Ethephon influences flowering, height, and branching of several herbaceous perennials

Scientia Horticulturae 91 (2001) 305±323

Ethephon in¯uences ¯owering, height, and branching of several herbaceous perennials Takahiro Hayashia, Royal D. Heinsb,*, Arthur C. Cameronb, William H. Carlsonb a

Graduate School of Agriculture, Kyoto University, Oiwake-cho, Kitashirakawa, Kyoto 606-8502, Japan b Department of Horticulture, A228 Plant and Soil Sciences Building, Michigan State University, East Lansing, MI 48824, USA Accepted 4 January 2001

Abstract Effects of ethephon (2-chloroethylphosphonic acid) were determined on ¯owering, plant height, and branching of Achillea millefolium L. `Weser River Sandstone', Coreopsis verticillata L. `Moonbeam', Echinacea purpurea Moench `Bravado', Leucanthemum  superbum Bergmans ex. J. Ingram `Thomas Killen', Liatris spicata Willd. `Kobold', Monarda didyma L. `Blue Stocking', Phlox paniculata L. `Mt. Fuji', and Physostegia virginiana Bentham `Summer Snow'. Spraying ethephon three times at 1000 mg l 1 (6.92 mM) delayed the ¯owering of Echinacea, Monarda, and Physostegia by 6, 7 and 9 days, respectively. Ethephon reduced height by 23, 42, 46, 40, or 46% when applied three times at 1000 mg l 1 on Achillea, Echinacea, Leucanthemum, Monarda, or Physostegia, respectively, compared to that of control plants at anthesis. Effects of ethephon on the in¯orescence and shoot count per pot varied among species. The number of in¯orescences per pot was increased by ethephon application to Achillea (36%), Coreopsis (52%), and Phlox (25%), but was decreased in Echinacea (33%), Leucanthemum (21%), Monarda (62%), and Physostegia (24%). Treatment with ethephon at 1000 mg l 1 caused necrosis of Monarda foliage. In¯orescence diameter of Leucanthemum decreased with increasing ethephon dosage. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Ethylene; Plant height; Herbaceous perennials

*

Corresponding author. Tel.: ‡1-517-353-6628; fax: ‡1-517-353-0890. E-mail address: [email protected] (R.D. Heins). 0304-4238/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 4 2 3 8 ( 0 1 ) 0 0 2 2 5 - 4

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1. Introduction The market for herbaceous perennial plants recently has expanded rapidly. Growers make efforts to produce inexpensive attractive plants at desirable times. Hence, manipulation of the ¯owering date, height, and lateral branching becomes a major challenge in plant management. Manipulating the ¯owering date is important to avoid overconcentration of ¯owering plants on a single date, and to extend the shipping period. Height control is also important to avoid unacceptably tall plants that require more space and labor, and have higher shipping costs. Moreover, lateral branching control is important for attractiveness of plants. Even small improvements in quality can generate signi®cant economic returns. Growth retardants such as ancymidol, chlormequat, daminozide, and paclobutrazol have been used successfully to control plant height, branching, and ¯owering of many plants for many years (Heins et al., 1976; Larson, 1985). For example, height of chrysanthemums, lilies, poinsettias, and many bedding plants is regulated practically by growth retardants. In addition to suppressing internode elongation, growth retardants often increase the number of lateral shoots or suppress the vegetative shoots that develop below the ¯owers, resulting in more in¯orescences (Miranda and Carlson, 1980; Whealy et al., 1988; Keever and Foster, 1989). Flowering time may be unaltered, accelerated, or delayed as a result of treatment with growth retardants (Cathey, 1964). Although growth retardant treatments generally do not alter the number of days to ¯ower of poinsettias and zinnias, they may accelerate ¯owering of geraniums and azaleas (Cathey, 1964; Miranda and Carlson, 1980), while ¯owering in chrysanthemums and Cleome may be delayed (Cathey and Stuart, 1961). Ethephon, an ethylene-releasing compound, also can be used to retard stem elongation, promote lateral branching, and manipulate ¯owering date. Since ethylene acts as an antigibberellin (Lieberman, 1979), ethephon can affect plant height after absorption. Ethephon is used to reduce stem height in daffodils (Moe, 1980) and hyacinths (Shoub and DeHertogh, 1975). Besides height control, ethephon promotes development of axillary shoots without damaging the apical meristem or growing point. Ethephon is used widely to increase branching on crop species such as azalea, chrysanthemum, Fuchsia, geranium, New Guinea impatiens, Lantana, and Verbena (Dole and Wilkins, 1999). Moreover, ethephon inhibits ¯ower initiation and aborts young ¯owers in many species (Dole and Wilkins, 1999). Flowering of seed geraniums treated with ethephon at 3000 mg l 1 was delayed for 10 weeks because of ¯ower bud abortion (Semeniuk and Taylor, 1970). Growers can now promote out-of-season early ¯owering in many species of herbaceous perennials by manipulating temperature and photoperiod (Heins et al., 1997). Out-of-season late ¯owering in the high temperatures and long

