© 2009 Plant Management Network.
Effect of Sulfosulfuron on ‘Penncross’ Creeping Bentgrass Seedlings When Applied Before or After Seeding
James M. Rutledge, Graduate Research Assistant, Daniel V. Weisenberger, Research Agronomist, and Zachary J. Reicher, Professor, Department of Agronomy, Purdue University, West Lafayette, IN 47907-2054
Rutledge, J. M., Weisenberger, D. V., and Reicher, Z. J. 2009. Effect of sulfosulfuron on ‘Penncross’ creeping bentgrass seedlings when applied before or after seeding. Online. Applied Turfgrass Science doi:10.1094/ATS-2009-0710-01-RS.
Sulfosulfuron is labeled for roughstalk bluegrass (Poa trivialis L.) control in creeping bentgrass (Agrotis stolonifera L.) fairways. Between or following applications, managers often overseed creeping bentgrass to repopulate bare or thin areas left by dying roughstalk bluegrass. Our objective was to establish safe application intervals for sulfosulfuron before or after seeding creeping bentgrass. Treatments were arranged in a 3 × 8 factorial with three sulfosulfuron application rates (13, 26, or 52 g ai/ha) and eight application times [-3, -2, -1, 0, 1, 2, 3, and 4 weeks after seeding (WAS)]. Sulfosulfuron at 13 g ai/ha applied -3 WAS was the safest of all the pre-seeding herbicide treatments at 5 WAS in 2004, with creeping bentgrass cover equal to that of the untreated control and > 20% higher than any other treatment. Seeding creeping bentgrass should be delayed at least two weeks after the last application of sulfosulfuron at 13 g ai/ha and this rate of sulfosulfuron should not be applied to seedling creeping bentgrass sooner than three weeks after seeding. Applications at 26 g ai/ha can be safely applied three weeks before or four weeks after seeding creeping bentgrass. Sulfosulfuron applied at 52 g ai/ha was not safe on creeping bentgrass seedlings at any application timing assessed in this study.
Selectively controlling grassy weeds in creeping bentgrass (Agrotis stolonifera L.) fairways is difficult due to similar growth habits, life cycles, and physiology of the weeds and desirable species. Sulfosulfuron was recently introduced as Certainty and provides postemergent control or suppression of roughstalk bluegrass (Poa trivialis L.) and annual bluegrass (Poa annua L.) in established creeping bentgrass fairways when applied at 13 to 26 g ai/ha (1,5,9,11). Overseeding following sulfosulfuron application to creeping bentgrass fairways is recommended to repopulate thin areas left after weed control (1). However, little is known about the effect of sulfosulfuron applied at rates labeled for roughstalk bluegrass control before or after seeding creeping bentgrass.
Sulfosulfuron is an acetolactate synthase (ALS) inhibitor which can inhibit root growth and reduce seedling establishment when applied to immature turfgrass seedlings (3,4). Residual activity of sulfosulfuron likely inhibits creeping bentgrass seedling root growth, thus delaying reseeding following application (1,6). Sulfosulfuron half-life values in agricultural soils range from 3.97 to 6.30 days and up to 21% of the applied sulfosulfuron remains active in soil 15 days after application (8,12). Lycan and Hart (6) reported that sulfosulfuron applied at 34 or 67 g ai/ha one or two weeks before seeding creeping bentgrass reduced establishment cover. However, it is unknown if loss of cover may be reduced or eliminated by applying sulfosulfuron at lower rates of 13 to 39 g ai/ha, which are recommended for roughstalk bluegrass control in creeping bentgrass (1). These lower rates may result in reduced residual activity and allow for shorter reseeding intervals.
Sulfosulfuron has been shown to injure mature creeping bentgrass (7,9), but the effects on immature creeping bentgrass are not well known. Sulfosulfuron applied to mature creeping bentgrass may result in temporary phytotoxicity, commonly persisting for less than two weeks (7,9,11). Although the effect of sulfosulfuron on seedling creeping bentgrass is not well understood, the effect of other ALS inhibitors on seedling creeping bentgrass has been assessed. Dernoeden et al. (2) applied bispyribac-sodium, also an ALS inhibitor, to seedling ‘Southshore’ creeping bentgrass four weeks after emergence at rates ranging from 49 to 148 g ai/ha, resulting in no significant loss of cover three weeks after application. Better understanding tolerance of creeping bentgrass seedlings to sulfosulfuron may lead to shorter application intervals following reseeding and improved control of annual bluegrass and roughstalk bluegrass during establishment. Our objective was to establish safe application intervals for sulfosulfuron before or after seeding creeping bentgrass.
