In the daffodil pot plant forcing industry, ethephon sprays have been the most common method of height control (de Hertogh, 1996), but they are not always effective (W.B. Miller, personal communication; Moe, 1980). In a previous paper (Miller et al., 2012), the potential of ethephon substrate drenches for height control in Narcissus was presented. For a wide range of cultivars, ethephon substrate drenches were effective in the range of 100 to 500 mg·L−1, (12 to 60 mg/pot) when delivered in 120-mL drench volume (which is a typical volume used for substrate drenches in floriculture for crops growing in 15-cm pots).
For daffodil, unlike most other floriculture crops, growth control is needed more in the post-greenhouse retail and consumer phases than during commercial greenhouse production. This is because the optimum retail period is during the phase of rapid stem elongation, and therefore most daffodils are shipped from production greenhouses when they are only 1/3 to 1/2 of their final height.
For industry adoption, additional information on ethephon drench efficacy under different application scenarios is needed. For example, if a constant dose of ethephon is given, does drench volume alter the growth retarding effect? What effect does plant size at the time of treatment have on response to ethephon? How does greenhouse temperature influence efficacy of ethephon substrate drenches? How does substrate temperature affect ethylene evolution from ethephon in the root zone?
For this work, we chose three cultivars with dramatically different growth habits. The cultivars Primeur and Ice Follies are large flowered daffodils, with a single (usually) flower per stem, with 1–3 stems per bulb. Tete-a-Tete is a multistemmed and multiflowered cultivar that, even though compact when flowers first open, exhibits significant leaf and stem elongation during the postharvest phase. In addition to examining plant response, we also determined substrate temperature effects on ethylene release from ethephon and the extent of ethephon leaching from a peat-based substrate.
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