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© 2006 Plant Management Network.
Accepted for publication 22 May 2006. Published 11 August 2006.

Creeping Bentgrass Tolerance and Annual Bluegrass Control With Bispyribac-Sodium Tank-Mixed With Iron and Nitrogen

Steven J. McDonald, Former Graduate Research Assistant, and Peter H. Dernoeden, Professor, Department of Plant Science and Landscape Architecture, University of Maryland, College Park 20742; and John E. Kaminski, Assistant Professor, Department of Plant Science, University of Connecticut, Storrs 06269

Corresponding author: John E. Kaminski. john.kaminski@uconn.edu

McDonald, S. J., Dernoeden, P. H., and Kaminski, J. E. 2006. Creeping bentgrass tolerance and annual bluegrass control with bispyribac-sodium tank-mixed with iron and nitrogen. Online. Applied Turfgrass Science doi:10.1094/ATS-2006-0811-01-RS.

Abstract

Annual bluegrass (Poa annua L.) (ABG) is considered by many turfgrass managers to be an intractable weed problem, particularly in creeping bentgrass (Agrostis stolonifera L.) (CBG) fairways. Bispyribac-sodium (BPS) is labeled for the control of ABG, but it can elicit objectionable levels of chlorosis in CBG. Little information exists regarding the longevity of chlorosis, other potential phytotoxic effects or the ability of BPS to control ABG in CBG. The primary objectives of this field study were to determine if the chlorosis elicited by BPS could be masked by tank-mixing the herbicide with a chelated iron plus nitrogen product and to determine an effective BPS rate for controlling ABG. Bispyribac-sodium was applied to mature fairway height CBG three times at 49 and 111 g ai/ha and two or three times at 74 g ai/ha on a two-week interval. Chlorosis appeared within one week and generally persisted for 14 to 21 days, but there was no BPS rate effect on the level or longevity of the CBG chlorosis. Tank-mixing BPS with Fe + N effectively masked the chlorosis, regardless of herbicide rate. All BPS rates and timing provided similar levels (≥ 82%) of ABG control.

Introduction

Annual bluegrass (ABG) is a problematic weed for golf course managers in many regions of the US. Creeping bentgrass (CBG) is a desirable species for golf course fairways in many regions; however, ABG can be an aggressive competitor and can rapidly dominate the stand. Annual bluegrass is considered undesirable by many golf course managers since it generally is less tolerant of winter and summer stresses and is more susceptible to chronic disease and insect problems, when compared to CBG.

Attempts to remove ABG selectively with herbicides from CBG have been fraught with problems, including severe discoloration, thinning, and sometimes death of the CBG (2). In 2004, bispyribac-sodium (2,6-bis[(4,6-dimethoxy-2- pyrimidinly)oxy] benzoic acid) (BPS) was labeled for use on CBG fairway turf. Researchers have reported effective ABG control with multiple applications of BPS; however, the herbicide can elicit an objectionable chlorosis or "yellow flash" in CBG, (1,4,5). Quinclorac (3,7-dichloro-8-quinolinecarboxylic acid), which generally is applied in summer to control crabgrass (Digitaria spp.), also elicits chlorosis in CBG. The yellowing caused by quinclorac can be partially masked by tank-mixing the herbicide with chelated iron and nitrogen (3).

Little information exists in the Mid-Atlantic and northeast regions of the US on the discoloration and other potential negative effects of BPS on fairway height CBG quality or its ability to control ABG. Therefore, information regarding effective BPS rates for ABG control and ways to minimize the yellowing induced by the herbicide are warranted. The objectives of these field studies were to: (i) determine the ability of an Fe + N product to mask the chlorosis elicited by BPS in CBG; (ii) determine if Fe + N would impact the level of ABG control provided by BPS; and (iii) determine an effective use rate for ABG control with BPS.

Study and Site Descriptions

Field studies were conducted in 2004 and 2005 in Maryland and in 2005 in Connecticut. Turf at all sites was irrigated as needed to prevent drought stress and mowed three times per week to a height of 1.3 cm. Plots measured 1.5 × 1.5 m and were arranged in a randomized complete block with three (2004) or four (2005) replications. Chemical treatments were applied with a CO₂ pressurized (262 kPa) backpack sprayer in 467 liters of water per ha. Treatments were applied on roughly two-week intervals on the dates footnoted in the data tables. All sites were treated in April with dithiopyr [(S,S-dimethyl 2-difluoromethyl)-4-(2 methylpropyl)-6-(trifluromethyl)-3,5-pyridinedicarbothioate] to preemergently control summer grassy weeds.

