Published online 3 May 2006
Published in Agron J 98:788-794 (2006)
DOI: 10.2134/agronj2005.0282
© 2006 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
Production Papers
Weed Control and Response to Herbicides during Tifton 85 Bermudagrass Establishment from Rhizomes
Twain J. Butlera,*,
James P. Muirb and
Joyce Tredaway Ducarc
a The Samuel Roberts Noble Found., 2510 Sam Noble Parkway, Ardmore, OK 73401
b Texas A&M Univ. Res. & Ext. Cent., 1229 N. Hwy. 281, Stephenville, TX 76401
c Berry College, 2277 Martha Berry Hwy., Mt. Berry, GA 30149
* Corresponding author (tjbutler{at}noble.org)
Received for publication October 10, 2005.
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ABSTRACT
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Field studies were conducted in 2001 to 2003 to determine the effects of herbicides and application timings during establishment of ‘Tifton 85’ hybrid bermudagrass (Cynodon dactylon Pers. x C. nlemfuensis Vanderyst). The experimental design was a split plot with three replications. Main plot consisted of three herbicide application timings of 1, 14, and 28 d after planting (DAP), and subplots were 16 herbicide treatments. Hormone-like herbicides (picloram + 2,4-D amine and 2,4-D amine + dicamba) applied 1 DAP controlled large crabgrass [Digitaria sanguinalis (L.) Scop.] 70 to 82%, did not injure Tifton 85, and consistently aided in Tifton 85 establishment, resulting in 23 to 30% ground cover in 2001 and 2002 compared with 3 to 4% in the untreated control. Imazapic (0.02, 0.035, and 0.05 kg a.i. ha–1) applied 1 and 14 DAP injured Tifton 85, ranging from 4 to 48% injury across years, yet these plots consistently had greater ground cover compared with the control, ranging from 9 to 56%. Glyphosate (0.28 kg a.i. ha–1) applied 14 DAP injured Tifton 85 less than 9%, controlled large crabgrass 76%, broadleaf signalgrass (Urochloa platyphylla Munroe ex C. Wright) 91%, and had 38, 45, and 17% ground cover in 2001, 2002, and 2003, respectively. Trifloxysulfuron (0.02 kg ha–1) applied 1 and 14 DAP controlled broadleaf signalgrass (>90%) and yellow nutsedge (Cyperus esculentus L.) (>90%), did not injure Tifton 85, and resulted in 41 to 67% ground cover in 2002 and 2003. These data illustrate that Tifton 85 establishment was improved when weeds were controlled.
Abbreviations: DAP, days after planting • DAT, days after treatment
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INTRODUCTION
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BERMUDAGRASS is the most important pasture grass in the southern United States (Mitich, 1989; Burton and Hanna, 1995). It is estimated that bermudagrass occurs on 12 million ha for livestock grazing and hay production (Taliaferro et al., 2004). Tifton 85 bermudagrass was released in 1992 (Burton et al., 1993), and the area planted in Tifton 85 bermudagrass has rapidly increased in recent years (D.M. Ball, personal communication, 2005). The major advantage of Tifton 85 bermudagrass is greater yields and improved animal performance compared with other varieties (Burton et al., 1993). Tifton 85 is unique in that it has greater concentrations of neutral detergent fiber (NDF) (which normally decreases forage quality); however, the NDF in Tifton 85 bermudagrass is more digestible than other bermudagrasses. West et al. (1997) reported greater rate and extent of NDF digestion of Tifton 85 bermudagrass compared with corn (Zea mays L.) silage and alfalfa (Medicago sativa L.), which improved the rate of passage despite the high fiber content. Mandebvu et al. (1999) reported that Tifton 85 had 34% higher dry matter yield, 47% higher digestible yield, and superior animal performance with growing steers compared with Coastal bermudagrass. In the southeastern USA and Texas, Tifton 85 bermudagrass has become the new standard to compare all bermudagrass varieties, due to its superior production and quality (Hill et al., 2001; Evers et al., 2004). Tifton 85 bermudagrass establishes more rapidly than other bermudagrass hybrids (Hill et al., 1995); however, the response to herbicide treatments (Etheredge, 2003) and to weed competition would be similar to Coastal bermudagrass (T.J. Butler, unpublished data, 2006). A major concern in bermudagrass management is the lack of effective weed management tools during the establishment period (Smith and Martin, 1992). Competition from weeds, especially warm-season annual grasses, can result in loss of stand or delay the establishment of bermudagrass (Burton and Hanna, 1995). Trifloxysulfuron {2-pyridinesulfonamide, N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]-3-(2,2,2-trifluroethoxy)-monosodium} and imazapic {(+)-2-[4,5-dihydro-4-methyl-4-(1-methyl)-5-oxo-1H-imidazol-2-yl]-5-methyl-3-pyridine carboxylic acid} (Beran et al., 1999) control certain warm-season annual grasses and yellow nutsedge (Grichar and Nester, 1997; McElroy et al., 2003) and may have potential to improve bermudagrass establishment.
