Developing a successful growth control program is one of the greatest challenges facing bedding plant producers. Many of the popular vegetatively propagated bedding plant species are highly vigorous and require plant growth regulator applications to achieve the accepted product form for retail sales in 4- to 5-inch-diameter containers.
Paclobutrazol is a widely used plant growth regulator for size control of commercially produced ornamental crops such as bedding plants, bulb crops, herbaceous perennials, and flowering woody crops (Barrett and Nell, 1992; Gent, 2004; Gibson and Groninger, 2006; Ranwala et al., 2005; Starman and Williams, 2000). Paclobutrazol is highly active when applied as a foliar spray, drench, or subirrigation application (Barrett and Bartuska, 1982; Million et al., 1999).
Recent growth regulator research has reported that earlier applications such as treating substrate at planting, seed soaks, and bulb dips produce the desired response while allowing for more efficient chemical use (Barrett et al., 2003; Magnitskiy et al., 2006; Ranwala et al., 2005). The liner dip or soak is a technique for delivering the recommended early dose of plant growth regulators with specific protocols to maximize plant growth regulator efficacy. With this application technique, containerized rooted cuttings are dipped in a solution containing the desired concentration of growth regulator before transplant into the final container (Schnelle et al., 2005; Schnelle and Barrett, 2006). Whipker et al. (2000) reported effective control of scaevola in finished containers with 30-s liner dips with 2 to 4 mg·L−1 paclobutrazol solutions. Preliminary research on this technique reported variable size control following liner dips in solutions containing the same plant growth regulator concentration (Cerveny and Barrett, 2002). This led to the hypotheses that in addition to paclobutrazol concentration, dip duration, moisture status of the root substrate, and location of the treatment (indoors vs. outdoors) may impact the efficacy of a liner dip application (Schnelle et al., 2005; Schnelle and Barrett, 2006). This study was designed to test these hypotheses.
Barrett, J.E., Schoellhorn, R.K., Bartuska, C.A., Clark, D.G. & Nell, T.A. 2003 Uniconazole application to container substrate surface prior to planting bedding plants HortScience 38 169 172
Blanchard, M.G. & Runkle, E.S. 2007 Dipping bedding plant liners in paclobutrazol or uniconazole inhibits subsequent stem extension HortTechnology 17 178 182
Boldt, J.L. 2008 Whole plant response of chrysanthemum to paclobutrazol, chlormequat chloride, and (s)-abscisic acid as a function of exposure time using a split-root system MS Thesis, Univ. Florida Gainesville
Cerveny, C.B. & Barrett, J.E. 2002 Limiting variability in sumagic liner dip treatments Southern Nursery Assn. Res. Conf. Proc. 50 378 382
Gent, M.P.N. 2004 Efficacy and persistence of paclobutrazol applied to rooted cuttings of rhododendron before transplant HortScience 39 105 109
Magnitskiy, S.V., Pasian, C.C., Bennett, M.A. & Metzger, J.E. 2006 Controlling plug height of verbena, celosia, and pansy by treating seeds with paclobutrazol HortScience 41 158 161
Million, J.B., Barrett, J.E., Nell, T.A. & Clark, D.G. 1999 Inhibiting growth of flowering crops with ancymidol and paclobutrazol in subirrigation water HortScience 34 1103 1105
Ranwala, N.K.D., Ranwala, A.P. & Miller, W.B. 2005 Paclobutrazol and uniconazole solutions maintain efficacy after multiple lily bulb dip events HortTechnology 15 551 553