THE USE OF GROWTH REGULATORS IN NURSERY PRODUCTION OF WOODY ORNAMENTAL PLANTS - I. APPLICATION OF GROWTH HABIT CONTROL OF SOME WOODY ORNAMENTAL PLANTS

These substances represent smallest market share of the principal categories of pesticides reaching about 125 mln. US $ in the United States in 1980. However it shows the fastest growth rate. The largest single market for growth regulators in the United States is as harvest aids for defoliating cotton which is 25 mln. US $ and substances used to control suckers in tobacco 15 mln. US. $. The largest uses for growth regulators outside the USA are of chlormequat chloride on wheat in Europe, ethephon on rubber in Malaysia and ripeners on sugarcane throughout the tropics /Nickell, 1982/. The market of growth regulators used in nursery production of ornamental plants is still marginal.

Plant hormones and synthetic growth regulators can modify plant rooting, flowering, fruit set and development, plant size, axillary bud formation, abscission, plant shape and cell metabolism /Hudson, 1976; Wareing, 1976; Pharis, Ross, 1976; Sachs, Hackett, 1972/. Some of these possible modes of action were used in practice for improving the yield or control the growth of horticultural crops /Cathey, Meredith, 1983; Soczek, 1979; Jourdan, Oplinger, 1983/.

In the nursery production of woody ornamental plants commercial uses for growth substances have been to promote rooting of cuttings and to control weeds /McGuire, Flock, 1975/. The use of plant growth regulators for shaping woody ornamental plants is not commercial and it is still in the phase of research. The main difficulty is a great number of species and cultivars of ornamental plants which differ in their reaction to the plant growth substances. The literature on the problem of chemical shaping of woody ornamentals is scant, if compared to all the information concerning the growth regulators problem. Table 1 shows some results of research concerning the influence of some growth regulators on woody ornamental plants. The results concern the low number of cultivars,

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