The most important thing  to remember is to apply the plant growth regulator (pgrs) before the crop needs it. The rate and volume of application is also important and if incorrect often leads to stunted growth or phytotoxicity. The pgr's should be selected according to their effectiveness on given crops. If a slow growing crop lies next to a faster growing crop, it is easy to overdose the slow-growing crop and unwanted spray drift can also cause unexpected problems. The efficiency of some pgr's that are active also in the substrate can be reduced by certain components such as bark and other organic materials. while others pgr's are temperature sensitive.  The report briefly describes some specific characteristics of: Atrimmec (dilkegulac sodium): A-Rest (ancymidol),  Bonzi (paclobutrazol), B-Nine (daminozide), Cycocel (chlormequat chloride), Floral (ethepon), GibGro (gibberellic acid), Sumagic (uniconazole), and Topflor (flurprimidol). Jennifer Duffield White, "GrowerTalks"  www.growertalks.com For  precise information on rates of application check www.ces.ncsu.edu/depts/hort/floriculture/software/pgr.html  Another source of information consists of the comprehensive reference book "Tips on Regulating the Growth of Floriculture Crops" by industry professionals and academics. English language, 124 pages, full colour with 140 photographs and illustrations. The book also provides explanations of the influence of the greenhouse environment on plant growth and development, with sections on non-chemical growth control. Fax 001 614 487 1216 E-mail: ofa@ofa.org www.ofa.org