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307

photoperiods of spring and summer is more dif®cult to control. Many herbaceous perennial species ¯ower during a very short time period under these conditions, especially if the plants have been vernalized. If ethephon could be used to delay ¯owering of herbaceous perennials without eliminating ¯owering for the entire season, it could become a useful means of manipulating ¯owering date, allowing scheduled shipping past the normal ¯owering dates. The purpose of this experiment was to determine if ethephon could be used to delay ¯owering of several popular herbaceous perennials, while determining the effects of ethephon on plant height and in¯orescence number. Ethephon concentration and application frequency were tested to determine how ethephon might be used to regulate ¯owering, plant height, and branching. 2. Materials and methods 2.1. Plant materials and culture Eight species were used in this experiment: Achillea millefolium `Weser River Sandstone', Coreopsis verticillata `Moonbeam', Echinacea purpurea `Bravado', Leucanthemum  superbum `Thomas Killen', Liatris spicata `Kobold', Monarda didyma `Blue Stocking', Phlox paniculata `Mt. Fuji', and Physostegia virginiana `Summer Snow'. Air temperature was monitored with a 36-gauge (0.127 mm) thermocouple connected to a CR10 datalogger (Campbell Scienti®c, Logan, UT). The datalogger collected temperature data every 10 s and recorded the hourly average. Overall average daily air temperature during the experiment was 22.98C. Average day temperature was 23.48C and night temperature was 22.08C. Plants in 19.5 cm pots (5.37 l) with a soilless medium composed of 60% (by volume) composted pine bark, 25% sphagnum peat, 8% horticultural grade perlite, and 7% vermiculite (Fafard Mix No. 52; Fafard, Agawam, MA) were received from a commercial grower in Michigan on 11 May 1998. Plants were placed in a glass greenhouse under natural light supplemented with high-pressure sodium lamps to provide 16-h days. From 08:00 to 24:00 h, lighting was initiated when the photosynthetic photon ¯ux (PPF) was below 200 mmol m 2 s 1 and terminated when it exceeded 400 mmol m 2 s 1. Lamps provided 50 mmol m 2 s 1 at plant height. Plants were irrigated as necessary with 7 mM N, 0.7 mM P, and 2 mM K from a 20N±4.4P±16.6K water-soluble fertilizer (Peter's professional Peat-lite special; Grace-Sierra Horticultural Products, Milpitas, CA). 2.2. Ethephon treatment Foliar sprays of ethephon at 500 (3.46 mM) or 1000 mg l 1 (6.92 mM) were applied once (14 May 1998), twice (14 and 28 May) or three times (14 and 28

