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© 2009 Plant Management Network.
Accepted for publication 18 May 2009. Published 20 July 2009.

Herbicide Tolerance on ‘Sea Spray’ Seashore Paspalum Seedlings

Aaron J. Patton, Assistant Professor, Jon M. Trappe, Program Technician, Michael D. Richardson, Professor, Department of Horticulture, University of Arkansas, Fayetteville, AR 72701; and Eric K. Nelson, The Scotts Company, Marysville, OH 43041

Corresponding author: Aaron J. Patton. ajpatton@uark.edu

Patton, A. J., Trappe, J. M., Richardson, M. D., and Nelson, E. K. 2009. Herbicide tolerance on ‘sea spray’ seashore saspalum seedlings. Online. Applied Turfgrass Science doi:10.1094/ATS-2009-0720-01-RS.

Abstract

There are no reports of herbicide tolerance on seedling seashore paspalum (Paspalum vaginatum Sw.). The objective of this study was to determine which herbicides cause the least amount of injury to seashore paspalum seedlings and allow for maximum establishment. Field studies were conducted in 2007 and 2008 to assess the tolerance of ‘Sea Spray’ seashore paspalum to 23 herbicides. Herbicide treatments were applied two weeks after emergence of seedlings and compared to an untreated control. MSMA, imazaquin, fluazifop, triclopyr, siduron, and ethofumesate injured seedlings and reduced establishment. Clopyralid, halosulfuron, metsulfuron, quinclorac, carfentrazone, and salt water provided the least injury to seashore paspalum seedlings while allowing maximum establishment.

Introduction

A number of new seashore paspalum (Paspalum vaginatum Sw.) cultivars have appeared on the market in the past decade as several commercial and academic breeding programs have begun to identify and work with new germplasm. The interest in this species, which is known for its excellent turf quality and salinity tolerance (9), has increased worldwide with 7,510 acres now used on golf courses in the United States (16). Although more commonly used on golf courses and athletic fields, it is also used in home lawns in Florida and other coastal areas (28).

Seeded cultivars provide a quick, easy, and economical way to establish turf. Seeded seashore paspalum cultivars provide quality similar to vegetatively established seashore paspalum cultivars (23). As seeded cultivars are relatively new compared to vegetatively established cultivars of seashore paspalum, there are several factors that need to be investigated. A study by Shim et al. (26) showed that priming the seed with KNO₃ was useful for improving germination. Certain cover technologies are known to provide for improved seashore paspalum establishment from seed (22). However, weed control is often important in establishing warm-season grasses from seed as effective weed control programs will decrease competition, increase establishment rate, and decrease the grow-in period (20).

The ability to control weeds during the first six to eight weeks after emergence is a key factor to the success of seeded warm-season grasses. Summer annual grasses such as crabgrass [Digitaria sanguinalis (L.) Scop.] and goosegrass [Eleusine indica (L.) Gaertn.] are competitive with seedlings and broadleaf weeds may also create problems by shading seedlings. Therefore, competition shortly after seeding could significantly prolong stand establishment and reduce overall stand density. Additionally, perennial grassy weeds such as bermudagrass [Cynodon spp. (L.) Rich.] continue to be problematic in seashore paspalum swards.

Although there are limited herbicides with any label recommendations for seashore paspalum, most of those herbicides are specified for use on established seashore paspalum (Table 1). On established ‘Salam’ seashore paspalum, the postemergence herbicides clopyralid, dicamba, halosulfuron, imazaquin, mecoprop + 2,4-D + dicamba, metsulfuron, and quinclorac were found to cause little toxicity (30). Halosulfuron and quinclorac are also safe to use on other cultivars of established seashore paspalum (11). Benefin, bensulide, dithiopyr, prodiamine, pronamide, oxadiazon, and pendimethalin are reportedly safe preemergence herbicides for the control of weeds in established seashore paspalum turf (8,13). During establishment of eight seashore paspalum cultivars from plugs, dicamba, quinclorac, halosulfuron and oxadiazon did not cause turfgrass injury (12), but oxadiazon did injure turf when applied immediately prior to planting sprigs (27). Lastly, sea water has been found to be an effective control for postemergence control of weeds in established ‘Adalyad’ seashore paspalum (31). Other herbicides such as atrazine, diclofop, ethofumesate, fenoxaprop, imazaquin, metribuzin, MSMA, sethoxydim, simazine, and triclopyr are known to cause injury to established seashore paspalum (5,7,10,11,13,14,17,27).

