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1 EVALUATION OF FL URPRIMIDOL ON ORNAMENTAL SPECIE S IN RELATION TO PRUNING TIME AND METHOD OF APPLICATION By HUNTER CLAYTON SMITH A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2013
2 2013 Hunter Clayton Smith
3 To my wife Kali, for her support throughout this incredible experience and to my parents who provided me with a solid foundation of values to be successful
4 ACKNOWLEDGMENTS This project has been an incredible and challenging two year experience. I wish to thank, first and foremost, my graduate advisor, Dr. Jason Ferrell. His experience and gui dance helped shape the vision for th is project and without his support this work would not have been possible. He is devoted to the success of his graduate students and I am truly grateful for his dedication. I would like to thank my committee members, Dr Jim Barrett, Dr. Bob Stamps, and Dr. Brent Sellers, for their input and suggestions in the development of this project. I would especially like to thank Jose Fernandez, Sarah Berger, Mike Durham, and Daniel Abe for their hard work a nd assistance While conducting research of their own, they always made themselves available whenever I needed help. I would like to thank Dr. Tyler Koschnick and SePRO Corporation for the funding of this project. They provided the framework and resources to make this project a success I want to thank my parents and brother who have provided unconditional support and encouragement throughout my graduate studies. While I do not see them as often fe, Kali, for her sacrifices and patience during this process. Her faith and fortitude are what drives me to be a better person and husband.
5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 7 LIST OF FIGURES ................................ ................................ ................................ .......... 8 LIST OF ABBREVIATIONS ................................ ................................ ............................. 9 ABSTRACT ................................ ................................ ................................ ................... 10 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 12 Landscaping Industry ................................ ................................ .............................. 12 Plant Growth Regulators ................................ ................................ ......................... 13 Gibberellic Acid Biosynthesis ................................ ................................ ........... 15 Flurprimidol ................................ ................................ ................................ ....... 16 Paclobutrazol ................................ ................................ ................................ .... 17 Application Techniques ................................ ................................ ........................... 18 2 EVALUATION OF HOW TR IMMING TIME INFLUENC ES FLURPRIMIDOL PERFORMANCE ON VIBUR NUM SPECIES ................................ ......................... 21 Background ................................ ................................ ................................ ............. 21 Materials and Methods ................................ ................................ ............................ 22 Result s and Discussion ................................ ................................ ........................... 23 3 DETERMINE WHICH APPLICATION METHOD PROVIDES BEST PLANT GROWTH REGULATION ................................ ................................ ....................... 31 Background ................................ ................................ ................................ ............. 31 Materials and Methods ................................ ................................ ............................ 32 Result s and Discussion ................................ ................................ ........................... 33 4 EVALUATION OF PACLOBUTRAZOL/FLURPRIMIDOL DRENCH APPLICATION EFFICACY ON LIGUSTRUM HEDGES ................................ ......... 41 Background ................................ ................................ ................................ ............. 41 Materials and Methods ................................ ................................ ............................ 42 Result s and Discussion ................................ ................................ ........................... 43 5 CONCLUSIONS ................................ ................................ ................................ ..... 47
6 A PPENDIX: UNTREATED VIBURNUM ODORATISSIMUM AND V. SUSPENSUM REGROWTH, BIOMASS, AND VISUAL ASSESSMENT DATA ............................. 49 LIST OF REFERENCES ................................ ................................ ............................... 51 BIOGRAPHICAL SKETCH ................................ ................................ ............................ 53
7 LIST OF TABLES Table page 3 1 Visual assessment rating to evaluate overall growth regulation in E. pungens and L. chinense (2013) ................................ ................................ ...................... 38 4 1 Visual assessments to evaluate overall growth regulation in L. japonica .......... 46 A 1 Regrowth and Biomass data of untreated V. odoratissimum and V. suspensum in relation to trimming time (2012 13). ................................ ............. 49 A 2 Visual assessments in untreated V. odoratissimum (2013). ............................... 50 A 3 Visual assessments in untreated V. suspensum (2013). ................................ ... 50
8 LIST OF FIGURES Figure page 1 1 Isoprenoid pathway for the production of Gibberellic acid. A simplified schematic of the steps involved in GA biosynthesis and site of action for specific PGRs (Radmacher 2000). ................................ ................................ ..... 20 2 1 Shoot regrowth (15 WAT) of flurprimidol treated Viburnum odoratissimum compared to an UTC. Error bars represent the standard error of the means for each treatment (n=60). ................................ ................................ .................. 27 2 2 Biomass (15 WAT) of flurprimidol treated Viburnum odoratissimum compared to an UTC. Error bars represent the standard error of the means for each treatment (n=60). ................................ ................................ .................. 28 2 3 Shoot regrowth of flur primidol treated Viburnum suspensum compared to an UTC Letters indicate a significant difference between the treatment means. Error bars represent the standard error of the means for each treatment. ......... 29 2 4 Biomass of flurprimidol treated Viburnum suspensum compar ed to an UTC (18 WAT)(2012 13). Error bars represent the standard error of the means for each treatment (n=60). ................................ ................................ ....................... 30 3 1 Shoot regrowth of Elaeagnus pungens treated by a granular or drench flurprimidol application compared to an untreated control (2012 13). Error bars represent the standard error of the means for each treatment (n=30). ....... 36 3 2 Biomass of Elaeagnus pungens treated b y a granular or drench flurprimidol application compared to an untreated control (15 WAT) (2012 13). Error bars represent the standard error of the means for each treatment (n=30). ............... 37 3 3 Shoot regrowth of Loropetalum chinense treated with a granular or drench flurprimidol application compared t o an untreated control (2012 13). Error bars represent standard error of the means for each treatment (n=30). ............. 39 3 4 Biomass of Loropetalum chinense treated by a granular or drench flurprimidol application compared t o an untreated control (2012 13). Error bars represent standard error of the means for each treatment (n=30). ............. 40 4 1 Shoot regrowth of Ligustrum japonica treated with three rates of flurprimidol/paclobutrazol solution compared to an untreated control (2012 13). Error bars represent the standard error of the means for each treatment. .. 45
