Quantifying the Influence of Select Plant Growth Regulators On

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Quantifying the Influence of Applications of Select Plant Growth Regulators on Height and Tillering of Ornamental Grasses

Sonali Padhye and Jude Groninger

Department of Environmental Horticulture, University of Florida, West Florida Research and Education Center (WFREC) 5988 Highway 90, Bldg 4900, Milton, FL 32583 Introduction The popularity of ornamental grasses has soared in the recent years, increasing their market demand. Ornamental grasses are not only used in the landscape, but have become a prominent design element in mixed containers, a growing segment of the floriculture industry. Ornamental grasses comprise of grasses and grass-like plants are monocots from several families including Poaceae (grass family), Cyperaceae (sedge family), Juncaceae (rush family), Restionaceae (restio family) and Typhacea (cat- tail family).

Regulating the plant height and increasing the number of tillers per plant and are significant to commercial ornamental grass growers for improving the crop quality. Since grasses are monocots, applications of plant growth retardants (PGRs) developed for the height control of dicots such as common bedding plants provide varying degrees of height control and published information on height control of ornamental grasses is limited. Additionally, to our knowledge, no published studies have investigated the influence of benzyladenine on increasing branching of ornamental grasses. The objective of this study was to quantify the influence of applications of select plant growth regulators on height control and tillering of ornamental grasses.

Materials and Methods Young propagules of Carex buchananii, Carex comans ‘Frosted Curls’, Carex flagellifera ‘Toffee Twist’, Cortaderia selloana ‘Rosea’, Miscanthus sinensis ‘Gracillimus’, and Muhlenbergia capillaries were received from a commercial grower (Figure 1). Figure 1. Plugs of Carex buchananii (A), Carex comans ‘Frosted Curls’ (B), Carex flagellifera ‘Toffee Twist’ (C), Cortaderia selloana ‘Rosea’ (D), Miscanthus sinensis ‘Gracillimus’ (E), and Muhlenbegia capillaris (F) at the initiation of the experiment. A B C

D E F

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©Padhye and Groninger, University of Florida 2008 Not for Publication Plants were transplanted in a peat-based medium (Fafard 3B) and grown in a polycarbonate greenhouse at WFREC, Milton under a 16-hour photoperiod provided as a day-extension from 5 pm to 12 am using high-pressure sodium lamps. Plants received two foliar sprays of PGRs (volume of 2 quarts/100 ft2, with Capsil as a surfactant). The treatments are outlined in the table below: Plant Growth Regulator Application Rate Benzyladenine [(BA) Configure; Fine Americas] 500 or 1000 ppm (mg·L−1) Concise (Uniconazole; Fine Americas) 20 or 40 ppm Trinexapac-ethyl (turf PGR for comparison; Primo; Syngenta) 220 ppm (label rate)

Figure 2. Timing of the The first PGR application was made after the plants were established in containers and the roots of plants were visible around the containers first PGR application. (Figure 2).

The experimental schedule is below: Date Activity Species 6/24/2008 Plug receipt and transplant Carex, Cortaderia, Miscanthus, Muhlenbergia 7/15/2008 Spray 1 Carex 7/22/2008 Spray 1 Cortaderia, Miscanthus, Muhlenbergia 7/31/2008 Spray 2 Carex, Cortaderia, Miscanthus, Muhlenbergia 7/29/2008 2-week data Carex 8/6/2008 2-week data Cortaderia, Miscanthus, Muhlenbergia 8/12/2008 4-week data Carex 8/19/2008 4-week data Cortaderia, Miscanthus, Muhlenbergia 9/8/2008 8-week data Carex 9/17/2008 8-week data Cortaderia, Miscanthus, Muhlenbergia

A non-sprayed control was maintained. Ten plants were subjected to each treatment combination. The fertility and pest management was as per standard protocols developed at WFREC. The plant height (from surface of the medium to the tallest point of grass) and the number of tillers per plant were recorded at weeks 2, 4 and 8 weeks after the first PGR application.

Results and Discussion

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©Padhye and Groninger, University of Florida 2008 Not for Publication Figure 3. The influence of PGR sprays on the height of ornamental grasses.