Maryland Sites

2004. Forty-five, 15-cm diameter and 10- to 12-cm deep plugs of ABG were removed from a fairway at a local golf course on 8 June 2004. Three plugs were planted immediately into each plot of mature ‘Southshore’ CBG at the University of Maryland Turfgrass Research Facility in College Park. Soil at both Maryland sites was a Keyport silt loam with a pH of 5.7 to 5.9 and 2.1 to 2.3% organic matter. The area was irrigated frequently to prevent wilt stress in the ABG and plants appeared healthy and had a canopy height equal to the CBG before treatments were initiated. Prior to applying BPS treatments, the site received N at 25 kg/ha from urea on 25 June 2004. Bispyribac-sodium was applied on 28 June, 10 and 23 July 2004 at either 49 or 111 g ai/ha (Table 1). The aforementioned BPS treatments were applied alone or in combination with a chelated Fe + N product (Lesco’s 12-0-0 Chelated Iron Plus Micronutrients, Lesco Inc., Cleveland, OH). The liquid Fe + N product was tank-mixed with BPS to provide  FeSO₄ at 1.1 kg/ha + N at 2.2 kg/ha + S at 0.7 kg/ha + Mn at 0.4 kg/ha. The nontreated controls in both of the Maryland sites consisted of a plot with three ABG plugs that were left untreated with BPS.

Table 1. ‘Southshore’ creeping bentgrass color and Poa annua control as influenced by bispyribac-sodium (BPS) applied alone or tank-mixed with Fe + N in College Park, MD, 2004.

 ^v Treatments were applied 28 June, 10 and 23 July 2004.

 ^w Color was rated visually on a 0 to 10 scale with 0 = brown turf, 7.5 = minimal acceptable yellowing for fairway turf, and 10 = optimal greenness.

 ^x Poa annua plants were counted within each of three 177-cm² plugs and an average was obtained.

 ^y Means in a column followed by the same letter are not significantly different (P ≤ 0.05) according to Tukey’s protected least significant difference test.

 ^z Significance levels are as follows: * = P < 0.05, ** = P < 0.01, and *** = P < 0.001.

2005. Eighty-four plugs of ABG were obtained on 21 March 2005 from fairways of the same golf course sampled in 2004. Annual bluegrass plugs of the same size and number per plot used in 2004 were planted immediately in a mature stand of ‘Southshore’ CBG as previously described. Bispyribac-sodium was applied alone or tank-mixed with Fe + N three times at either 49 or 74 g ai/ha or twice at 74 g ai/ha. These treatments were applied 8 and 21 June, and 6 July 2005 (Table 2). The site received N at 50 and 25 kg/ha from urea on 22 March and 17 May 2005, respectively.

Table 2. ‘Southshore’ creeping bentgrass color and Poa annua control as influenced by bispyribac-sodium (BPS) applied alone or tank-mixed with Fe + N in College Park, MD, 2005.

 ^u Color was rated visually on a 0 to 10 scale with 0 = brown turf, 7.5 = minimal acceptable yellowing for fairway turf, and 10 = optimal greenness.

 ^v Poa annua plants were counted within each of three 177-cm² plugs and an average was obtained.

 ^w Treatments were applied 8 and 21 June, and 6 July 2005.

 ^x Means in a column followed by the same letter are not significantly different (P ≤ 0.05) according to Tukey’s protected least significant difference test.

 ^y Treatments were applied 8 and 21 June 2005.

 ^z Significance levels are as follows: ** = P < 0.01, and *** = P < 0.001.

Connecticut Sites

Field studies were conducted in ‘Southshore’ CBG at the University of Connecticut Plant Science Research and Education Facility located in Storrs and ‘Penncross’ CBG at The Country Club of Farmington located in Farmington. Soil at Storrs was a Woodbridge fine sandy loam with a pH of 6.4 and 2.7% organic matter. The Storrs site received N at 125 kg/ha from urea in the spring prior to BPS application. Soil at Farmington was a Rippowan fine sandy loam with a pH of 5.3 and 3.4% organic matter. This study site received N at 73 kg/ha from urea in spring prior to the application of the BPS. The BPS treatments applied to both Connecticut locations were identical to those used in Maryland in 2005. The BPS treatments at the Storrs site were applied applied 13 and 27 June, and 9 July 2005 (Table 3). Treatments at the Farmington site were applied applied 24 June, 19 July, and 8 August 2005 (Table 4).

Table 3. ‘Southshore’ creeping bentgrass color as influenced by bispyribac-sodium (BPS) applied alone or tank-mixed with Fe + N in Storrs, CT, 2005.

 ^v Color was rated visually on a 0 to 10 scale with 0 = brown turf, 7.5 = minimal acceptable yellowing for fairway turf, and 10 = optimal greenness.

 ^w Treatments were applied 13 and 27 June, and 9 July 2005.