9 LIST OF ABBREVIATIONS ABA Abscisic acid DAA Days after application DBA Days before application GA Gibberellic acid, Gibberellins IFAS Institute of Food and Agricultural Sciences PGR Plant Growth Regulator MAT Months after treatment UTC Untreated control WAT Weeks after treatment
10 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for th e Degree of Master of Science EVALUATION OF FLURPR IMIDOL ON ORNAMENTA L SPECIES IN RELATION TO PRUNING TIME AND METHOD OF A PPLICATION By Hunter Clayton Smith December 2013 Chair: Jason Ferrell Major: Agronomy The plant growth regulator flurprimidol (Cutless G) is registered for use on ornamental plants to reduce internode elongation and reduce trimming frequency. It has been hypothesized that timing of the trimming event can be related to the efficacy of the f lurprimidol treatment. Granular flurprimidol was applied to well establish plants at a standard rate of 22.5 g ai (15 lbs product) /1000ft 2 on April 23 rd 2012 and May 1 st 2013 Two common Florida landscaping species, Viburn um odoratissimum and V. suspensum were selected to be trimmed at different times to investigate flurprimidol efficacy by measuring plant regrowth biomass, and visual appearance The five trimming treatments occurred at 7 days before (flurprimidol) application (DBA ), 0 DBA, 7 days after application (DAA), 14 DAA and 21 DA A No significant differences were o bserved in trimming times for flurprimidol treated V. odoratissimum or V. suspensum V. odoratissimum shoot regrowth was significantly reduced in flurprimidol treated plants compared to the UTC. Shoot regrowth and biomass of f lurprimidol treated V. suspensum was also not significantly different from the UTC. Two application methods (granular and drench) f or flurprimidol were evaluated o n E laeagnus pungens and L oropetalum chinense in Ap opka, FL. I n E. pungens, both application methods reduced
11 shoot regrowth and biomass while sustaining a higher aesthetic value than the control. Plant biomass was significantly reduced in both treatments compared to the untreated control ( 17.0% granular a nd 13.9% drench). In L. chinense, visual ratings were similar as both applications displayed a significant difference in overall plant growth regulation compared to untreated plots for at least 15 WAT. Plant shoot regrowth was significantly decreased 39.5 % and 38.2 %, compared to the untreated, by the granular and drench treatments, respective ly. A paclobutrazol/flurprimidol drench was investigated on Ligustrum hedges in 2012 and 2013 at the University of Florida Energy Park in Gainesville, FL. Three rates were investigated (6, 8, and 12g ai /plant) to determine an effective dose to control the growth rate of the difficult species. Shoot regrowth and visua l ratings were measured every other week to assess r ate efficacy. The lowest rate (6g ai) produced the least amount of regrowth but was not significantly different from the other chemical treatments. Visually ratings indicated that all rates were not significantly different.
12 CHAPTER 1 INTRODUCTION Landscaping Industry The upkeep of commercial landscapes is a major bu siness throughout the country as groundskeepers are required to produce high quality landscaping year round One responsibility is to properly maintain woody ornamental shrubs requiring numerous trimmings throughout t he growing season. Each trim ming event requires great amounts of time a nd energy, in addition to labor costs associated with cleanup and disposing of clipped material As a solution to high operational costs, landscaping companies have experimented with applying plant growth regulators (PGRs) to decrease trimming frequencies on the fast growing species. PGRs have been used commercially for several decades with debatable levels of success, but recent advances in different modes of action and product formu lation are improving PGR performance. Plant growth regulators are classified by mechanism of action within the plant. The early PGRs performed like growth inhibitors rather than growth regulators. Often applied as a foliar spray, chemicals would arrest pl ant growth and development by interfering with cell division. Though the effects were rapid, the resulting phytotoxicity and/or irregular performance hindered their acceptance (March et al. 2013). Current PGRs are able to interrupt a specific mechanism th at is much less likely to result in growth habit, fewer required trimmings with less biomass, and reductions in operational costs (i.e. equipment wear and labor)
13 Pla nt Growth Regulators As stationary organisms, plants are completely dependent on abiotic factors to survive and promote new growth. Temperature, water, light, and nutrients all influence plant health and growth rate as plants constantly adapt to the change s in its environment Plants respond to these factors as growth is internally regulated by the movement of carbohy drates produced from photosynthesis and the ratio of phytohormones that affect specific plant mechanisms. Trimming (the removal of terminal bu ds) has been shown to stimulate the redistribution of carbohydrate reserves to mend injured tissue and promote new growth (Heyden and Stock 1996) Landscapers often select species which are relatively tolerant to abiotic factors as this decreases the amoun t of input required to maintain the plants. But independent of species, healthy and growing plants will always require trimming throughout the year. As the plants become older and more established, trimming becomes more difficult and time consuming. Certai n species become so large that worker safety becomes a significant issue for landscaping companies. Plant growth regulators are applied to decrease trimming frequency, plant biomass, labor, equipment wear, and worker safety concerns. Plant growth regulato rs are classified into five main classes (A E) based on site of action within the plant Class A (i.e. trinexapac ethyl) PGRs prevent the conversion of GA 20 into GA 1 at the end of the gibberellin pathway (March et al. 2013). Though various types of gibbere llins are produced, they are never converted to the active form (GA 1 ) which is primarily responsible for cell elongation (Rademacher 2000). Class B (i.e. chlormequat chloride, flurprimidol, paclobutrazol, uniconazole) compounds interfere much earlier in th e GA biosynthetic pathway by inhibiting the enzyme ent kaurene oxidase which converts ent kaurenol into ent kaurnal (McCullough 2005). These