Control Benzyladenine Uniconazole Trinexapac-ethyl 90 Carex buchananii A Carex buchananii B Carex buchananii C Carex buchananii D

60 500 mg·L-1 20 mg·L-1 1000 mg·L-1 40 mg·L-1 50 Carex comans E Carex comans F Carex comans G Carex comans H 45

35 500 mg·L-1 20 mg·L-1 1000 mg·L-1 40 mg·L-1 30 90 Carex flagellifera I Carex flagellifera J Carex flagellifera K Carex flagellifera L

80 500 mg·L-1 20 mg·L-1 1000 mg·L-1 40 mg·L-1 70

Height (cm) Height Cortaderia selloana 175 Cortaderia selloana M Cortaderia selloana N Cortaderia selloana O P

500 mg·L-1 20 mg·L-1 150 1000 mg·L-1 40 mg·L-1 125

100

140 Miscanthus sinensis Q Miscanthus sinensis R Miscanthus sinensis S Miscanthus sinensis T

120

100

80 500 mg·L-1 20 mg·L-1 1000 mg·L-1 40 mg·L-1 60 120 Muhlenbergia capillaris U Muhlenbergia capillaris V Muhlenbergia capillaris W Muhlenbergia capillaris X

105 500 mg·L-1 20 mg·L-1 1000 mg·L-1 40 mg·L-1 90

60 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 Time (weeks) Height Control and Branching of Ornamental Grasses Page 4

©Padhye and Groninger, University of Florida 2008 Not for Publication Figure 4. The influence of PGR sprays on the tiller number of ornamental grasses. Control Benzyladenine Uniconazole Trinexapac-ethyl

Carex buchananii A Carex buchananii B Carex buchananii C Carex buchananii D 80

-1 -1 60 500 mg·L 20 mg·L 1000 mg·L-1 40 mg·L-1

Carex comans E Carex comans F Carex comans G Carex comans H 200

500 mg·L-1 20 mg·L-1 150 1000 mg·L-1 40 mg·L-1

100

0 Carex flagellifera I Carex flagellifera J Carex flagellifera K Carex flagellifera L 140

500 mg·L-1 20 mg·L-1 105 1000 mg·L-1 40 mg·L-1

Tillers (no.) Cortaderia selloana Cortaderia selloana Cortaderia selloana Cortaderia selloana 12 M N O P

500 mg·L-1 20 mg·L-1 9 1000 mg·L-1 40 mg·L-1

0 Miscanthus sinensis Q Miscanthus sinensis R Miscanthus sinensis S Miscanthus sinensis T 100

500 mg·L-1 20 mg·L-1 80 1000 mg·L-1 40 mg·L-1

Muhlenbergia capillaris U Muhlenbergia capillaris V Muhlenbergia capillaris W Muhlenbergia capillaris X 160

500 mg·L-1 20 mg·L-1 120 1000 mg·L-1 40 mg·L-1

0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 Time (weeks) Height Control and Branching of Ornamental Grasses Page 5

©Padhye and Groninger, University of Florida 2008 Not for Publication Table 1. Increase in the average plant height between two measurements ± standard error (SE) of 10 replicates for six ornamental grass species.

Increase in the average plant height between two measurements (cm) ± SE C. C. Weekz of Week of comans flagellifera C. preceding succeeding C. ‘Frosted ‘Toffee selloana M. sinensis M. measurement measurement buchananii Curls’ Twist’ ‘Rosea’ ‘Gracillimus’ capillaris Control

0 2 5.3 ± 1.4 1.3 ± 0.5 2.6 ± 0.7 41.8 ± 2.6 23.3 ± 2.6 8.4 ± 1.9 2 4 3.7 ± 1.0 3.6 ± 0.8 7.1 ± 1.2 32.9 ± 1.5 15.5 ± 1.1 7.9 ± 1.6 4 8 6.7 ± 2.3 3.6 ± 0.9 17.8 ± 1.3 19.5 ± 1.5 14.7 ± 2.2 22.2 ± 3.0