Table 1. Herbicide common name, trade name, and application rate evaluated in 2007 and 2008 on seashore paspalum seedlings.

 ^w Table sorted alphabetically by primary ingredient.

 ^x Labeled for use in established seashore paspalum as of 18 March 2009. Labels accessed at www.cdms.net or directly from company websites.

 ^y Herbicide names mentioned are registered trademarks. No endorsement of any herbicide listed is implied by the authors. No discrimination is intended against products not mentioned.

 ^z Labeled for use on seashore paspalum seedlings.

Little is known about effective herbicides that may be used during the establishment of seashore paspalum from seed. There are no reports of herbicide tolerance on seedling seashore paspalum, and currently only quinclorac is labeled for use on seashore paspalum seedlings (2,3). The objective of this study was to determine which herbicides cause the least amount of injury to Sea Spray seashore paspalum seedlings and allow for maximum establishment.

Field Analysis of Herbicide Tolerance on Sea Spray Seashore Paspalum

A field study was conducted at the Arkansas Agricultural Research and Extension Center, Fayetteville, AR. The soil at the site is a Captina silt loam (fine-silty mixed mesic Typic Fragiudalt) with an average pH of 6.2. Experiments were seeded 20 June 2007 and 13 June 2008 with 44 kg pure live seed/ha of Sea Spray seashore paspalum in areas that were fumigated with methyl bromide at 732 kg/ha in 2007. The experimental area was tilled and raked immediately prior to seeding and lightly raked after seeding to improve seed-to-soil contact. Fumigation provided a relatively weed-free site on which herbicide injury and turfgrass establishment could be closely monitored. Additional weed germination was minimal in the plot area, and those weeds were mechanically removed so not to interfere with data collection.

Plots were covered for 10 to 14 days after seeding with a germination blanket (Deluxe, 0.5 oz., Dewitt Company, Sikeston, MO) to prevent movement of seed and promote germination. The experimental area was irrigated as needed to encourage germination and establishment. Experimental design was a randomized complete block with four replications of each herbicide treatment and an individual plot size of 1.2 by 1.5 m. Plots were treated with various herbicides (Table 1) at two weeks after emergence (WAE). Emergence occurred on 4 July 2007 and 25 June 2008 and was defined as a uniform stand of one-leaf seedlings. A non-ionic surfactant (Latron AG-98, 0.25% v/v) was added to each herbicide prior to application on either 19 July 2007 or 8 July 2008. Herbicides were applied in 280 liter of water per ha with a CO₂-pressurized sprayer at 207 kPa using a single 8001VS flat-fan nozzle. A salt water treatment was included and applied as 32,000 mg/liter (50 dS/m) in 2,700 liters/ha per plot using NaCl. Salt water was applied on three consecutive days starting at 2 WAE. Plots were mown as needed at 1.3 cm when seedlings first reached 1.9 cm. Nitrogen was applied as urea (46-0-0) at emergence and again one month later at a rate of 49 kg/ha.

Digital image analysis was used to determine seashore paspalum coverage (25) starting 2 weeks after herbicide application (WAA) and until the coverage of the majority of the plots neared 100%. Herbicide injury was rated visually during the first 10 days after application using a scale of 0 to 100 where 0 = no visible injury and 100 = brown turf. Untreated checks were included for comparison. Data from each experiment were analyzed using PROC GLM (v. 9.1, SAS Institute Inc., Cary, NC) and year by herbicide interactions were significant, so data for each year were analyzed and presented separately. Herbicide injury means were separated using Fisher's protected least significant difference when F tests were significant at α = 0.05.

