ASHS 2025 Conference

Our objective was to evaluate the efficacy of benzyladenine or ethephon foliar spray applications to control growth and improve branching of ‘Dragon Wing® Red’ begonia (Begonia interspecific). On 10 Sep 2024, a 288-cell plug tray of ‘Dragon Wing® Red’ begonia was received from a commercial propagator. Plugs were transplanted into 15.2-cm-diameter containers filled with a commercially available soilless peat-based substrate. Plants were grown in a glass-glazed greenhouse under supplemental and day-extension lighting provided by 780-W light-emitting diode lamps from 0600 to 2200 HR (16-h photoperiod) with an air temperature set point of 20 °C. At 7 d after transplant, 10 single-plant replicates were treated with a solution containing benzyladenine or ethephon and a surfactant. Plants received a foliar spray (vol. 0.2 L·m–2) containing deionized water (0 mg·L–1; untreated) or 10, 30, 50, 70, or 90 mg·L–1 benzyladenine or 125, 250, 500, 750, 1,000, or 2,000 mg·L–1 ethephon. Benzyladenine and ethephon foliar spray applications influenced begonia growth and development differently. Benzyladenine concentrations increasing from 10 to 90 mg·L–1 suppressed growth index, an integrated measurement of height and diameter, by 1% to 3%, respectively, compared to untreated plants. Branch number increased by 32% to 64% (3 to 5 branches) as concentrations increased from 30 to 90 mg·L–1 benzyladenine compared to untreated plants. Shoot dry weight (SDW) decreased as benzyladenine concentrations increased, but time to flower (TTF) was unaffected. Ethephon concentrations increasing from 125 to 2,000 mg·L–1 influenced plant height, plant diameter, growth index, branch number, SDW, and TTF. Growth index was suppressed as ethephon concentrations increased from 125 to 2,000 mg·L–1, resulting in plants that were 11% to 30% smaller than untreated plants. Compared to untreated plants, ethephon concentrations increasing from 125 to 1,000 mg·L–1 improve branching with 1 to 2 more branches developed per plant. Ethephon concentrations of 125 to 2,000 mg·L–1 limited SDW by 23% to 49% compared to untreated plants. Time to flower was delayed by 3 to 10 d as concentrations increased from 125 to 2,000 mg·L–1 ethephon. Begonia plants sprayed with ≥750 mg·L–1 ethephon developed phytotoxicity and had reduced ornamental quality. Our results indicate that growers can attain growth control and enhance branching with foliar spray applications of 30 to 90 mg·L–1 benzyladenine or 125 to 500 mg·L–1 ethephon, but these should be used as an initial range for trials during greenhouse production.