Overseeding preparation techniques for fairway seashore paspalum

Overseeding practices for bermudagrass do not always work for seashore paspalum. A combination of herbicide, mowing and verticutting is key to successful transition.

D.M. Kopec, Ph.D., J. Gilbert, M.S., M. Pessarakli, Ph.D., and S.P. Nolan

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This research was funded in part by the Environmental Institute for Golf.

Overseeding preparation techniques for fairway seashore paspalum: photo 1

Research plots show a range of responses to overseed preparation treatments on seashore paspalum at the University of Arizona’s Karsten Turfgrass Research Center in Tucson.
Photos by J. Gilbert

Seashore paspalum (Paspalum vaginatum) does not respond well to the mechanical disturbance of stolons caused by deep divots, vertical mowing or scalping resulting from mowing. Past observations over several years have shown that excessive regrowth periods are often required during the summer for recovery from such events. Spring transition also can be extremely slow and prolonged when fall vertical mowing (similar in intensity to vertical mowing practiced on bermudagrass) is used as a preparation technique for fall overseeding.

With this in mind, a three-year field experiment was conducted on Sea Isle 1 seashore paspalum to evaluate the cultural management effects of adjusted mowing heights; vertical mowing; and the use of a herbicide, plant growth regulator or plant desiccant — all as management tools for preparing the turf surface of seashore paspalum for overseeding.

Materials and methods

A 10-year-old stand of Sea Isle 1 seashore paspalum located at the Karsten Turfgrass Research Center in Tucson, Ariz., was used as the test site. The turf previously had been mowed three times weekly at 0.625 inch (1.58 centimeters) from March until November each year. Starting in 2009, 42 treatment combinations of preparatory mowing heights, vertical mowing (none vs. two passes at 0.375 inch [0.95 centimeter]) and five chemical treatments (none, Finale, Scythe, Reward or Turflon Ester; see Table 1) were repeated on the same plots for three years.

Mowing treatments

Overseeding preparation techniques for fairway seashore paspalum: table 1

Mowing treatments were developed as follows. At eight days before overseeding, all mowing was ceased. At the day of overseeding, plots were either mowed back to 0.625 inch or 0.375 inch, or remained unmowed until the first mowing of the overseeded perennial ryegrass (Lolium perenne) (Table 2).

At the time of the first mowing after perennial ryegrass emergence, the unmowed turf had reached a height of 0.875 inch (2.22 centimeters) to 1.125 inches (2.85 centimeters).

Vertical mowing took place immediately after mowing treatments were implemented, and all cultivated plots had clippings removed by a rotary mower with a grass catcher at 2 inches (5.08 centimeters).

Chemical treatments

The herbicide Turflon Ester is labeled for use for overseed preparation of bermudagrass, as are desiccants Scythe and Reward. The nonselective herbicide Finale will produce necrotic straw, but has no effect on stolons or rhizomes and therefore was investigated as a potential candidate for use.

Chemical applications were made five days before the overseeding mechanical treatments, which occurred during the seashore paspalum’s elongation period.

Cultural treatments

The perennial ryegrass cultivar Two Streams was seeded at a rate of 625 pounds pure live seed/acre (700.53 kilograms/hectare). Seeding was followed by hand brooming the plots in two directions, and a single pass with an 875-pound (396.89-kilogram) mechanical (Brouwer) turf roller (32-inch wide × 28-inch tall [81.28 × 71.12 centimeters]).

All turf plots were irrigated for emergence and then mowed to 0.625 inch when the majority of the plots were 0.875 inch tall. Afterward, the plots were mowed three times weekly at 0.625 inch throughout the test. Fertility was 0.25 pound nitrogen/1,000 square feet (1.22 grams/square meter) per month from a 15-15-15 complete water-soluble fertilizer source. Each January the turf received Sequestrene 138 chelated iron, applied at 3 ounces product/1,000 square feet (0.92 gram/ square meter) in a solution delivery volume of 57 gallons/acre (533.17 liters/hectare).

Data collection and analysis

Overseeding preparation techniques for fairway seashore paspalum: table 2

The turf was rated for percent plot overseeding (perennial ryegrass) cover, percent plot straw when applicable on a 1%-100% scale. Plots were also rated for turfgrass color, density and overall turfgrass quality using the NTEP visual assessment scale (1-9, where 1 is dead turf and 9 is the best possible). The test was conducted in three successive years, (2009-2010, 2010-2011, 2011-2012) with the same treatments appearing on the same plots.

The treatments were analyzed as the specific combinations of preparatory mowing heights, vertical mowing and chemical amendment additions (n = 42 treatments). Data are presented for overall turfgrass quality, which includes the visual integration of density, smoothness and uniformity of color.