Herbicide Injury on Seedling Sea Spray Seashore Paspalum

Herbicide injury was 17% and 15% greater in 2007 than 2008 across herbicides when measured 3 and 6 days after application (DAA), respectively (Table 2). There were significant differences in injury among herbicides within each year. At 3DAA in 2007, MSMA and sulfentrazone were most injurious (> 73%) while clopyralid, metsulfuron, halosulfuron, dithiopyr, quinclorac, salt water, pendimethalin, oxadiazon, pronamide, siduron, and prodiamine were least injurious (< 18%) (Table 2). Herbicide injury 6 DAA was highest (> 76%) for fluazifop, MSMA, imazaquin, ethofumesate, 2,4-D + MCPP + dicamba, and triclopyr in 2007. Herbicide injury was least (< 24%) for clopyralid, salt water, halosulfuron, quinclorac, metsulfuron, carfentrazone, oxadiazon, prodiamine, pronamide, and pendimethalin 6 DAA in 2007.

Table 2. Herbicide injury to seashore paspalum seedlings at various timings after application in 2007 and 2008.

 ^v DAA, days after application.

 ^w Treatments sorted by mean coverage across years (data not shown) similar to Table 3.

 ^x Values in a column followed by the same letter are not significantly different from one another (LSD, α = 0.05).

 ^y Mean of treatments excluding the untreated check.

 ^z Herbicide injury in two untreated plots were pooled in 2007 to represent the untreated check. Five untreated plots were pooled in 2008 to represent the untreated check.

In 2008, herbicide injury was highest for MSMA 3 DAA (Table 2). Fluazifop, MSMA, and triclopyr produced similar injury (> 76%) by 6 DAA in 2008. Injury was highest (> 83%) 8 DAA for triclopyr and fluazifop. Herbicides that were the least injurious in 2008 on all three dates evaluated included: carfentrazone, pendimethalin, clopyralid, prodiamine, halosulfuron, metsulfuron, quinclorac, sulfosulfuron, dithiopyr, and salt water.

Among the preemergence herbicides, dithiopyr, oxadiazon, pendimethalin, and prodiamine reportedly are not injurious on various cultivars of seashore paspalum when applied at label rates during establishment from plugs (12). However, minor injury (< 24%) was observed with applications of oxadiazon and dithiopyr to seedling seashore paspalum in our study, which is not unexpected since dinitroaniline herbicides are only recommended for use on well-established turf (29).

Among the postemergence herbicides, halosulfuron, clopyralid, and quinclorac were the least injurious in our study, which is consistent with previous reports on established seashore paspalum (11,12,27,30). Injury from applications of salt water was also minimal (< 16%) (Table 2) and consistent with data from the use of ocean water (55 dS/m) on established seashore paspalum (31). Common three-way herbicide combinations (2,4-D, MCPP, dicamba) were injurious (< 78% 6 WAA) to seedlings in our study, which is consistent with other reports documenting injury to seashore paspalum from these herbicide combinations (5,7,10,30). Injury from combination products was greater in 2007 than 2008 on seedling turf, and in general these products caused more injury on seedlings than reports on established turf (5,7,10,30). This is consistent with previous reports in bermudagrass and zoysiagrass, where herbicide tolerance of seedlings improves as they mature (19,21).

Injury to seashore paspalum seedlings from triclopyr was high, which is consistent with other reports on established seashore paspalum (7,10). Ethofumesate is known to injure established seashore paspalum similar to our findings with seedlings (14,30). Ethofumesate injury is not severe enough to kill established seashore paspalum and has been proposed as a control method for bermudagrass in seashore paspalum (14), but not recommended for use on seashore paspalum by others (30). Reports on herbicide injury to seashore paspalum from imazaquin are also variable. Unruh et al. (30) reported less than 4% injury from imazaquin applications to Salam seashore paspalum, whereas Johnson and Duncan (11) reported that imazaquin decreased the turf quality of four seashore paspalum cultivars and Tavares and DeFrank (27) reported injury when applied 23 days after sprigging. In this research, MSMA caused greater than 77% injury in both years of our study, which is consistent with reports in established turf where MSMA or combinations products containing MSMA caused severe injury to established seashore paspalum (5,6,10).