14 chemicals are commonly applied to high value turf grass and container grown plants to reduce clippings and produce a high quality ae sthetic appearance (Krug et al. 2005; Totten et al. 2006). Symptoms include reduced internode length, dark green foliage, or sup pressed compact growth (Norcini 1991). Class C (i.e. maleic hydrazide mefluidide) are cell division inhibitor s. This chemistry, previously known as the Type I PGRs, is primarily applied to plant foliage to suppress growth through in hibition of mitosis (Rademacher 2000). In recent years, the use of these products has declined due to phytotoxicity concerns. Class D (i.e. imazapic, sulfometuron) is known as the herbicide category as they interrupt vital physiological plant processes (March et al. 2013). These compounds are most often applied to turfgrass at sub lethal doses to stunt plant growth by inhibiting amino a cid and fatty acid biosynthesis (Kaufman 1986). Class E (i.e. ethephon) chemicals are metabolized into ethylene inside the plant and are principally 2000). landscaping market. T he efficacy of these chemicals on woody landscape plants is adequate but occasionally inconsistent. This means that some shoots are properly regulated while others are not, giving the plant profile an uneven appe arance. Several biotic and abiotic variables (environment, plant size, species, etc.) are known to affect the performance of PGRs, as well as movement of the chemical with in the plant (Graebe 1987). If the active chemical is not adequately translocated to all parts of the plant, undesired growth can result. It is currently unknown whether inconsistent performance is the result of plant metabolism, translocation efficiency or application technique. The inhibition of GA synthesis is a complicated mechanism i nvolved in
15 various plant functions. Cell division continues but p lant cells do not expand as seen in normal growth, thus redu cing stem internode length (Graebe 1987). The mechanisms for GA synthesis are well understood, but the function of all forms of GA is not. Gibberellic Acid Biosynthesis Gibberellic acid biosynethsis is a complex pathway that varies from species to species. There are three critical steps in the production of GAs: a) biosynthesis of ent kaurene, b) biosynthesis of GA 12 aldehyde, c) prod uction of GA 1 from GA 12 aldehyde (Graebe 1987). GAs are diterpenoid compounds that depend on the production of ent kaurene which can be synthesized via two pathways. It was originally accepted that all GAs were formed solely from the mevalonic acid (MVA ) pathway the source of s terols and other terpenoids. Mevalonic acid is phosphorylated then decarboxylated to form isopentenyl diphosphate (IPP), a precursor for ent kaurene (Rademacher 2000). Recent studies have shown that IPP can be synthesized from pathways other than MVA. M. Rohmer (1999) discovered that D glyceraldehyde 3 phosphate plus pyruvate produces 1 deoxy D xylulose 5 phosphate that can be converted to IPP. Three molecules of IPP combine with two diphosphate compounds to form geranylgeranyl diphosphate (GGPP) which is cyclized to produce ent kaurene (Rademacher 2000). The oxidation of ent kaurene is catalyzed by monooxygenases in a several step process involving cytochrome P450 to form GA 12 aldehyde. An intermediate specific for GA production GA 12 aldehyde is further oxidized to form GA 12 Site specific hydroxylation occurs with GA 12 to produce the various forms of GA found throughout plants (Rademacher 2000). While there are more than 125 GAs produced, there are only GA 1 and GA 4 are actively involved in the elongation of plant cells (Bai and Chaney 2001; Rademacher 2000). GA 1 is recognized as the dominate form to affect cell expansion in most plant species
16 (Rademacher 2000). The steps of these pathways will prove to be important when discussi ng the mechanisms of action for flurprimidol and paclobutrazol later in this paper (Figure 1). Flurprimidol Cutless G is a granular, ornamental plant growth regulator commercially available for use in landscaping, nurseries, and greenhouses. The active i ngredient is flurprimidol (0.33%) [alpha (1 methylethyl) alpha (4 (trifluoromethoxyphenyl) 5 pyrimidine menthanol] which is a Class B PGR that restricts cell elongation by inhibition of active GAs specifically production of the GA 1 hormone (Sun and Kamiya 1994). Gibberellins are naturally occurring phytohormones directly related to vegetative growth and flower development (Hooley 1994). Flurprimidol inhibits gibber ellin production early in the isoprenoid pathway by binding to proheme iron of cytochrome P45 0 and inactivating the monooxygenase enzymes responsible for the conversion of ent kaurene to GA 12 aldehyde (Grossman 1992). Although the production of GA differs in many plant species and even among plants of the same species, several growth regulators perform by inhibiting this pathway without adversely affecting inter nal plant functions (Rademacher 2000). It is suggested that f lurprimidol may produce broader physiological effects than inhibition of GA synthesis. Graham et al. (1994) observed flurprimid ol treatments not only blocked GA 1 but also caused a significant decrease in abscisic acid (ABA), another major plant hormone. ABA is responsible for signaling plant response due to environmental stresses and may cause plants to reallocate GA (Hansen and G rossman 2000). G ibberellin inhibitors can cause heavier bud, flower, and seed sets along with pigment intensification (Redding et al. 1994)
17 Flurprimidol is stable in granular form but becomes available for plant uptake when dissolved in water (Grey et al 2009). The granular formulation designed to slow the release of flurprimidol into the soil over time This decreases the likelihood of leaching the chemical below the root zone and can allow for more consistent movement through the soil Flurprimidol possesses a high binding affinity for soil organic matter which will increase persistence and re duce leaching (Grey et al. 2009) Grey et al. (2009) found that pine bark mulch with sand decreased soil movement o f flurprimidol with only 14 and 13% recoveries at 5 and 10 cm respectively after 22 continuous days of irrigation (2.5 cm ). Compare this to sand only media which had a 71% recovery (Grey et al. 2009). Residual soil concentration is important for long term growth regulation as the physi ochemical properties of flurprimidol allow active molecules to persistent in soil for 1 1. 5 years (Sterrett and Tworkoski 1987), however this is completely dependent upon environmental conditions and irrigation frequency. The half life (DT 50 ) of flurprimid ol increases with increased soil d epths. With daily irrigation (2.5 cm ), flurprimidol displayed a DT 50 of 6 days in 1 cm of sand. However, DT 50 increased to 18 and 35 days, in sand, at depth s of 5 and 10 cm, respectively. Paclobutrazol Paclobutrazol is a highly active compound commonly applied to turf and ornamental plant species. A Class B PGR and member of the triazole group, paclobutrazol has a similar mechanism of action to flurprimidol as it inhibits the conversion ent kaurene to GA 12 aldehyde, the precursor for inactive gibberillins (GA 12 and GA 53 ) which can later be converted into the active forms (GA 1 and GA 4 ) (Topp and Rasmussen 2012). Paclobutrazol consists of a two enantiomer structures, the (2S, 3S) form which is involved in p lant growth regulation and the (2R, 3R) form that inhibits
18 sterol biosynthesis (Rademacher 2000) (Figure 5 1). Zhang et al. (2011) found that the negatively charged (2S,3S) enantiomer was 3.1 times more active than the positively charged (2R,3R) form. Pacl obutrazol is known to be a more active compound for GA inhibition compared to flurprimidol. Although not fully understood, Rademacher (2000) suggests the structural difference in the enantiomers is the reasoning behind this increased activity. Paclobutrazo l is able to bind to specific enzymes involved in sterol biosynthesis which limits the production of MVA (a precursor of ent kaurene) as well as interrupt the conversion of ent kaurene to GA 12 aldehyde (Rademacher 2000). This enables paclobutrazol to be a highly effective plant growth regulator even in the more PGR tolerant species. However, this increased activity comes a t a cost as paclobutrazol can be over applied and cause extreme growth stunting a nd malformation of foliage (Keever et al. 1990) Applica tion Techniques Flurprimidol and paclobutrazol are both xy lem mobile compounds that move into the plant root zone with a soil application. As previously stated, flurprimidol is less active than paclobutrazol and is considere d non phytotoxic to woody plant species Sterrett and Tworkoski (1987) found maximum flurprimidol activity occurred within 10 cm of the root collar and that no growth inhibitor activity was detected 50 cm from the root collar of white ash and black walnut Excavation results suggested th at most of the plant uptake was performed by large lateral roots directly below the soil surface (Sterrett and Tworkoski 1987 ) Drench applications of plant growth regulators have been shown to effectively reduce shoot growth, but there has not been a stud y to compare the efficacy of granular flurprimidol to a drench application (Steffens 1988; Sterrett and Tworkoski 1987). Redding et al. (1994) found that a f lurprimidol drench application resulted in dual