500 mg·L−1 Benzyladenine

0 2 6.2 ± 2.1 1.0 ± 0.5 1.7 ± 1.0 30.9 ± 2.4 26.8 ± 1.6 6.9 ± 2.6 2 4 2.5 ± 0.7 0.8 ± 0.3 3.1 ± 0.7 31.5 ± 1.5 17.3 ± 1.6 0.8 ± 0.5 4 8 11.6 ± 2.5 0.4 ± 0.3 18.2 ± 1.4 14.3 ± 1.7 14.6 ± 1.8 19.4 ± 3.2

1000 mg·L−1 Benzyladenine 0 2 2.8 ± 1.0 0.9 ± 0.5 3.3 ± 1.2 28.5 ± 5.1 30.9 ± 1.9 5.1 ± 1.5 2 4 3.3 ± 0.8 0.7 ± 0.2 1.8 ± 0.5 30.6 ± 1.5 15.5 ± 2.7 0.4 ± 0.2 4 8 10.6 ± 1.9 0.2 ± 0.1 12.4 ± 1.9 14.9 ± 2.4 12.9 ± 2.1 18.0 ± 2.9

20 mg·L−1 Uniconazole 0 2 2.6 ± 1.0 0.7 ± 0.3 2.5 ± 1.0 20.4 ± 3.9 23.7 ± 2.6 9.5 ± 2.5 2 4 0.8 ± 0.3 0.2 ± 0.1 0.8 ± 0.3 22.8 ± 1.8 16.2 ± 1.4 5.2 ± 1.6 4 8 2.2 ± 1.1 0.1 ± 0.1 6.2 ± 2.0 7.7 ± 3.0 11.2 ± 1.4 20.7 ± 2.2

40 mg·L−1 Uniconazole 0 2 5.6 ± 2.1 0.5 ± 0.2 1.5 ± 0.4 12.9 ± 4.1 23.0 ± 2.7 6.9 ± 2.5 2 4 0.4 ± 0.3 0.0 ±0.0 0.2 ± 0.1 21.0 ± 2.3 15.2 ± 2.8 3.4 ± 1.4 4 8 1.0 ± 0.6 0.0 ±0.0 4.4 ± 1.8 5.8 ± 2.3 23.3 ± 2.4 27.9 ± 1.7

220 mg·L−1 Trinexapac-ethyl 0 2 1.7 ± 0.4 1.4 ± 1.0 0.5 ± 0.3 8.5 ± 1.8 11.9 ± 2.0 3.3 ± 0.8 2 4 0.5 ± 0.3 0.5 ± 0.2 0.5 ± 0.2 15.1 ± 1.5 2.2 ± 0.3 0.1 ± 0.1 4 8 10.2 ± 2.8 0.0 ±0.0 6.1 ± 1.6 4.0 ± 1.2 14.9 ± 3.1 0.2 ± 0.1 zweek of the first PGR application was considered as week 0.

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©Padhye and Groninger, University of Florida 2008 Not for Publication Table 2. Increase in the average tiller number between two measurements for six ornamental grass species.

Increase in the average tiller number between two measurements (no.) C. Weekz of Week of C. comans flagellifera C. preceding succeeding C. ‘Frosted ‘Toffee selloana M. sinensis M. measurement measurement buchananii Curls’ Twist’ ‘Rosea’ ‘Gracillimus’ capillaris Control 0 2 4.4 ± 0.6 16.3 ± 1.1 9.1 ± 1.1 0.1 ± 0.1 16.8 ± 2.8 2.6 ± 0.6 2 4 13.5 ± 0.9 62.2 ± 3.4 37.4 ± 2.2 3.0 ± 0.7 53.6 ± 4.2 53.7 ± 2.6 4 8 25.9 ± 4.1 123.4 ± 15.7 48.6 ± 2.3 2.9 ± 0.3 28.8 ± 4.4 77.1 ± 4.4

