2017 ASHS Annual Conference

Anecdotal reports of phytotoxicity (stem or leaf burn) on stem cuttings caused by alcohol-based solutions of auxin in commercial propagation have raised questions from propagators about safe rates and use of such alcohol-containing solutions. As part of a study examining this issue, two experiments were conducted using stem cuttings of Impatiens (interspecific) ‘Coral’. Solutions were prepared with three rates of isopropyl alcohol (0%, 25%, or 50%) in combination with three rates of indole-3-butyric acid (IBA; as water-soluble salts): 0, 1000, or 2000 ppm in Expt. 1 for application using a basal quick-dip; or 0, 100, or 200 ppm in Expt. 2 for application using total immersion. Cuttings were rooted in plug trays under intermittent mist in a greenhouse. None of the alcohol/IBA treatments produced stem or leaf burn using either application method in the two experiments. After transplanting rooted cuttings into 10-cm pots and growing to saleable size, stem epinasty was observed on plants grown from cuttings that had been immersed in solutions containing 50% alcohol in combination with 100 ppm or 200 ppm IBA in Expt. 2, whereas no epinasty was observed on any plants from Expt. 1. Following harvest of shoots from plants grown in the 10-cm pots from cuttings initially treated with the nine alcohol/IBA treatments using a basal quick-dip in Expt. 1, shoot dry weights were similar among IBA rates in combination with both 0% and 25% alcohol, whereas shoot dry weight was greater for 0 ppm IBA than for either 100 ppm or 200 ppm IBA in combination with 50% alcohol. In Expt. 2, shoot dry weight was greatest when cuttings had been treated using total immersion in alcohol/IBA solutions containing 50% alcohol, regardless of IBA rate.