|
|
|
© 2003 Plant Management Network. Foliar Applications of Magnesium and Iron Encourage Annual Bluegrass in Shaded Creeping Bentgrass Putting Greens James C. Stiegler, Payne County Extension Office, Stillwater, OK, 74074; Gregory E. Bell and Dennis L. Martin, Department of Horticulture and Landscape Architecture, Oklahoma State University, Stillwater 74078 Corresponding author: Gregory E. Bell. bgregor@okstate.edu Stiegler, J. C., Bell G. E., and Martin D. L. 2003. Foliar applications of magnesium and iron encourage annual bluegrass in shaded creeping bentgrass putting greens. Online. Crop Management doi:10.1094/CM-2003-0821-01-RS. Abstract Annual bluegrass (Poa annua L.) is the most common weed in creeping bentgrass (Agrostis stolonifera L.) putting greens and is especially competitive in shade. The objectives of this study were to determine if foliar magnesium plus foliar iron applications, alone and in combination with activity enhancers, were effective for suppressing indigenous annual bluegrass in shaded and full-sun creeping bentgrass putting greens. Multi-year field studies were conducted in three locations. A linear contrast between plots receiving Mg/Fe and plots not receiving Mg/Fe indicated that Mg/Fe applications caused an increase in annual bluegrass proportion in a mixed sward of creeping bentgrass and annual bluegrass in shade but had no significant effect in full sun. The research suggested that using Mg/Fe to enhance chlorophyll synthesis in shade favored the most phytosynthetically efficient species, annual bluegrass, in a mixed stand of turf. According to these results, Mg/Fe applications in shade are advisable for turf managers who wish to improve annual bluegrass persistence but not for those who would like to reduce annual bluegrass populations. Applications of Mg/Fe had no effect on annual bluegrass populations in full sun. Introduction Annual bluegrass is the most important weed in creeping bentgrass golf greens in most of the United States and many other countries. Although it is a desirable species in some locations, it is generally considered a very opportunistic and invasive weed. Possible control methods include: pre-emergence herbicides (4), plant growth regulators (9), selective herbicides (3), varying irrigation regimes (6), various nutritional inputs (5), and phytopathogenic bacteria (8). Despite these and other projects spanning over 60 years of scientific research, annual bluegrass remains a tenacious weed in cool-season turf. The life cycle of annual bluegrass is highly variable (10). In cooler climates, it often survives as a perennial, while in warmer regions it usually persists as an annual. Historically, the perennial forms of the species have proven the most difficult to control (2,9). Annual bluegrass effectively competes for resources with desirable species (1) and poses several other management problems. Poor heat tolerance, overall poor cold tolerance, poor drought tolerance, and susceptibility to death from ice encasement combine to make annual bluegrass undesirable and difficult to manage effectively. It is susceptible to fungal attack under low or high nutrient levels and is slow to recover from damage. Therefore, a mixed sward of annual bluegrass and creeping bentgrass requires more precise management practices and more inputs (nutrients, water, and pesticides) than a pure stand of creeping bentgrass. Variations in photosynthetic efficiency and pigment levels between the two species were suggested as a possible means of discouraging the spread of annual bluegrass in creeping bentgrass (2). In that study, researchers were able to significantly reduce young (<2 years growth) annual bluegrass populations in a creeping bentgrass fairway by 64% using foliar magnesium + foliar iron applications. Traditional methods of control, plant growth regulator (trinexapac-ethyl) and selective herbicide (ethofumesate), had no significant effects. Although increases in chlorophyll content may occur in both species within a mixed sward treated with magnesium/iron, the treatment should be increasingly detrimental to the more photosynthetically efficient annual bluegrass in comparison to creeping bentgrass (2). Bell et al. (2) suggested that applications of magnesium/iron created a competitive advantage for creeping bentgrass, which over time resulted in reductions of annual bluegrass populations in newly-seeded turf. Xu and Mancino (13) found that applications of iron and magnesium encouraged growth of creeping bentgrass, but did not affect annual bluegrass. During a second year’s study, however, Bell et al. (2) determined that iron and magnesium did not affect the annual bluegrass cover in a mature creeping bentgrass fairway and green. Magnesium/iron applications may have promise for effective, inexpensive, and environmentally sound reduction of annual bluegrass cover in creeping bentgrass turf. However, because of conflicting results, continued research with foliar magnesium/iron applications is necessary to determine if the technique is truly effective. The objectives of this study were to determine if foliar magnesium plus foliar iron applications, alone and in combination with activity enhancers, were effective for suppressing indigenous annual bluegrass in shaded and full-sun creeping bentgrass putting greens. Multi-year Field Studies in Three locations Shade study. A research site was selected at the Oklahoma State University Turfgrass Research Center, Stillwater, OK to test the effects of Mg/Fe applications in a shaded environment. It was seeded to ‘Penncross’ creeping bentgrass in 1992 on a sand base amended with composted rice hulls (90:10 v/v) and maintained as a putting green. The soil texture was 95% sand, 2.5% silt, and 2.5% clay. The soil magnesium