500 mg·L−1 Benzyladenine 0 2 2.7 ± 0.8 12.5 ± 1.9 14.8 ± 1.5 0.2 ± 0.1 7.5 ± 1.5 4.5 ± 1.1 2 4 16.7 ± 2.3 72.9 ± 7.9 43.1 ± 2.0 3.8 ± 0.4 53.3 ± 4.8 47.4 ± 1.9 4 8 2.7 ± 3.4 116.2 ± 16.0 46.3 ± 2.9 3.9 ± 0.5 30.3 ± 2.9 95.0 ± 4.0

1000 mg·L−1 Benzyladenine 0 2 3.0 ± 0.6 19.3 ± 3.2 15.2 ± 2.2 0.0 ± 0.0 8.8 ± 1.9 4.3 ± 1.3 2 4 16.2 ± 1.6 60.7 ± 5.5 42.0 ± 1.6 3.4 ± 0.5 47.0 ± 3.7 53.8 ± 3.0 4 8 22.7 ± 2.7 138.1 ± 16.6 50.0 ± 1.3 4.7 ± 0.9 25.4 ± 4.2 84.3 ± 6.4

20 mg·L−1 Uniconazole 0 2 2.8 ± 0.9 12.4 ± 2.5 9.3 ± 1.4 0.3 ± 0.2 8.0 ± 2.2 3.7 ± 1.1 2 4 12.7 ± 3.0 39.1 ± 2.5 41.3 ± 1.9 4.2 ± 0.6 56.9 ± 3.7 47.1 ± 2.0 4 8 36.5 ± 6.5 108.3 ± 15.0 88.4 ± 8.4 5.3 ± 0.8 29.8 ± 2.9 86.2 ± 3.0

40 mg·L−1 Uniconazole 0 2 2.7 ± 0.5 10.7 ± 2.2 7.8 ± 1.0 0.1 ± 0.1 5.9 ± 1.2 6.7 ± 1.0 2 4 11.1 ± 1.5 47.1 ± 2.7 37.8 ± 2.6 4.4 ± 0.6 50.1 ± 3.2 44.2 ± 2.5 4 8 39.9 ± 3.8 65.2 ± 10.9 56.2 ± 3.0 5.5 ± 1.0 22.0 ± 1.7 73.1 ± 3.1

220 mg·L−1 Trinexapac-ethyl 0 2 4.2 ± 0.7 13.1 ± 1.9 5.5 ± 1.1 0.6 ± 0.2 7.0 ± 1.6 7.8 ± 1.8 2 4 9.2 ± 1.7 47.9 ± 4.3 46.8 ± 2.0 3.2 ± 0.5 52.5 ± 3.6 34.4 ± 1.5 4 8 21.5 ± 2.4 312.6 ± 10.3 39.8 ± 3.3 6.5 ± 0.6 28.3 ± 3.6 51.3 ± 4.1 zweek of the first PGR application was considered as week 0.

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©Padhye and Groninger, University of Florida 2008 Not for Publication Carex buchananii Figure 6. The influence of PGR applications on height and tiller number of Carex buchananii.

Height Control  Overall, at the concentrations tested, BA did not influence the average plant height compared with the average height of controls (Figure 3A and B, Table 1).  Uniconazole suppressed the increase in height by 52 to 89% between measurements compared with the height increase of controls (Figure 3A and C). Forty ppm uniconazole suppressed the increase in height at weeks 4 and 8 more compared with the height suppression by the 20 ppm uniconazole treatment.  Trinexapac-ethyl strongly suppressed the height for 4 weeks after the first application (Figure 3 A and D). However, after 8 weeks, the effect of trinexapac-ethyl wore off and the average height after 8 weeks was higher than the heights of controls.

Tiller Number  At the rates tested, BA, uniconazole, and trinexapac-ethyl application did not consistently influence tiller production compared with the tiller production of controls (Figure 4A to D, Table 2).

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©Padhye and Groninger, University of Florida 2008 Not for Publication

Carex comans ‘Frosted Curls’ Figure 7. The influence of PGR applications on height and tiller number of Carex comans ‘Frosted Curls’.

Height Control  Compared with the controls, all PGRs tested provided height control for 8 weeks after the first spray with an exception of trinexapac-ethyl after 2 weeks (Figure 3E to H, Table 1). This suppression of height increased ranged between 20 to 100% depending on the PGR treatment and timing of data recording.  The low and high rates of BA and uniconazole elicited similar height responses.  When produced in 1-gallon containers, Carex comans ‘Frosted Curls’ may not need height control.