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May and 11 June). A factorial combination (two concentrations  three application times) of treatments in a completely randomized design plus a nontreated control group was used as the experimental design. Ten replicate plants of each of eight species were used in each treatment. Eighty plants in each treatment were put on a 1.2 m by 4.2 m bench. Sprays were applied at 0.2 l m 2 by using a hand-held sprayer to wet foliage and stems of the 80 plants uniformly. 2.3. Data collection and analysis Three randomly sampled shoot apices of each of seven species except Liatris were examined through a binocular microscope to determine whether each species was still vegetative or had undergone ¯ower initiation before the ®rst ethephon application. Plants were considered vegetative if no ¯oral primordia were visible. The height of each plant was measured every week. The dates of ®rst visible bud (VB) and ¯ower (FLW) were recorded. We de®ned VB as the emergence of the ¯ower bud from the unfolding leaves at the top of a shoot, and FLW as opening of the ®rst ¯ower. Days to VB and FLW were calculated from the start of the experiment (14 May 1998) to VB and FLW, respectively. At anthesis, ®nal plant height was measured, and the number of in¯orescences and shoots was counted. In¯orescence diameter was measured on Leucanthemum  superbum `Thomas Killen' and stem diameter was measured on L. spicata `Kobold' because differences between treatments became obvious on these two species during the course of the experiment. Data were analyzed using SAS's general linear model (PROC GLM) for analysis of variance (SAS Institute, Cary, NC). Plant height data were graphed, and we estimated the duration of ethephon's effect on stem elongation by making visual comparisons between heights of control and treated plants as depicted on the graphs. A reduction in elongation was assumed to indicate persistence of ethephon's effect. Heights were measured once each week so this was the minimum duration of persistence that could be estimated. 3. Results 3.1. A. millefolium `Weser River Sandstone' Achillea had formed in¯orescence primordia before the ®rst application of ethephon. In¯orescences became visible 6 days after the ®rst application, irrespective of treatments. Ethephon treatment had no effect on days to VB (Tables 1 and 2) but increased the time to FLW by up to 2 days (Table 3). Height

Species

A. millefolium `Weser River Sandstone' C. verticillata `Moonbeam' E. purpurea `Bravado' Leucanthemum  superbum `Thomas Killen' L. spicata `Kobold' M. didyma `Blue Stocking' P. paniculata `Mt. Fuji' P. virginiana `Summer Snow' a

Daysa VB

FLW

0 0 ‡* 0 0 ‡*** ‡** 0

‡* 0 ‡** 0 0 ‡* 0 ‡***

Height at first FLW (cm) ***

0

*** ***

0 0

*** ***

INFL per pot

Shoots per pot

INFL per shoot

‡*** ‡** 0

0 0 0

‡** 0

0

0 0 0 0

**

0 0

***

*

**

0 NT 0 ‡** **

The symbol `‡' indicates an increase in the measured parameter, ` ' indicates a decrease, `0' indicates no change, and `NT' indicates the factor was not tested. * Signi®cantly different from the control at P  0:05. ** Signi®cantly different from the control at P  0:01. *** Signi®cantly different from the control at P  0:001.

T. Hayashi et al. / Scientia Horticulturae 91 (2001) 305±323

Table 1 In¯uence of ethephon on days to visible bud (VB), ¯owering (FLW), height, in¯orescence (INFL) number, shoot number, and INFL per shoot in selected species of herbaceous perennialsa

309

310

T. Hayashi et al. / Scientia Horticulturae 91 (2001) 305±323

Table 2 In¯uence of ethephon on time to visible bud (VB) in selected species of herbaceous perennials Treatments

Days to VB

0 500  1 500  2 500  3 1000  1 1000  2 1000  3 Contrasts Control vs 500 mg l 1 Control vs 1000 mg l 1 500 mg l 1 vs 1000 mg l 1 500 mg l 1  2 vs 1000 mg l Linear for 500 mg l 1 Quadratic for 500 mg l 1 Linear for 1000 mg l 1 Quadratic for 1000 mg l 1

1

1

E. purpurea `Bravado'

M. didyma `Blue Stocking'

P. paniculata `Mt. Fuji'

20 21 20 21 22 24 24

25 28 26 30 33 32 36

43 43 43 44 44 44 45

*

***

**

*

***

**

***

***

**

***

NS NS NS NS NS

NS NS NS *

NS

a

NS NS NS NS

a

Nonsigni®cant. Signi®cant at P  0:05. ** Signi®cant at P  0:01. *** Signi®cant at P  0:001. *

of untreated plants is shown in Fig. 1. Plant height decreased with increasing concentration and number of applications. Plants sprayed three times with ethephon at 1000 mg l 1 were 13 cm shorter than control plants (Table 4). The effect of ethephon at 500 mg l 1 on stem elongation was not pronounced, but that of 1000 mg l 1 was in proportion to the number of applications (Fig. 2). The number of in¯orescences per pot was increased by ethephon, while that of shoots per pot was unaffected (Table 1). Ethephon applied at 1000 mg l 1 reduced stem elongation for up to 2 weeks following application (Fig. 2). 3.2. C. verticillata `Moonbeam' Coreopsis plants were reproductive at the start of the experiment and showed in¯orescences 6 days after the ®rst ethephon application. Neither days to VB nor FLW were affected by ethephon applications, nor was plant height (Table 1). Height of untreated plants is shown in Fig. 1. The number of in¯orescences per pot was increased by ethephon; treatment with 1000 mg l 1 ethephon increased the number of in¯orescences by about 40% compared to that of the untreated

