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Plant Growth Regulators Plant Growth Regulators are naturally occurring or synthetic compounds that affect plant growth and development 3 Types of Chemical Plant Growth Regulators Growth-inhibiting chemicals Growth-promoting chemicals Root-promoting chemicals Plant Hormones “Chemical Messengers” Auxins Cytokinins Gibberellins Ethylene Rooting Hormones Auxin, which stimulates rooting, is the main component IAA (indoleacetic acid) IBA (indolebutyric acid) NAA (naphthaleneacetic acid) Rooting Hormones Combination of IBA and NAA Powder Formulations Hormodin Hormo-Root Rhizopon Liquid AA Formulations Woods Rooting Compound Dip’ N Grow Liquid Hormones Powder Hormones Cytokinins Responsible for shoot initiation Present in rapidly dividing tissue Benzyladenine (BA) synthetic cytokinin increases offset formation in hosta Gibberellic Acid (GA) Promotes cellular elongation (stretched internodes) Increases fruit set Pro-Gibb: Enlarges flowers and elongates peduncles (stems supporting flowers) Ethylene Gas Affects cell division and development Cause flowering Causes fruit ripening Causes leaf abscission Plant Growth Retardants (PGRs) are any chemicals that slow cell division and elongation in shoot tissues Why Control Growth? Blow-over Plants out-grow pots Watering becomes difficult Increased shipping costs Leggy, low quality plants Methods of Growth Control Pruning costly and time consuming Genetics not always available consumers wary of GMOs Methods of Growth Control Environmental Low controls fertility Negative DIF (Temp) Water Stress Brushing, vibrations, and other mechanical disturbances Many growers find chemical plant growth retardants to be an effective and inexpensive method of growth control How do they work? Gibberellin Inhibitors Release Biosynthesis of Ethylene Notice branching effects Notice height control Synergistic effects of two PGRs Increasing PGR Effectiveness In Non-responsive Perennials Additional Benefits: Control production schedule Increase branching Induce flowering Drought tolerant Pollution tolerant Additional Benefits: Intensely green foliage Resistant to mechanical damage Protection from some pests (whiteflies) Overall higher quality and aesthetic value PGRs for use in Greenhouses: B-Nine Cycocel Bonzi Sumagic Florel A-Rest Chemical PGRs B-Nine (Daminozide) labeled for annuals and herbaceous perennials low activity (relatively safe) Cycocel not (Chlormequatchloride) labeled on many crops causes yellowing above 1500 ppm Chemical PGRs B-Nine/Cycocel Synergistic tank mixes combination Cycocel 800-1,500 ppm B-Nine 800-5,000 ppm Chemical PGRs A-Rest (Ancymidol) intermediate broad label activity Chemical PGRs Bonzi (Paclobutrazol) broad spectrum label high activity Sumagic broad (Uniconazole) spectrum label most active PGR Chemical PGRs Florel, Ethrel, Pistill, (Ethephon) causes plant to release ethylene narrow-spectrum label PGR Efficacy Application timing Dosage Target tissue foliage/stems substrate PGR Efficacy Environmental Conditions environment at application status of plant post-application treatment Application Technique Application Chemical must be accurately measured ALWAYS wear long sleeves, pants, gloves, and shoes with closed toes when mixing and applying PGRs!!!!!! Media Drenches specific volume/pot Foliar Sprays Specific volume/area (0.5gallons/ 100ft2) PGR overdose Example: Bonzi overdose on pansies Ways To Reverse gibberellins (Pro-Gibb) high-N nutrition QUESTIONS?