19 flushes of growth in maple and oak tree species th e first being well regulated while the second exhibiting a period of unregulated growth before sufficient regulation. The defoliation of plants is known to stimulate carbohydrate reserves and translocate to promote new growth (Heyden and Stock, 1996). Tri mming may play a major role on the uptake and translocation of soil applied plant growth regulators but little research has been done to investigate the impact of trimming time and date of growth regulator application. Redding et al. (1994) found s ignifica nt differences between the trees trimmed at or a fter the growth regulator treatment verses tho se trees that were trimmed months prior to the treatment which showed less regulation
20 Figure 1 1 Isoprenoid pathway for the production of Gibberellic acid. A simplified schematic of the steps involved in GA biosynthesis and site of action for specific PGRs (Radmacher 2000)
21 CHAPTER 2 EVALUATION OF HOW TR IMMING TIME INFLUENC ES FLURPRIMIDOL PERFORMANCE ON VIBUR NUM SPECIES Background The Viburnum genus comprises many species of shrubs that are popular and commonly found in landscapes across the southeastern United States. These hedge forming ornamentals are often planted along a fences or walls to provide a more natural appearance to delineate pro perty boundaries. However, the rapid growth habit and length of these hedges make them one of the more difficult species to manage as they require numerous trimmings throughout the growing season to maintain an accepta ble appearance. Once trimmed plants w ill reallocate carbohydrate reserves in orde r to mend the injured tissue which can stimulate water uptake and growth (Heyden and Stock, 1996, Steffens, 1988, Waltz & Whitwell, 2005). This growth habit then translates into near year round trimming in the su b tropical climates of the deep south. Flurprimidol is a root absorbed PGR that is translocated through the xylem along with plant water uptake (Sterrett and Tworkoski, 1987). Though the growth regulation effects of flurprimidol are well established, inco nsistent performance is still common Whether between two different species of hedge, or even within species, the emergence of unregulated shoots regularly occurs after the flurprimidol application It has been hypothesized that the inconsistent performanc e in flurprimidol is due, in part, to the timing of trimming. If trimming occurs too soon after flurprimidol application, regrowth may occur before the xylem mobile compound can reach the apical buds. Conversely if trimming is delayed too long the remov al of buds containing flurprimidol may result, leaving an insufficient concentration in the plant for growth
22 regulation. T herefore, the objective of this experiment was to better understand the impact of trimming timing on the growth regulation on two spec ies of viburnum shrubs. Materials and Methods V iburnum odoratissium and V suspensum were chosen for this research. Both species were well established and greater than 10 years of age. Th e hedges were divided into 3.1 m x 1.5 m plots, three plants per plot, in a split plot design where flurprimidol was the whole plot factor and trimming time was the split. Due to inadequate hedge length at any given location, three replications were blocked in space at multiple sites at the University of Flo rida, Gainesville c ampus. In 2012, the V. odoratissium experiment had one replication at three locations: Broward Hall, UF Turfgrass Envirotron, and UF Waste Water Treatment Plant (WWTP). In 2013, the V. odoratissimum experiment had two replications at Bro ward Hall and one replication at the UF Envirotron. For both years (2012 13), the V. suspensum experiment had two replications at Elmore Hall and one replication at UF Turfgrass Envirotron. Flurprimidol applications, in the form of Cutless G, were made Ap ril 23 rd 2012 and May 1 st 2013 at a rate of 0 or 22.5 g/9.3m 2 (which corresponds to 15 lb Cutless G per 1000 ft 2 ). Applications were made using a hand held rotary granular spreader with granules directed under the foliage at the base of the plant. C alibr ation was performed using multiple 0.093m 2 (1ft 2 ) calibration tray s All hedges were trimmed to a standard, even rectangular shape. Trimming treatments were designed around the flurprimidol application date to evaluate the effect of trimming timing on growth regulation. Treatments consisted of five trimming times: 7 days before application (DBA), 0 DBA, 7 days after application (DAA), 14 DAA, and 21 DAA. Since flurprimidol is a root absorbed chemical, hedges were divided into flurprimidol treated and untreated control (UTC)
23 sections. This was to prevent treatment overlap and produce a more consistent plant response across replications. Trimming treatments were applied to the flurprimidol treated and untreated sections to compare the flurprimidol performance against a control. Flurprimidol performance was evaluated by measuring shoot regrowth length, plant biomass, and visual assessment Nine plant shoots per plot were tagged to monitor shoot regrowth throughout the summer and shoots were not tagged until active growth was observed. Plant biomass was harvested, per plot, at 15 to 17 weeks after application each year and dried at 50 C fo r one week and dry weights (g) were recorded Visual assessments were also used to evaluate flurprimidol performance across the entire plot. This assessment was a quality rating based on a 0 to 10 scale with 0 equaling a poor, uneven appearance and 10 equa ling a perfect aesthetic appearance We designated a quality rating of 3 to indicate when a hedge would need to be trimmed. The purpose of the visual assessment was to provide a quality rating for the entire plot in case the individually tagged shoots gre w abnormally fast or slow relative to the entire hedge. Data were collected every two weeks following the final trimming treatment and continued until normal plant growth returned 4 to 5 months after the flurprimidol application. Collected data were ana lyzed using analysis of variance to determine the presence of main effects and interaction. Means were Results and Discussion Previous reports have documented that flurprimidol is an effective p lant growth regulator used to control the growth of woody plants (Norcini 1991 ; Steffens 1988; Sterrett and Tworkoski 1987). It is widely known that PGR applications come with a
