
| Benefin +trifluralin | Team | trifluralin = 2,6 -dinitro-N-N-dipropyl-4-(trifluoro-methyl)benzenamine;
benefin given above |
DowElanco | |
| Benefin + oxadiazon | Goosegrass/
Crabgrass Control |
bensulide = 0,0-bis(1-methyl-oxadiazonethyl) S-[2-[(phenylsulfonyl)
amino]ethyl]phosphorodithioate;
oxadiazon = 3-[2,4-dichloro-5- (1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one |
O.M.Scott | |
| Butralin | EXP 30910A EXP31068A | 4-(1,1-dimethylethyl)-N-(1methylpropyl)-2,6-dinitrobenzen-amine | Rhone-Poulenc | |
| Diclofop | Illoxan | (±)-2-[4-(2,4-dichlorophenoxy) phenoxy]propanoic acid | AgrEvo | |
| Dithiopyr | Dimension | S,S-dimethyl 2-(difluoromethyl)-4-(2-methylpropyl)-6-(trifluoro-methyl)-3,5-pyridinedicarbothioate | Monsanto
Rohm & Haas |
|
| Metribuzin | Sencor | 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one | Miles | |
| Metolachor | Pennant | 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide | CIBA | |
| MSMA | Daconate 6 | monosodium salt of MAA | ISK Biotech | |
| Oxyfluorfen + oryzalin | Rout | oxyfluorfen = 2-chloro-1-(3-ethoxy)- 4-nitrophenoxy)-4-(trifluoromethyl)benzene;
oryzalin - given above |
Grace/Sierra | |
| Oryzalin | given above | DowElanco | ||
| Oxadiazon | Ronstar | given above | Rhone-Poulenc | |
| Oxadiazon + benefin | Regalstar | given above | Regal | |
| Pendimethalin | PRE-M Turfweed-Grass Control | N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitro-benzenenamine | Lesco
O.M. Scott |
|
| Prodiamine | Barricade
RegalKade |
N3,N3-di-n-propyl 2,4-dinitro-6-(trifluoro-methyl)-m-phenylenediamine | Sandoz
Regal |
|
| Quinclorac | Drive | 3,7-dichloro-8-quinoline-carboxylic acid | BASF | |
Table 2. Location of Weed Control Studies in Turfgrasses. 1991-1994.
| Experiment | Turfgrass | Location | Date applied |
| Preemergence large crabgrass/goosegrass control | Kentucky bluegrass | Butternut Creek Golf Course, Blairsville, GA | 1992: March 2,May 4 |
| Preemergence large crabgrass/goosegrass control | Common bermudagrass | Cabin Creek Golf Course, Griffin, GA | 1992: April 1,May 26 |
| Preemergence large crabgrass control | Common bermudagrass | Georgia Station Griffin, GA | 1991: February 25, April 25
1992: February 24, April 22 |
| Preemergence goosegrass control | Common bermudagrass | Beaver LakeGolf and Country Club, Gay, GA | 1993: February 22, April 20 |
| Preemergence large crabgrass/goosegrass control | Common bermudagrass | Beaver Lake Golf and Country Club, Gay, GA | 1994: February 21, April 20 |
Preemergence herbicides were applied to a Kentucky bluegrass (Poa pratensis L.) at Butternut Creek Golf Course, Blairsville and to common bermudagrass at Cabin Creek Golf Course, Griffin, Beaver Lake Golf and Country Club, Gay, and Georgia Station, Griffin. Weeds were indigenous to each site. Weeds evaluated were large crabgrass and goosegrass at Butternut Creek and Beaver Lake, goosegrass at Cabin Creek, and large crabgrass at the Georgia Station. The soil type was Cecil sandy loam at the Georgia Station, Cabin Creek, and Beaver Lake golf courses, and Hatboro loam at Butternut Creek golf course.
Benefin plus oryzalin, benefin plus trifluralin, bensulide plus oxadiazon, butralin, dithiopyr G, oxyfluorfen plus oryzalin, oxadiazon, and oxadiazon plus benefin were formulated as granules and mixed with sand and applied by hand. All other herbicides were applied as a broadcast spray with a CO2 backpack sprayer using 24 PSI to deliver 40 gal water per acre.
Actively-growing Kentucky bluegrass on fairways at the Butternut Creek Golf Course was mowed weekly with a reel mower to a height of approximately 1½ inches. The turfgrass was not fertilized or irrigated. However, rainfall distribution was favorable with total rainfall from March through August of 34 inches. Actively-growing common bermudagrass on fairways at Cabin Creek and Beaver Lake were mowed weekly with a reel mower to a height of approximately 3/4 to 1-inch. Common bermudagrass at the Georgia Station was mowed three times per week at ¾-inch. Turfgrass clippings were returned to the sod at all locations. Turfgrasses at Cabin Creek and Georgia Station were irrigated as needed to maintain optimum growth, while turfgrass at Beaver Lake was not irrigated. Turfgrass at Beaver Lake in 1993 received only 4.2-inches of rainfall from mid-May until early August and severe drought stress occurred for two to three-week periods during June and again during July. By mid- to late August, the turfgrass was actively growing. Rainfall at Beaver Lake during 1994 was above normal with 32 inches. All common bermudagrass was fertilized with 10 lb/1000 ft2 of 10-10-10 in April, with additional N from ammonium nitrate at 1.0 lb/1000 ft2 applied late May and July at Cabin Creek and Georgia Station.
Herbicides at rates given in tables 3 through 5 were applied
for large crabgrass and goosegrass control in Kentucky bluegrass at Butternut
Creek Golf Course, Blairsville, during 1992. Herbicides applied for large
crabgrass control in common bermudagrass at the Georgia Station are given
in table 6 during 1991 and 1992, and at Beaver Lake Golf and Country Club,
Gay are given in tables 7 through 9 during 1994. Herbicides applied for
goosegrass control in common bermudagrass at Cabin Creek Golf Course, Griffin
are given in tables 11 through 12 during 1992, at Beaver Lake Golf and
Country Club, Gay in tables 13 through 15 during 1993, and tables 7 through
9 during 1994. With the exception of Cabin Creek location in 1992, herbicides
were applied initially on February 25 ± 4 days. At Cabin Creek,
herbicides were applied on April 1. When a second application was made,
it was applied approximately eight weeks later (table 2).