Turfgrass quality results are provided as an overall season mean for each year; a quality index score (the number of rating events at which the treatment had a quality mean score of 6.0 or greater); and the percentage of the total of yearly ratings that achieved a mean quality score of 6.0 or greater (Table 3). In addition, the plot composition of the turf at a noteworthy spring transition is also provided.

These data show how much of the plot surface in each treatment is composed of either living perennial ryegrass, living paspalum or necrotic straw (dead leaves/stems) during a critical stage of spring transition.

Results and discussion

The treatments reported include: group 1 — those that had the best quality means for two or three years; group 2 — treatments that included no chemical treatments, but received only mechanical treatments; and group 3 — treatments that received only a chemical treatment.

These three groups represent a sample of 20 of 42 total treatments that address the questions of what the results are from (a) mechanical manipulation alone, (b) chemicals alone, and (c) the combination of mechanical and chemical conditions that, in fact, produced the best overall turfgrass quality and spring transition (Table 3).

Group 1 results: Best treatments

The following treatments had the greatest number of rating events that had mean quality scores of 6.0 or greater.

  • Treatment 19 (mowed to 0.375 inch, verticut and sprayed with Reward). This treatment had quality mean scores of 6.0 or greater on nine of 10 dates in 2010, on six of seven dates in 2011 and on six of seven dates in 2012. This was the only single treatment combination that consistently had high yearly mean quality scores in all three years: 6.7 in year 1 and 7.1 in years 2 and 3 (Table 1).
  • Treatment 23 (mowed to 0.375 inch, verticut and sprayed with Scythe). This treatment combination had quality scores of 6.0 or greater six of seven rating dates in 2011, on six of seven dates in 2012, but only on five of 10 rating dates in year 1 (2009-2010 season).
  • Treatment 27 (mowed to 0.375 inch, verticut and sprayed with Finale). This treatment had good quality in years 2 and 3, but was marginal in year 1.
  • Treatment 31 (mowed to 0.375 inch, verticut, plus Turflon Ester). This treatment had excellent quality in all three years, but had a poor-quality transition in year 3 (with 29% straw, which lingered for several weeks), which influenced the quality ratings for six weeks.
  • Treatments that received chemical applications, but were not verticut, and had generally acceptable quality index scores included:
  • Treatment 29 (mowed to 0.375 inch, no verticut, plus Turflon Ester). For this treatment, half of its 2010 ratings were 6.0 or greater; either five or six of its seven ratings were 6.0 or greater in quality in years 2 or 3.
  • Treatment 17 (mowed to 0.375 inch, no verticut, plus Reward). This treatment had high quality index scores in years 2 and 3, but was nominal only in 2010 (five of 10 scores) due to having 44% plot straw at transition in 2010 (year 1). Also, this treatment had a slow start in establishment of its overseed cover in 2010 (data not shown).
  • Notice that in groups 1 and 2, most of these treatments were “prep-mowed” at 0.375 inch, with only treatment 28 mowed at 0.625 inch. Overall, when averaged across all verticutting and chemical treatments, the 0.375- inch mowing height produced better-quality turf than the treatments mowed at 0.625 inch when the 0.625-inch preparatory mowing height was also averaged over vertical mowing and chemical applications.

Group 2: Nonchemical (mechanical) treatments

Overseeding preparation techniques for fairway seashore paspalum: figure 1

Figure 1. Percent plot cover of seashore paspalum, straw and perennial ryegrass under four selected treatments at spring transition in three years (2010-2012) at the Karsten Turfgrass Research Center, University of Arizona, Tucson. From left to right: Treatment 3: 0.375-inch mowing height, verticutting, no chemical treatment; Treatment 19: 0.375-inch mowing height, verticutting, Reward; Treatment 11: no mowing, verticutting, no chemical treatment; Treatment 9: no mowing, no verticutting, no chemical treatment.

Treatments in group 2 are provided to show the effect of mechanical treatments (or none at all) in the absence of any chemical. These treatments included treatments 11, 9, 3, 1, 7 and 5.

When paspalum was left to elongate five days before overseeding (treatment 11) and was then verticut without any other treatment, acceptable-quality turf appeared on only 50%-70% of the rating times across all three years. If paspalum was mowed to 0.375 inch in preparation for overseeding, not verticut and not treated with a chemical (treatment 1), quality results proved inconsistent between years (29%-71% of events had acceptable turf quality across all years).

The least favorable combinations of overseed preparation without the addition of a chemical included the following: treatment 9 (the untreated control: no mowing until emergence, no verticutting and no chemicals). This treatment had decreasing quality events in years 2 and 3 and mean quality scores of 5.4 in year 1, 4.5 in year 2 and 6.2 in year 3.