content at the site was 160 lbs/acre (180 kg/ha) and the iron content was 42 lbs/acre (47 kg/ha) at a pH of 7.0. The site also contained high levels of other important nutrients except for a low level of K. Phosphorous was present at 102 lbs/acre (115 kg/ha), K at 88 lbs/acre (99 kg/ha), and SO42- at 17 lbs/acre (19 kg/ha). Mowing was performed six days per week at 0.125 inches (3 mm). Nitrogen fertilizer was applied at 142 lbs/acre (159 kg/ha) per year. Potassium and other nutrients were applied based on annual soil tests. The site was shaded throughout the morning until 1 h after solar noon and historically supported annual bluegrass invasion from fall until mid-summer. When the first applications were applied on September 1, 1998, the site was completely free of annual bluegrass suggesting that only annual biotypes were present. The research site was divided into 3-×-5-ft (0.9-×-1.5-m) plots arranged
in a randomized design with three replications. Each plot received one of 8
spray applications: (i) foliar magnesium + foliar iron (Mg/Fe); (ii) trinexapac-ethyl
[4-(cyclopropyl- Species composition was rated in November 1998, November 1999, and November 2000. Evaluations of species proportions were performed visually using a template that divided each plot into eight equal 0.98-×-0.98-ft (30-×-30-cm) sections. Species proportion was determined for each section and a mean calculated for each plot in a manner introduced by Bell, et al. (2). Turf clippings were collected monthly for chlorophyll analysis from September through November 1998 and from March through August 1999, 15 days after treatments were applied. Chlorophyll was extracted in N,N dimethylformamide (11) and concentrations determined using high performance liquid chromatography (7). Golf course studies. Five spray applications were chosen, based on potential performance, for application to established golf course greens at two Oklahoma golf courses beginning in fall 1999. Plots were established at LaFortune Park Golf Course, Tulsa, OK and Coffee Creek Golf Course in Edmond, OK. Measurements were made for annual bluegrass cover at these sites in April 1999, April 2000, February 2001, and February 2002. Annual bluegrass measurements were also made in September 1999 and August 2000 to estimate the proportion of annual and perennial-acting biotypes of annual bluegrass present. The first nutrient applications were applied on October 1, 1999 following the same monthly schedule used at the shaded Turfgrass Research Center site through October 2000. The application schedule was altered in 2001. Results of the shaded Turfgrass Research Center trials suggested that Mg/Fe applications encouraged annual bluegrass competition with creeping bentgrass in relatively cool, low-light conditions. For that reason, Mg/Fe applications were only applied during the warm, high-light intensity months of May, June, July, and August at the GC sites in 2001. Annual bluegrass cover was determined using the same procedure that was used at the shaded Turfgrass Research Center site. Turf color and density were not measured on the golf course studies. Full-sun study. In 2000, a fourth, independent study site was selected at the Turfgrass Research Center to investigate Mg/Fe applications in full sun. The area was located on the same research putting green as the shaded study but was in full sun for approximately 90% of each day. The site was located 49 ft (15 m) east of the shaded Turfgrass Research Center study and consisted of ‘A4’ creeping bentgrass and indigenous annual bluegrass. Soil analysis was nearly identical to that of the shaded site and turf maintenance was the same. Plot size was consistent with the shaded site and treatments were arranged in a randomized design. The experiment was a two-by-five factorial with two levels of application frequency, monthly and every 14 days, and application rates at six levels including 0.0, 0.5, 1.0, 1.5, 2.0, and 2.5 lbs/acre (0.0, 0.6, 1.1, 1.7, 2.2, and 2.8 kg Mg and Fe per ha). Applications of ammonium sulfate, ammonium nitrate, and trinexapac ethyl were not used in this study. Spray applications were applied monthly in March through October in 2000 and in May, June, July, and August in 2001. The initial annual bluegrass cover was rated in February 2000 and the initial applications were made in March 2000. Annual bluegrass cover was measured again in February 2001 and February 2002. Measurement procedures were consistent with those described for the shade and golf course studies. Mg and Fe in Shade Favors Annual Bluegrass Shade study. Two years’ research was concluded at the Turfgrass Research Center shaded site in October 2000. The regular applications of Mg and Fe were not sufficient to affect the soil content of these nutrients over the course of the study but foliar applications were sufficient to affect turf color (Table 1). The overall color ratings over the entire study indicated that Mg/Fe, ammonium nitrate, Mg/Fe/ammonium nitrate, Mg/Fe/ammonium sulfate, and Mg/Fe/trinexapac ethyl improved turf color compared with the control. Applications of Mg/Fe increased turf color compared with the control and the addition of Mg/Fe to the ammonium sulfate and trinexapac ethyl applications improved color compared with their respective applications alone. A contrast between spray applications containing Mg/Fe and those without indicated that Mg/Fe enhanced color significantly. Table 1. Turf visual color, density, and change in annual bluegrass proportion observed on a creeping bentgrass/annual bluegrass putting green from fall 1998 to fall 1999 and fall 1999 to fall 2000. Treatments were applied monthly from September 1998 through November 1998; March 1999 through November 1999; and March 2000 through October 2000.