Trials of Sulfosulfuron Application Intervals for Creeping Bentgrass Seeding
A field study was conducted in West Lafayette, IN, at the W. H. Daniel Research and Diagnostic Center on a Stark silt loam (fine-silty mixed mesic Aeric Ochraqualf) with pH of 7.2 and 3.8% organic matter. The planting area was sprayed four and six weeks prior to initiation of the study with glyphosate (2% solution) to kill existing creeping bentgrass cover. Treatments were arranged in a 3 × 8 factorial with sulfosulfuron applied at three rates on eight application dates, plus an untreated control. Single applications of sulfosulfuron at 13, 26, or 52 g ai/ha were applied weekly beginning three weeks prior to seeding and ending four weeks after seeding. Application timings are referred to as -3, -2, -1, 0, 1, 2, 3, and 4 weeks after seeding (WAS) throughout the paper. Applications began on 2 August 2004 and 2007 and continued through 23 September 2004 or 19 September 2007 (Table 1). All sulfosulfuron applications included 0.25% v/v nonionic surfactant (MON 0818). Treatments were applied using a hand-held three-nozzle boom with 8003 (Teejet Technologies, Wheaton, IL) nozzles at 240 kPa in 800 liters/ha to 1.5 × 1.5-m plots separated by 0.5-m borders to allow for drift and over-spray. Plots were seeded on 22 August 2004 and 24 August 2007 with ‘Penncross’ creeping bentgrass at 36.6 kg pure live seed/ha. Penncross was used because many fairways with significant roughstalk bluegrass contamination are 10 to 20 years old and thus older creeping bentgrass varieties like Penncross predominate. The seedbed was prepared by cultivating the surface 1 cm with an engine-driven power-rake (Slice N Rake, Turfco Manufacturing Inc., Blaine, MN), followed by drop seeding in two directions. Starter fertilizer (6-24-24) was applied at 73 kg P2O5 per ha and lightweight germination blankets (PR1712, A. M. Leonard, Piqua, OH) were placed over the plots for one week. Plots were lightly irrigated twice daily to ensure a moist seedbed until germinating between 1 and 6 September of both years, after which plots were irrigated to prevent drought stress. Plots were mowed with a reel mower at 1.25 cm beginning three weeks after seeding to simulate typical golf course fairway management practices.
Table 1. Application dates of sulfosulfuron made between
* WAS = weeks after seeding
Experiments were arranged in a randomized complete block with three replications. Phytotoxicity and percent cover of creeping bentgrass were visually rated weekly beginning three weeks after seeding. Phytotoxicity was assessed on a scale of 1 to 9 where 1 = brown turf, 5 = mild chlorosis, 7 = acceptable turf, and 9 = no visible phytotoxicity. Percent cover was rated from 0 to 100, where 0 = no turf cover and 100 = complete turf cover. All cover data were arcsin-transformed and analyzed using SAS statistical software (version 9.1; SAS Institute Inc., Cary, NC). Error variances were not homogeneous between years and therefore data were analyzed and presented separately for each year. The data presented were recorded 5 and 8 WAS, which was the period of maximum reduction in cover for the pre-seeding and post-seeding applications of sulfosulfuron, respectively. Means were separated using a Fisher’s protected LSD and back-transformed means are presented (13). Sulfosulfuron applied 1 WAS in 2004 resulted in complete death of creeping bentgrass and thus was not included in the analysis due to zero variance across all rating dates.
Effect of Sulfosulfuron Rate and Timing
Main effects of application timing and rate of sulfosulfuron were significant over both years and rating dates (Table 2). Application timing affected creeping bentgrass cover throughout the study as applications made 0 and 1 WAS were most damaging, especially in 2004 (Table 2). Creeping bentgrass cover decreased as rates increased from 13 g ai/ha to 52 g ai/ha (Table 2). Although most treatments caused phytotoxicity, creeping bentgrass recovered by three weeks after application with no treatments remaining below the acceptable level of seven (data not shown), which is similar to other reports (7,9). Since there were significant application timing × rate interactions, these data are most useful to the turf practitioner due to their need for a specific application rate and date. Managers rarely have the luxury to make applications at specific timings and thus providing a range of application timings and appropriate rates is beneficial.