As mentioned previously, bermudagrass is an invasive weed of seashore paspalum that is difficult to control once established. Herbicides commonly used to suppress or control bermudagrass include fluazifop, triclopyr, siduron, and ethofumesate (14,18,19). In the present study, all caused severe injury to seashore paspalum seedlings and do not appear to be viable options for use in controlling bermudagrass in seashore paspalum seedlings.

Sea Spray Seashore Paspalum Establishment as Affected by Herbicides

Turfgrass coverage was 59% greater in 2007 than 2008 across herbicides when measured 2 WAA (Table 3). The reason for increased establishment and decreased herbicide injury in 2008 is not clear since temperatures were similar in each year (Table 4) and photosynthetically active radiation was also similar between years (data not shown). Within each year there were significant differences in injury among herbicides following application.

Table 3. Seashore paspalum coverage at various weeks after herbicide application in 2007 and 2008 as well as recommendations on the application safety of these herbicides to seashore paspalum seedlings.

Table 4. Seashore paspalum seeding date, emergence, herbicide application date, establishment rate, and mean daily high temperatures during the experiment.

 ^x WAE, weeks after emergence of Sea Spray seashore paspalum seedlings.

 ^y WAA, weeks after herbicide application.

Turfgrass coverage 2 WAA was highest (> 34%) among clopyralid, halosulfuron, metsulfuron, salt water, and the untreated check and lowest (< 12%) among dithiopyr, 2,4-D + MCPP + dicamba + carfentrazone, sulfosulfuron, siduron, fluroxypyr, 2,4-D + MCPP + dicamba, MCPP + 2,4-D + dicamba, MSMA, imazaquin, triclopyr, ethofumesate, and fluazifop in 2007 (Table 3). Coverage 4 WAA was highest (> 73%) among clopyralid, halosulfuron, metsulfuron, carfentrazone, pronamide, pendimethalin, salt water, and the untreated check (Table 3). Siduron, MSMA, imazaquin, ethofumesate, triclopyr, and fluazifop had the lowest (< 15%) coverage 4 WAA in 2007. Coverage 8 WAA in 2007 was highest (> 80%) among halosulfuron, salt water, quinclorac, carfentrazone, sulfentrazone, oxadiazon, pronamide, metsulfuron, 2,4-D + MCPP + dicamba + carfentrazone, clopyralid, sulfosulfuron, pendimethalin, prodiamine, fluroxypyr, 2,4-D + MCPP + dicamba, MCPP + 2,4-D + dicamba, dithiopyr and the untreated check. Triclopyr, fluazifop, and ethofumesate had the lowest (< 19%) coverage 8 WAA in 2007.

Turfgrass coverage for plots treated with salt water, halosulfuron, clopyralid, carfentrazone, metsulfuron, quinclorac, pendimethalin, pronamide, oxadiazon, prodiamine, sulfentrazone, 2,4-D + MCPP + dicamba + carfentrazone, sulfosulfuron, fluroxypyr, 2,4-D + MCPP + dicamba, and MCPP + 2,4-D + dicamba was similar to the untreated check on all three dates measured in 2008 (Table 3). Plots treated with ethofumesate, siduron, triclopyr, or fluazifop had the lowest (< 7%) coverage 2 WAA in 2008. Siduron, triclopyr, and fluazifop treated plots had the lowest (< 3%) coverage 3 WAA and fluazifop treated plots had the lowest coverage 6 WAA.

Although overall establishment rates were slower in 2007 than 2008 (Table 1), treatment rankings and the final establishment of the plots was similar in both years with the exception of imazaquin and MSMA treated plots. Imazaquin and MSMA injured seashore paspalum seedlings in both years of the trial, but final turf coverage was not different from the untreated control in 2008. Imazaquin and MSMA are known to suppress seashore paspalum when tank mixed with other products (6,15) or when applied alone (5,10,11). MSMA and imazaquin are not recommended for use on established seashore paspalum (5,10,11,17,27) and they should also not be used on seashore paspalum seedlings.