a Measurements are the average of three replications over the months of September through August excluding December, January, and February. Data were blocked by rating date to remove seasonal variation. b Measurements are the average of three replications over the months of September through August excluding December, January, and February. Data were blocked by rating date to remove seasonal variation. c Measurements are the average of three replications. Change is calculated as increase or decrease from the initial rating in November. Over the course of the study, Mg/Fe/ammonium nitrate, Mg/Fe/ammonium sulfate, trinexapac ethyl, and Mg/Fe/trinexapac ethyl improved turf density compared with control (Table 1). A linear contrast between spray applications containing Mg/Fe and those without Mg/Fe indicated that Mg/Fe applications did not have a significant effect on turf density. Trinexapac-ethyl alone and combined with Mg/Fe and the combinations of Mg/Fe/ammonium nitrate and Mg/Fe/ammonium sulfate improved turf density compared with control. The ammonium nitrate and ammonium sulfate did not improve turf density significantly unless they were combined with Mg/Fe. Ratings in September 1998, August 1999, and August 2000 (data not shown) indicated that no annual bluegrass was present at the site and that the indigenous annual bluegrass population consisted entirely of annual varieties. The annual bluegrass cover increased from 6% to 14% in the control plots between November 1998 and November 1999 (Table 1). This increase was due to a combination of low mowing height, a shaded site, and mild winter weather. None of the spray applications were effective for reducing the population of annual bluegrass at the site from November 1998 to November 1999 and none of the spray applications suppressed encroachment compared with control (Table 1). Plots treated with Mg/Fe consistently had larger numeric increases in the proportion of annual bluegrass in swards at the end of the first experimental year (November 1999) than plots treated with corresponding plant growth regulator and nutrients alone (Table 1). For example, annual bluegrass cover was higher in plots treated with Mg/Fe compared with control and in plots treated with ammonium sulfate compared with Mg/Fe/ammonium sulfate during the first season. Statistical analysis (an apriori, single degree of freedom contrast) of data collected at the end of the first experimental year indicated that spray applications containing Mg/Fe increased the proportion of annual bluegrass in the mixed sward compared with spray applications that did not contain Mg/Fe. From November 1999 to November 2000, annual bluegrass cover at the site remained the same in the control plots, while applications of Mg/Fe continued to enhance annual bluegrass populations (Table 1). As in the first experimental year, a significant contrast was found between spray applications including Mg/Fe and those without Mg/Fe. In each case, plots treated with Mg/Fe had larger numeric increases in the proportion of annual bluegrass in mixed swards than plots treated with corresponding plant growth regulator and nutrients alone over the second season. From November 1998 to November 2000, applications of Mg/Fe and Mg/Fe applied with ammonium nitrate and ammonium sulfate caused significant increases in annual bluegrass compared with control. Those results along with a slight numeric increase in the Mg/Fe/trinexapac ethyl when compared with trinexapac ethyl alone resulted in a significant contrast between applications containing Mg/Fe and those without over the course of the study. The findings from this two-year field trial indicated that applications of Mg/Fe applied to this shaded site favored the spread of annual bluegrass compared with creeping bentgrass. Applications of N and Fe are known to increase chlorophyll synthesis in higher plants (12). However, there was no indication that N or Fe consistently enhanced chlorophyll synthesis from September 1998 through August 1999 in the mixed stand of turf (Table 1). None of the spray applications caused a significant increase in chlorophyll a plus chlorophyll b compared with control over that period. However, applications of Mg/Fe did affect chlorophyll synthesis on a seasonal basis during that period. Spray applications