Table 3. Influence of Preemergence Herbicides on Large
Crabgrass and Goosegrass Control in Kentucky Bluegrass. Butternut Creek
Golf Course, Blairsville, GA. 1992.
6.0 + 1.5 + 3.0* + 0.75*
4.0 + 1.12 + 4.0* + 1.12* 5.7
5.9 6.2
6.6 100
89 88
88 86
93 + 0.98* + 0.52* Table 4. Influence of Preemergence Herbicides on Large
Crabgrass and Goosegrass Control in Kentucky Bluegrass. Butternut Creek
Golf Course, Blairsville, GA. 1992.
+ oryzalin Table 5. Influence of Preemergence Herbicides on Large
Crabgrass and Goosegrass Control in Kentucky Bluegrass. Butternut Creek
Golf Course, Blairsville, GA. 1992.
Weed control and turfgrass quality ratings were visually
estimated at various times during the growing season. Weed control ratings
were made in July and late August and based on 0 to 100 where 0 = no control,
<80% unacceptable, and 100 = complete control. Turfgrass quality ratings
were made initially in April and at monthly intervals through August, and
based on 1 to 10 where 1 = turf brown or dead and 10 = dark green with
uniform dense stand.
Herbicide treatments in all experiments were arranged
in a randomized complete block design with four replications. Plot size
was 5' by 10'. Data were analyzed statistically using the General Linear
Models Procedure (SAS Institute, 1982). Means were separated by LSD at
P = 0.05. Data in experiment at the Georgia Station are presented as an
average from two years. The data from golf course experiments are reported
for each year due to treatment by year interactions.
a. Herbicides were initially applied on March 2, 1992; an
asterisk indicates that a second application was made on May 4. Bensulide
plus oxadiazon, oxadiazon plus benefin, benefin plus trifluralin, and benefin
plus oryzalin were applied as single products.
Herbicide
Jun 22
Aug 31
Jun 22
Aug 31
Aug 31
lb/ac
%
Untreated
-
-
5.8
4.7
0
0
0
Bensulide+ oxadiazon
5.25 + 1.13 G
6.0 + 1.5
5.9
6.5
96
70
39
Oxadiazon + benefin
1.0 + 0.5
38-0-0 carrier2.0 + 1.0 2.0 + 1.0
+ 1.0* + 0.5*5.3
5.45.6
6.0100
10088
8229
68
Metolachlor
7.8 EC
4.0 + 4.0*
5.3
6.9
100
88
75
Pendimethalin + metolachlor
60 WDG + 7.8 EC
3.0 + 4.0*
5.3
6.5
100
82
75
Pendimethalin
60 WDG
3.0
1.5 + 1.5*
3.0 + 1.5*5.3
4.7
5.75.9
4.3
5.9100
100
10088
71
9443
46
96
Pendimethalin
30-3-10 carrier
1.5 + 1.5*
4.9
5.1
100
88
89
Oryzalin
4AS
1.5 + 1.5*
3.7
6.8
100
88
54
Benefin + trifluralin
1.3 + 0.7 G
0.98 + 0.52
4.2
7.0
100
82
50
Benefin + oryzalin
1.0 + 1.0 G
0.75 + 0.75
+ 0.75* + 0.75*4.9
6.3
100
76
89
Prodiamine
65 WDG
0.75
0.75 + 0.25*5.5
4.35.5
5.296
10092
9464
86
LSD (0.05)
NS
NS
8
12
21
b. Turfgrass quality ratings were based on 1 to 10 where
1 = turf brown or dead and 10 = dark green with uniform dense turf.
c. Large crabgrass and goosegrass control ratings were
based on 0 = no control and 100 = complete control.
a. Herbicides were initially applied on March 2, 1992; an
asterisk indicates that a second application was made on May 4. Oxyfluorfen
plus oryzalin were applied as a single product
Large crabgrass controlc
Goosegrass controlc
HERBICIDE
FORMULATION
RATE
JUN 22
AUG 31
AUG 31
AUG 31
lb/acre
1 to 10
--------------------%-------------------
Untreated
-
-
4.7
5.9
0
0
Butralin
5 G
5.0
6.0
3.0 + 2.0*5.4
5.3
4.36.2
5.8
5.479
100
867
7
0
Benefin
2.5 G
3.0
4.8
4.9
90
0
Oxyfluorfen
2 + 1.0 G
1.0 + 0.5
4.0 + 2.0
6.0 + 3.0
3.0 + 1.5
+ 3.0 + 1.5*4.7
4.5
3.1
2.76.5
6.8
5.7
5.990
91
86
8241
41
96
70
Pendimethalin
1.71 G
3.0
4.6
6.1
93
33
Oxadiazon + dithiopyr
2 + 0.1 G
2.0 + 0.125
1.0 + 0.1255.2
5.26.6
6.480
740
19
LSD (0.05)
1.4
NS
21
22
b. Turfgrass quality ratings were based on 1 to 10 where
1 = turf brown or dead and 10 = dark green with uniform dense turf.
c. Large crabgrass and goosegrass control ratings were
based on 0 = no control and 100 = complete control.
a. Herbicides were initially applied on March 2, 1992; an
asterisk indicates that a second application was made on May 4.