Previous research on forage bermudagrass response to herbicides has focused on fully established bermudagrass (Bovey et al., 1974; Brooks et al., 1996; Koger et al., 1997) or on turfgrass establishment (Bingham and Hall, 1985; Fagerness et al., 2002); however, herbicide response during establishment of Tifton 85 bermudagrass has not been reported. Herbicide labels for established bermudagrass indicate that herbicides can be utilized once the bermudagrass is established; however, it is unclear when the bermudagrass is considered to be established and if there is a difference in herbicide response during the establishment period. If herbicides were utilized during this important time, the speed and success of establishment could be increased, and faster utilization of the bermudagrass forage could occur. Therefore, the objectives of this study were to (i) determine the effects of application timings of all herbicides currently registered for fully established bermudagrass, (ii) compare these herbicides to currently registered herbicides for bermudagrass establishment from rhizomes (i.e., sprigging) [2,4-D ester (2,4-dichlorophenoxyacetic acid, 2-ethylhexyl ester), 2,4-D amine (2,4-dichlorophenoxyacetic acid, dimethyl amine), and 2,4-D + dicamba (3,6-dichloro-o-anisic acid)] (Anonymous, 2003a, 2003c, 2004, 2005), and (iii) evaluate potential herbicides (imazapic and trifloxysulfuron) that have annual grass and nutsedge activity for Tifton 85 bermudagrass establishment.
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MATERIALS AND METHODS
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Field experiments were conducted at the Texas A&M Research and Extension Center in Stephenville, TX (32°15' N, 98°12' W; altitude 395 m) in 2001, 2002, and 2003. The soil is a Windthorst fine sandy loam (fine, mixed thermic Udic Paleustalf). Soil pH ranged from 5.1 to 5.8, and soil organic matter was less than 1%. The experimental design was a randomized complete block with a split-plot treatment arrangement with three replications. Plots were 3 by 10 m. Tifton 85 rhizomes were planted 2.5 to 5.0 cm deep on 7 Apr. 2001, 12 Apr. 2002, and 19 Apr. 2003 with a bermudagrass sprigger (Bermuda King, Kingfisher, OK) by a custom applicator. Each year, sites were fertilized with 112 kg ha–1 18–46–0 (diammonium phosphate) before planting, according to soil P requirement. Additional N was not applied due to the high density of warm-season annual grassy weeds since these weeds would have utilized the N further competing with the bermudagrass during establishment (Taliaferro et al., 2004).
Main-plot treatments included three herbicide application timings of 1, 14, and 28 DAP. Herbicides were applied 8 Apr., 21 Apr., and 4 May in 2001; 13 Apr., 26 Apr., and 10 May in 2002; and 20 Apr., 3 May, and 20 May in 2003. Subplot treatments consisted of 16 herbicides (Table 1). A nonionic surfactant (Activator 90, United Agri Products, Greeley, CO) at 0.25% v/v was included with each of the treatments. All herbicides were applied using a CO2 backpack sprayer equipped with Teejet DG 8002 vs. flat-fan nozzles (TeeJet, Spraying Systems Co., Wheaton, IL), calibrated to deliver a spray volume of 140 L ha–1 at 260 kPa and traveling 1.5 m s–1.
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Table 1. Chemical names, and rates of herbicides used in 2001, 2002, and 2003 growing seasons during establishment of Tifton 85 bermudagrass at Stephenville, TX.
