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© 2005 Plant Management Network. Plant Growth Regulator Regimens Reduce Poa annua Populations in Creeping Bentgrass Patrick E. McCullough, Stephen E. Hart, and Darren W. Lycan, Department of Plant Biology and Pathology, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901-8520 Corresponding author: Patrick E. McCullough. mccullough@aesop.rutgers.edu McCullough, P. E., Hart, S. E., and Lycan, D. W. 2005. Plant growth regulator regimens reduce Poa annua populations in creeping bentgrass. Online. Applied Turfgrass Science doi:10.1094/ATS-2005-0304-01-RS. Abstract Plant growth regulators (PGRs) are commonly applied for annual bluegrass (Poa annua L.) suppression but various PGR regimens may be more applicable in creeping bentgrass (Agrostis palustris Huds.) management than exclusive applications. Two field experiments in Riverton, NJ investigated various regimens of paclobutrazol ((+/-)–(R*,R*)-b-[(4-chlorophenyl) methyl]-a-(1, 1-dimethyl)-1H-1,2,4,-triazole-1-ethanol) (PB) and trinexapac-ethyl ([4-(cyclopropyl-[a]-hydroxymethylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester]) (TE) for Poa annua control in creeping bentgrass golf course fairways. Over four years, Poa annua coverage was greater in the spring compared to summer and fall. In the first experiment, Poa annua reductions from initial populations were 22 and 30% in untreated turf and turf treated only with TE, respectively. Reductions in Poa annua were ≈ 55% for turf receiving PB with and without TE applications. In the second experiment, PB reduced Poa annua populations to approximately half those of the untreated plots but combinations with TE did not enhance turf quality or Poa annua suppression. Routinely applying PB at 0.14 kg/ha every 3 weeks provided similar Poa annua control to single applications of 0.56 kg/ha while both regimens gave better control than PB at 0.28 kg/ha applied in the spring and fall. Overall, PB will be an effective tool for suppressing Poa annua in creeping bentgrass fairways for northeastern golf courses; however, tank mixing TE with PB will likely not enhance these effects. Introduction Poa annua L. is the most troublesome winter annual weed in creeping bentgrass (1). Compared to creeping bentgrass, Poa annua has a lighter green color, greater heat sensitivity, and produces unsightly seedheads which disrupt surface uniformity and reduce bentgrass quality (3). Since selective herbicides provide erratic Poa annua control (9), plant growth regulators (PGRs) are commonly applied to suppress its growth and seedhead formation (10). PGRs that inhibit cell division and gibberellic acid (GA) synthesis are commonly applied to creeping bentgrass for Poa annua suppression (10,13). Gibberellic acid inhibitors are more frequently used than cell division inhibitors because of less likelihood for leaf burn and turfgrass injury (10). Paclobutrazol and TE are widely used GA inhibitors with differing mechanisms of action. PB acts as an early GA biosynthesis inhibitor by preventing the enzyme ent-kaurene oxidase from oxidation of ent-kaurene, ent-kaurenol, and ent-kaurenal to form GA12-aldehyde (11). Heterocyclic nitrogen atoms of PB bind to protoheme iron atoms in cytochrome P-450 systems resulting in the inhibition of gibberellins as well as P450 enzymes involved in brassinosteroid synthesis (5). Woosely et al. (14) found multiple PB applications at 0.14 and 0.28 kg/ha reduced Poa annua populations by 85% or more in creeping bentgrass fairways and significantly enhanced turfgrass quality. Johnson and Murphy (8) found PB at 0.3 kg/ha suppressed Poa annua more effectively in creeping bentgrass putting greens than another early GA inhibitor, flurprimidol. Bell et al. (2) found similar Poa annua suppression applying PB at biweekly intervals to creeping bentgrass putting greens. Trinexapac-ethyl is a widely used PGR for reducing creeping bentgrass mowing requirements that is foliarly absorbed and blocks the 3b-hydroxylase conversion of GA20 to GA1 late in GA biosynthesis (11). For creeping bentgrass, TE enhances turf quality under stressful conditions, does not affect root growth, and may suppress dollar spot (Sclerotinia homoeocarpa F. T. Bennett) (4,6,7). However, TE is not as effective in suppressing Poa annua populations or seedhead production as paclobutrazol (10). Field experiments were conducted over four years with TE integrated into PB programs for Poa annua control in creeping bentgrass. The objectives of the experiment were to determine if TE could enhance Poa annua control or enhance turfgrass quality when routinely applied in regimens with PB. Testing PB and TE Regimens for Poa annua Control in Creeping Bentgrass Two experiments were conducted at Riverton Country Club Golf Course, Riverton, NJ from April 2001 to August 2002 (Experiment 1) and April 2003 to August 2004 (Experiment 2). Experiment 1 investigated effects of two spring and fall PB applications with and without TE applied throughout the summer. Experiment 2 had similar regimens to Experiment 1 but included additional treatments such as applying PB at low rates throughout the spring, summer, and fall. Both experiments included untreated plots. Creeping bentgrass was a blend of ‘Penncross’ and ‘L-93’ maintained at a 1-cm mowing height. Soil medium was a Sassafras loamy sand with a pH of 6.5. Turf was irrigated sufficiently to prevent plant wilt and received N at ≈ 250 lbs/ha/year. Primary, secondary, and micronutrients were applied as needed to prevent deficiencies. Initial Poa annua populations were 50% (SE = 2.2) and 45% (SE = 1.5) in Experiments 1 and 2, respectively. PGR regimens, consisting of PB (Trimmit 2SC, Syngenta Corp., Greensboro, NC) and TE (Primo Maxx 1EC, Syngenta Corp., Greensboro, NC) are presented with the results in Tables 1 and 2. The experimental design was a randomized complete block with four replications of 1-×-3-m plots in both experiments. Plots used for Experiment 2 were adjacent to plots in Experiment 1. PGR applications were made by making two passes per plot in opposite directions with a single-nozzle CO2 pressured sprayer delivering a total 375 liter/ha. Nozzles used were 9504E and CO2 regulators were set for 220 kPa. Turf in Experiment 1 received PGR regimens from 26 April to 4 December 2001 and 16 April to 27 August 2002. In Experiment 2, applications were made 15 April to 17 November, 2003 and 20 April to 10 September, 2004. Table 1. Pooledv turf quality and Poa annua populations from four plant growth regulator regimens in field experiments, 2001-2002, Riverton, NJ.