Treatmentsa
Turfgrasss qualityb
Large
crabgrass controlcGoosegrass controlc
HERBICIDE
FORMULATION
RATE
JUN 22
AUG 31
AUG 31
AUG 31
lb/acre
1 to 10
--------------------%-------------------
Untreated
-
-
6.1
5.7
0
0
Dithiopyr
1 EC
0.5
4.9
7.2
89
81
0.25 + 0.25*
4.9
7.0
88
72
Dithiopyr
0.25 G
0.25
5.9
7.2
88
58
0.38
5.6
6.8
96
78
0.5
4.6
6.9
89
97
Pendimethalin
60 WDG
3.0
5.4
7.0
85
94
Oxadiazon
2 G
4.0
4.9
7.0
81
64
Dithiopyr
18-3-12 carrier
0.38
4.9
6.3
81
61
0.25 + 0.25*
5.8
6.7
96
94
0.25 + 0.125*
5.6
6.0
89
86
LSD (0.05)
NS
NS
8
22
b. Turfgrass quality ratings were based on 1 to 10 where
1 = turf brown or dead and 10 = dark green with uniform dense turf.
c. Large crabgrass and goosegrass control ratings were
based on 0 = no control and 100 = complete control.
RESULTS AND DISCUSSION
Large crabgrass control. The control of large crabgrass in Kentucky bluegrass at Butternut Creek golf course with all herbicides was >70% throughout the spring and summer in 1992 (tables 3, 4, and 5). Single applications of bensulide plus oxadiazon at 6.0 + 1.5 lb/acre, butralin at 5.0 lb/acre, oxadiazon plus dithiopyr at 1.0 + 0.125 lb/acre, two applications of pendimethalin at 1.5 lb/acre, and benefin plus oryzalin at 0.75 + 0.75 lb/acre were the only herbicides that controlled less than 80% large crabgrass by late August. Bensulide plus oxadiazon applied initially at 6.0 + 1.5 lb/acre, and followed by 3.0 + 0.75 lb/acre or when 4.0 + 1.12 lb/acre was applied twice controlled a higher percentage of large crabgrass (88%) than when applied once at 6.0 + 1.5 lb/acre (70%).
Sequential herbicide applications did not always improve large crabgrass control in Kentucky bluegrass. Pendimethalin applied at 1.5 lb/acre on March 2 and on May 4 did not control large crabgrass as effectively (71%) as when 3.0 lb/acre was applied in March (88%) (table 3). The poorer control was probably related to large crabgrass germination in plots treated at the reduced rate before the second pendimethalin application was made. In some instances, there was no difference in large crabgrass control in Kentucky bluegrass whether the preemergence herbicides were applied as a single or split application, providing the total rate for the year was applied at the recommended level. Examples were oxyfluorfen plus oryzalin applied once at 6.0 + 3.0 lb/acre, compared with two applications at 3.0 + 1.5 lb/acre (table 4) and dithiopyr EC applied once at 0.5 lb/acre compared with two applications at 0.25 lb/acre (table 5).
Effective large crabgrass control in Kentucky bluegrass turf was obtained with single applications of oxadiazon plus benefin, pendimethalin, prodiamine, dithiopyr, and oxyfluorfen plus oryzalin, while two applications were needed with bensulide plus oxadiazon, benefin plus trifluralin, and benefin plus oryzalin. Effective control of large crabgrass in Kentucky bluegrass with oryzalin, benefin plus oryzalin and benefin plus trifluralin differs from those reported (29 to 49%) at the same location in an earlier study (Johnson and Murphy, 1993). The difference in herbicide performance may be related in part to rainfall and/or competition from a higher large crabgrass density in the earlier study.
Pendimethalin and oxadiazon applied in one or two applications
provided good to excellent large crabgrass control in common bermudagrass
in late August (6 months after the initial application) at the Georgia
Station (table 6). Large crabgrass control with pendimethalin was similar
whether applied once at 3.0 lb/acre (96%) or twice at 1.0 lb/acre (90%).
However, there were differences in large crabgrass control from sequential
oxadiazon applications. The control was 97% when oxadiazon was applied
once at 4.0 lb/acre, but <84% when oxadiazon was applied sequentially
at 0.75 lb/acre initially, and followed by <1.0 lb/acre eight
weeks later (<84%). When the initial oxadiazon application was
1.0 lb/acre and followed by 0.75 lb/acre, large crabgrass control was consistently
greater (92%), compared to an initial application of 0.75 lb/acre, followed
by 1.0 lb/acre (84%). There was no difference in control when 1.0 lb/acre
was followed by 0.75 lb/acre, compared to one application at 4.0 lb/acre
rate.
Table 6. Influence of Sequential Preemergence Herbicide Treatments on Large Crabgrass spp. Control in Common Bermudagrass, Griffin, GA. Average 1991 and 1992.
|
|
|
|
||
| HERBICIDE | RATE | JUN 22 | AUG 25 | AUG 25 |
| lb/acre | 1 to 10 | -----------%--------- | ||
| Untreated | - | 6.6 | 4.4 | 0 |
| Pendimethalin | 3.0 | 7.3 | 7.2 | 96 |
| 1.5 + 1.5* | 6.8 | 6.8 | 91 | |
| 1.0 + 1.0* | 7.0 | 7.2 | 90 | |
| 1.0 + 2.0* | 7.0 | 7.2 | 89 | |
| 2.0 + 1.0* | 7.0 | 7.0 | 92 | |
| Oxadiazon | 4.0 | 7.4 | 6.9 | 97 |
| 0.75 + 0.75* | 7.3 | 7.3 | 81 | |
| 0.75 + 1.0* | 7.2 | 6.9 | 84 | |
| 0.75 + 1.5* | 7.2 | 7.0 | 90 | |
| 1.0 + 0.75* | 7.2 | 7.0 | 92 | |
| 1.0 + 1.0* | 7.2 | 7.1 | 93 | |
| 1.0 + 1.5* | 7.4 | 7.2 | 96 | |
| 1.5 + 0.75* | 7.3 | 7.0 | 93 | |
| 1.5 + 1.0* | 7.2 | 6.9 | 96 | |
| 1.5 + 1.5* | 7.3 | 7.0 | 97 | |
| 2.0 + 2.0* | 7.5 | 6.9 | 98 | |
| LSD (0.05) | 0.6 | 0.7 | 7 | |
To obtain consistent large crabgrass control with oxadiazon in common bermudagrass at the lowest total rate, it was necessary to apply 1.0 lb/acre as the initial treatment and follow with 0.75 lb/acre. When 0.75 lb/acre was applied initially, the rate for the second application needed to be increased to 1.5 lb/acre to maintain >90% control. There was no increase in control when the initial application was > 1.0 lb/acre regardless of the rate of the second application. In the southern United States, the recommended rates for large crabgrass control with pendimethalin and oxadiazon are 3.0 lb/acre and 3.0 to 4.0 lb/acre, respectively. However, when common bermudagrass is properly maintained, effective large crabgrass control can be obtained with reduced rates for pendimethalin (1.0 + 1.0 lb/acre) and oxadiazon (1.0 + 0.75 lb/acre).