 ^x Means in a column followed by the same letter are not significantly different (P ≤ 0.05) according to Tukey’s protected least significant difference test.

 ^y Treatments were applied 13 and 27 June 2005.

 ^z Significance levels are as follows: NS = not significant and *** = P < 0.001.

Ratings and Statistics

Ratings were obtained weekly following the first BPS application until three weeks after the last application. Bentgrass color was rated visually on a 0 to 10 scale with 0 = entire plot area brown or dead, 7.5 = minimal acceptable yellowing for a CBG fairway, and 10 = optimal greenness. The number of living ABG plants per 177-cm² plug were counted at the end of each study in Maryland. The mean number of living ABG plants in all three plugs per plot was used in the statistical analysis. Data were analyzed using SAS MIXED procedure (SAS Institute, Version 9.1, Cary, NC.) and means were separated (P ≤ 0.05) using Tukey’s least significant difference test.

Maryland Results

Treatments were applied 28 June and 10 and 23 July in 2004. On 2, 7 and 10 July, all BPS treatments decreased CBG color (i.e., increased yellowing) regardless of being applied alone or with Fe + N (Table 1; all data not shown). Plots treated with BPS alone at both rates exhibited a reduction in green foliar color, when compared to untreated CBG on 12 July. Plots receiving BPS + Fe + N, however, had color ratings equivalent to untreated CBG at this time. On 16 July, plots treated with BPS alone had lower color ratings when compared to plots treated with BPS + Fe + N and the untreated control. The untreated control plots, however, had higher color ratings than plots treated with BPS + Fe+ N at that time. On 21 July, CBG treated with BPS + Fe + N had color ratings equal to the untreated control, while CBG treated with BPS alone at 111 g ai/ha had the lowest color rating. On 28 July, five days following the final application, all BPS-treated plots had color ratings inferior to the untreated control. Plots treated with BPS + Fe + N (both rates), however, had better green color, when compared to plots receiving BPS applied at 111 g ai/ha without Fe + N. By 4 August, there were no color differences among BPS-treated plots, which had lower color ratings than the untreated control. While Fe + N improved foliar green color, differences were small and turf color was in the acceptable range on all rating dates, regardless of BPS rate.

On 4 August, the number of living ABG plants in each plug was counted. Both rates of BPS applied with or without Fe + N had greatly reduced ABG populations (Table 1). Statistically, there was no rate effect and Fe + N did not influence the level of control. However, numerically higher numbers of ABG plants survived the treatment in which 49 g ai/ha was tank-mixed with Fe + N. An average of 19, 39 and 112 ABG plants per plug for each of the three replicates was observed in the aforementioned treatment. Although unclear, the generally higher number of surviving plants in most treated plugs suggested that the Fe + N may have reduced the effectiveness of BPS at the lowest rate assessed (i.e., 49 g ai/ha).

Rates and timings were adjusted in 2005. BPS was applied at either 49 or 74 g ai/ha three times or twice at 74 g ai/ha. Treatments were applied 8 and 21 June and again on 6 July for plots receiving three applications. Five days after the initial treatment (13 June), all plots treated with BPS without Fe + N and the 74 g ai/ha rate with Fe + N had lower CBG color ratings, when compared to the untreated plots (Table 2). On 16 June, CBG treated with 74 g ai/ha of BPS-alone had a color rating below most other treatments, as well as the untreated control. Twelve days after the initial application (20 June), the yellowing had dissipated (data not shown). On 1 July, ten days after the second application of treatments, all BPS-treated plots had a lower green color rating versus untreated CBG. Regardless of timing or rate, plots treated with BPS + Fe + N exhibited improved color versus plots treated with BPS alone. The third and final application of selected treatments occurred on 6 July. On 13 July, plots treated with BPS twice at 74 g ai/ha and three times at 49 g ai/ha had lower color ratings than untreated CBG. Color ratings of BPS-treated turf improved by 18 July. Only plots treated three times at 49 g ai/ha BPS had color ratings lower than the untreated control. On the final rating date (5 August), no color differences were observed among treatments (data not shown). There again was no rate effect on the level or intensity of chlorosis in BPS-treated CBG. Although no treatment was below the minimum acceptable level, the statistical separations show that color can be enhanced or improved when BPS is mixed with Fe + N.

On 12 August, the number of ABG plants in each plug was counted. Because of severe heat stress during July and August 2005, the number of ABG plants per plug had declined since spring. Data again showed that there was no rate effect since all BPS-treatments provided an equivalent level of ABG control (Table 2). Data indicated that tank-mixing BPS with Fe + N did not antagonize or improve the level of ABG control provided by the herbicide.