24 c ertain amount of variability as s everal factors (i.e. water, environmental co nditions ) can contribute to plant growth One factor known to affect plant growth is the stim ulation of carbohydrates through plant trimming. Because of the variability associated with PGRs, trimming time was investigated to se e if a relationship was prese nt between trimming date and flurprimidol application date This was to determine if altering when plants are trim med would decrease the variability ass ociated with flurprimidol performance Five trimming dates were evaluated on Viburnum odoratissimum and V. suspensum species to observe this interaction. Flurprimidol treated hedges were measured against an untreated control trimmed at the same time, to compare the efficacy of each trimming time. It was determined that t he main effect of trimming time and all associated interactions, were not significant for shoot regrowth, biomass, or visual assessment in both Viburnum spec ies However, the main effects of year and flurprimidol application were significant, therefore data were presented as flurprimid ol treated hedges compared to the untreated control hedges. Although data collection occurred every two weeks, the regrowth and biomass data presented is 15 WAT for V. odoratissimum and 18 WAT for V. suspensum For V. odoratissimum s hoot regrowth was resp onsive to flurprimidol as significant differences were observed for 2 012 and 2013 (Figure 2 1 ). Biomass of flurprimidol treated V. odoratissimum was significantly different from the UTC in 2012 but it was not in 2013 (Figure 2 2 ) Th e reason for the biomass differences between years is unclear but shoot regrowth and biomass increased in 2013 This increase in growth could potentially mask the significant differences in biomass observed in 2012 Visual assessments of V. odoratissimum hedge quality wer e also collected. This was
25 conducted as a qualitative measure of overall hedge appearance. Since it would be impossible to measure all shoots within the hedge, the visual assessment provided a means of documenting regrowth on a plot by plot basis. Again it was observed that trimming timing or flurprimidol application had no impact on the visual quality of V. odoratissimum (data not shown) As previously stated, trimmin g time has no significant effect on the regrowth, biomass, or visual rating s of V. sus pensum. A treatment by year interaction was observed for shoot regrowth of V. suspensum and those data are shown separately by year. Data are presented as flurprimidol t reated hedges compared to an untreated control Flurprimidol had no impact on the shoot regrowth of V. suspensum as no significant differences were observed in 2012 or 2013 (Figure 2 3 ). No treatment by year interaction was observed for V. suspensum biomass measurements, therefore data were pooled across years. The bioma ss of flurprimidol treated hedges was not significantly different from the untreated control (Figure 2 4 ). Visual assessments were used to measure the overall aesthetic appearance of the hedges and again no differences among visual ratings were obse rved fo r V. suspensum (data not shown). Therefore, the lack of differences between trimming treatments for V. odoratissimum and V. suspensum was not expected. Moreover, there is no documentation in the literature, or on the Cutless G label (Anonymous 2008 ) tha t would indicate a lack of growth regulation within these two species. As mentioned previously, the flurprimidol treated and untreated hedges were separated in space, as blocks, to avoid overlap in roots between one plot and the next. While the shoot regrowth of flurprimidol treated V odoratissimum hedges were significantly reduced, the visual
26 qualit y ratings were not different from the untreated. This may have been due to the number of shoots tagged for the experiment. It was simply not practical to tag all of the plant shoots, which is why a visual rating was included. For V suspensum the untreated plots simply did not exhibit regular g rowth patterns after trimming and t he reason for the lack of growth in the untreated is not known. The untreated plants were in the same location as the treated hedges, therefore, fertility, rainfall, etc. should have been identical. It was common for one shoot to measure 5 cm in length while the next shoot measured 40 cm. This level of variability within a treatmen t made statistical comparisons difficult. The lack of differences in this trial is most likely due to the fact that V odoratissium and V suspensum were chosen as our species of interest. In general, landscape managers choose species that are hardy and reliable. This generally translates into plants with rapid growth, which is l ikely why flurprimidol did not provide sufficient growth regulation. Flurprimidol is preferred by many ground managers due to ytotoxicity (Sterrett and Tworkoski 1987 ). However, this may also mean that flurprimidol will struggle to manage the growth of highly aggressive plant species. In conclusion, it is likely that any effect of trimming timing was overshadowed by the inabili ty of flurprimidol to effectively manage the growth of V odoratissium and V suspensum Future research should focus on the efficacy of flurprimidol and the interaction trimming timing, provided that species with a history of known flurprimidol performanc e are chosen.
27 Figure 2 1 Shoot regrowth (15 WAT) of flurprimidol treated Viburnum odoratissimum compared to an UTC Means are compared for each year. Letters indicate a 0.05). Error bars represent the standard error of t he means for each treatment (n=6 0). 20 40 60 80 100 120 140 160 180 200 Average Shoot Regrowth per Plot (cm) 2012 2013 Flurprimidol Control b a b a
28 Figure 2 2 Biomass (15 WAT) of flurprimidol treated Viburnum odoratissimum compared to an UTC Means are compared for each year. Letters indicate a significant d 0.05). Error bars represent the standard error of the means for each trea tment (n=6 0). 500 700 900 1100 1300 1500 Average Biomass per Plot (g) 2012 2013 Fluprimidol Control b a *NS
29 Figure 2 3 Shoot regrowth of flurprimidol treated Viburnum suspensum compared to an UTC (18 WAT). Means are compared for each year. Letters indicate a 0.05). Error bars represent the standard error of the means for each treatment (n=60). 0 10 20 30 40 50 60 70 80 Average Shoot Regrowth per Plot (cm) 2012 2013 Flurprimidol Control *NS *NS
30 Figure 2 4 Biomass of flurprimidol treated Viburnum suspensum compared to an UTC (18 WAT)(2012 13). Letters indicate a significant difference between the 0.05). Error bars represent the standard error of the means for each treatment (n=60). 200 300 400 500 600 700 800 Average Biomass per Plot (g) Flurprimidol Control *NS
31 CHAPTER 3 DETERMINE WHICH APPLICA TION METHOD PROVIDES BEST PLANT GROWTH REGULATION Background Plant growth regulators, such as flurprimidol, are a way to reduce the overall management requirements of shrubs and o ther ornamental plants. T he granular formulation of flurprimidol (Cutless G) is designed to slow ly release the active ingredient into the root zone. Irrigation is required to dissolve the granule and facilitate uptake by the plant. Due to inconsistencies in performance, landscap ers have been apprehensive to adopt this technology. Cutless G is a 0.33% flurprimidol containing granule that must be spread on the soil/mulch surface, be dissolved with rainfall or irrigation, infiltrate the soil/mulch, and be absorbed by plant roots. Depending on the rate that the granules dissolve and reach the root zone, it is possible that irregular growth regulation results while the critical concentration of flurprimidol builds in different shoot tips. We believe that the lack of consistency is po ssibly due to application method. Cutless G is currently broadcast over the designated landscape bed with a modified leaf blower. Th erefore the application rate is potentially variable since inconsistent placement of the granules is likely. Though landsca pe managers rely on calibration trays placed in the application zone to guide the dosage, often they use prior experience to determine the amount of product required for a given landscape bed. The granular formulation is designed to slow flurprimidol movem ent through the soil profile. Grey et al. (2009) found that mulch and organic matter significantly decrease the dissipation rate of flurprimidol. It is possible that the inconsistent plant response to flurprimidol is due to the difficulty of getting a cri tical concentration into the root zone to