Salt water, halosulfuron, clopyralid, carfentrazone, metsulfuron, and quinclorac had coverage similar to the untreated check on each measurement date in both years (Table 3). This is consistent with other reports that salt water, halosulfuron, clopyralid, metsulfuron, and quinclorac are safe to use on seashore paspalum (11,12,27,30,31). There are no previous reports of herbicide tolerance of carfentrazone on seashore paspalum seedlings, but carfentrazone is labeled for use in established seashore paspalum (1). Carfentrazone is also safe on other warm-season grass seedlings such as bermudagrass and zoysiagrass (24,32).

Pendimethalin, pronamide, oxadiazon, prodiamine, sulfentrazone, 2,4-D + MCPP + dicamba + carfentrazone, sulfosulfuron, fluroxypyr, 2,4-D + MCPP + dicamba, dithiopyr, and MCPP + 2,4-D + dicamba produced coverage similar to the untreated check at the end of the study, but coverage in these treatments was not similar to the untreated check 2 WAA in 2007, indicating that establishment was reduced temporarily from these products. Among these products, seashore paspalum tolerance to 2,4-D + MCPP + dicamba + carfentrazone, sulfentrazone, sulfosulfuron, pronamide, and fluroxypyr has not previously been reported, while the tolerance of the preemergence herbicides pendimethalin, oxadiazon, prodiamine, and dithiopyr as well as the postemergence herbicides 2,4-D + MCPP + dicamba, and MCPP + 2,4-D + dicamba to established seashore paspalum is known.

When established by plugs, several cultivars of seashore paspalum have good tolerance to the preemergence herbicides dithiopyr, oxadiazon, and pendimethalin, and prodiamine (12). Although dinitroaniline herbicides are recommended for use on well-established turf (29), some dinitroaniline herbicides like dithiopyr are safe for use 2 WAE or later to bermudagrass and zoysiagrass seedlings (19) while other dinitroanilines such as prodiamine and pendimethalin are recommended safe for use on bermudagrass seedlings 3 WAE or later (4). Of the dinitroanilines tested in this study, dithiopyr was the most injurious and impeded establishment most (Tables 2 and 3). However, all dinitroanilines allowed for maximum coverage by 8 WAA in 2007 and 6 WAA in 2008 and any decrease in establishment shortly after application 2 WAE could be tolerated in light of the benefits of decreasing weed competition, especially in areas with heavy weed pressure.

The postemergence herbicides 2,4-D + MCPP + dicamba, and MCPP + 2,4-D + dicamba are reported to injure established seashore paspalum (7,10,30), but there are no reports of their effect on seedling establishment. In our study, these products decreased establishment from seed 2 and 4 WAA but not 8 WAA in 2007 or any date in 2008. Other products such as clopyralid, carfentrazone, metsulfuron, and quinclorac are safer to use instead of these three-way mixtures if broadleaf weeds are problematic 2 WAE. However, there were no long-term effects of these herbicides on seashore paspalum establishment and they might be used if some injury can be tolerated.

Ethofumesate caused a significant reduction in turfgrass establishment in both years of the study, with less than 14% establishment in 2007 and less than 87% in 2008. Fluazifop, triclopyr, and siduron also greatly reduced (< 40%) establishment in both years of the trial. At present, these products are not recommended for use on seashore paspalum seedlings.

Conclusions

Based on the results of these studies, the relative safety of various herbicide applications to seashore paspalums seedlings is summarized (Table 3). Clopyralid, halosulfuron, metsulfuron, quinclorac, carfentrazone, and salt water provide the most safety for applications to seashore paspalum seedlings while allowing maximum establishment. Collectively these products control a broad spectrum of weeds. Halosulfuron could be used for sedge control; carfentrazone, clopyralid, metsulfuron, and quinclorac for broadleaf weed control; metsulfuron for cool-season grass control; quinclorac for summer annual grassy weeds; and salt water could be used as a natural herbicide in coastal locations for weed control in seashore paspalum seedlings.

As additional cultivars of seeded seashore paspalum become available, they should also be screened with commonly used herbicides. There are numerous reports of differences in herbicide tolerance among vegetatively established cultivars of seashore paspalum (11,15), but it is not known whether seeded cultivars will tolerate herbicides differently.

Acknowledgments

Special thanks also to Mr. Antonio Pompeiano for assistance with plot maintenance and to The Scotts Company for funding this project.

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