Table 2. Percent cover of ‘Penncross’ seedling creeping bentgrass influenced by sulfosulfuron applied before, at, or after seeding on 22 August 2004 and 24 August 2007.
x WAS = weeks after seeding.
y Means within columns and main effects followed by the same letter are not significantly different at P ≤ 0.05. Means followed by an (*) do not differ from the untreated control.
z Percent cover in untreated control plots at 5 and 8WAS was 97 and 98%, respectively in 2004 and 96 and 100%, respectively in 2007. Analysis was conducted on arcsin-transformed data and back-transformed data are presented.
Pre-Seeding Application Effects
Sulfosulfuron at 13 g ai/ha applied -3 WAS was the safest of all the pre-seeding herbicide treatments at 5 WAS in 2004, with creeping bentgrass cover equal to that of the untreated control and > 20% higher than any other treatment (Fig. 1A). Some recovery occurred by 8 WAS as 13 g ai/ha applied -3 or -2 WAS provided creeping bentgrass cover similar to the untreated control (Fig. 2A). All pre-seeding treatments applied reduced cover compared to the untreated control at 5 WAS again in 2007, but sulfosulfuron at 13 and 26 g ai/ha applied -3 or -2 WAS were least damaging reducing cover only 4 to 16% compared to the untreated control (Fig. 1B). Some recovery occurred by 8 WAS and cover resulting from these same four treatments was similar to that of the untreated control (Fig. 2B). Lycan and Hart (5) recommend reseeding creeping bentgrass two to four weeks following sulfosulfuron at 34 or 67 g ai/ha while acknowledging reduced seeding intervals may be possible when applying lower rates. However, our study indicates that shorter sulfosulfuron application intervals are not consistently safe even at 13 g ai/ha.
Sulfosulfuron was safer in 2007 than in 2004, which could be attributed to temperature differences. Air temperatures after the -3, -2, and -1 WAS applications in 2007 were greater than in 2007 (Fig. 3). Since air temperatures generally reflect soil temperatures, warmer soils in 2007 likely increased herbicide degradation (3,10) resulting in less damage from the pre-seeding treatments in 2007 compared to 2004. Furthermore, air temperatures between 5 and 8 WAS remained higher in 2007, likely encouraging quicker and ultimately better recovery than in 2004.
Post-Seeding Application Effects
Even though results from data recorded 5 WAS are presented, full effects of 3 and 4 WAS applications were not evident by 5 WAS. Results from evaluations recorded 8 WAS were more representative and will be discussed. In 2004, only sulfosulfuron at 13 g ai/ha applied 4 WAS did not decrease cover of creeping bentgrass compared to the untreated control at 8 WAS (Fig 2A). However, 13 g ai/ha applied 3 or 4 WAS as well as 26 g ai/ha applied 4 WAS had no effect on creeping bentgrass cover 8 WAS in 2007 (Fig 2B). Our data are similar to that of Lycan and Hart (6) showing reduced damage in 2007 compared to 2004 was likely due to warmer air temperatures between 5 and 8 WAS in 2007 encouraging better recovery in 2007.
Under the conditions of our study, seeding Penncross creeping bentgrass following sulfosulfuron at 13 g ai/ha should be delayed at least two, or more conservatively, three weeks after the last summer application. Though 26 g ai/ha was safely applied two or three weeks before seeding in one year of our study, these applications may cause intolerable damage to creeping bentgrass in other years. When applying sulfosulfuron at recommended rates of 13 to 26 g ai/ha, overseeding creeping bentgrass should be conservatively delayed four weeks after the final application. This study did not include multiple applications of sulfosulfuron which may result in more residual herbicide in the soil that may lengthen safe reseeding intervals. However, in accordance with the label, subsequent sulfosulfuron applications should not exceed 13 g ai/ha and combined with a relatively short half-life of 3.97 to 6.30 days, is unlikely to result in significant reseeding delays following multiple applications (8,12).
Sulfosulfuron at 13 g ai/ha should be delayed at least three, or more safely, four weeks after seeding creeping bentgrass. Sulfosulfuron at 26 g ai/ha should be delayed four weeks after seeding creeping bentgrass. Sulfosulfuron at 52 g ai/ha should be avoided at least three weeks before to four weeks after seeding, and requires delays longer than we evaluated in this study.
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Purdue Agriculture Research Program Journal Number 2009-18406