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Crop Science Society of America
Dr. Keith Karnok, Editor, University of Georgia Dr. T L. Watschke, Professor Emeritus, Penn State University Dr. J.M. DiPaola, Syngenta Crop Protection, Inc. & Adjunct Professor, Ohio State University Dr. D.P. Shepard, Syngenta Crop Protection, Inc.
Turfgrass Slide Monograph Division C-5, Turfgrass, Crop Science Society of America
Turf Growth Regulation Dr. T.L. Watschke, Dr. J.M. DiPaola, and Dr. D.P. Shepard
Crop Science Society of America
Reviewers
Dr. Todd Bunnell—SePro Mr. Gary Custis—PBI Gordon Dr. David Spak—Bayer
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Copyright © 2011 by Crop Science Society of America
ALL RIGHTS RESERVED. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.
The views expressed in this publication represent those of the individual Editors and Authors.
These views do not necessarily reflect endorsement by the Publisher(s). In addition, trade names are sometimes mentioned in this publication. No endorsement of these products by the Publisher(s) is intended, nor is any criticism implied of similar products not mentioned.
Crop Science Society of America, Inc. 5585 Guilford Road, Madison, WI 53711-5801 USA www.crops.org
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Introduction • Plant growth regulators (PGRs) have been used on
turfgrass areas for more than 50 years. Slowing turfgrass vertical growth and seedhead suppression on low-quality turf areas were the initial primary uses of PGRs. There was little PGR use on high-quality turf areas like golf courses because the PGR products initially available could be phytotoxic to the turf.
• PGR use has increased greatly in recent years due to the development of new, safer PGR products, and they are now a key part of many turfgrass management programs.
• The goal of this presentation is to provide an overview of current PGR use with a focus on high quality turf areas.
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Information Sources • Our understanding of PGRs is the result of extensive
university research and practical applications discovered by turf managers. Several research projects have investigated PGR effects on plant physiology and morphology, which may be beyond the scope of this slide set.
• All of the PGR uses in this overview have been tested scientifically and/or evaluated by numerous turf managers. Data will be presented to support some uses but not all.
• The goal is to provide an overview of the different PGR uses, with the understanding that results will not always be consistent due to differences in turf management plans, environment, species, and cultivar, etc.
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Information Sources • “Plant Growth Regulators and Turfgrass Management.”
T.L Watschke, M.G. Prinster, and J.M. Breuninger. In Turfgrass. Agronomy Monograph 32. 1992. Available from American Society of Agronomy.
• “Applied Physiology of Natural and Synthetic Plant Growth Regulators on Turfgrass.” Erik H. Ervin and Xunzhong Zhang. In Handbook of Turfgrass Management and Physiology. Edited by Mohammad Pessarakli. Available from CRC Press.
• Plant Growth Regulator Society of America (PGRSA)
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Other PGR Information Sources • University research reports • Scientific publications • Trade publications • Info from manufacturers and
distribution sales reps • Discussions with other turf
managers • Internet chat rooms and
websites • The TGIF is an excellent
central resource for all areas of turfgrass research and management.
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Introduction to Turf Growth Regulator Use
• In today’s turf management, growth regulators are used in an array of turf settings.
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An organic compound, natural or synthetic, that when present (or applied) in small amounts results in a change in plant growth and/or development.
Change = Better color, increased density, fewer
clippings, no seedheads, enhanced establishment, improved recuperative potential, deeper roots, larger food reserves, etc.
What is a Turf Growth Regulator?
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Plant Growth Regulator Development
• Growth regulators for turf have been used since the 1950s. • Pre-1980s: Mefluidide developed—it slows turf growth by
slowing cell division. • 1980s: Flurprimidol and paclobutrazol developed—they slow
cell elongation by slowing the production of all forms of gibberellic acid (GA).
• 1990s: Trinexapac-ethyl developed—slows turf growth by slowing the production of GA1, the final form of GA. All other 120+ forms of GA that lead to formation of GA1 are not affected.
• 1990s: Ethephon research on turf initiated—slows turf growth by generating the plant hormone ethylene.
• 2000s: Experimentation with mixing different PGRs initiated.
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PGRs Impact Natural Plant Hormones Levels
• Abscisic Acid: closes stomates and inhibits germination, gibberellic acid (GA), and cytokinins
• Auxins: apical dominance, cell enlargement, root growth, inhibits axillary buds
• Cytokinins: cell division and enlargement, flowering senescence, and inhibits auxin
• Ethylene: stimulated by stress, root growth • Gibberellins: cell elongation, photoperiod response, and
chilling tolerance • Polyamines: increase growth and slow chlorophyll degradation
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The Ideal Turf Growth Regulator
• Slows vertical growth • Inhibits seedheads • Results in no decrease in turf recuperative potential • Improves turf quality • Provides economic savings by reducing mowing
and labor cost • Delivers consistent performance • Acts on all major turf species
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Old PGR Classification
• PGRs were originally classified as Type I and Type II. • Type I PGRs included products that slow turf growth
and seedhead development by slowing cellular division. • Type II PGRs included products that slow turf growth by
reducing the amount of the plant hormone gibberellic acid, which plays a role in cell elongation.
• As additional products were developed, a new PGR classification was proposed to further differentiate mode of action by uptake site and how the PGRs influence plant development.
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New PGR Classification • Class A: Late GA Synthesis Blockers
trinexapac-ethyl • Class B: Early GA Synthesis Blockers
paclobutrazol, flurprimidol • Class C: Mitotic Inhibitors
maleic hydrazide, mefluidide, amidochlor • Class D: Herbicidal with PGR Activity
sulfometuron-methyl, glyphosate, chlorsulfuron, ethofumesate • Class E: Ethylene Production Enhancement
ethephon • Class F: PGR Combinations
trinexapac-ethyl + flurprimidol, trinexapac-ethyl + ethephon