T. Hayashi et al. / Scientia Horticulturae 91 (2001) 305±323

311

Table 3 In¯uence of ethephon on time to ¯ower (FLW) in selected species of herbaceous perennials Treatments

Days to FLW

0 500  1 500  2 500  3 1000  1 1000  2 1000  3 Contrasts Control vs 500 mg l 1 Control vs 1000 mg l 1 500 mg l 1 vs 1000 mg l 1 500 mg l 1  2 vs 1000 mg l Linear for 500 mg l 1 Quadratic for 500 mg l 1 Linear for 1000 mg l 1 Quadratic for 1000 mg l 1

1

1

A. millefolium `Weser River Sandstone'

E. purpurea `Bravado'

M. didyma `Blue Stocking'

P. virginiana `Summer Snow'

32 33 33 33 34 34 34

44 45 45 46 46 48 50

46 48 47 49 50 51 53

49 55 53 59 56 55 58

*

**

*

***

*

**

*

***

***

**

NS NS NS

NS NS NS NS NS

NS NS NS

NS NS NS NS NS NS

a

***

NS

*

NS NS

a

Nonsigni®cant. Signi®cant at P  0:05. ** Signi®cant at P  0:01. *** Signi®cant at P  0:001. *

plants (Table 5). The number of shoots per pot was not affected by ethephon (Table 1). 3.3. E. purpurea `Bravado' Plants were vegetative at ®rst ethephon application. Ethephon treatment signi®cantly increased days to VB and FLW, although absolute differences were small; 1±6 days (Tables 2 and 3). Time to VB and FLW was delayed more by ethephon at 1000 mg l 1 than 500 mg l 1. Time to VB and FLW increased linearly up to 4 and 6 days, respectively, with number of applications at 1000 mg l 1. Height of untreated plants is shown in Fig. 1. Although there were large individual differences in plant height within treatments, mean plant height decreased up to 42 cm as dosage increased (Table 4). There was a signi®cant linear decrease in ®nal plant height with increasing number of applications in both groups of plants treated with ethephon at 500 or 1000 mg l 1. The reduction in the stem elongation rate persisted for up to 2 weeks following ethephon application (Fig. 3).

312

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Fig. 1. Plant height over time of several species of herbaceous perennials not treated with growth regulators. Heights were measured weekly until the ®rst ¯ower on each plant opened.

3.4. Leucanthemum  superbum `Thomas Killen' One-third of surveyed plants possessed an in¯orescence primordium at ®rst ethephon application. Ethephon application did not affect days to VB or FLW (Table 1). Height of untreated plants is shown in Fig. 1. Final plant height decreased as ethephon dosage increased (Table 4). A single application of ethephon at 1000 mg l 1 was nearly as effective in reducing elongation as two applications at 500 mg l 1. Height of plants treated with three applications at 1000 mg l 1 was 44% less than that of the untreated plants. Number of in¯orescences and shoots per pot decreased as ethephon dose increased (Tables 5

Table 4 In¯uence of ethephon on height at ¯ower of selected species of herbaceous perennials Treatments

Height (cm)

Contrasts Control vs 500 mg l 1 Control vs 1000 mg l 1 500 mg l 1 vs 1000 mg l 1 500 mg l 1  2 vs 1000 mg l Linear for 500 mg l 1 Quadratic for 500 mg l 1 Linear for 1000 mg l 1 Quadratic for 1000 mg l 1

1

1

E. purpurea `Bravado'

Leucanthemum  superbum `Thomas Killen'

M. didyma `Blue Stocking'

P. virginiana `Summer Snow'

57 57 55 53 52 49 44

101 94 88 75 89 73 59

64 55 54 50 56 44 36

97 75 75 67 73 63 58

83 77 66 57 72 54 45

***

***

***

***

***

***

***

***

***

***

***

***

***

***

***

NS

NS

NS

NS NS

NS *

a

***

**

***

NS

NS

NS

*

***

***

NS

NS

NS

NS

***

***

***

***

NS

T. Hayashi et al. / Scientia Horticulturae 91 (2001) 305±323

0 500  1 500  2 500  3 1000  1 1000  2 1000  3

A. millefolium `Weser River Sandstone'

a

Nonsigni®cant. Signi®cant at P  0:05. ** Signi®cant at P  0:01. *** Signi®cant at P  0:001. *

