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Plant growth regulators (PGRs) are
• naturally occurring or synthetic compounds• inhibit, retard or promote growth of plant or specific organs• do not include substances for plant nutrition/trace elements/
amendments• treated as pesticides
Uses of PGRs
• Chemical growth retardants (CGRs) control plant height (there are non-chemical methods too!)
• Stimulate lateral branching• Promote flower initiation or early flowering• Fruit ripening• Rooting cuttings• Substitute for cold storage
Chemical Product
Ancymidol A-Rest (height control of plugs)
Chlormequat Cycocel (height control of poinsettias/geraniums)
Daminozide B-nine (height control, do not apply as drench)
Ethephon Florel (flower bud abortion/promote vegetative growth)
Paclobutrazol Bonzi (very popular, growth control)
Uniconizole Sumagic (for perennials)
Benzyladenine Configure (promote branching/flower set)
Gibberellin (GA3) ProGibb (promote growth/over application of growth retardants)
BA +GA(4+7) Fascination (avoid leaf yellowing/drop, overcome effects of growth retardants)
Indole Acetic/Butyric Acid Hormo-Root/RooTone (inducing roots)
Common PGRs used in the ornamental industry
Considerations for applying PGRs
Timing:
• Apply after sufficient plant growth has happened or rapid growth has started
• Earlier applications may stop growth completely• Remember PGRs can’t reduce already existing growth• Timing based on physiological stage and not on chronological
stage
Considerations for applying PGRs
Target:
• Drenches use larger volume but lower concentration• Foliar sprays should be uniform• If dipping, use consistent soaking time, 10 sec• Some PGRs are effective if applied to roots (ex: Bonzi)
Considerations for applying PGRs
Dosage:
• Read label• Dosage = concentration x volume applied• Dip (B-nine) and drench (Bonzi) methods can be fairly accurate)• Spray can be uneven, half gal per 100 ft2; base spray application
on areas and not plants
Considerations for applying PGRs
Environment:
• Drenching may not be suitable in some substrates with bark media
• Morning applications when evaporation is low are best• Plants should not be stressed at application• Plants should not be watered too soon after application
Crop growth retardants (CGRs)
• Blow over• Watering becomes difficult• Increased shipping costs• Leggy low quality plants• Damage during shipping• Customer preference
How to control crop growth?
• Pruning• Genetics• Environmental control• Mechanical stress• Chemical control
Micro Tina Tomatoes
Environmental control (modify fertility)
0.12 0.65 1.18 1.71 2.24 2.77 dS/m
0.12 0.65 1.18 1.71 2.24 2.77dS/m
Environmental control (negative DIF)
• DIF stands for difference in night and day temperature
• Negative DIF indicates that night temperature is greater than day temperature (night 60, day 55 deg F)
• Negative DIF for 3-4 h during the morning can reduce plant height
• This is possible in northern states during winter months by allowing outside air in the greenhouse
Mechanical Stress
• Thigmamorphogenesis: growth and developmental responses of plants to rubbing, twisting, or physical contact
• Using mechanical stress, we can control plant height, improve plant strength, stress tolerance, insect resistance (Latimer, 1998)