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Each year, two plants per plot were permanently marked with a flag 14 DAP, and stolon length was measured at 0, 30, 60, and 90 d after treatment (DAT). Bermudagrass injury and weed control were visually estimated using a scale of 0% (no weed control or Tifton 85 bermudagrass injury) to 100% (complete weed control or bermudagrass death) (Frans et al., 1986). In 2001, large crabgrass was the dominant weed, and it was the only species rated. In 2002, large crabgrass, yellow nutsedge, and broadleaf signalgrass were present; however, only yellow nutsedge and broadleaf signalgrass were evaluated due to uniformity. In 2003, junglerice [Echinochloa colona (L.) Link], broadleaf signalgrass, and large crabgrass were present; although weed density was high, it was too variable between replications to obtain ratings. Ground cover percentage of bermudagrass was visually estimated 90 DAP. All weed control and bermudagrass injury data were analyzed as square-root transformations; however, nontransformed data are reported. Data were analyzed by analysis of variance using PROC GLM (SAS Inst., 1999), and means were separated within each season and application timing using Fisher's protected LSD at P = 0.05 level of significance.
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RESULTS AND DISCUSSION
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Year x application timing and year x herbicide treatment interactions were significant (P < 0.001) for stolon length, percentage visual injury, weed control, and ground cover. Therefore, means are reported by year and by application timing.
Stolon Length
There were no differences in Tifton 85 bermudagrass stolon length before any herbicide applications (data not shown). Stolon length averaged 0, 7, and 15 cm before the 1, 14, and 28 DAP application timings, respectively. Imazapic at 0.035 and 0.05 kg ha–1 applied 1 DAP were the only herbicide treatments to reduce stolon length 30 DAT (P < 0.01). In 2001, when rainfall was 53% below average, 0.035 and 0.05 kg ha–1 imazapic applied 1 DAP reduced stolon length by 55 and 77% (P < 0.001) relative to the untreated control 30 DAT, respectively (data not shown). In 2002, when rainfall was 37% above average, there were no differences in stolon length (data not shown). In 2003, when the rainfall amount was approximately average, 0.05 kg ha–1 imazapic reduced stolon length by 52% (P < 0.01), whereas 0.02 and 0.035 kg ha–1 imazapic did not differ from the untreated control (data not shown). There were no differences in stolon length for the 14 or 28 DAP application timings or 60 or 90 DAT evaluation for any application timing (data not shown). Stolon length measurement was not a good indicator of overall effectiveness, which is evident by the fact that visual injury, weed control, and Tifton 85 bermudagrass ground cover percentage were different between treatments. This may be attributed to variability in stolon length and that stolons were elongated in the reduced light with competition compared with a prostrate growth habit in full light where competition was absent, which negated any treatment differences relative to stolon length (Radosevich et al., 1997).
Visual Injury
Tifton 85 bermudagrass injury with imazapic applied at 0.02, 0.035, and 0.05 kg ha–1 varied with application timing (Table 2). Injury at 30 DAT was greatest at 1 DAP in 2001 (20 to 48%) and 2003 (4 to 38%), but at 14 DAP in 2002 (27 to 48%). This may be explained by the differences in rainfall distribution. In 2001, the 2-wk rainfall totaled 9 mm following 1 DAP application, and in 2003, the 2-wk rainfall totaled 15 mm following the 1 DAP application (Fig. 1
). However, in 2002, 116 mm of rain occurred in the 2 wk before application and 49 mm was received following 1 DAP application compared with only 1 mm received in the 2-wk period following the 14 DAP application. This response indicated that bermudagrass injury with imazapic was greater when moisture was limited. One possible reason is that the moisture present in the soil allowed the bermudagrass to continue to grow, possibly metabolizing the imazapic and reducing the injury. Smith (1993) reported that picloram (4-amino-3,5,6-trichloropicolinic acid) plus 2,4-D applied during extremely dry periods reduced the yield and density of Coastal bermudagrass. Butler and Muir (2006) also reported that imazapic reduced the yield of Coastal bermudagrass and that yield loss was greater when rainfall was limited. Since imazapic caused greater bermudagrass injury when applied during times of limited rainfall, it may be concluded that applications to Tifton 85 bermudagrass should only be done if there is adequate moisture already present in the soil profile to minimize bermudagrass injury.