All preemergence herbicides controlled >90% large
crabgrass in common bermudagrass at six months after the initial treatment
at Beaver Lake Golf & Country Club during 1994 with the exception of
butralin (tables 7, 8, and 9). The control with butralin was 79%. Sequential
applications did not improve large crabgrass control. One application of
bensulide plus oxadiazon, oxyfluorfen plus oryzalin, pendimethalin, dithiopyr,
prodiamine, oxadiazon plus benefin, oryzalin, and benefin plus oryzalin
effectively controlled large crabgrass, compared to sequential applications.
Table 7. Influence of Preemergence Herbicides on Large Crabgrass and Goosegrass Control in Common Bermudagrass. Beaver Lake Golf and Country Club, Gay, Ga. 1994.
|
|
|
Large crab grass controlc | Goose grass controlc | ||||
| HERBICIDE | FORMULATION | RATE | APR 4 | APR 20 | MAY 23 | AUG 26 | AUG 26 |
| ib/acre | 1 to 10 (%) | ||||||
| Untreated |
|
- | 5.7 | 5.7 | 5.7 | 0 | 0 |
| Oryzalin | 4AS | 1.5 + 1.5 | 3.1 | 5.0 | 5.7 | 97 | 83 |
| 2.0 | 3.8 | 5.0 | 5.8 | 98 | 30 | ||
| 3.0 | 2.6 | 4.7 | 4.7 | 99 | 31 | ||
| Ronstar | 2G | 3.0 | 4.3 | 5.8 | 6.0 | 90 | 74 |
| Pendimethalin | 60 WDG | 1.5 + 1.5* | 4.2 | 5.3 | 5.7 | 98 | - |
| 3.0 | 3.7 | 4.8 | 6.0 | 99 | - | ||
| 30-3-10 carrier | 1.5 + 1.5* | 5.4 | 6.0 | 6.5 | 94 | - | |
| 1.15 % | 3.0 | 4.2 | 5.2 | 7.2 | 97 | - | |
| Dithiopyr | 1 EC | 0.38 + 0.38* | 3.9 | 5.3 | 5.9 | 100 | 90 |
| 0.5 | 3.8 | 5.3 | 6.3 | 97 | 45 | ||
| 0.25 + 0.25* | 3.8 | 5.0 | 5.8 | 99 | 83 | ||
| 0.25 + .125 | 3.7 | 4.9 | 6.0 | 99 | 71 | ||
| 0.25 G | 0.5 | 3.2 | 4.3 | 6.2 | 100 | 36 | |
| 0.25 + 0.25* | 3.9 | 4.6 | 6.2 | 98 | 74 | ||
| 0.25 + 0.125* | 3.8 | 4.5 | 6.0 | 99 | 73 | ||
| Prodiamine | 65 WDG | 0.5 | 4.9 | 5.6 | 6.1 | 63 | - |
| 0.75 | 5.4 | 5.4 | 6.3 | 93 | - | ||
| 1.0 | 4.8 | 5.2 | 5.7 | 95 | - | ||
| 0.75 + 0.38* | 4.6 | 5.9 | 6.2 | 100 | 76 | ||
| 0.75 + 0.5* | 4.3 | 5.2 | 5.7 | 100 | 48 | ||
| Prodiamine | 32-3-12 carrier | 0.5 | 4.9 | 5.5 | 6.5 | 88 | - |
| 0.5 % | 0.75 | 5.2 | 6.2 | 6.8 | 90 | 20 | |
| 0.75 + 0.38 | 5.1 | 5.4 | 6.7 | 96 | - | ||
| 0.75 + 0.5* | 4.1 | 5.2 | 5.9 | 100 | |||
| LSD (0.05) | 1.2 | 0.8 | NS | 10 | 33 | ||
Table 8. Influence of Preemergence Herbicides on Large Crabgrass and Goosegrass Control in Common Bermudagrass. Beaver Lake Golf and Country Club, Gay, GA 1994.