32 adequately regulate growth. In order to achieve more consistent results, a more consistent application method may be needed. It is our hypothesis that changing the application technique of flurprimidol could impro ve overall plant uptake and growt h regulation consistency. To test this we applied Cutless G as a drench, rather than a s a granule. By dissolving the granules with additional water, the drench method could allow flurprimidol to reach the roots in a shorte r amount of time. This also concentrates flurprimidol in a smaller area and can increase the probability of it reaching the targeted root zone. The objective of this study is to determine if the drench application will improve the plant growth regulation e fficacy compared to the granular formulation of flurprimidol. Materials and Methods Two species were selected for the application method experiment, Elaeagnus pungens (Silverthorn elaeagnus) in Gainesville, FL and Loropetalum chinense in Apopka, FL for 201 2 and 2013 Both of these hedges are well established and greater than 10 years in age. Flurprimidol was applied at 22.5g ai (15 lbs product) /1000ft 2 for both species. Plots included 4 6 plants and plot size was roughly 13.9m 2 (150ft 2 ). Three plants were selected as data plants and the others were used as barrier plants to prevent treatment overlap. Two application methods of flurprimidol were evaluated as the experimental variables. The first treatment applied flurprimidol according to the label ndations This included applying the granules with a rotary granular spreader and directing th em und er the dripline of the plant, followed by 1.3 cm of irrigation. The second treatment consisted of a drench method by dissolving an e quivalent amount of flurprimidol in water (6 L) and app lying it as a drench 30 45 cm from the base of each plant The determined amount of product required for each plot
33 was divided into two 3 liter bottles of water and shaken vigorously until the granules completely dissolve d. One bottle was applied to each side of the hedge, resulting in a volume of 40 L per 92.9m 2 ( 1000ft 2 ) This method was designed to concentrate flurprimidol in a small area which should increase plant uptake and translocation efficiency. Untreated contr ol plots (UTC) were also used to divide application types and prevent overlapping in flurprimidol application methods. Flurprimidol application method was evaluated by measuring shoot regrowth length, plant biomass, and a visual quality rating. From the t hree data plants, nine shoots were tagged per plot to monitor shoot regrowth throughout the summer (May Sept). Plants were not tagged for approximately 2 3 weeks after trimming to ensure that tags would be placed on actively growing shoots. Since it is not practical to measure every shoot on each plant, we evaluated flurprimidol performance with a visual assessment rating. This was used to measure the aesthetic quality of the plot and determine the efficacy of flurprimidol method. Hedge quality was evaluate d on a 0 10 scale with 10 being a pristine hedge and a 3 indicating the time to trim. Data were collected every two weeks following the initial trimming and continued until normal plant growth returned. Plant biomass was harvested, per plot, in September e ach year and dried at 50 C for one week and weights (g) were recorded after the drying period. Collected data were analyzed using ANOVA and means were then separated with at a 0.05 significance level. Results and Discussion S hoot grow th of E. pungens was reduced 4.3 and 13.9% by the granular and drench applications, respectively (Figure 3 1), but were not significantly different from one another or the UTC. Biomass collected from both application methods were
34 compared to the same untre ated control plots as a percent reduction. The granular application effectively reduc ed biomass (25.1%) but was not significantly different from the drench (16.9%) (Figure 3 2). The drench method has previously been shown to be an effective application method as Redding et al. (1994) found that a flurprimidol drench significant ly decreas ed oak biomass by 46 72%. Visual ratings determined that the drench method provided a significa nt difference at 15 WAT in aesthetic appearance and overall growth regulation compared to the untreated control but was not significantly different from the granular treatment (Table 3 1). The vigorous growth habit of E. pungens may explain the lack of s ig nificant differences in biomass The impact of flurprimidol on L. chinense was more pronounced than that observed in E. pungens L. chinense regro wth was significantly reduced by both application methods compared to the untreated control (Figure 3 3). Sh oot regrowth was decreased 39.5 and 38.2% by the granular and drench treatments, respectively (Figure 3 3). Plant biomass was significantly reduced in both treatments compared to the UTC (17.0% by granular and 13.9% by drench) but biomass between the appl ica tion methods was not significantly different (Figure 3 4). By visual assessment, the drench method was significantly different from the UTC at 15 WAT but n o differences in visual ratings were observed between flurprimidol application methods (Table 3 1) B oth the granular and drench applications of flurprimidol provided a rating of 8 or more for the 15 week observation period (Table 3 1). Flurprimidol reduce d shoot regrowth and biomass in both E. pungens and L. chinense However, i t was determined that application me thod (granular or drench) had little impact on the efficacy of flurprimidol. Therefore, our hypothesis that the granule
35 formulation impedes the growth regulator effect by its slow release characteristics is not likely Just as in the pr evious chapter, i t is again questioned if species sensitivity is what primarily impacts the efficacy and consistency of flurprimidol performance For example, E. punge n s is a robust, fast growing species that requires many more trimmings per year compared to L. chinense a woody, slow growing shrub. In this example, L. chine n se was adequately regulated by flurprimidol while E. punge n s was inconsistent. It is possible that flurprimidol alone will not sufficiently regulate certain shrub species.
36 Figure 3 1. Shoot regrowth of Elaeagnus pungens treated by a granular or drench flurprimidol application compared to an untreated control (15 WAT) (2012 13) Error bars represent the standard error of the means for each treatment (n=30) 0 50 100 150 200 250 Average Shoot Regrowth per Plot (cm) Granular Drench Control *NS
37 Figure 3 2. Biomass of Elaeagnus pungens t reated by a granular or drench flurprimidol application compared to an untreated control (15 WAT) (2012 13) Error bars represent the standard error of the means for each treatmen t (n=30). 0 500 1000 1500 2000 2500 3000 3500 4000 Average Biomass per Plot (grams) Granular Drench Control ab b a
