| Plant growth retardants (PGRs) can cause dwarfing of Plants. They can be used for inhibiting growth of lawn grasses, and thus reducing the number of mowing However, the effect will not be satisfactory if they are not applied properly. In this study, the effects of four PGRs on growth rate and quality of the two lawn species Bermudan grass (C.dactylon×C.transvadlensis) and ryegrass (Lolium perenne L.) at different concentrations were investigated. The results obtained Showed:1. The four PGRs were different in effect, with uniconazole having the strongest effect on dwarfing of Bermudan grass and ryegrass, B9 having no obvious effect, chlormequat and mepiquat chloride being intermediate.2. The effect of the same PGR varied with the concentration used. Uniconazole at 50mg/L, chlormequqt at 1000mg/L, and mepiquat chloride at 1000mg/L were the optimum concentration for spraying according to combined coordination of dwarfing effects and economic and ecological benefits.3. The PGRs influenced growth of the lawn species mainly by (1) retarding growth and thus reducing mowing; (2) promoting tillering and thus increasing plant densities; (3) elevating the content lf chlorophyll in leaves and thus prolonging duration of green leaves, and (4) increasing the ratio of roots to shoots and thus improving creeping growth.4. The optimum stage for application of the PGRs was the vigorous grow stage of the grassed. The satisfactory results could be achieved when the warm-seasoned grasses were treated from June to July and the cool-seasoned grasses from April to May or from September to October.5. The duration of effects of the PGRs varied with the PGRs and their concentrations used, times of spraying, grass species and the local climate. In this study, the effect of PGRs is in 40-60 days.6. Use of PGRs will lower the cost by reducing mowing and fertilization, which will bring about a remarkable economic return when applied right in lawn management.
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