|
|
Turfgrasss qualityb | Large crabgrass controlc | Goosegrass controlc | ||||
| HERBICIDE | FORMULATION | RATE | APR 4 | APR 20 | MAY 23 | AUG 26 | AUG 26 |
| lb/acre | 1 to 10 -------------%------------- | ||||||
| Untreated | - | - | 4.3 | 5.8 | 6.3 | 0 | 0 |
| Oxadiazon | 2 G | 3.0 | 3.5 | 5.6 | 5.8 | 96 | 74 |
| Oxadiazon
+ benefin |
1.0 + 0.5
38-0-0 carrier |
2.0 + 1.0 | 3.5 | 5.7 | 6.6 | 99 | 64 |
| 2.0 + 1.0 + 1.0* + 0.5* | 4.4 | 5.7 | 6.4 | 100 | 68 | ||
| Oxyfluorfen + oryzalin | 2 + 1.0 G | 1.0 + 0.5 | 3.8 | 5.3 | 6.1 | 91 | 0 |
| 2.0 + 1.0 | 3.1 | 5.0 | 6.5 | 97 | 73 | ||
| 4.0 + 2.0 | 2.4 | 4.8 | 6.1 | 100 | 80 | ||
| 1.0 + 0.5 + 1.0* + 0.5* | 3.8 | 5.3 | 6.3 | 96 | 94 | ||
| Bensulid + oxadiazon | 5.25 + 1.31 G | 6.0 + 1.5 | 4.1 | 5.8 | 5.6 | 90 | 55 |
| 6.0 + 1.5 + 3.0* + 0.75* | 4.0 | 5.4 | 6.3 | 90 | 33 | ||
| 4.5 + 1.12 + 4.5* + 1.12 | 4.6 | 5.9 | 6.0 | 98 | 28 | ||
| LSD (0.05) | 1.0 | 0.9 | NS | 24 | 31 | ||
Table 9. Influence of Preemergence Herbicides on Large Crabgrass and Goosegrass Control in Common Bermudagrass. Beaver Lake Golf and Country Club, Gay, GA 1994
|
|
|
Large crabgrass controlc | Goosegrass controlc | ||||
| HERBICIDE | FORMULATION | RATE | APR 4 | APR 20 | MAY 23 | AUG 26 | AUG 26 |
| lb/acre |
|
|
|||||
| Untreated | - | - | 4.7 | 5.4 | 5.8 | 0 | 0 |
| Benefin + oryzalin | 1.0 + 1.0 G | 1.0 + 1.0 | 3.8 | 4.3 | 5.3 | 93 | 79 |
| 1.5+1.5 | 3.0 | 4.3 | 5.5 | 93 | 41 | ||
| 0.75 + 0.75
+ 0.75 + 0.75 |
4.0 | 4.7 | 5.5 | 97 | 84 | ||
| Benefin
+ trifluralin |
1.3 + 0.7 G | 1.96 + 1.04 | 2.3 | 3.7 | 5.3 | 90 | 60 |
| 0.98 + 0.52 + 0.98* + 0.52* | 3.3 | 4.5 | 5.9 | 81 | 68 | ||
| Butralin | 5 G | 5.0 | 4.4 | 5.3 | 5.3 | 79 | 59 |
| LSD (0.05) | 1.0 | 0.6 | NS | 19 | 20 | ||
Goosegrass control. Goosegrass control from preemergence herbicides was not as good as it was for large crabgrass in Kentucky bluegrass at Butternut Creek Golf Course in 1992 (tables 3, 4, and 5). For example, 37 herbicide treatments were applied at various rates during this period and goosegrass control was >80% in only 12 of these treatments. Sequential applications of herbicides were needed for effective goosegrass control.
Bensulide plus oxadiazon applied at 6.0 + 1.5 lb/acre provided 39% goosegrass control at six months after the initial application (table 3). The control was improved to >86% when this herbicide combination was applied initially at 6.0 + 1.5 lb/acre and followed by 3.0 + 0.75 lb/acre eight weeks later, or when 4.0 + 1.12 lb/acre was applied twice. Goosegrass control was better in plots treated twice with pendimethalin WDG (3.0 + 1.5 lb/acre) (96%) and prodiamine (0.75 + 0.25 lb/acre) (86%) than pendimethalin at 3.0 lb/acre (43%) and prodiamine at 0.75 lb/acre (64%) applied alone.
Dithiopyr at 0.5 lb/acre controlled goosegrass (>80%) in Kentucky bluegrass regardless of formulation (table 5). However, when dithiopyr was applied on a fertilizer carrier at 0.25 lb/acre, and followed eight weeks later with >0.125 lb/acre, goosegrass control was better than when this formulation was applied once at 0.38 lb/acre. Oxyfluorfen plus oryzalin did not effectively control goosegrass in Kentucky bluegrass except when applied at the highest rate (6.0 + 3.0 lb/acre) (table 4). The control was better in plots treated once at 6.0 + 3.0 lb/acre (96%) than 3.0 + 1.5 lb/acre applied twice (70%). Therefore, it was necessary to apply an initial rate of oxyfluorfen plus oryzalin rate greater than 3.0 + 1.5 lb/acre to maintain the desired goosegrass control level throughout the spring and summer.
Goosegrass control was acceptable in Kentucky bluegrass when benefin plus oryzalin was applied twice at 0.75 + 0.75 lb/acre (89%), while the control was unacceptable when oryzalin was applied twice at 1.5 lb/acre (54%) (table 3). Oxadiazon at 4.0 lb/acre did not adequately control goosegrass (64%) (table 5). In an earlier study at the same location, goosegrass control was 82 to 83% at the same rate (Johnson and Murphy, 1993).
Pendimethalin WDG and prodiamine effectively controlled goosegrass (>84%) at Cabin Creek in 1992. (table 10). The control with pendimethalin WDG was similar whether 3.0 lb/acre was applied once or 1.5 lb/acre applied twice. Pendimethalin on fertilizer carrier applied twice at 1.5 lb/acre provided 70% goosegrass control. There was no advantage in goosegrass control when prodiamine was applied once at 0.75 lb/acre or 0.75 lb/acre followed by 0.25 lb/acre eight weeks later. Both provided > 84% goosegrass control.
Two applications of oxadiazon plus benefin controlled
goosegrass better (76%) in common bermudagrass at Cabin Creek Golf Course
in 1992 than the combination applied once (56%) (table 10). Control was
75% when benefin plus oryzalin were applied twice at 0.75 + 0.75 lb/acre.
Goosegrass control with bensulide plus oxadiazon applied initially at 6.0
+ 1.5 lb/acre, and followed by 3.0 + 1.5 lb/acre was greater than control
from the same herbicides applied twice at 4.0 + 1.12 lb/acre.