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Table 2. Percentage injury 30 d after treatment (DAT) during establishment of Tifton 85 bermudagrass in response to various herbicides applied 1, 14, and 28 d after planting (DAP) in 2001, 2002, and 2003.
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Fig. 1. Precipitation distribution on 2-wk intervals during 2001, 2002, and 2003 establishment period compared with the 30-yr monthly rainfall average at Stephenville, TX.
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Tifton 85 bermudagrass injury was influenced by imazapic rate. Injury increased as imazapic rate increased regardless of application timing (Table 2). Imazapic applied at 0.02, 0.035, and 0.05 kg ha–1 1 DAP injured bermudagrass 20, 35, and 48%, respectively, in 2001. Imazapic at the same rates applied 14 DAP injured Tifton 85 bermudagrass 27, 40, and 48%, respectively, in 2002 and 4, 24, and 38%, respectively, when applied 1 DAP in 2003. By 60 DAT, injury with 0.02 and 0.035 kg ha–1 imazapic was not apparent; only with 0.05 kg ha–1 imazapic, applied 1 DAP in 2001 and 2003, and 14 DAP in 2002, was injury visible (<15%) to the bermudagrass (P < 0.05). By 90 DAT, imazapic injury was not apparent at any rate or application timing (data not shown), indicating Tifton bermudagrass injury was transient with these rates of imazapic.
The herbicides currently registered for established bermudagrass (Table 1) did not injure Tifton 85 regardless of application timing (Table 2). In addition, 0.02 kg ha–1 trifloxysulfuron did not injure Tifton 85 regardless of application timing. Glyphosate at 0.28 kg ha–1 applied 14 and 28 DAP caused minimal injury (6 to 9%) in 2001–2003 when evaluated 30 DAT. By 60 DAT, glyphosate [N-(phosphonomethyl)glycine] injury was not apparent (data not shown). Low rates of glyphosate (0.28 kg ha–1) have been documented to control certain annual grasses with minimal injury to the perennial grass crops (Anonymous, 2003b; Beck et al., 1995). In this 3-yr field study, vegetatively propagated Tifton 85 bermudagrass was similar to other perennial grass crops in their response to low rates of glyphosate.
Weed Control
Large Crabgrass
In 2001, all herbicide treatments applied 1 DAP, except trifloxysulfuron, reduced large crabgrass compared with the untreated control. Treatments containing 0.02, 0.035, 0.05 kg ha–1 imazapic, 0.19 kg of picloram + 0.19 kg ha–1 fluroxypyr {[(4-amino-3,5-dichloro-6-fluoro-2-pyridinyl)oxy]acetic acid}, 0.08 kg of picloram + 0.28 kg ha–1 2,4-D amine, 0.15 kg of picloram + 0.56 kg ha–1 2,4-D amine, 2.2 kg of 2,4-D amine + 1.2 kg ha–1 dicamba, and 2.3 kg ha–1 2,4-D ester applied 1 DAP controlled large crabgrass 70% or better (Table 3). Smith and Martin (1992) reported only 30% large crabgrass control with 2,4-D ester pre-emergence when applied to dormant bermudagrass in mid-March. This difference was probably due to the close proximity between timing of herbicide and germination of the large crabgrass in this study. At 1 DAP, 0.02, 0.035, and 0.05 kg ha–1 imazapic reduced large crabgrass by 81, 89, and 95%, respectively. Beran et al. (1999) also reported excellent control of large crabgrass with imazapic. At the 14 DAP application timing, when large crabgrass was in the one- to two-leaf stage, only imazapic at 0.035 and 0.05 kg ha–1 provided excellent (>95%) control while 0.28 kg ha–1 glyphosate provided 76% control. This was similar to research by Culpepper et al. (2001) reporting that 0.3 kg ha–1 glyphosate controlled large crabgrass 80%. At the 28 DAP application timing, when large crabgrass was in the fifth-leaf stage, only 0.05 kg ha–1 imazapic provided acceptable (>70%) control, which indicated that reduced rates of imazapic and glyphosate can provide satisfactory control when large crabgrass is very small; however, higher rates of imazapic and glyphosate would be required once it reached the fifth-leaf stage.
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Table 3. Percentage control of broadleaf signalgrass, large crabgrass, and yellow nutsedge in Tifton 85 bermudagrass 30 d after treatment in response to various herbicides applied 1, 14, and 28 d after planting (DAP).
