Ancymidol and uniconazole are plant growth regulators that slow plant growth by inhibiting sterol and gibberellin biosynthesis (Henry, 1985; Shive and Sisler, 1976). These growth regulators have been shown to restrict height of several floricultural crops, including poinsettia [Euphorbia pulcherrima (Holcomb et al., 1983)], chrysanthemum [Dendranthema × grandiflorum (Barrett, 1982)], lily [Lilium speciosum (Bailey and Miller, 1989)], and several bedding plant species (Barrett and Nell, 1992).
Use of plant growth regulators during woody ornamental plant production is less common than in floriculture crop production. Several studies have tested nursery crop response to uniconazole (Frymire and Cole, 1992; Frymire and Henderson-Cole, 1992; Henderson and Nichols, 1991; Norcini and Knox, 1989; Warren, 1990; Warren et al., 1991). Woody plant response to growth regulators varies with environment, application rate and method, and species being treated. Recommendations for rate and timing of effective growth regulators for a variety of woody species are needed (Warren et al., 1991).
Oakleaf hydrangea is an important container crop for many nurseries in the southern and midwestern United States. It is used in the landscape as a border or as a solitary specimen plant. In commercial practice, shearing is required at least once or twice during the production cycle to produce a salable plant. After shearing, however, oakleaf hydrangea is susceptible to dieback, especially when excess moisture is present (P. Havenar, personal communication). A search of the literature revealed no reports regarding research on control of plant size of oakleaf hydrangea with growth regulators; however, uniconazole has been shown to reduce shoot length, stem dry weight, leaf area, and inflorescence dry weight of florists’ hydrangea [Hydrangea macrophylla (Bailey, 1989)]. The objective of this research was to determine whether foliar or substrate surface applications of ancymidol or uniconazole, or pinching reduces plant growth of oakleaf hydrangea.
Barrett, J.E. 1982 Chrysanthemum height control by ancymidol, PP333, and EL-500 dependent on medium composition HortScience 17 896 897
Bonamino, V.P. & Larson, R.A. 1978 Influence of potting media, temperature, and concentration of ancymidol on growth of Chrysanthemum morifolium Ramat J. Amer. Soc. Hort. Sci. 103 752 756
Davidson, H., Mecklenburg, R. & Peterson, C. 2000 Nursery management administration and culture. 4th ed. Prentice-Hall, Upper Saddle River, N.J
Frank, R. & Day, E.W. 1976 Ancymidol, p. 475–482. In: G. Zweig (ed.). Analytical methods for pesticides, plant growth regulators, & food additives. Academic Press, Waltham, MA
Frymire, R.M. & Cole, J.C. 1992 Uniconazole effect on growth and chlorophyll content of pyracantha, photinia, and dwarf burford holly J. Plant Growth Regulat. 11 143 148
Frymire, R.M. & Henderson-Cole, J.C. 1992 Effect of uniconazole and limited water on growth, water relations, and mineral nutrition of ‘Lalandei’ pyracantha J. Plant Growth Regulat. 11 227 231
Henderson, J.C. & Nichols, T.H. 1991 Pyracantha coccinea ‘Kasan’ and ‘Lalandei’ response to uniconazole and chlormequat chloride HortScience 26 877 880
Henry, M.J. 1985 Plant growth regulating activities of sterol and gibberellin biosynthesis inhibitors Bul. Plant Growth Regulat. Soc. Amer. 13 2 9 11
Holcomb, E.J., Ream, S. & Reed, J. 1983 The effect of BAS 106, ancymidol, and chlormequat on chrysanthemum and poinsettia HortScience 18 364 365
Murray, G.E., Sanderson, K.C. & Williams, J.C. 1986 Application methods and rates of ancymidol on plant height and seed germination of bedding plants HortScience 21 120 122
Norcini, J.G. & Knox, G.W. 1989 Response of Ligustrum ×ibolium, Photinia ×fraseri, and Pyracantha koidzumii ‘Wonderberry’ to XE-1019 and pruning J. Environ. Hort. 7 126 128
Shive, J.B. & Sisler, H.D. 1976 Effects of ancymidol (a growth retardant) and triarimol (a fungicide) on the growth, sterols, and gibberellins of Phaseolus vulgaris (L.) Plant Physiol. 57 640 644
Snell, M. & Eysell, E. 1974 Ancymidol, a new growth regulator for ornamental plants. Proc. Brit. Weed Control Conf. 12:115–122
Tschabold, E.E., Meredith, W.C., Guse, L.R. & Krumkalns, E.V. 1975 Ancymidol performance as altered by potting media composition J. Amer. Soc. Hort. Sci. 100 142 144
Warren, S.L., Blazich, F.A. & Thetford, M. 1991 Whole-plant response of selected woody landscape species to uniconazole J. Environ. Hort. 9 163 167
Wulster, G.J. & Gianfagna, T.J. 1991 Freesia hybrida respond to ancymidol, cold storage of corms, and greenhouse temperatures HortScience 26 1276 1277