38 Table 3 1 Visual assessment rating to evaluate overall growth regulation in E. pungens and L. chinense (2013) Visual Quality Rating E. pungens L. chinense WAT Granular Drench Control Granular Drench Control 9 8.0 a 8.7 a 7.3 a 9.0 a 9.0 a 9.0 a 11 5.0 a 6.0 a 4.3 a 9.0 a 9.0 a 8.3 a 13 4.3 a 5.3 a 2.7 b 8.7 a 8.7 a 7.0 b 15 3.0 ab 4.7 a 2.3 b 8.7 a 8.7 a 6.3 b Note: Bimonthly visual assessments were measured on a (0 10) scale with 10 representing the highest aesthetic value and 3 represents when trimming would occur. Means within a row, within a given species, followed by different letters are significantly diff n=15)
39 F igure 3 3. Shoot regrowth of Loropetalum chinense treated with a granular or drench flurprimidol application compared to an untreated control (17 WAT) (2012 13) Error bars represent standard error of the means for each treatment (n=30) 0 20 40 60 80 100 120 140 160 180 Average Shoot Regrowth per Plot (cm) Granular Drench Control b b a
40 Figure 3 4. Biomass of Loropetalum chinense treated by a granular or drench flurprimidol application compared to an untreated control (17 WAT) (2012 13) Error bars represent standard error of the means for each treatment (n=30) 0 200 400 600 800 1000 Average Biomass per Plot (grams ) Granular Drench Control b b a
41 CHAPTER 4 EVALUATION OF PACLOBUTRAZOL/FLURPRIMIDOL DRENCH APPLICA TION EFFICACY ON LIGUSTRUM HEDGES Background Large perennial plants are often use d on both commercial and private property to disguise a fence line or to provide privacy along a property line Considering the purpose of these plants, it is common to selec t species that are large and rapidly growing. Therefore, t he Florida landscape industry has the difficult task of maintaining the rather aggressive plants in a manner that is aesthetic ally pleasing throughout a yearlong growing season. P lant growth regulators are an effective way to reduce the number of trimming s required per year and decrease the biomass produced But due to inconsistencies in PGR performance, some landscapers have been apprehensive to adopt this technology. Flurprimido l and p aclobutrazol are two PGRs that have been used in the ornamental industry for over 30 years. These GA biosynthesis inhibitors are similar in mechanism, but very different in applicability for plant growth regulation. Based on our previous experience, flurprimidol has shown to be an efficient growth regulator for small, woody plants such as L oropetal u m but does not have the activity to regulate certain larger species like Elaeagnus ( Smith [Chapter 3] 2013 ). Paclobutrazol is known to be a much more act ive PGR as it possesses two enantiomer forms that effectively inhibit two separate enzymes within the GA pathway (Radmacher 2000, Zhang et al. 2011) (Figure 1 1). Commonly used to control trees and other aggressive plant species, problems arise with paclob utrazol if the application rates become too high. Previous research has shown paclobutrazol has shown the potential to stunt tree growth for more than year (Sterrett and Tworkoski 1987). It is also possible for paclobutrazol to cause
42 malformation of foliag e if sensitive species receive an over application and the plants may never fully recover (Keever et al. 1990). Needless to say, the potential for injury is of great concern in the ornamental industry. As previously mentioned, t he addition of paclobutra zol reduces the buildup of GA precursors, specifically IPP, in the isoprenoid pathway (Radmacher 2000) (Figure 1 1). Since flurprimidol and paclobutrazol have similar but different sites of action in the same pathway, it is questioned if combining these wi ll allow for reduced paclobutrazol rates. Potentially we could increase plant growth regulation while also reducing the likelihood of injury and over regulation from paclobutrazol To our knowledge, t his is the first product targeting large ornamental h edge species by combining flurprimidol and paclobutrazol For this study, we selected Ligustrum japonicum since it has previously been shown to be tolerant to flurprimidol alone (personal observation) The refore, the objective of this study was to determine the efficacy of flurprimidol plus paclobutrazol on growth regulation of Ligustrum japonicum Materials and Methods In 2012 and 2013, trial s w ere conducted at the Energy Park of the University of Florida in Gainesv ille, FL. A flurprimidol and paclobutrazol solution ( SP 5900 11, 20% ai v/v, SePRO Corp. Carmel, IN ) was evaluated as a n individual plant treatment on 2.5 3 meters tall Ligustrum japonicum hedges To determine the efficacy of the provided ratio p hytotoxicity, i ndividual shoot growth, and overall plant regulation were assessed. Each plot was 5 m eters long and included 3 plants. Plots were arranged in a randomized complete block design with 4 treatments and 3 replications. The site was not irrigate d and no mulch was present. Barrier plants were inclu ded between plots to prevent treatment overlap.
43 Treatments consisted of a drench application at 0, 6, 8, 12 g ai in 1 gallon of water per plant. All treatment applications were made using a CO 2 press urized backpack sprayer with a single nozzle directing the spray 12 the trunk of each plant targeting the root zone. Applications were made August 10 th 2012 and June 5 th 2013, 10 days before the hedges were to be trimmed. Efficacy of the flur primidol/paclobutrazol product rates were evaluated by measuring shoot regrowth length. Plant shoots were randomly selected and tagged with zip ties as discussed in previous chapters. Overall plant appearance was rated on a 0 to 10 scale, with 10 being t he optimum aesthetic appearance and a 3 would indicate the desired time to trim. Visual assessment ratings were used to evaluate product performance across the entire plot rather than focusing on individual shoots Data were collected every two weeks follo wing the initial trimming and continued until normal plant growth returned. Collected data were analyzed for main effects and interactions using ANOVA and means were at a 0.05 significance level. R esults and Discussion Data were combined across years (2012 13) as there were no interactions between years, treatment, or replication. At the lowest rate (6g ai/plant), the flurprimidol/paclobutrazol solution was able to significantly reduce shoot regrowth by 64.4% compared to the UTC. At 8g and 12g per plant, L. japonica regrowth was reduced 25.1% and 28.2%, respectively and was not significantly different from the UTC (Figure 4 1). The PGR combination was able to reduce average shoot regrowth >25% across all treatments compared to the UTC. As discussed in previous chapters, measuring shoot length is inherently variable. This is likely why the 6g rate alone provided a statistical difference relative to the UTC.
44 Therefore, t o provide a representation of overall plant regulation, visual assessments were collected to compare rate treatments to UTC. Visual assessments of the 8g and 12g treatments were significantly different from the UTC at 15 WAT while visual assessments were not different among treatments at all other observation times (Table 4 1). Paclobutrazol has previously been shown to effectively regulate large, woody species for more than a year (Sterrett and Tworkski 1987). In this experiment, the addition of paclobutrazol provided the growth regulation capacity to reduce regrowth in L. japonica plants. The combination of flurprimidol and paclobutrazol was able to control the growth of large Ligustrum species as this specific ratio may effectively regulate other difficult species. The activity of paclobutrazol was evident by the effective growth regulation of L. japonica even at the lowest rate. For future research, the paclobutrazol/flurprimidol ratio should be further investigated on other difficult to control species.
