QBARS - v34n4 Nutrient Mist Propagation of Azaleas

Nutrient Mist Propagation of Azaleas
G. J. Keever and H. B. Tukey, Jr.

Foliar nutrition has been used during propagation of cuttings to correct nutrient deficiencies brought about by the leaching action of intermittent mist, and to provide nutrients for new growth produced during propagation (1,2,4,5). Azaleas are propagated by stem tip cuttings in large numbers, and have a large leaf area for absorption, and low nutritional requirements (3). For these reasons azalea cuttings were used to evaluate the effectiveness of foliar nutrition in meeting nutritional requirements during, and perhaps, after propagation.

Materials and Methods
Cuttings of Rhododendron cvs. 'Gloria', 'Prize', 'Solitaire', 'Whitewater', 'Dorothy Gish', 'Skyliner', and 'Kingfisher' were treated with rooting substance, inserted in vermiculite and placed under an intermittent mist system with either tap or distilled water. For comparison, similar cuttings were misted with either tap or distilled water to which a soluble fertilizer (Ra-Pid-Gro Plant Food, analysis 23 N-8 P-14 K.) was added, at concentrations varying from 1 oz to 6 oz/gal of mist.

At the beginning of each experiment and at 1-3 week intervals throughout propagation, 2 replicate samples were harvested from each treatment. Differences in fresh weight and rooting were noted; degree of rooting was based on a 1-10 rooting scale, i.e. 1 - no roots, 10 - heavily rooted. Dried and weight cutting samples were analyzed for N, K, Mg, Ca, and P.

Results and Discussion
Cuttings of all cultivars increased in fresh and dry weight during propagation. However, there was no change in total N /sample in cuttings propagated under distilled water. Cuttings of all cultivars under nutrient mist were deeper green with increases in N and P during propagation as compared with those under water mist.

Cuttings under nutrient mist were frequently damaged, especially at higher nutrient concentrations. Symptoms of damage appeared initially as salt deposits along margins of leaves. As the condition worsened, browning of the stems, terminal bud and younger leaves was observed. Leaf drop was frequently heavy. As concentration of nutrients in mist was increased, the time required to initiate and develop roots increased and the rooting index decreased in all cultivars

Cultivars differed in sensitivity to nutrient mist. For example, under 4-oz. nutrient mist treatment, 'Gloria' cuttings rooted poorly during the 9-week propagation period (2.6 rooting index) with extensive foliar burn, and browning of the stems. In contrast, cuttings of 'Prize' rooted better (8.6 rooting index after 9 weeks) with much less injury to the foliage. 'Solitaire', 'Whitewater', 'Dorothy Gish' and 'Kingfisher' responded similarly to 'Prize'.

In addition, cultivars differed in response to low nutrient levels. Rooting of 'Gloria' cuttings under distilled water mist (Fig. 1) was greatly inhibited (3.8 rooting index) and symptoms resembling K deficiency were observed, i.e. an interveinal chlorosis of the foliage, necrosis of basal portions of leaves, and heavy leaf drop. In contrast, cuttings of 'Prize' rooted well (Fig. 1) under distilled water mist (10 rooting index), without K deficiency symptoms. Potassium concentrations were similar in both cultivars during propagation (0.7% dry wt at week 7), at which time deficiency symptoms were present in 'Gloria', but not in 'Prize' and other cultivars. This suggests that minimum K level necessary to avoid deficiencies varies among cultivars, and should be considered in developing recommendations for azaleas based on foliar analysis. Concentrations of N, P, and Mg were low in Gloria cuttings propagated under distilled water mist and it is possible that the deficiency symptoms resulted from a combined effect of several elements rather than K alone.

Azaleas were influenced by both high soluble salts and low nutrient levels. A small amount of nutrients appeared necessary for rooting, but a higher concentration than found in tap water provided no additional benefits, especially to cuttings from stock plants of adequate nutrition. It is recommended that commercial propagators not add nutrients to mist. Furthermore since azaleas are so sensitive to soluble salts salt levels in the water supply must be considered in any successful propagation program.

Literature Cited
1. Dick, J. B., 1960, The rooting and subsequent growth of Chrysanthemum morifolium as influenced by nutrient solution applied in low pressure mist propagation systems, M.S. Thesis, Univ. of Conn., Storrs.

2. Good, G. L. and H. B. Tukey, Jr., 1966, Leaching of metabolites from cuttings propagated under intermittent mist, Proc. Amer. Soc. Hort. Sci., 89:727-733.

3. Keever, G. J., 1979, The effect of intermittent mist on the propagation of azaleas, M.S. Thesis, Cornell Univ., Ithaca, NY.

4. Morton, W. M., 1963, Some effects of low pressure intermittent mist-fertilizer in the vegetative propagation of Euphorbia pulcherrima and Chrysanthemum morifolium, M.S. Thesis, Cornell Univ., Ithaca, NY.

5. Wott, J. A. and H. B. Tukey, Jr., 1967, Influence of nutrient mist on the propagation of cuttings, Proc. Amer. Soc. Hort. Sci., 90:454461.