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Broadleaf Signalgrass
In 2002, imazapic, glyphosate, and trifloxysulfuron provided the best control at the 14 DAP application timing when a majority of the broadleaf signalgrass was in the one- to three-leaf stage (Table 3). At 14 DAP, 0.02 kg ha–1 trifloxysulfuron provided 99% control while 0.035 and 0.05 kg ha–1 imazapic provided 90 and 93% control, respectively, and 0.28 kg ha–1 glyphosate controlled 91% of the broadleaf signalgrass. Shaw and Arnold (2002) reported excellent (95%) broadleaf signalgrass control with 0.28 kg ha–1 glyphosate. Broadleaf signalgrass control with 0.02 kg ha–1 trifloxysulfuron contradicts Porterfield et al. (2003) and Crooks et al. (2003) who reported that trifloxysulfuron did not control broadleaf signalgrass. In their studies, however, much lower rates were utilized (0.004 to 0.005 kg ha–1). At the 1 DAP application timing, imazapic at 0.02, 0.035, and 0.05 kg ha–1 controlled broadleaf signalgrass 30, 57, and 75%, respectively, while trifloxysulfuron provided excellent control (92%). Herbicides applied 28 DAP controlled broadleaf signalgrass 33, 83, and 83% with 0.02, 0.035, and 0.05 kg ha–1 imazapic, respectively; 58% with 0.02 kg ha–1 trifloxysulfuron; and 73% with 0.28 kg ha–1 glyphosate. The herbicides currently registered for bermudagrass did not control broadleaf signalgrass at any application timing.
Yellow Nutsedge
Trifloxysulfuron controlled yellow nutsdege 90% or greater (Table 3) regardless of application timing in 2002, which is similar to the findings of McElroy et al. (2003) and Porterfield et al. (2002). Imazapic control of yellow nutsdege was influenced more by rate than timing (Grichar and Nester, 1997). Yellow nutsedge control was 87 to 95% with 0.05 kg ha–1 imazapic and 75 to 93% with 0.035 kg ha–1 imazapic, while 0.02 kg ha–1 imazapic only provided 20 to 53% control (Table 3). Neither glyphosate nor any of the currently registered herbicides controlled yellow nutsdege, regardless of application timing.
Ground Cover Percentage
Tifton 85 bermudagrass ground cover varied among years, application timings, and herbicide treatments (Table 4). Differences in years were primarily due to weed species present each year while application timing differences can be attributed to herbicide efficacy of weeds, bermudagrass injury, and the ability of the bermudagrass to spread and cover the area with the various treatments. Percentage ground cover was a sensitive indicator of the overall effectiveness of the herbicide treatments, integrating both weed control and crop injury.
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Table 4. Ground cover percentage 90 d after planting (DAP) during establishment of Tifton 85 bermudagrass in response to various herbicides applied 1, 14, and 28 DAP in the 2001, 2002, and 2003 growing seasons.
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In 2001, when large crabgrass was predominant, the best herbicide treatments were 0.02, 0.035, and 0.05 kg ha–1 imazapic applied 14 DAP, which resulted in 52 to 56% ground cover. Imazapic caused bermudagrass injury early in the season; however, bermudagrass ground cover was greater with imazapic since the bermudagrass injury was transient and the large crabgrass was controlled. In the 1 DAP application timing, bermudagrass ground cover with 0.035 kg ha–1 imazapic was greater than all other chemicals but was similar to the cover provided by its lower and higher rates. These high and low rates of imazapic did not differ from the hormone-like herbicides, which resulted in 21 to 28% Tifton 85 bermudagrass ground cover compared with 3% in the untreated control. Imazapic and these hormone-like herbicides improved bermudagrass ground cover due to large crabgrass control when applied 1 DAP. These hormone-like herbicide treatments and trifloxysulfuron did not differ from the untreated control when applied 14 DAP since there was no large crabgrass control at this timing. In addition, plots treated with 0.28 kg ha–1 glyphosate 14 DAP had 38% bermudagrass ground cover compared with 5% ground cover in the untreated control. The 28 DAP application timing was the least effective timing when only 0.28 kg ha–1 glyphosate and 0.02, 0.035, and 0.05 kg ha–1 imazapic improved Tifton 85 bermudagrass establishment, which had 16 to 28% ground cover compared with 3% in the untreated control.
