Efficacy of ethephon on vegetative annuals

Plant response to ethephon treatment was tested on 27 cultivars of vegetative annuals that have spreading and trailing growth habits. A control treatment was compared to 500 and 1000 mg.L(-1) (ppm) foliar spray treatments of ethephon. Plant height and/or width index were significantly reduced for 81% of the cultivars tested. Responsive cultivars were alternanthera (Alternanthera dentata), brachyscome (Brachyscome iberidifolia) 'Toucan Tango'; calibrachoa (Calibrachoa hybrids) 'Colorburst Red', 'Million Bells Cherry Pink', and 'Trailing Pink'; diascia (Diascia x hybrida) 'Sunchimes Rose' and 'Red Ace'; double impatiens (Impatiens wallerana) 'Tioga Red' and 'Tioga White'; sweetpotato vine (Ipomoea batatas) 'Sweet Caroline Bronze'; lantana (Lantana camara) 'Patriot Cherry' and 'Samantha'; nemesia (Nemesia x hybrida) 'Aromatica Dark Lavender', 'Blue Bird', and 'Blueberry Sachet'; nolana (Nolana paradoxa) 'Blue Eyes'; ivy geranium (Pelargonium hybrida) 'King of Balcon'; petunia (Petunia x hybrida) 'Cascadia Pink', 'Mini Bright Pink', and 'Supertunia Mini Purple'; bacopa (Sutera cordata) 'Bridal Showers'; and vinca vine (Vinca minor) 'Illumination'. Ethephon was not effective on monopsis (Monopsis unidentata) 'Royal Flush', persicaria (Persicaria microcephala) 'Red Dragon', or calibrachoa 'Liricashower Rose'. Different cultivars of petunia showed varied responses to ethephon treatments as did trailing snapdragon (Antirrhinum majus) 'Chandelier Yellow' and 'Luminaire Yellow'. Flower number was reduced in 55% of the cultivars due to a delay in flowering. The experiment finds efficacy of ethephon for most cultivars treated at rates greater than or equal to that used commercially, however more research is needed to determine optimum concentrations for the specific cultivars. Chemical name used: ethephon (2-chloroethyl) phosphonic acid.