For a number of flower bulb crops, pre-plant dips or soaks into antigibberellin PGRs are an effective method of height control (Krug et al., 2006a, 2006b; Larson et al., 1987; Ranwala et al., 2005). Previous research has shown that a given solution may be used to dip numerous bulbs without loss of efficacy. For example, at least 55 lily bulbs can be dipped into 1 L of paclobutazol or uniconazole (Ranwala et al., 2005) and 100 hyacinth bulbs can be dipped into 1 L of flurprimidol (Krug et al., 2006b) without loss of efficacy as dipping proceeds. A different question is related to the stability of such solutions over time, that is, how long does a PGR solution remain effective when used in a production situation? Data showing stability over multiple-week time scales would reduce the need to make fresh solutions, thereby reducing cost, minimizing disposal issues, and potentially reducing chemical load into the environment. Such information would be very helpful to bulb forcers and other horticultural users of flurprimidol.
The long-term stability of PGR solutions is not generally known, and typical industry practice is to apply spray or drench solutions within several hours of preparation. Dip solutions offer a complication in that the solution is usually reused many times and potentially over a long period with accumulation of organic matter (peatmoss, plant debris, etc.). In the case of flurprimidol, previous research (Chand and Lembi, 1994) showed the molecule has a half-life of 8.4 and 9.8 d in full sun (for initial concentrations of 0.075 and 0.2 mg·L−1, respectively) as an aquatic herbicide in systems consisting of Eurasian watermilfoil, sediment, and water. This result suggests a high likelihood of rapid degradation of the material, especially if exposed to sunlight. Such conditions, however, are quite different from normal floriculture practice in which most bulb dipping activity would be in a headhouse and not in direct sunlight.
The objectives of this experiment were to determine the longevity of flurprimidol solutions when used in a typical commercial fashion and to confirm whether photolysis of flurprimidol occurs in a horticultural situation. Flurprimidol is widely effective as a dip on many bulbous crops (Miller, 2012a, 2013) and for this reason was chosen for this work.
Anonymous 2012a Flurprimidol. Crop protection database. 17 Nov. 2012. <http://www.agropages.com/AgroData/Detail-697.htm>
Anonymous 2012b Kaye and Laby online. 17 Nov. 2012. <http://www.kayelaby.npl.co.uk/chemistry/3_4/3_4_2.html>
Chand, T. & Lembi, C.A. 1994 Dissipation of gibberellin synthesis inhibitors in small-scale aquatic systems J. Aquat. Plant Mgt. 32 15 20
Krug, B.A., Whipker, B.E. & McCall, I. 2006b Hyacinth height control using preplant bulb soaks of flurprimidol HortTechnology 16 370 375
Larson, R.A., Thorne, C.B., Milks, R.R., Isenberg, Y.M. & Brisson, L.D. 1987 Use of ancymidol bulb dips to control stem elongation of Easter lilies grown in a pine bark medium J. Amer. Soc. Hort. Sci. 112 773 777
Lilly Research Laboratories 1983 Technical report on EL-500. Eli Lilly and Company, Indianapolis, IN
Miller, W.B. 2012a Website for the Flower Bulb Research Program at Cornell University. 17 Nov. 2012. <http://www.flowerbulbs.cornell.edu/>
Miller, W.B. 2012b Narcissus dip summary table. 17 Nov. 2012. <http://www.flowerbulbs.cornell.edu/forcing/narcissus/narcissus_dip_summary.pdf>
Miller, W.B. 2012c Hyacinth dip summary table. 17 Nov. 2012. <http://www.flowerbulbs.cornell.edu/forcing/hyacinth/dip_summary_table.pdf>
Miller, W.B. 2013 Production chain, forcing physiology and flower production systems, p. 287–332. In: Kamenetsky, R. and H. Okubo, eds. Ornamental geophytes: From basic science to sustainable production. CRC Press, Boca Raton, FL
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