containing Mg/Fe caused a significant increase in tissue chlorophyll in April 1999 and a significant decrease in June 1999 with corresponding non-significant effects in other months during the spring and early summer. High concentrations of chlorophyll in a photosynthetically efficient species like annual bluegrass may help it better compete with a less efficient species like creeping bentgrass in shade. This advantage is likely to be greater in the spring when the annual grass is producing rapid vegetative growth followed by prolific seed. The light saturation point of annual bluegrass plants may not be reached in shaded environments. For that reason, applying Mg/Fe to turf grown in light levels below saturation may enhance the photosynthetic capacity of the plants instead of the hypothesized light enhanced decline (2). Such an affect favors the more photosynthetically efficient plant, in this case, annual bluegrass, in a mixed sward. LaFortune Park Golf Course. The research site at LaFortune Park Golf Course was 17% annual bluegrass in the control in May 1999, increased to 36% in March 2000, decreased to 28% in February 2001, and was 63% in February 2002 (data not shown). Spray applications of Mg/Fe, Mg/Fe/trinexapac-ethyl, Mg/Fe/ammonium nitrate, and Mg/Fe/ammonium sulfate were applied at the site in October and November 1999 but no effect was indicated in March 2000. In September 1999 over 65% of the annual bluegrass observed in May 1999 had died. In August 2001 only 3.4% of the control plots were annual bluegrass, resulting in 88% death of the species compared with February 2001. These results indicated that most of the annual bluegrass population at the site was composed of annual varieties. This site was shaded during the early morning but received full sun during late morning and most of the afternoon. Spray applications of Mg/Fe and Mg/Fe plus plant growth regulator or quick-release N did not affect annual bluegrass population significantly at this site during the two years of the study. Coffee Creek Golf Course. The initial annual bluegrass population in the control plots averaged 77% in May 1999, increased to 79% in March 2000, decreased to 45% in February 2001, and was 58% in February 2002 (data not shown). In August 2001 the annual bluegrass cover in the control plots at Coffee Creek was 5%, indicating that most of the annual bluegrass did not have perennial tendencies. Spray applications of Mg/Fe and Mg/Fe plus plant growth regulator or quick-release N did not affect annual bluegrass population significantly at this site during the two years of the study. This site was located in full sun throughout the growing season. Full-sun study. At the full-sun Turfgrass Research Center study, annual bluegrass cover in control was 15% in February 2000. The annual bluegrass proportion in control increased to 16% in February 2001 and to 22% in February 2002. Annual bluegrass cover was not affected when Mg/Fe was applied at 14-day and monthly intervals at six different application rates. Application frequency and rate of Mg/Fe had no effect on turf density for the duration of the study. Study-long analysis of turf visual color, however, indicated a significant color improvement with 14-day applications opposed to monthly applications. Summary The two golf course studies and the full-sun Turfgrass Research Center study gave no indication that Mg/Fe applications affected annual bluegrass cover on the creeping bentgrass greens in full sun. These results are contrary to those found on a newly-established creeping bentgrass fairway trial reported by Bell et al. (2) but support the findings on indigenous annual bluegrass in that study. It is important to note that successful reductions in annual bluegrass populations observed by Bell et al. (2) were attained on young turf grown from seed collected in the Northwest region of the United States (Oregon) and grown in the Midwest region (Ohio). The turf used in the present study was mature and consisted of indigenous annual bluegrass plants that were well adapted to the area. The important findings were not found in full sun but in shade. Application of Mg/Fe increased the competitive ability of annual bluegrass compared with creeping bentgrass in shade. It would appear that applications of Mg/Fe have potential