Table 10. Influence of Preemergence Herbicides on Goosegrass Control in Common Bermudagrass.Cabin Creek Golf Course, Griffin, Ga. 1992.
|
|
Turfgrass qualityb | Goosegrass | |||
| Herbicide | Formulation | Rate | May 26 | Aug 25 | Aug 26 |
| lb/acre | ----------1 to 10 ---------- | % | |||
| Untreated | - | - | 6.9 | 5.1 | 0 |
| Bensulide + oxadiazon | 5.25 + 1.13 G | 6.0 + 1.5 | 7.1 | 7.6 | 64 |
| 6.0 + 1.5 | |||||
| + 3.0* + 0.75* | 6.6 | 7.6 | 74 | ||
| 4.0 + 1.12 | |||||
| + 4.0* + 1.12* | 5.7 | 6.3 | 46 | ||
| Oxadiazon | 1.0 + 0.5 | ||||
| + benefin | 38-0-0 carrier | 2.0 + 1.0 | 6.0 | 7.8 | 56 |
| 2.0 + 1.0 | |||||
| + 1.0* + 0.5* | 6.7 | 7.9 | 76 | ||
| Metolachlor | 7.8 EC | 4.0 + 4.0* | 6.9 | 7.8 | 32 |
| Pendimethalin + metolachlor | 60 WDG + 7.8 EC | 3.0 + 4.0* | 5.4 | 7.9 | 88 |
| Pendimethalin | 60 WDG | 3.0 | 6.8 | 8.0 | 88 |
| 1.5 + 1.5* | 5.7 | 8.1 | 84 | ||
| 3.0 + 1.5* | 7.3 | 8.1 | 92 | ||
| Pendimethalin | 30-3-10 carrier | 1.5 + 1.5* | 5.5 | 7.3 | 70 |
| Oryzalin | 4AS | 1.5 + 1.5* | 5.5 | 7.9 | 64 |
| Benefin + trifluralin | 1.3 + 0.7 C | 0.98 + 0.52 | |||
| + 0.98* + 0.52* | 6.7 | 6.1 | 0 | ||
| Benefin + oryzalin | 1.0 + 1.0 G | 0.75 + 0.75 | |||
| + 0.75* + 0.75* | 6.0 | 7.9 | 75 | ||
| Prodiamine | 65 WDG | 0.75 | 7.1 | 8.2 | 84 |
| 0.75 + 0.25* | 6.0 | 7.8 | 88 | ||
| LSD (0.05) | NS | 2.0 | 18 | ||
Goosegrass control in common bermudagrass with butralin applied at 6.0 lb/acre (94%) was greater in 1992 than when applied at 5.0 lb/acre (59%), or when applied at 3.0 lb/acre, and followed by 2.0 lb/acre (57%) (table 11). Oxadiazon, dithiopyr, and combinations of dithiopyr with oryzalin, pendimethalin, or oxadiazon effectively controlled goosegrass in 1992 (table 12). Dithiopyr EC and dithiopyr fertilizer carrier formulations applied at 0.38 lb/acre also effectively controlled goosegrass. These results show that a single application of pendimethalin, prodiamine, oxadiazon, dithiopyr, butralin, and oxyfluorfen plus oryzalin effectively controlled goosegrass during 1992.
Goosegrass control in common bermudagrass at Beaver Lake
Golf and Country Club varied with preemergence herbicides at six months
after the initial treatment in 1993 (tables 13, 14, and 15). Oxadiazon
and pendimethalin consistently controlled >80% goosegrass. However,
goosegrass control in most instances was not as good in 1993 when treated
with prodiamine, dithiopyr, oxadiazon plus benefin, and oxyfluorfen plus
oryzalin as they did at Cabin Creek location in 1992 (tables 10, 11, and
12). The test areas in 1992 were irrigated as needed to maintain optimum
turfgrass growth while the areas in 1993 were not irrigated. During May
through July 1993, only 7-inches of rainfall occurred. This was 10-inches
below normal. Therefore, drought stress likely influenced the 1993 results.
Table 11. Influence of Preemergence Herbicides on Goosegrass Control in Common Bermudagrass. Cabin Creek Golf Course, Griffin, GA. 1992.
|
|
Turfgrass qualityb | Goosegrass
controlc |
|||
| Herbicide | Formulation | Rate | May 26 | Aug 26 | Aug 26 |
| ib/acre | ----------1 to 10---------- | % | |||
| Untreated | - | - | 5.9 | 6.4 | 0 |
| Oxadiazon | 2 G | 2.0 | 6.4 | 7.9 | 96 |
| 4.0 | 6.4 | 8.0 | 98 | ||
| Butralin | 5 G | 5.0 | 6.1 | 8.0 | 59 |
| 6.0 | 6.0 | 8.3 | 94 | ||
| 3.0 + 2.0* | 5.6 | 7.9 | 57 | ||
| Benefin | 2.5 G | 3.0 | 5.7 | 7.9 | 57 |
| Oxyfluorfen + oryzalin | 2 + 1.0 G | 1.0 + 0.5 | 6.1 | 8.0 | 90 |
| 2.0 + 1.0 | 5.7 | 7.8 | 96 | ||
| 4.0 + 2.0 | 5.1 | 7.9 | 94 | ||
| 6.0 + 3.0 | 5.1 | 7.4 | 100 | ||
| 1.0 + 0.5 | |||||
| + 1.0* + 0.5* | 6.3 | 8.0 | 88 | ||
| 3.0 + 1.5 | |||||
| + 3.0* + 1.5* | 5.7 | 7.7 | 92 | ||
| Pendimethalin | 1.71 G | 3.0 | 6.2 | 7.9 | 90 |
| Oxadiazon + dithiopyr | 2 + 0.1 G | 2.0 + 0.25 | 5.7 | 7.9 | 94 |
| 1.0 + 0.25 | 5.5 | 7.7 | 92 | ||
| 2.0 + 0.125 | 6.2 | 8.0 | 86 | ||
| 1.0 + 0.125 | 5.3 | 7.7 | 82 | ||
| LSD (0.05) | NS | 0.6 | 15 | ||
Table 12. Influence of Preemergence Herbicides on Goosegrass Control in Common Bermudagrass. Cabin Creek Golf Course, Griffin, GA. 1992.