Connecticut

Storrs. One week after treatments were initiated, BPS applied alone (all rates) resulted in unacceptable CBG yellowing (6.6 to 6.9) (Table 3). Discoloration from the aforementioned treatments generally remained unacceptable for 2 to 3 weeks following the last application, regardless of BPS rate or number of applications. On 7 out of 8 rating dates, BPS (both rates and application timings) tank mixed with Fe + N resulted in equivalent and improved CBG color, when compared to the untreated control. On 25 July, all BPS + Fe + N-treated plots generally exhibited better green color than even untreated CBG. By 18 August (40 days following the last application), all BPS-treated plots had equivalent color ratings. On all rating dates, CBG treated with BPS + Fe + N had color ratings ≥ 8.0.

Farmington. Levels of CBG discoloration or yellowing similar to that at Storrs were observed. Treatments began on 24 June and one week later CBG color within plots treated with BPS-alone had declined. Plots receiving the high rate of BPS-alone exhibited poor color (6.0 to 6.3), while plots receiving the low rate (49 g ai/ha) were marginally acceptable (7.4) (Table 4). When tank-mixed with Fe + N, however, all BPS-treated plots had equal color levels, which were equivalent to untreated CBG on 1 July. All BPS-treated plots exhibited color ratings equivalent to the control by 19 July (25 days after treatment). On 26 July (1 week after second application), all treatments not containing Fe + N again exhibited unacceptable color. There were no color differences among rates of BPS applied alone. Plots treated with BPS + Fe + N had color levels equivalent to untreated CBG on 26 July. On 8 August, plots receiving BPS at 49 g ai/ha and tank-mixed with Fe + N exhibited the highest color rating. There were, however, few color differences among all other treatments and all plots had acceptable color at this time. Plots receiving three applications were re-treated on 8 August and by 18 August only plots receiving the third applications of BPS-alone had unacceptable color. Regardless of BPS rate, the addition of Fe + N generally resulted in improved CBG color (≥ 8.0) on all rating dates, when compared to the untreated control.

Table 4. ‘Penncross’ creeping bentgrass color as influenced by bispyribac-sodium (BPS) applied alone or tank-mixed with Fe + N in Farmington, CT, 2005.

 ^v Color was rated visually on a 0 to 10 scale with 0 = brown turf, 7.5 = minimal acceptable yellowing for fairway turf, and 10 = optimal greenness.

 ^w Treatments were applied 24 June, 19 July, and 8 August 2005.

 ^x Means in a column followed by the same letter are not significantly different (P ≤ 0.05) according to Tukey’s protected least significant difference test.

 ^y Treatments were applied 24 June and 19 July 2005.

 ^z Significance levels are as follows: NS = not significant, * = P < 0.05, and *** = P < 0.001.

Conclusion

These field studies showed that the chlorosis induced by multiple BPS applications ranging from 49 to 111 g ai/ha to fairway height CBG was effectively masked by tank-mixing the herbicide with Fe + N. The chlorosis appeared within one week of treatment and generally persisted about 14 to 21 days following the final BPS application. No thinning, major tip burn, or other injury was observed in any year or site. The level of chlorosis observed within each site was similar, regardless of BPS rate. Correspondingly, the level of color improvement provided by the Fe + N generally was similar, regardless of BPS rate. In Maryland, all rates and timings resulted in a similar level of ABG control, regardless of using Fe + N. According to field notes, however, the addition of Fe + N appeared to delay the activity of the low rate of BPS (49 g  ai/ha) for about one week, and may have caused some reduction in ABG control in 2004. On a plant count basis, ≥ 82% ABG control was achieved with all treatments. Branham and Calhoun (1) found that three or four BPS applications at 74 g ai/ha on a 14-day interval were required to provide > 90% ABG control in Illinois. They stated that the number of BPS applications may be more important than rate. Results from this study generally support Branham and Calhoun (1), since no significant BPS rate effects were observed.

Literature Cited

1. Branham, B., and Calhoun, R. 2005. Velocity: Poa annua control at last? Golf Course Man. 10:73-77.

2. Dernoeden, P. H. 2000. Creeping Bentgrass Management: Summer Stress, Weeds, and Selected Maladies. John Wiley & Sons, Inc., Hoboken, NJ.

3. Dernoeden, P. H., Bigelow, C. A., Kaminski, J. E., and Krouse, J. M. 2003. Smooth crabgrass control in perennial ryegrass and creeping bentgrass tolerance to quinclorac. HortScience 38:607-612.

4. Lycan, D. W., Hart, S. E., and Falsey, J. 2003. Potential use of V-10029 for weed control in cool-season turfgrass. Proc. N.E. Weed Sci. Soc. 57:96.

5. McCullough, P. E., and Hart S. E. 2006. Nitrogen and trinexapac-ethyl influence bispyribac-sodium efficacy. Proc. N.E. Weed Sci. Soc.60:89.