Influence of Growth Regulators on Growth, Bulbing, Maturity and Yield in Onions1

Abstract

Short, medium, and long-day onions ( Allium cepa L.) were field grown under normal spring conditions of increasing daylength. Three growth regulators, (2-chloroethyl)phosphonic acid (ethephon), gibberellic acid (GA 3 ), and succinic acid-2,2-dimethylhydrazide (SADH) were applied as sprays at different concentrations at the 4, 6, and 10 leaf stages of development. Ethephon reduced plant height and number of leaves and initiated earlier bulbing. Ethephon-treated plants also had a higher bulbing index (bulb/neck diameter) early in the season due to more rapid bulb enlargement but difference did not persist to maturity and at harvest ethephon significantly reduced both bulb diameter and yield. Ethephon failed to bring about earlier maturity based on plant lodging at harvest. GA 3 increased the number of leaves per plant and percentage of plants initiating multiple growing points. No measurable responses to SADH were noted.