|
|
Turfgrass qualityb | Goosegrass controlc | ||||||
| Herbicide | Formulation | Rate | May 26 | Aug 25 | Aug 26 | |||
| lb/acre | ----------1 to 10---------- | % | ||||||
| Untreated | - | - | 5.8 | 7.8 | 0 | |||
| Oxadiazon | 2 G | 4.0 | 5.4 | 7.2 | 92 | |||
| Dithiopyr | 1 EC | 0.38 | 5.4 | 7.1 | 83 | |||
| 0.75 | 5.2 | 7.2 | 100 | |||||
| 0.25 + 0.25* | 5.5 | 7.9 | 75 | |||||
| Dithiopyr+ oryzalin | 1 EC + 4 AS | 0.5 + 1.5 | 5.1 | 6.6 | 100 | |||
| Dithiopyr + pendimethalin | 1 EC + 60 WDG | 0.5 + 1.5 | 5.4 | 7.0 | 92 | |||
| Dithiopyr + oxadiazon | 0.25 G + 2 G | 0.38 + 1.0 | 5.6 | 7.1 | 80 | |||
| 0.5+ 1.0 | 4.9 | 7.1 | 75 | |||||
| 0.5 + 2.0+ 2.0 | 4.9 | 6.9 | 91 | |||||
| Dithiopyr | 18-3-12 carrier | 0.38 | 6.0 | 7.7 | 88 | |||
| 0.25 + 0.25* | 59 | 8.2 | 73 | |||||
| 0.25 + 0.125* | 4.7 | 7.1 | 37 | |||||
| LSD (0.05) | NS | NS | 18 | |||||
Table 13. Influence of Preemergence Herbicides on Goosegrass Control in Common Bermudagrass. Beaver Lake Golf and Country Club, Gay, GA. 1993.
| Turfgrass qualityb | Goosegrass controlc | ||||||
| Herbicide | Formulation | Rate | May 10 | June 17 | Aug 18 | July 28 | Aug 18 |
| lb/acre | 1 to 10 | % | |||||
| Untreated | - | - | 3.8 | 3.9 | 7.8 | 0 | 0 |
| Butralin | 5 G | 5.0 | 4.5 | 5.0 | 7.6 | 0 | 15 |
| 6.0 | 3.5 | 4.1 | 6.1 | 30 | 38 | ||
| Ronstar | 2 G | 3.0 | 5.1 | 6.2 | 7.8 | 78 | 87 |
| Bensulide+ oxadiazon | 5.25 1.31 G | 6.0 + 1.5 | 3.5 | 3.9 | 7.5 | 0 | 0 |
| 6.0 + 1.5 | |||||||
| + 3.0*+ 0.75* | 4.6 | 5.6 | 7.4 | 0 | 0 | ||
| 4.5 + 1.12 | |||||||
| + 4.5* + 1.12* | 3.3 | 4.2 | 8.0 | 0 | 0 | ||
| Pendimethalin | 60 WDG | 3.0 | 3.7 | 4.8 | 6.4 | 74 | 85 |
| 3.0 + 1.5* | 3.3 | 4.5 | 7.6 | 100 | 97 | ||
| 1.5 + 1.5* | 4.2 | 3.8 | 7.2 | 100 | 100 | ||
| Oxyflourfen + oryzalin | 2 + 1.0 G | 1.0 + 0.5 | 5.0 | 5.0 | 7.7 | 0 | 51 |
| 2.0 + 1.0 | 3.7 | 3.7 | 7.8 | 13 | 38 | ||
| 4.0 + 2.0 | 3.0 | 5.2 | 7.6 | 74 | 79 | ||
| 1.0 + 0.5 | |||||||
| + 1.0* + 0.5* | 3.8 | 3.9 | 8.2 | 78 | 79 | ||
| 3.0 + 1.5 | |||||||
| + 3.0* + 1.5* | 3.1 | 4.9 | 7.7 | 96 | 95 | ||
| LSD (0.05) | NS | 2.1 | NS | 28 | 30 | ||
Table 14. Influence of Preemergence Herbicides on Goosegrass Control in Common Bermudagrass. Beaver Lake Golf and Country Club, Gay, GA. 1993.
|
|
Turfgrass qualityb | Goosegrass controlc | |||||||
| Herbicide | Formulation | Rate | May 10 | June 17 | Aug 18 | July 28 | Aug 18 | ||
| lb/acre | ---------------1 to 10--------------- | ----------%---------- | |||||||
| Untreated | - | - | 6.3 | 5.8 | 4.5 | 0 | 0 | ||
| Oxadiazon | 1.0 + 0.5 | ||||||||
| + benefin | 38-0-0 carrier | 2.0 + 1.0 | 4.9 | 4.5 | 7.6 | 65 | 9 | ||
| 2.0 + 1.0 | |||||||||
| + 1.0* + 0.5* | 5.1 | 5.6 | 7.9 | 91 | 88 | ||||
| Prodiamine | 65 WDG | 0.5 | 4.8 | 5.6 | 6.0 | 7 | 38 | ||
| 0.75 | 3.5 | 3.4 | 6.1 | 26 | 27 | ||||
| 0.75 + 0.38* | 4.6 | 5.1 | 7.1 | 63 | 35 | ||||
| 0.75 + 0.5* | 4.6 | 4.4 | 7.5 | 84 | 85 | ||||
| Prodiamine | 32-3-12 carrier | 0.5 | 4.8 | 5.4 | 5.2 | 0 | 8 | ||
| 0.75 | 4.1 | 4.8 | 4.8 | 0 | 20 | ||||
| 0.75 + 0.38* | 3.8 | 3.5 | 6.0 | 9 | 38 | ||||
| 0.75 + 0.5* | 4.7 | 5.2 | 6.6 | 63 | 33 | ||||
| LSD (0.05) | 1.4 | NS | 2.1 | 24 | 23 | ||||
Table 15. Influence of Preemergence Herbicides on Goosegrass Control in Common Bermudagrass. Beaver Lake Golf and Country Club, Gay, GA 1993.