313

314

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Fig. 2. Effects of ethephon on stem elongation of A. millefolium `Weser River Sandstone': difference between treated and untreated plants' height. Arrows indicate times of ethephon applications.

and 6). Ethephon decreased in¯orescence diameter in proportion to the dosage; a high dosage resulted in small ¯owers (data not presented). Effect of the ethephon treatment persisted about 5 weeks following a single application of 1000 mg l 1 (Fig. 4). 3.5. L. spicata `Kobold' The response to ethephon was highly variable among plants. Mean time to VB and FLW tended to increase, but contrasts between the control and the treatment were not signi®cant (Table 1). There was a signi®cant increase in stem diameter with increasing concentration and number of applications (data not presented). Height of untreated plants is shown in Fig. 1. The effects of ethephon on stem elongation, in¯orescence number, and shoot number were not detectable. 3.6. M. didyma `Blue Stocking' Plants were vegetative at the start of the experiment. Time to VB and FLW were delayed up to 11 and 7 days, respectively, as the concentration and number of applications of ethephon increased (Tables 2 and 3). Height of untreated plants is shown in Fig. 1. Ethephon suppressed stem elongation (Table 4) and decreased

Table 5 In¯uence of ethephon on in¯orescence number in selected species of herbaceous perennials Treatments

Inflorescences per pot

Contrasts Control vs 500 mg l 1 Control vs 1000 mg l 1 500 mg l 1 vs 1000 mg l 1 500 mg l 1  2 vs 1000 mg l Linear for 500 mg l 1 Quadratic for 500 mg l 1 Linear for 1000 mg l 1 Quadratic for 1000 mg l 1

1

1

C. verticillata `Moonbeam'

Leucanthemum  superbum `Thomas Killen'

M. didyma `Blue Stocking'

157 186 213 191 191 183 187

491 527 653 667 699 649 683

24 21 20 21 22 21 19

74 69 64 62 45 34 28

***

**

**

***

***

**

**

***

NS NS

NS NS NS NS NS NS

***

NS *

NS *

NS NS

a

*

NS NS NS

**

NS NS

*

NS

T. Hayashi et al. / Scientia Horticulturae 91 (2001) 305±323

0 500  1 500  2 500  3 1000  1 1000  2 1000  3

A. millefolium `Weser River Sandstone'

a

Nonsigni®cant. Signi®cant at P  0:05. ** Signi®cant at P  0:01. *** Signi®cant at P  0:001. *

315

316

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Fig. 3. Effects of ethephon on stem elongation of E. purpurea `Bravado': difference between treated and untreated plants' height. Arrows indicate times of ethephon applications.

Fig. 4. Effects of ethephon on stem elongation of Leucanthemum  superbum `Thomas Killen': difference between treated and untreated plants' height. Arrows indicate times of ethephon applications.

Table 6 In¯uence of ethephon on number of shoots per pot, and in¯orescence number per shoot in selected species of herbaceous perennials ( signi®cant at P  0:001)

0 500  1 500  2 500  3 1000  1 1000  2 1000  3 Contrasts Control vs 500 mg l 1 Control vs 1000 mg l 1 500 mg l 1 vs 1000 mg l 1 500 mg l 1  2 vs 1000 mg l Linear for 500 mg l 1 Quadratic for 500 mg l 1 Linear for 1000 mg l 1 Quadratic for 1000 mg l 1

Inflorescences per shoot

1

1

Leucanthemum  superbum `Thomas Killen'

A. millefolium `Weser River Sandstone'

E. purpurea `Bravado'

P. paniculata `Mt. Fuji'

P. virginiana `Summer Snow'

20.7 17.3 16.0 17.8 19.6 18.4 15.8

8.2 9.0 10.3 9.9 9.5 9.8 8.8

7.3 5.5 6.7 6.1 5.6 4.8 5.1

20.7 30.1 27.6 31.6 27.4 26.9 26.3

19.4 18.7 10.8 12.7 14.9 9.6 7.2

**

**

*

**

**

**

**

*

**

**

NSa

NS NS NS NS NS NS

NS NS NS NS NS NS

NS NS NS NS NS NS

NS NS NS NS

*

NS NS **

NS

*

T. Hayashi et al. / Scientia Horticulturae 91 (2001) 305±323

Treatments

NS

a

Nonsigni®cant. Signi®cant at P  0:05. ** Signi®cant at P  0:01. *

317

318

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Fig. 5. Effects of ethephon on stem elongation of M. didyma `Blue Stocking': difference between treated and untreated plants' height. Arrows indicate times of ethephon applications.

