The most recently developed growth retardants are 16, 17-dihydro-GAs. These compounds were evaluated initially for activity as inducers of flowering in Lolium temulentum, but were found to act as effective growth retardants on Graminaceous species (15), with exo-16, 17-dihydro-GA5 (applied as the 13-acetate) being one of the most effective examples. Like the acylcyclohexanediones these compounds also inhibit 2-oxoglutaratedependent dioxygenases, but are more specific for the GA-metabolizing enzymes since the retardant mimics the GA substrate, rather than 2oxoglutarate, which is common for all reactions.