45 Figure 4 1. Shoot regrowth of Ligustrum japonica treated with three rates of flurprimidol/paclobutrazol solution compared to an untreated control (13 WAT) (2012 13) Error bars represent the standard error of the means for each treatment ( protected LSD n=30) 0 10 20 30 40 50 60 Average Shoot Regrowth per Plot (cm ) 6g ai 8g ai 12g ai Control ab ab b a
46 Table 4 1 V isual assessments to evaluate overall growth regulation in L. japonica Treatment Rates WAT 6g ai 8g ai 12g ai Control 7 8.7 a 9.0 a 8.7 a 9.0 a 9 8.3 a 8.3 a 8.3 a 8.0 a 11 8.0 a 8.0 a 8.3 a 7.0 a 13 7.3 a 7.0 a 7.7 a 6.0 a 15 6.3 ab 7.0 a 7.3 a 5.3 b Note: Bimonthly visual assessments were measured on a (0 10) scale with 10 representing the highest aesthetic value and 3 denotes when trimming would be necessary (2013) The letters indicate means which ar protected LSD n=15)
47 CHAPTER 5 CONCLUSIONS The performance of plant growth regulators has previously been shown to be highly variable (Graham et al. 1994; Steffens, 1988). In this study, species tolerance has demonstrated to have a major impact on the efficacy of flurprimidol. Evaluating the response in plants of the same genus, V. odoratissimum and V. suspen sum were both tolerant to the flurprimidol application This assessment was based the amount of shoot growth regulation observed in both Viburnum species and the biomass produced compared to the untreated control These parameters have previously been show n to effectively evaluate the performance of plant growth regulators on woody landscape plants (Redding et al., 1994; Steffens, 1988; Sterrett and Tworkoski, 1987). At 14 WAT, V. odoratissimum visual ratings averaged 2 4 across a ll trimming treatments com pared to ratings of 6 8 for V. suspensum (data not shown). Trimming time relative to application date was shown to have no significant impact on flurprimidol performance in V odoratissimum or V. suspensum This finding further confirms the variability ass ociated with plant growth regulators and plant species There were no significant differences observed between granular or drench applications in flurprimidol performance. The drench application seemed to provide longer aesthetic value in E. pungens but produced more shoot regrowth and biomass compared to the granular application. In L. chinense the flurprimidol application methods performed almost identically in every parameter being evaluated. Flurprimidol was effective in regulating shoot regrowt h and biomass in both the granular and drench application methods.
48 The lowest rate of the flurprimidol/paclobutrazol solution (6g ai) was the only treatment to provide significant growth regulation of Ligustrum japonicum compared to the untreated contro l. A notoriously difficult species to control, we were unable to regulate the growth of this species with flurprimidol alone. Flurprimidol and paclobutrazol have been shown to effectively control plant growth on a variety of woody species but there has bee n little research on the combination of both GA inhibitors (Redding et al., 1994, Steffens, 1988). Further research should investigate species sensitivity to flurprimidol and paclobutrazol so that rate recommendations can be made.
49 APPENDIX UNTREATED V IB URNUM ODORATISSIMUM AND V SUSPENSUM REGROWTH, BIOMASS, AND VISUAL ASSESSMENT DATA Table A 1. Regrowth and Biomass data of untreated V. odoratissimum and V. suspensum in relation to trimming time (2012 13) V. odoratissimum V. suspensum Tr imming Regrowth (cm) Biomass (g) Regrowth (cm) Biomass (g) 7 DBA 129.3 1139.1 67.3 717.6 0 DBA 123.6 1351.1 63.0 552.8 7 DAA 124.7 1196.7 50.4 610.6 14 DAA 121.1 1161.4 40.2 523.1 21 DAA 97.8 1186.3 46.4 485.2
50 Table A 2 V isual assessments in untreated V. odoratissimum (2013) Visual Assessment WAT 7 DBA 0 DBA 7 DAA 14 DAA 21 DAA 10 5.7 5.3 5.7 5.3 6.3 12 3.7 3.0 3.0 3.3 4.7 14 1.7 1.7 1.7 1.7 2.3 Note: Bimonthly visual assessments were measured on a (0 10) scale with 10 representing the highest aesthetic value and 3 denotes when trimming would be necessary. Table A 3 Visual assessments in untreated V. suspensum (2013) Visual Assessment WAT 7 DBA 0 DBA 7 DAA 14 DAA 21 DAA 14 6.3 5.7 6.3 7.7 7.3 16 5.7 5.0 6.0 6.7 6.3 18 3.7 4.3 5.3 5.7 5.7 Note: Bimonthly visual assessments were measured on a (0 10) scale with 10 representing the highest aesthetic value and 3 denotes when trimming would be necessary.
51 LIST OF REFERENCES 600 Carmel, IN 46 032. EPA Register number: 67690 13. Bai S, Chaney W (2001) Gibberellin Synthesis Inhibitors Affect Electron Transport in Plant Mitochondria. Journal of Plant Growth Regulation 35: 257 262 Graebe JE (1987) Gibberellin Biosynthesis and Control. Annual Review of Plant Physiology and Plant Molecular Biology 38: 419 465 Graham JS, Hobbs SD, Zaerr JB (1994) The Effects of Flurprimidol on Bud Flush, S hoot Growth, and on Endogenous Gibberellins and Abscisic Acid of Douglas Fir Seedlings. Journal of Plant Growth Regulation 13: 131 136 Grey TL, Czarnota M, Potter T, Bunnell BT (2009) Time Release of Flurprimidol from a Granular Formulation in Mulches a nd Sand. Hortscience 44(2): 512 515 Grossman K (1992) Plant Growth Retardants: Their Mode of Action and Benefit for Physiological Research. Progress in Plan t Growth Regulation Pp 788 797 Hansen H, Grossman K (2000) Auxin Induced Ethylene Triggers Abscisic Acid Biosynthesis and Growth Inhibition. Plant Physiology 124: 1437 1448 Heyden FV, Stock WD (1996) Regrowth of a Semiarid Shrub Following Simulated Browsing: The Role of Reserve Carbon. Functional Ecology 10: 647 653 Hooley R (1994) Gibberellins: Perce ption, Transduction, and Responses. Plant Molecular Biology 26: 1529 1555 Kaufmann JE (1986) Growth Regulators for Turf Grounds Maintenance 21(5):72 Keever GJ, Foster WJ, Stephenson JC (1990) Paclobutrazol Inhibits Growth of Woody Landscape Plants. Journ al of E nvironmental Horticulture 8: 41 47 Krug BA, Whipker BE, McCall I, Dole JM (2005) Comparison of Flurprimidol to Ethephon, Paclobutrazol, and Uniconazole for Hyacinth Height Control. HortTechnology 15: 872 874 March SR, Martins D, McElroy JS (2013) Growth Inhibitors in Turfgrass. Planta Daninha Vicosa MG Volume 31 n 3: 733 747 McCull ough PE (2005) Dwarf Bermudagrass Respones to Flurprimidol and Paclobutrazol. Hortscience 40 n. 5: 1549 1551 Norcini JG (1991) Gr owth and Water Status of Pruned and Unpruned Woody Landscape Plants Treated with Sumagic (Uniconazole), Cutless (Flurprimidol), or Atrimmec (Dikegulac) Journal of E nvironmental Horticulture 9 231 235
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53 BIOGRAPHICAL SKETCH Hunter C. Smith grew up in northeast Arkansas graduati ng with a degree in b iology in 2009 and hemistry in 2010 both from Arkansas State University located in Jonesboro, AR. With an interest in agriculture, he scouted cotton for three years while in college. He was accepted into the Ag ronomy graduate program at the University of Florida in the fall of 2011. Under the direction of f 2013, he accepted a PhD position under Dr. Ferrell to continue studying weed science beginning in the spring of 2014. Hunter was married to Kali James of Malden, MO in October of 2013.