the number of in¯orescences (Table 5) as dosage increased. Ethephon's effect on stem elongation persisted about 3 weeks, regardless of concentration (Fig. 5). 3.7. P. paniculata `Mt. Fuji' Plants were vegetative at the start of the experiment. Control plants took 43 and 60 days from the start of experiment to reach VB and FLW, respectively. Spraying ethephon caused a slight (1±2 days) but signi®cant increase in time to VB (Table 2). Time to FLW was delayed up to 5 days by ethephon application, but differences were not signi®cant. Height of untreated plants is shown in Fig. 1. Ethephon had no effect on plant height, the number of in¯orescences per pot, or the number of shoots per pot but did increase the number of in¯orescences per shoot (Tables 1 and 6). 3.8. P. virginiana `Summer Snow' Plants were vegetative at the ®rst application of ethephon. The response to ethephon varied among Physostegia plants. Ethephon did not affect time to VB, but ¯owering was delayed up to 10 days (Table 3). Height of untreated plants is shown in Fig. 1. Plant height decreased linearly with increasing ethephon concentration and number of applications (Table 4). Treatment with the highest

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319

Fig. 6. Effects of ethephon on stem elongation of P. virginiana `Summer Snow': difference between treated and untreated plants' height. Arrows indicate times of ethephon applications.

concentration of ethephon …1000 mg l 1  3† retarded stem elongation by 45% compared with that of the control. Ethephon decreased the number of in¯orescences per shoot (Table 6). The magnitude of stem elongation suppression was proportional to the dosage applied (Fig. 6). Ethephon's effect on stem elongation persisted 2±3 weeks at either concentration. 4. Discussion The effects of ethephon on plant growth and ¯owering varied among species. The chemical delayed VB, ¯owering, or both in those species which were vegetative when the experiment began: Echinacea, Monarda, Phlox, and Physostegia. Ethephon also reduced height in all species except Coreopsis, Liatris, and Phlox. Branching was promoted or suppressed by ethephon, depending on species. Achillea, Coreopsis, and Leucanthemum already had initiated in¯orescences when sprayed with ethephon at the start of this experiment. In¯orescence development of these species was not suppressed by ethephon, nor did ¯owers abort. Further experiments must be done to determine whether ethephon would delay ¯owering when applied at earlier vegetative stages or at higher rates on these species.

