Ethephon Drenches and Sprays for Height Control in Spring Bulbs

Ethephon has long been used as a growth regulator for spring bulb production, and is commonly applied to daffodils and hyacinths as 1000–2000 mg/L sprays.  Recently we showed efficacy of ethephon as a substrate drench in daffodil. Over the last three years, we have conducted numerous experiments to develop further information on ethephon as a substrate drench for spring bulb crops.  These experiments have resulted in the following main conclusions that will be presented in detail: 1) ethephon substrate drenches are effective over a range of forcing temperatures that are used in the industry; 2) the height controlling response is related to dose received per pot, such that varying drench volumes and concentrations possible as long as a consistent dose (mg ethephon) is delivered per pot; 3) a continuum of application volumes from drench to heavy spray (“sprench”) also gives similar results; and 4) within a rather wide range, a uniform final height is achieved with application dates varying from 1 to 10+ days in the greenhouse. In other words, plant height at treatment is not related to final height at flowering or at flower senescence, a rather unusual result. Surprisingly, given the well-known negative response of tulip bulbs to ethylene, ethephon drenches and sprays are proving effective for height control in tulip.  Preliminary results showing the efficacy of ethephon in tulip will be presented.