The single-most detrimental nonchemical treatment combination occurred for treatment 5 (prep mowed at 0.625 inch; no verticut mowing). This treatment had acceptable turfgrass quality index values (6.0 or more for quality), which occurred on 40% of rating dates in year 1, 29% in year 2 and 14% in year 3. While raising the mowing height alone before overseeding and mowing back to the base height is often effective preparation in bermudagrass overseeding, it was surely not the case for seashore paspalum. This treatment lacked density in the first half of the entire overseed season in all three years of testing (density data not shown).

Comparison of % canopy composition

Overseeding preparation techniques for fairway seashore paspalum: photo 2

Overseeded paspalum showing responses to different preparatory mowing heights, with and without vertical mowing, when treated with Turflon Ester herbicide.

Figure 1 shows the percent canopy composition (percent plot paspalum, living perennial ryegrass and percent straw) for comparison purposes as a simple representation of treatments that include the untreated control (overseeded only = treatment 9); dropping the mowing height down to 0.375 inch the day of overseeding, plus vertical mowing without a herbicide (treatment 3); vertical mowing plus mowing to 0.375-inch plus Reward (treatment 19); and vertical mowing without a herbicide plus no mowing at all until the emerged perennial ryegrass was first mowed (treatment 11). Figure 1 also shows the yearly quality score and the percent of rating dates on which each treatment had a mean quality of score of 6.0 or more.

For the superintendent, the most desirable field condition is to have the least of the amount of living perennial ryegrass, minimal to no straw and the most paspalum present at transition. In general, there was more straw on all treatments in year 2 (2011 spring); however, treatment 11 had no straw in year 2.

Although treatment 9 shows a large percent of pasaplum present at transition, its overall quality was low on too many occasions, because of poor perennial ryegrass establishment and low density for most of the fall and winter months (data not shown).

If a herbicide was used alone, without any vertical mowing, and allowed to grow 10 days without mowing before overseeding, turfgrass quality was often not acceptable (see treatments 33, 34, 35 and 36) (Table 1). All four herbicides in this case had yearly quality averages of less than 6.0 in years 1 and 2, but in year 3, Reward and Scythe had yearly quality averages of 6.2 or greater.

Conclusions

We can draw five primary conclusions from our three-year field trial.

  • Paspalum does not always have the same response as bermudagrass to mechanical overseed and transition practices such as (a) simple verticutting alone (treatment 5: turf quality = 3.7 for year 1, 3.4 for year 2 and 4.5 for year 3), or (b) elevating the mowing height for leaf internode elonga tion, followed by a simple return to the base mowing height of 0.625 inch (treatment 12: turf quality = 3.7 for year 1, 3.4 for year 2 and 4.5 for year 3) (data not shown).
  • The use of chemicals alone (without some form of mechanical canopy manipulation) did not produce acceptable turfgrass quality. All four treatments that included only chemicals (treatments 33, 34, 35 and 36) did not have yearly quality score averages of 6.0 in any of the three years.
  • When mowed at 0.375 inch and verticut, turf plots treated with Scythe, Turflon Ester or Finale had quality index values of 6.0 in 57%–100% of all cases, but only in two of the three years of the trial (see treatments 23, 37 and 31).
  • When seashore paspalum was mowed back to 0.375 inch and then verticut in treatment 3 (no herbicides), yearly quality means were 6.2 in year 1, 7.3 in year 2 and 6.3 in year 3. However, in year 3, quality was only 6.0 or greater on four of the seven (57%) rating events. In year 3, quality was reduced at transition for this treatment.
  • The three-way combination of the 0.375- inch preparatory mowing height, verticut mowing and use of Reward (treatment 19) resulted in quality scores of 6.0 or greater for 86%–90% of all ratings for all three years. Treatment 19’s overall quality means were 6.7 for year 1 and 7.1 for years 2 and 3. This treatment produced the best season-long overall turfgrass quality, with temporary straw production at transition (which occurred for 10 to 12 days at most), and proved to be consistent for turfgrass quality within years and from year to year.

Funding

The authors thank the Environmental Institute for Golf (the philanthropic organization of GCSAA) and the Golf & Environmental Foundation of Arizona and the Cactus and Pine Golf Course Superintendents Association for providing funding for this research.

References

  1. Duncan, R.R., and R.W. Carrow. 1999. Seashore paspalum — The environmental turfgrass. John Wiley and Sons, Hoboken, N.J.
  2. Volterrani, M., S. Miele, S. Magni, M. Gaetani and G. Pardini. 2001. Bermudagrass and seashore paspalum winter overseeded with seven cool-season turfgrasses. International Turfgrass Society Research Journal  

D.M.Kopec is an Extension specialist in turfgrass science and culture, J. Gilbert is a senior research specialist, M. Pessarakli is a research professor and S.P. Nolan is a student research assistant in the school of plant sciences at the University of Arizona, Tucson.