Tiller Number  At the rates tested, BA and Trinexapac-ethyl did not influence the tiller number compared with the controls (Figure 4E, F and H, Table 2).

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©Padhye and Groninger, University of Florida 2008 Not for Publication  Four and 8 weeks after the first spray, plants treated with uniconazole had fewer tillers compared with the controls (Figure 4E and G).

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©Padhye and Groninger, University of Florida 2008 Not for Publication Carex flagellifera ‘Toffee Twist’ Figure 8. The influence of PGR applications on height and tiller number of Carex flagellifera ‘Toffee Twist’.

Height Control  Although BA application provided some height control for up to 8 weeks from the first application, this response was somewhat inconsistent between the rates used and timing of data collection (Figure 3I to J and Table 1).  The average height increase of plants treated with uniconazole was suppressed for 8 weeks from the first spray compared with that of the controls (Figure 3I and K). Four weeks from the first spray, the percent suppression of height increase with 20 and 40 ppm uniconazole-treated plants was 89 and 97% compared with the height increase of the controls, respectively.  Trinexapac-ethyl suppressed the increase in height by 83, 93, and 67% after 2, 4, and 8 weeks compared to that of controls (Figure 3I and L).

Tiller Number  The tiller number of BA-treated plants increased by over 60% compared with the tiller increase of the controls 2 weeks after the first spray application (Figure 4I and J, Table 2). However after

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©Padhye and Groninger, University of Florida 2008 Not for Publication 4 and 8 weeks there was minimal to no increase in the number of tillers produced compared with the controls.  With an exception of an 80% increase in tiller production of 20 ppm uniconazole treated plants between week 4 and 8 after the first PGR application, the tillers of uniconazole and trinexapac- ethyl treated plants did not increase considerably (Figure 4I, K and L).

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©Padhye and Groninger, University of Florida 2008 Not for Publication Cortaderia selloana ‘Rosea’ Figure 9. The influence of PGR applications on height and tiller number of Cortaderia selloana ‘Rosea’.

Height Control  All PGRs provided some height control (Figure 3M to P, Table 1). Both concentrations of BA provided similar height suppression and at week 2 and 8 from the first spray, the suppression of height increase was over 20% compared with the height increase in the controls. At week 4 from the first application, the suppression of height increase was minimal (less than 10%) compared with the height increase of the controls.  The suppression in height increase by uniconazole was dose-dependent with height increase in 40 ppm uniconazole-treated plants being suppressed more than that of the 20 ppm uniconazole treatment. At weeks 2, 4, and 8 from the first sprays, the height increase of 40 ppm uniconazole- treated plants was suppressed by 69, 36, and 70%, respectively compared with the height increase of the controls. Height Control and Branching of Ornamental Grasses Page 13

©Padhye and Groninger, University of Florida 2008 Not for Publication  Trinexapac-ethyl suppressed the height increase the strongest compared with BA and uniconazole. At weeks 2, 4, and 8 from the first sprays, the height increase of 40 ppm uniconazole-treated plants was suppressed by 80, 54, and 80%, respectively compared with the height increase of the controls.

Tiller Number  On average, Cortaderia selloana ‘Rosea’ plants had 3 to 10 tillers for up to 8 weeks (Figure 4M to P). Although the average increase in tillers for PGR-treated plants and controls somewhat varied, due to low tiller numbers, no conclusions can be drawn regarding the influence be PGRs on the increase in tillers compared with that of the controls (Table 2).

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©Padhye and Groninger, University of Florida 2008 Not for Publication Miscanthus sinensis ‘Gracillimus’ Figure 10. The influence of PGR applications on height and tiller number of Miscanthus sinensis ‘Gracillimus’.

