Progress Report on Rooting
R. L. Ticknor
North Willamette Experiment Station
Oregon State University, Aurora, Oregon
This report as given at the 1966 Annual Meeting at Tacoma, Washington, included information from the work of David G. Adams for his Ph.D. thesis, entitled "A Morphological Approach to Predicting the Rooting Potential of the Rhododendron Shoot" as well as information from the North Willamette Experiment Station. Dr. Adams will discuss his work in future Quarterly Bulletin articles.
The experiment conducted at the North Willamette Experiment Station was to determine whether foliar application of hormones was as effective as the normal basal application. Three replications of ten cuttings each of Rhododendron 'Mrs. G. W. Leak' were used in this trial, initiated on October 13, 1965. The cuttings were inserted in peat-perlite 1:1 in screen-bottom flats maintained at 70° F. under a mist system. All cuttings were wounded on two sides for maximum root development. The treatments used were an untreated check, Hormodin No. 3 (0.8% indolebutyric acid in talc), Speed Dip No. 2 (0.533% indolebutyric acid, 0.533r, naphthaleneacetic acid, 0.01% phenyl mercuric acetate, 0.0175% boron in 50% alcohol), and Speed Dip No. 2 without the boron. Jiffy Gro No. 2 is the present name for Speed Dip No. 2. Jifly Gro contains 05% rather than 0.533%. indolebutyric acid and naphthaleneacetic acid and does contain 0.0175% boron. Speed Dip, with and without boron, was used both as a basal clip and as a foliar spray, before the cuttings were inserted, at the following concentrations: Full strength, diluted 1 part with 4 parts water, and diluted 1 part with 9 parts water.
The results of this experiment are shown in Table 1. The root systems were evaluated in terms of the size pot necessary to hold the root system that had developed. The per cent in each size category for the 30 cuttings in each treatment is shown in the table.
All hormone treatments produced more large root systems than the check. On these cuttings, which were taken late in the propagating season, the full strength Speed Dip with or without boron gave the highest per cent of heavily rooted cuttings. Almost as high a per cent resulted from a foliar application of Speed Dip No. 2 without boron. Generally, the other spray applications produced root systems about equal to those resulting from the use of Hormodin No. 3.
It may be that the greatest use for spray applications will be to supplement the original basal application for cuttings which remain in the bench for long periods. This idea is under trial by several growers in the Portland area and the results look promising.
In conclusion, an active program is underway at Oregon State University to identify the factors influencing the rooting of Rhododendron cuttings.
These factors include timing, variety, type of buds (flower or vegetative), and type and method of rooting hormone application. The work of Dr. D. G. Adams is being continued by Mr. Charles Johnson, so further information will be available.
The author wishes to thank Klupenger, Kraxberger, and Wil-Chris Nurseries for the un-rooted cuttings of Rhododendron 'Mrs. G. W. Leak' which they donated for this trial.
Per cent of Rhododendron 'Mrs. G. W. Leak' rooted following basal and foliar application of hormones
Cuttings were inserted on October 13, 1965, and results recorded on February 16, 1966
Root Ball Size Treatment 3" 2" 1" Callused Dead Check 13.3 43.3 40.0 3.3 Hormodin No. 3 10.0 30.0 33.3 20.0 6.7 Speed Dip No. 2 Dip 50.0 33.3 6.7 10.0 Speed Dip No. 2 1:5 Dip 20.0 23.3 20.0 20.0 16.7 Speed Dip No. 2 1:10 Dip 13.3 63.3 16.7 6.7 Speed Dip No. 2 Spray 30.0 46.7 13.3 10.0 Speed Dip No. 2 1:5 Spray 13.3 26.7 36.7 20.0 3.3 Speed Dip No. 2 1:10 Spray 10.0 30.0 33.3 20.0 6.7 Speed Dip No. 2 + B Dip 40.0 40.0 10.0 6.7 3.3 Speed Dip No. 2 + B 1:5 Dip 23.3 26.7 30.0 10.0 10.0 Speed Dip No. 2 + B 1:10 Dip 3.3 30.0 50.0 16.7 Speed Dip No. 2 + B Spray 13.3 23.3 36.7 16.7 10.0 Speed Dip No. 2 + B 1:5 Spray 6.7 20.0 30.0 33.3 10.0 Speed Dip No. 2 + B 1:10 Spray 20.0 20.0 23.3 30.0 6.7