v Results were pooled over 16 observation dates from April 2001 to August 2002. w Initial spring applications were April 24, 2001 and April 16, 2002.
Initial fall applications were September 27, 2001. WAIT = weeks after initial
treatments.
x Bentgrass quality was visually rated on a 1 to 9 scale where 1 = completely dead turf and 9 = uniform, ideal turf. Ratings below 7 were considered unacceptable. y Reductions from initial Poa annua populations. z Different letters indicate a significant difference at the 0.05 probability level by column. Table 2. Pooledv creeping bentgrass quality and Poa annua populations from plant growth regulator regimens, 2003-2004, Riverton, NJ.
v Results were pooled over 15 observation dates from April 2003 to August 2004. w Initial spring applications were April 15, 2003 and April 20, 2004.
Initial fall applications were September 15, 2003. WAIT = week after initial
treatment.
x Bentgrass quality was visually rated on a 1 to 9 scale where 1 = completely dead turf and 9 = uniform, ideal turf. Ratings below 7 were considered unacceptable. y Reductions from initial Poa annua populations. z Different letters indicate a significant difference at the 0.05 probability level by column. Turf quality was rated visually on 1 to 9 scale where 1 = dead turf and 9 =
dark green, uniform turf. Ratings below 7 were considered unacceptable. Poa
annua populations were visually assessed on a percent scale basis (0 to
100%). All ratings were made triweekly. Poa annua reductions were
calculated by the following formula: Data were subjected to analysis of variance with SAS General Linear Model procedure (12). Mean separations were based on Fischer’s Protected LSD test at the 0.05 probability level. Since additional treatments were added in Experiment 2, data were analyzed and presented separately by experiment. Effects on Poa annua of Adding TE to PB Treatments Season (data collected in spring, summer, or fall) by experiment interactions occurred for Poa annua populations in untreated turf; therefore, seasonal differences are presented by experiment. Spring Poa annua coverage in untreated turf was 48 and 40% in Experiment 1 and 2, respectively, then decreased in the summer and fall to ≈ 30 to 40% in both experiments (Table 3). Turf quality of untreated turf increased 7% from spring to fall in Experiment 1. In Experiment 2, turf quality was similar in the spring and fall but increased 6% in summer. Table 3. Pooled seasonal quality and Poa annua populations of untreated creeping bentgrass from 2001 to 2002 (Experiment 1) and 2003 to 2004 (Experiment 2) at Riverton, NJ.