In 2002, when yellow nutsedge and broadleaf signalgrass were present, the best herbicide treatment was 0.02 kg ha–1 trifloxysulfuron applied 1 and 14 DAP, which resulted in 62 to 67% ground cover in 2002 compared with only 2 to 4% in the untreated controls. This was attributed to the excellent control of both broadleaf signalgrass (>90%) and yellow nutsedge (>90%) with 0.02 kg ha–1 trifloxysulfuron and that it did not injure Tifton 85 bermudagrass. In the 1 DAP application timing, 0.02, 0.035, and 0.05 kg ha–1 imazapic and the hormone-like herbicide treatments were equally effective at improving Tifton 85 bermudagrass establishment, which ranged from 22 to 37% ground cover compared with only 4% in the untreated control. In the 14 DAP application timing, 0.02, 0.035, 0.05 kg ha–1 imazapic and 0.28 kg ha–1 glyphosate were equally effective at improving Tifton 85 bermudagrass ground cover, which ranged from 37 to 52% compared with 2% in the untreated control. The herbicides currently registered for bermudagrass did not show improved ground cover when applied 14 or 28 DAP. In the 28 DAP application timing, 0.28 kg ha–1 glyphosate; 0.02, 0.035, and 0.05 kg ha–1 imazapic; and 0.02 kg ha–1 trifloxysulfuron were equally effective at improving Tifton 85 bermudagrass establishment, which ranged from 27 to 35% ground cover compared with only 2% in the untreated control.
In 2003, when broadleaf signalgrass and junglerice were present, the best herbicide treatment was 0.02 kg ha–1 trifloxysulfuron 1 DAP, which resulted in 57% bermudagrass ground cover followed by 0.035 kg ha–1 imazapic 1 DAP (42%) and 0.02 kg ha–1 trifloxysulfuron 14 DAP (41%) compared with 4% in the untreated control. Tifton 85 bermudagrass establishment was also improved with 27% ground cover for 0.05 kg ha–1 imazapic applied at 1 DAP, 17% with 0.28 kg ha–1 glyphosate, 24% with 0.035 kg ha–1 imazapic, and 22% with 0.05 kg ha–1 imazapic applied 14 DAP compared with 3 to 4% cover in the untreated controls. At the 28 DAP application timing, only 0.035 and 0.05 kg ha–1 imazapic improved Tifton 85 establishment, resulting in 12 to 13% ground cover compared with 3% in the untreated control. Glyphosate applied at 0.28 kg ha–1, 0.02 kg ha–1 imazapic, and 0.02 kg ha–1 trifloxysulfuron did not differ from the untreated control when applied 28 DAP in 2003. In addition, the herbicides currently registered for bermudagrass did not differ from the untreated control in 2003 at any application timing. The overall effectiveness of these herbicides was reduced in 2003 compared with previous years, possibly due to the lack of junglerice control.
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CONCLUSIONS
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Results of this study indicate that herbicides labeled for fully established bermudagrass pastures did not injure Tifton 85 bermudagrass and could also be used at any time during establishment. Tifton 85 bermudagrass establishment was greatly increased when weeds were controlled, especially at the early application timings when the weeds were small. Application of hormone-like herbicides at planting can suppress large crabgrass and aid in bermudagrass establishment. In addition, a reduced rate of glyphosate (0.28 kg ha–1) 14 DAP provided acceptable control of large crabgrass and broadleaf signalgrass, when applied early to small, actively growing plants. Glyphosate could provide an acceptable alternative for suppressing annual grass weeds with minimal injury to Tifton 85 bermudagrass; however, there is still a need for herbicides with yellow nutsedge and other grass activity to become registered for establishment. Herbicides like imazapic and trifloxysulfuron that control broadleaf signalgrass and yellow nutsedge have the potential to increase Tifton 85 bermudagrass establishment and thus should be considered.
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ACKNOWLEDGMENTS
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This project was partially funded by Dow Agro Sciences, BASF Corporation, and Texas Cooperative Extension. The authors would like to thank Lynn Hagan, custom bermudagrass sprigger, summer students for their technical assistance, and the Texas A&M Research & Extension Center at Stephenville, TX.
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ABSTRACT
INTRODUCTION