320

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Ethephon affects ¯owering in various ways, depending on species and dosage. Ethylene-releasing compounds induced ¯owering in bromeliads (Dole and Wilkins, 1999) and Plumbago indica L. (Nitsch and Nitsch, 1969), but high concentrations of ethephon inhibited ¯ower initiation or caused ¯ower abortion in some plants. Five applications of 1000 mg l 1 delayed ¯owering in Chrysanthemum by up to 123 days (Cockshull and Horridge, 1978). Time to FLW was 180 days from sowing in geraniums sprayed with ethephon at 3000 mg l 1, while control plants ¯owered in 110 days (Semeniuk and Taylor, 1970). No Hebe  franciscana `Variegata' ¯owered when sprayed with ethephon at 2400 mg l 1 (Kristensen and Adriansen, 1988). A slight delay in ¯owering has been observed in some species treated with ethephon at 500±1000 mg l 1. For example, time to FLW was delayed 6 days in Hebe  franciscana `Variegata' sprayed with ethephon at 600 mg l 1 (Kristensen and Adriansen, 1988). Flowering of the ®rst and second in¯orescences was delayed 5 and 10 days, respectively, in seed-propagated geraniums sprayed with ethephon at 1000 mg l 1 (Carpenter and Carlson, 1970), while days to FLW in cutting geraniums was not affected by an ethephon spray at 500 mg l 1 (Tayama and Carver, 1990). In this experiment, spraying ethephon three times at 1000 mg l 1 delayed the ¯owering of Achillea, Echinacea, Monarda, and Physostegia by 2, 6, 7 and 9 days, respectively (Table 3). The concentrations used in this experiment did not cause ¯ower abortion. Although time to FLW tended to increase, effects of ethephon on the ¯owering of Liatris could not be determined because of differences in ¯owering among the plants. Days to FLW varied from 35 to 52 days, even in the control plants (data not shown). Uniformity in plant growth and ¯owering is required for the production of seed-propagated perennials, so uniformity of Liatris plant material should be improved. Plant height control is a vital issue in commercial greenhouses because extremely tall plants are dif®cult to handle, and require more space during production and shipping. Ethephon effectively controlled the height of Achillea, Echinacea, Leucanthemum, Monarda and Physostegia, and could be a valuable tool for growers of these species. Height reductions from control plants at anthesis were 23, 42, 46, 40 and 46%, respectively, when ethephon was applied three times at 1000 mg l 1 (Table 4). These species frequently become excessively tall in container production. Monarda also spreads and branches excessively. Ethephon reduced both height and width in Monarda (data not presented), but caused severe phytotoxicity when applied at 1000 mg l 1. Final plant height of Liatris decreased up to 28% with ethephon treatment, but there was no signi®cant difference between the mean value of treatments and that of the control because some of the treated plants responded only slightly to ethephon. Some Echinacea, Leucanthemum, and Physostegia plants did not respond to ethephon. Emery et al. (1994) investigated the phenotypic plasticity of

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Stellaria longipes stem elongation in response to ethylene and wind, and concluded the ability to synthesize and respond to ethylene could partially account for the plasticity difference between alpine and prairie forms (low and high plasticity, respectively). The exact cause for the variability we observed within species used in this experiment is unclear. We selected experimental subjects for uniform appearance from a larger population, but individuals may have differed in their ability to respond to ethylene. Effects of ethephon on the number of in¯orescences and shoots per pot varied among species. In¯orescence count per pot was increased by ethephon application in Achillea and Coreopsis, and decreased in Leucanthemum and Monarda. Ethephon increased the number of in¯orescences and shoots in geraniums (Carpenter and Carlson, 1970, 1972; Semeniuk and Taylor, 1970; Tayama and Carver, 1990) and the number of ¯owers and branches per plant in azaleas (Shanks, 1969). In contrast, Hebe  franciscana `Variegata' plants sprayed with ethephon had lower in¯orescence counts per pot than untreated plants (Kristensen and Adriansen, 1988). Ethephon reduced the in¯orescence size in Leucanthemum in proportion to the amount applied. Similar results on hydrangea were reported by Shanks (1969). Three applications of ethephon at 1000 mg l 1 resulted in unattractive plants with small in¯orescences. Only those droplets of a spray treatment which are retained on a plant's surface contribute to the dose available for controlling physiological processes (Bukovac et al., 1995). Therefore, the surface area of the plant is one factor that in¯uences the amount of ethephon absorbed from a spray treatment. Plants with small leaves like Coreopsis presumably absorb less solution, which may partly account for the small reduction in Coreopsis stem elongation we observed in response to ethephon. The results of this experiment suggest that the suitable concentration of ethephon for height control of Echinacea, Leucanthemum, Liatris, and Physostegia is about 1000 mg l 1. Two applications of ethephon at 500 mg l 1 were as effective as one application at 1000 mg l 1, so application frequency and rates may be altered according to differences in species, plant height, climate, and culture methods. For Leucanthemum, no more than one application at 1000 mg l 1 should be used to avoid an excessive reduction in ¯ower size. Concentrations lower than 1000 mg l 1 are recommended for Monarda because of severe phytotoxicity on young foliage. Additional experiments using ethephon concentrations higher than 1000 mg l 1 should be conducted on Achillea, Coreopsis, and Phlox, since ethephon had little effect on plant growth and ¯owering at the concentrations used in this work. One of our objectives was to determine if ethephon could be used to delay ¯owering of several popular herbaceous perennials. Under our experimental conditions, ethephon was not an effective tool to signi®cantly delay ¯owering on the tested species.