|
|
Turfgrass qualityb | Goosegrass controlc | ||||
| Herbicide | Formulation | Rate | May 10 | Aug 18 | July 28 | Aug 18 |
| lb/acre | ----------1 to 10---------- | ---------- % ---------- | ||||
| Untreated | - | - | 4.2 | 7.4 | 0 | 0 |
| Dithiopyr | 1 EC | 0.5 | 4.4 | 7.7 | 66 | 60 |
| 0.75 | 4.3 | 7.8 | 82 | 80 | ||
| 0.25 + 0.25* | 4.2 | 7.9 | 86 | 84 | ||
| 0.25 + 0.125* | 4.1 | 7.5 | 71 | 64 | ||
| Dithiopyr | ||||||
| + oxadiazon | 0.25 G + 2 G | 0.38 + 1.0 | 4.3 | 7.9 | 77 | 71 |
| 0.38 + 2.0 | 3.3 | 7.6 | 84 | 80 | ||
| 0.5 + 1.0 | 3.5 | 7.8 | 57 | 64 | ||
| 0.5 + 2.0 | 3.9 | 7.9 | 75 | 67 | ||
| Oxadiazon | 2 G | 3.0 | 5.1 | 7.9 | 80 | 87 |
| Prodiamine | 65 WDG | 0.75 | 4.1 | 7.2 | 23 | 0 |
| LSD (0.05) | NS | NS | 18 | 22 | ||
Oxyfluorfen plus oryzalin applied twice at 3.0 + 1.5 lb/acre in common bermudagrass controlled 95% goosegrass in 1993 (table 13). Goosegrass control from oxyfluorfen plus oryzalin at < 2.0 + 1.0 lb/acre was not acceptable. Prodiamine WDG at 0.75 lb/acre controlled goosegrass 27% in common bermudagrass during 1993 (table 14). The control was improved to 85% when prodiamine was applied at 0.75 lb/acre, and followed with 0.5 lb/acre eight weeks later. Prodiamine applied on a fertilizer carrier in 1993 did not control goosegrass effectively (<38%) regardless of number of applications.
To maintain >80% goosegrass control in common bermudagrass during 1993 with the dithiopyr EC, it was necessary to apply 0.75 lb/acre once, or 0.25 lb/acre twice (table 15). The control was unacceptable when one application was made at 0.5 lb/acre. Combinations of dithiopyr G at 0.38 lb/acre plus oxadiazon at 2.0 lb/acre controlled goosegrass 80%.
Goosegrass control during the drought stress year of 1993 was better with oxadiazon and pendimethalin during drought stress than from other preemergence herbicides. Although oxadiazon plus benefin does not always control goosegrass as effectively as oxadiazon or pendimethalin (table 10), it was effective during the 1993 drought period when applied sequentially (table 13). Higher rates were required for oxyfluorfen plus oryzalin, prodiamine, and dithiopyr to maintain an acceptable goosegrass control level during drought stress, compared to irrigation areas.
Dithiopyr EC applied twice at 0.38 lb/acre was the only herbicide that controlled 90% goosegrass in common bermudagrass at Beaver Lake Golf and Country Club during 1994 (tables 7, 8, and 9). The control was 83 to 84% in plots treated once with oxyfluorfen plus oryzalin at 4.0 + 2.0 lb/acre and twice with oryzalin at 1.5 lb/acre, dithiopyr EC at 0.25 lb/acre, and benefin plus oryzalin at 0.75 + 0.75 lb/acre. Goosegrass control was 70 to 79% in plots treated once with oxadiazon at 3.0 lb/acre, benefin plus oryzalin at 1.0 + 1.0 lb/acre, oxyfluorfen plus oryzalin at 2.0 + 1.0 lb/acre, twice with dithiopyr at 0.25 lb/acre, and prodiamine at 0.75 lb/acre, followed by 0.38 lb/acre. During this period, goosegrass control was <70% when treated with prodiamine applied as a fertilizer carrier formulation, and with butralin, oxadiazon plus benefin, bensulide plus oxadiazon and benefin plus trifloralin.
Dithiopyr and prodiamine are the most recently registered
preemergence herbicide for use in turfgrasses. Dithiopyr EC applied twice
at 0.25 lb/acre consistently controlled large crabgrass and goosegrass
better than 0.5 lb/acre applied once. Control from sequential dithiopyr
applications averaged 94% for large crabgrass and 79% for goosegrass, and
is similar to that reported in an earlier study (Johnson and Murphy, 1993).
These results indicate that a single application of prodiamine at 0.75
lb/acre is sufficient for large crabgrass control, but split applications
are needed for consistent goosegrass control.
Turfgrass response.
Kentucky bluegrass. Oxyfluorfen plus oryzalin applied once at 6.0 + 3.0 lb/acre of twice at 3.0 + 1.5 lb/acre were the only herbicides that significantly reduced Kentucky bluegrass quality when ratings were made in June (table 4). Although the difference was not significant, Kentucky bluegrass quality was reduced in June when treated twice with oryzalin at 1.5 lb/acre (table 3). In an earlier study (Johnson and Murphy, 1993), oryzalin applied at 2.0 lb/acre significantly reduced the quality of Kentucky bluegrass at four weeks after treatment. The lack of significance in the present study may be related to the presence of white clover (Trifoliumrepens L.) in the test area. White clover competed with Kentucky bluegrass, resulting in a lower quality turfgrass. No herbicide affected Kentucky bluegrass by late August (tables 3, 4, and 5).
Common bermudagrass. Preemergence herbicides applied to bermudagrass in late winter for summer weed control may influence turfgrass quality for several weeks during spring green-up. Due to climatic effects, a herbicide effects on turfgrass quality may vary among years. None of the herbicides evaluated reduced quality of common bermudagrass when compared with untreated turf in May 1991 and 1992 (tables 6, 10, 11, and 12). Similar results were noted in 1993, with the exception of prodiamine (tables 13, 14, and 15). The quality of turf treated with prodiamine was lower than untreated turf, regardless of whether treated with the prodiamine WDG or on a fertilizer carrier. However, reduction in quality was temporary and the turfgrass recovered by mid-June.
The spring transition of common bermudagrass was three to four weeks earlier in 1994 than previous years. This resulted in a shorter time period fro