Ethephon Applications Delay and Diminish Flowering of Streptocarpus

Streptocarpus (Streptocarpus ×hybridus) are flowering potted plants that grow and flower freely in interior or shaded outdoor areas. The ‘Ladyslippers’ series is a new series of streptocarpus that are propagated through tissue culture. While these plants produce showy finished, flowering plants they flower prematurely during greenhouse production, requiring hand labor to remove inflorescences. Our objectives were to quantify the impact of foliar applications of ethephon on flowering and growth of several ‘Ladyslippers’ streptocarpus cultivars. ‘Ladyslippers Blue Halo’, ‘Ladyslippers Deep Blue Vein’, and ‘Ladyslippers Red Rose’ streptocarpus were planted in 6-in-diameter containers filled with a soilless substrate. Foliar spray applications of solutions containing 0, 125, 250, 500, or 1000 ppm ethephon were applied to 10 plants of each cultivar either two weeks after planting (one application) or two and four weeks after planting (two applications). Plants were grown in a glass-glazed greenhouse with supplemental light provided from high-pressure sodium lamps and irrigated with water supplemented with a water-soluble soluble fertilizer providing 150 ppm nitrogen. After 13 weeks the total number of inflorescences was recorded and the height from the surface of the substrate to the tallest growing point and the diameter of the plant at the widest growing point and 90° from this point were recorded and the Growth Index (GI) was calculated. The impact of ethephon sprays depended on the concentration, number of applications, and cultivar. For example, a single application of 250−1000 ppm ethephon delayed flowering of ‘Ladyslipper Deep Blue Vein’ by 9−27 d, whereas when one application of 1000 ppm was applied to ‘Ladyslipper Red Rose’ flowering was delayed by 9 d. Similarly, two applications of any ethephon concentration delayed flowering of ‘Ladyslipper Deep Blue Vein’ by 13−37 d, while flowering of ‘Ladyslipper Red Rose’ was delayed by 17 d when 1000 ppm was applied. The GI of ‘Ladyslipper Deep Blue’ and ‘Ladyslipper Red Rose’ was unaffected by ethephon and, while the GI of ‘Ladyslipper Blue Halo’ was smaller than untreated plants when one or two applications of 500 or 1000 ppm ethephon was applied, these smaller plants were still of marketable size and quality. Based on our data, we conclude that ethephon may be used to delay the onset of flowering and reduce the number of inflorescences formed prior to finishing with minimal impact on finished plant size.