A foliar spray application of indole-3-butyric acid promotes rooting of herbaceous annual cuttings similarly or better than a basal dip

Abstract

Foliar rooting hormone applications containing indole-3-butyric acid (IBA) to unrooted vegetative cuttings have gained popularity as they reduce labor costs and the risk of spreading diseases compared to standard basal dips. The objective of this study was to quantify if foliar applied 20% IBA promotes adventitious rooting of herbaceous annuals similarly to a basal dip application of IBA + 1-napthaleneacetic acid (NAA). Dahlia (Dahlia pinnata) Venti™ ‘Passion Fruit’, osteospermum (Osteospermum ecklonis) Serenity™ ‘Lavender Frost’, scaevola (Scaevola aemula) Scalora® ‘Brilliant’ and geranium (Pelargonium × hortorum) Sunrise™ ‘Lavender + Red Eye’ cuttings received a foliar spray of 0, 150, 300, or 600 mg·L–1 IBA at 0.2 L·m–2; 150 or 300 mg·L–1 IBA at 0.8 L·m–2; or a basal dip of 100 mg·L–1 + 50 mg·L–1 or 200 mg·L–1 + 100 mg·L–1 IBA + NAA. In most cases, cuttings receiving a foliar application of 300 mg·L–1 IBA at 0.8 L·m–2 had either comparable or greater root dry mass than cuttings receiving a basal dip of IBA + NAA and outperformed the control. After 14 d, root dry mass was generally greatest when cutting were treated with 300 mg·L–1 IBA at 0.8 L·m–2 and was an equal or better alternative to a basal dip. For the most effective results, rooting hormones should be utilized when the DLI integral is <12 mol·m–2·d–1.