Height Control  BA provided minimal to no height control of Miscanthus sinensis ‘Gracillimus’ (Figure 3Q and R, Table 1).  Twenty and 40 ppm uniconazole provided 19 and 22% suppression of height increase 2 weeks after the first spray however, after 4 and 8 weeks this height increase suppression was either negligible or inconsistent (Figure 3Q and S).  Trinexapac-ethyl provided the most suppression of height increase compared with that provided by BA and uniconazole treatments (Figure 3Q to T). Two, 4, and 8 weeks after the first application, the height increase of plants treated with trinexapac-ethyl was suppressed by 59, 86, and 0%, respectively compared with that of the controls.

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Tiller Number  No PGR application elicited a greater percent increase in tillers compared with that of controls (Figure 4Q to R, Table 2).

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©Padhye and Groninger, University of Florida 2008 Not for Publication Muhlenbergia capillaris Figure 11. The influence of PGR applications on height and tiller number of Muhlenbergia capillaris.

Height Control  The increase in height of BA-treated plants was suppressed by 17 to 96% compared with that of the controls in up to 8 weeks from the first BA application (Figure 3U and V, Table 1). The highest height increase suppression was recorded at week 4 and was 90 and 96% for 500 and 1000 ppm BA treatments, respectively.  The height control provided by uniconazole was somewhat inconsistent (Figure 3U and W). The maximum (57%) suppression of height increase was recorded by 40 ppm uniconazole treatment at 4 week from the first spray.  Trinexapac-ethyl elicited the strongest height suppression compared with the other PGR treatments (Figure 3U to X). Two, 4, and 8 weeks after the first application, the height increase of plants treated with trinexapac-ethyl was suppressed by 61, 99, and 99%, respectively compared with that of the controls.

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Tiller Number  Tillers of all PGR-treated plants increased more between week 0 and 2 compared with that of the controls however, since this increase in tiller number ranged between 4 to 8 additional tillers only (Figure 4U to X). This increase in tiller numbers was diminished or inconsistent after 4 and 8 weeks from the first spray.

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©Padhye and Groninger, University of Florida 2008 Not for Publication Conclusions Benzyladenine (BA)  BA applications suppressed height increase of Carex comans ‘Frosted Curls’, Cortaderia selloana ‘Rosea’, and Muhlenbergia capillaris by 20 to 96, 4 to 32, and 13 to 96% compared with that of the controls, respectively, depending on the application rate and timing of data collection. Although some BA treatments suppressed the height increase of Carex flagellifera ‘Toffee Twist’ compared with that of controls, this suppression was inconsistent with BA rates and timing of data reporting. BA either did not suppress the height increase or suppressed it inconsistently for Carex buchananii and Miscanthus sinensis ‘Gracillimus’.

 BA application enhanced the increase in tiller number by more than 60% after 2 weeks from the first application compared with that of controls for Carex flagellifera ‘Toffee Twist’ and Muhlenbergia capillaris. Conversely, after 4 and 8 weeks, this enhancement was either diminished or inconsistent. BA did not enhance the tiller production in Carex buchananii, Carex comans ‘Frosted Curls’, and Miscanthus sinensis ‘Gracillimus’. However, due to the low overall tiller numbers, the enhancement in tiller production of Cortaderia selloana ‘Rosea’ was inconclusive.

Uniconazole  Overall, uniconazole provided stronger height suppression than that with controls in the three Carex species tested which belong to the sedge family. However, Trinexapac-ethyl suppressed the height more strongly compared with the uniconazole in the three remaining ornamental grasses from the grass family. Typically, the suppression in height increase elicited by 40 ppm uniconazole treatment was not considerably higher than the 20 ppm treatment. Uniconazole treatment did not suppress the height increase of Miscanthus sinensis ‘Gracillimus’ and Muhlenbergia capillaris while the height increase in the remaining species was successfully suppressed by uniconazole.

 Uniconazole did not influence the increase in tiller number.

Trinexapac-ethyl  Trinexapac-ethyl provided a strong height control of Cortaderia selloana ‘Rosea’, Miscanthus sinensis ‘Gracillimus’, and Muhlenbergia capillaris. Overall, this PGR also controlled the heights of the three Carex species, although typically uniconazole elicited a stronger height control.

 Trinexapac-ethyl did not enhance tiller production compared with the controls.

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