for enhancing annual bluegrass growth in shade. Although the original hypothesis of this study was not sustained, information from the project is useful for turf practitioners who manage annual bluegrass in shade. Turf managers often apply foliar Fe and sometimes combinations of foliar Mg/Fe to enhance turf color without encouraging rapid growth. The work of Bell et al. (2) may lead practitioners to believe that annual bluegrass populations are reduced or not affected by these applications, when, in fact, Mg/Fe applications are likely to encourage annual bluegrass competition in shade. Acknowledgements Approved for publication by the director, Oklahoma Agricultural Experiment Station. Funding provided by the Golf Course Superintendent’s Association of America, grant number AG-99-RS-042, The Oklahoma Golf Course Superintendent’s Association, and The Oklahoma Agricultural Experiment Station, project number OKLO 2392. Literature Cited 1. Ashton, F. M., and Monaco, T. J. 1991. Weed Science: Principles and Practices. John Wiley and Sons, Inc., New York, NY. 2. Bell, G. E., Odorizzi, E., and Danneberger, T. K. 1999. Reducing populations of annual bluegrass and rough bluegrass in creeping bentgrass fairways: A nutritional approach. Weed Technol. 13:829-834. 3. Branham, B. E. 1990. A selective annual bluegrass control-finally. USGA Green Sect. Rec. 28:6-8 4. Callahan, L. M., and McDonald, E. R. 1992. Effectiveness of bensulide in controlling two annual bluegrass (Poa annua) subspecies. Weed Technol. 6:97. 5. Dest, W. M., and Guillard, K. 1987. Nitrogen and phosphorus nutritional influence on bentgrass-annual bluegrass community composition. J. Amer. Soc. Hort. Sci. 112:769-773. 6. Gaussoin, R. E., and Branham, B. E. 1989. Influence of cultural factors on species dominance in a mixed stand of annual bluegrass/creeping bentgrass. Crop Sci. 29:480-484. 7. Gilmore, A. M., and Yamamoto, H. Y. 1991. Resolution of lutein and zeaxanthin using a non-endcapped, lightly carbon-loaded C18 high performance liquid chromatographic column. J. Chromatogr. 543:137-145. 8. Imaizumi, S., Nishino, T., Miyabe, K., Fujimori, T., and Yamada, M. 1997. Biological control of annual bluegrass (Poa annua L.) with a Japanese isolate of Xanthomonas campestris pv. poae (JT-P482). Biol. Control 8:7-14. 9. Johnson, B. J., and Murphy, T. R. 1996. Suppression of a perennial subspecies of annual bluegrass (Poa annua spp. reptans) in a creeping bentgrass (Agrostis stolonifera) green with plant growth regulators. Weed Technol. 10:705-709. 10. Mitich, L. W. 1998. Annual bluegrass (Poa annua L.). Weed Technol. 12:414-416. 11. Moran, R. 1982. Formulae for determination of chlorophyllous pigments extracted with N,N-dimethylformamide. Plant Physiol. 69:1376-1381. 12. Walker, C. J., Yu, G. H., and Weinstieng, J. D. 1997. Comparative study of heme and Mf-protoporphyrin (monomethyl ester) biosynthesis in isolated pea chloroplasts: Effects of ATP and metal ions. Plant Physiol. Biochem. (Paris) 35:213-221. 13. Xu, X., and Mancino, C. F. 1998. Annual bluegrass and creeping bentgrass response to varying levels of iron. Agron. Abstr. October 18-22, Baltimore, MD. |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
-hydroxy-methylene)-3,5-dioxo-cyclohexane-carboxylic acid ethyl
ester], a plant growth regulator; (iii) Mg/Fe + trinexapac ethyl (Mg/Fe/trinexapac
ethyl); (iv) ammonium nitrate fertilizer; (v) Mg/Fe + ammonium nitrate
(Mg/Fe/ammonium nitrate); (vi) ammonium sulfate fertilizer; (vii) Mg/Fe + ammonium
sulfate (Mg/Fe/ammonium sulfate); and (viii) control. Spray applications were made
on the first day (±2 days) of each month from September 1998 through November
1998; March 1999 through November 1999; and March 2000 through October 2000.
Iron (FeSO4•7H2O) and Mg (MgSO4•7H2O) were applied at 1.5 lbs ai/acre (1.68 kg
ai/ha), trinexapac ethyl (Primo liquid formulation) at 0.043 lbs ai/acre
(0.048 kg ai/ha), and ammonium nitrate and ammonium sulfate at 5.45 lbs/acre
(6.1 kg/ha) with a wheelchair CO2 sprayer at 40 gal/acre (374 liter/ha). Visual
ratings for color were made using a 1 through 9 scale (1 = brown; 5 = yellow-green;
9 = blue-green). Visual density was also rated on a 1 through 9 scale (1 = very
low density; 9 = very high density). Ratings were performed 15 days after spray
applications were made.