x Reductions from initial Poa annua populations. y Different letters indicate a significant difference at the 0.05 probability level by column and experiment. Date by treatment interactions did not occur for turf quality or Poa annua populations, therefore, results were pooled and presented as overall treatment means. In Experiment 1, visual quality for turf treated with PGRs differed no more than 5% from untreated turf and was always acceptable (Table 1). Turf receiving TE exclusively averaged 4% higher visual quality than untreated turf and other PGR regimens. Turf receiving PB regimens, with or without TE (Treatments 2, 3, and 4), averaged 3% reduced turf quality from the untreated. Poa annua coverage in untreated turf was 41% while turf receiving PGRs had 25 to 31% coverage (Table 1). Poa annua reductions were 22% in untreated turf but increased to 30% from exclusive TE applications (Treatment 1). Reductions in Poa annua were ≈ 55% for turf receiving PB with and without TE applications (Treatments 2, 3, and 4). In Experiment 2, visual quality of PGR treated turf was similar to the untreated and was always acceptable (Table 2). Turf treated only with TE every 3 weeks had 35% Poa annua coverage and was similar to the untreated. Poa annua coverage was 22 to 28% in turf receiving PB (Treatments 2 to 6). Reductions from initial Poa annua populations were 25% for untreated turf. Applications of PB reduced Poa annua 45 to 54% with and without TE (Treatments 2 to 6). Low rates of PB, 0.14 kg/ha, applied triweekly (Treatment 6) reduced Poa annua populations similarly to higher PB rates applied twice in the spring or fall. Applying PB at 0.28 kg/ha twice in the spring and fall (Treatment 5) was not as effective in suppressing Poa annua as higher PB rates. Turf treated exclusively with TE had similar Poa annua reductions to the untreated. Discussion and Recommendations Greater Poa annua coverage warrants emphasis on PGR use in the spring for northeastern creeping bentgrass managers. Regimens that included PB suppressed Poa annua populations similarly to previous experiments in creeping bentgrass fairways and putting greens (2,8,14). The addition of TE to PB regimens did not enhance Poa annua suppression. Furthermore, incorporating TE with PB had no significant effects on turf quality despite quality enhancements observed when TE was applied alone. Frequent applications of low PB rates, 0.14 kg/ha every3 weeks, suppressed Poa annua populations similarly to repeated applications of 0.56 kg/ha at six week intervals in creeping bentgrass fairways. Similar results were observed by Bell et al. (2) with biweekly PB applications of 0.11 kg/ha on creeping bentgrass putting greens. Routinely applying PB at 0.14 kg/ha provided similar Poa annua control to higher rates applied twice in the spring and fall. Although differences in turf quality were not detected, routinely applying low PB rates may provide alternative options for Poa annua control if turf quality reductions from higher PB rates are a concern. Reducing PB application rates to 0.28 kg/ha in the spring and fall suppressed Poa annua populations but not as effectively as 0.42 and 0.56 kg/ha. Overall, PB will be an effective tool for suppressing Poa annua in creeping bentgrass fairways for northeastern golf courses; however, integrating TE into PB regimens will likely not enhance these effects. Literature Cited 1. Beard, J. B. 1973. Turfgrass: Science and Culture. Prentice-Hall, Inc. Englewood Cliffs, NJ. 2. Bell, G., Stiegler, C., and Koh, K. 2004. Poa control: Perhaps there’s hope. Golf Course Manage. 72(3):123-126. 3. Engel, R. E., and Ilnicki, R. D. 1969. Turf weeds and their control. Pages 240-282 in: Turfgrass. Agron. Monog. No. 14. A. A. Hanson and F. V. Juska, eds. Am. Soc. Agron., Madison, WI. 4. Fagerness, M. J., and Yelverton, F. H. 2001. Plant growth regulator and mowing height effects on seasonal root growth of ‘Penncross’ creeping bentgrass. Crop Sci. 41:1901-1905. 5. Fletcher, R. A., Gilley, A., Davis, T. D., and Sanklha, N. 2000. Triazoles as plant growth regulators and stress protectants. Hort. Rev. 24:55-138. 6. Golembiewski, R. C., and Dannerberger, T. K. 1998. Dollar spot severity as influenced by trinexapac-ethyl, creeping bentgrass cultivar, and nitrogen fertility. Agron. J. 90:466-470. 7. Goss, R. M., Baird, J. H., Kelm, S. L., and Calhoun, R. M. 2002. Trinexapac-ethyl and nitrogen effects on creeping bentgrass grown under reduced light conditions. Crop Sci. 42:472-479. 8. Johnson, B. J., and Murphy, T. R. 1995. Effect of paclobutrazol and flurprimidol on suppression of Poa annua spp. reptans in creping bentgrass (Agrostis stolonifera) greens. Weed Technol. 9:182-186. 9. McCarty, B., Murphy, T., Whitwell, T., and Yelverton, F. 2005. Turfgrass Weeds. Pages 663-703 in: Best Golf Course Management Practices, 2nd ed. L. B. McCarty, ed. Prentice-Hall, Upper Saddle River, NJ. 10. Murphy, T. R., McCarty, B., and Yelverton, F. H. 2005. Turfgrass plant growth regulators. Pages 705-714 in: Best Golf Course Management Practices, 2nd ed. L. B. McCarty, ed. Prentice-Hall, Upper Saddle River, NJ. 11. Rademacher, W. 2000. Growth retardants: effects on gibberellin biosynthesis and other metabolic pathways. Ann. Rev. Plant Phys. Plant Molec. Biol. 51:501-531. 12. SAS Institute. 1999. The SAS system for Windows. v. 8.2. SAS Inst., Cary, NC. 13. Watschke, T. L., Prinster, M. G., and Brenninger, J. M. 1992. Plant growth regulators and turfgrass management. Pages 557-588 in: Turfgrass Agron. Monog. No. 32. D. V. Waddington, R. N. Carrow, and R. C. Shearman, eds. Am. Soc. Agron., Madison, WI. 14. Woosely, P. B., Williams, D. W., and Powell, A. J. 2004. Postemergence control of annual bluegrass (Poa annua spp. reptans) in creeping bentgrass (Agrostis stolonifera) turf. Weed Technol. 17:770-776. |
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