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Acknowledgements We gratefully acknowledge the donation of plant materials from Bordine Better Blooms, Clarkston, MI. We also thank Dr. Martin J. Bukovac (Michigan State University) for his useful suggestions and Mr. Dan Tschirhart for his greenhouse technical help. References Bukovac, M.J., Leon, J.M., Cooper, J.A., Whitmoyer, R.E., Reichard, D.L., Brazee, R.D., 1995. Spray droplet : plant±surface interaction and deposit formation as related to surfactants and spray volume. In: Proceedings of the Fourth International Symposium on Adjuvants for Agrochemicals, Melbourne, Australia, October 3±6, 1995. Carpenter, W.J., Carlson, W.H., 1970. The in¯uence of growth regulators and temperature on ¯owering of seed propagated geraniums. HortScience 5, 183±184. Carpenter, W.J., Carlson, W.H., 1972. Improved geranium branching with growth regulator sprays. HortScience 7, 291±292. Cathey, H.M., 1964. Physiology of growth retarding chemicals. Annu. Rev. Plant Physiol. 15, 271± 302. Cathey, H.M., Stuart, N.W., 1961. Comparative plant growth-retarding activity of AMO-1618, Phosfon, and CCC. Bot. Gaz. 123, 51±57. Cockshull, K.E., Horridge, J.S., 1978. 2-Chloroethylphosphonic acid and ¯ower initiation by Chrysanthemum morifolium Ramat. in short days and in long days. J. Hort. Sci. 53, 85±90. Dole, J.M., Wilkins, H.F., 1999. Plant growth regulation. In: Dole, J.M., Wilkins, H.F. (Eds.), Floriculture: Principles and Species. Prentice-Hall, Englewood Cliffs, NJ, pp. 90±104. Emery, R.J.N., Reid, D.M., Chinnappa, C.C., 1994. Phenotypic plasticity of stem elongation in two ecotypes of Stellaria longipes: the role of ethylene and response to wind. Plant Cell Environ. 17, 691±700. Heins, R.H., Widmer, R.E., Wilkins, H.F., 1976. Growth regulator recommendations for ¯oricultural crops. Minnesota State Florists Bulletin, June 1, 1976. Heins, R.D., Cameron, A.C., Carlson, W.H., Runkle, E., Whitman, C., Yuan, M., Hamaker, C., Engle, B., Koreman, P., 1997. Controlled ¯owering of herbaceous perennial plants. In: Goto, E., Kurata, K., Hayashi, M., Sase, S. (Eds.), Plant Production in Closed Ecosystems. Kluwer Academic Publishers, Dordrecht, pp. 15±31. Keever, G.J., Foster, W.J., 1989. Response of two ¯orist Azalea cultivars to foliar applications of a growth regulator. J. Environ. Hort. 7, 56±59. Kristensen, L.N., Adriansen, E., 1988. Growth and ¯owering in Hebe  franciscana `Variegata' treated with plant growth regulators. Scientia Hort. 36, 139±149. Larson, R.A., 1985. Growth regulators in ¯oriculture. Hort. Rev. 7, 399±481. Lieberman, M., 1979. Biosynthesis and action of ethylene. Annu. Rev. Plant Physiol. 30, 533±591. Miranda, R.M., Carlson, W.H., 1980. Effect of timing and number of applications of chlormequat and ancymidol on the growth and ¯owering of seed geraniums. J. Am. Soc. Hort. Sci. 105, 273± 277. Moe, R., 1980. The use of ethephon for control of plant height in daffodils and tulips. Acta Hort. 109, 197±204. Nitsch, C., Nitsch, J.P., 1969. Floral induction in a short-day plant, Plumbago indica L., by 2chloroethanephosphonic acid. Plant Physiol. 44, 1747±1748.

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Semeniuk, P., Taylor, R., 1970. Effects of growth retardants on growth of geranium seedling and ¯owering. HortScience 5, 393±394. Shanks, J.B., 1969. Some effects and potential uses of ethrel on ornamental crops. HortScience 4, 56±58. Shoub, J., DeHertogh, A.A., 1975. Floral stalk topple: a disorder of Hyacinthus orientalis L. and its control. HortScience 10, 26±28. Tayama, H.K., Carver, S.A., 1990. Zonal geranium growth and ¯owering responses to six growth regulators. HortScience 25, 82±83. Whealy, C.A., Nell, T.A., Barrett, J.E., 1988. Plant growth regulator reduction of bypass shoot development in azalea. HortScience 23, 166±167.