Dr. Wes Totten Major Professor

Transcription

1 To the Graduate Council: I am submitting herewith a thesis written by Max Carlton entitled Seedhead Suppression of Empire Zoysiagrass (Zoysia spp.) Using Plant Growth Regulators. I have examined the electronic copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Master of Science, with a major in Agriculture and Natural Resources. Dr. Wes Totten Major Professor We have read this thesis and recommend its acceptance: Dr. Barbara Darroch Dr. Craig Darroch Accepted for the Council Dr. Victoria S. Seng Associate Vice Chancellor for Academic Affairs and Dean of Graduate Studies (Original signatures are on file with official student records)

2 Seedhead Suppression of Empire Zoysiagrass (Zoysia spp.) Using Plant Growth Regulators A Thesis Presented for the Master of Science Degree The University of Tennessee at Martin Max Carlton December 2015

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4 Acknowledgements I would especially like to thank my parents, Nyle and Cathy, for all the support and love they ve given me throughout my life. I wouldn t be where I am today if it weren t for them and I m truly grateful. I also want to thank my supervising professor and mentor Dr. Wesley Totten for being a passionate and positive role model, and pushing me to accomplish things I never thought were possible. I would like to thank Dr. Barbara Darroch and Dr. Joey Mehlhorn for all the support and advising to help throughout my time at UT Martin. I would also like to thank Dr. Craig Darroch for his help with reviewing my thesis and adding his expertise with the statistics. Last but not least I d like to thank our Lord and savior for giving me strength to overcome all obstacles. ii

5 Abstract Empire zoysiagrass (Zoysia japonica Steud.) is becoming an increasingly popular and well adapted warm-season turfgrass in the southern and transitional climate zones. Environmental extremes within these climate zones promote development of inflorescences that considerably reduce aesthetic quality and increase maintenance requirements. This study evaluated seedhead suppression efficacy of various plant growth regulators on Empire zoysiagrass. Research was conducted from 2012 to 2013 at the Plant Science Complex at The University of Tennessee at Martin. Experimental design was a randomized complete block with four replications. Atrazine, ethephon, and mefluidide were applied alone and combined at 1.0, 3.5, and 0.6 kg a.i./ha, respectively. Combinations of atrazine plus flurprimidol at 1.0 and 0.5 kg a.i./ha, ethephon plus trinexapac-ethyl at 3.5 and 0.04 kg a.i./ha, and mefluidide plus trinexapacethyl at 0.6 and 0.04 kg a.i./ha were also applied. Treatments were applied every four weeks throughout the growing seasons giving a total of five applications. Treatments were evaluated every seven days for seedhead populations, seedhead height and turfgrass quality and injury. Percent lateral regrowth was evaluated weekly after the 1 st, 3 rd and 5 th applications. Residual scalping was evaluated at the end of each application. Data was subjected to analysis of variance (ANOVA) using Statistical Analysis System (SAS v. 9.3), and treatment means were separated using Fisher s LSD test (α = 0.05). Significant treatment by year interactions were detected for all ratings except residual scalping, so results were separated by year. Mefluidide applied alone at 0.6 kg a.i./ha and combined with trinexapac-ethyl at kg a.i./ha yielded the greatest seedhead population reductions, significantly lower than untreated 3-8 and weeks after initial treatment (WAIT). Seedhead populations were significantly reduced by mefluidide + iii

6 trinexapac-ethyl for all dates after 10 WAIT in 2012 and for all rating dates except the initial date in These treatments also yielded the greatest reductions in turfgrass quality in 2012, with significantly lower quality ratings for all dates except 1 and 2 WAIT for mefluidide. Unacceptable quality (rating < 7) was observed 5-12, 15, and WAIT for mefluidide and mefluidide + trinexapac-ethyl in Turfgrass quality was also lower for all dates in 2013 after mefluidide was applied alone, and for all dates except 16 WAIT after applications of mefluidide + trinexapac-ethyl. Both treatments had unacceptable quality ratings 1-2, 5 and 20 WAIT in 2013; unacceptable quality was also observed 3 WAIT for mefluidide. The significant reductions of seedhead populations and turfgrass quality observed for both mefluidide and mefluidide + trinexapac-ethyl in the current study are similar to population reductions detected in prior research on tall fescue (Festuca arundinacea), common bermudagrass (Cynodon dactylon) and Meyer zoysiagrass. Future studies should focus on applying these two treatments at differing rates while reducing the number of applications throughout the growing season. iv

7 Table of Contents Chapter I... 1 Introduction... 1 Chapter II... 2 Literature Review... 2 Zoysiagrass... 2 Zoysia Species... 3 Empire Zoysiagrass... 4 Plant Growth Hormones... 4 Synthetic Plant Growth Regulators... 5 Class A and B... 6 Class C... 7 Class D... 7 Class E... 8 Class F... 8 Research Objectives... 9 Chapter III Materials and Methods Chapter IV Results Precipitation Seedhead Populations Seedhead Height Turfgrass Quality Turfgrass Injury Lateral Regrowth Residual Scalping Chapter V Discussion Seedhead Populations v

8 Seedhead Height Turfgrass Quality Turfgrass Injury Lateral Regrowth Residual Scalping Chapter VI Conclusion List of References Vita vi

9 List of Tables Table 1. List of trade names, active ingredients, and manufacturers of the plant growth regulators used in the study Table 2. Effects of plant growth regulators on Empire zoysiagrass seedhead populations 1-6 weeks after initial treatment (WAIT) in Table 3. Effects of plant growth regulators on Empire zoysiagrass seedhead populations 7-13 weeks after initial treatment (WAIT) in Table 4. Effects of plant growth regulators on Empire zoysiagrass seedhead populations weeks after initial treatment (WAIT) in Table 5. Effects of plant growth regulators on Empire zoysiagrass seedhead populations 1-6 weeks after initial treatment (WAIT) in Table 6. Effects of plant growth regulators on Empire zoysiagrass seedhead populations 7-13 weeks after initial treatment (WAIT) in Table 7. Effects of plant growth regulators on Empire zoysiagrass seedhead populations weeks after initial treatment (WAIT) in Table 8. Effects of plant growth regulators on Empire zoysiagrass seedhead height 1-6 weeks after initial treatment (WAIT) in Table 9. Effects of plant growth regulators on Empire zoysiagrass seedhead height 7-13 weeks after initial treatment (WAIT) in Table 10. Effects of plant growth regulators on Empire zoysiagrass seedhead height weeks after initial treatment (WAIT) in Table 11. Effects of plant growth regulators on Empire zoysiagrass seedhead height 1-6 weeks after initial treatment (WAIT) in Table 12. Effects of plant growth regulators on Empire zoysiagrass seedhead height 7-13 weeks after initial treatment (WAIT) in Table 13. Effects of plant growth regulators on Empire zoysiagrass seedhead height weeks after initial treatment (WAIT) in vii

10 Table 14. Effects of plant growth regulators on Empire zoysiagrass quality 1-8 weeks after initial treatment (WAIT) in Table 15. Effects of plant growth regulators on Empire zoysiagrass quality 9-16 weeks after initial treatment (WAIT) in Table 16. Effects of plant growth regulators on Empire zoysiagrass quality weeks after initial treatment (WAIT) in Table 17. Effects of plant growth regulators on Empire zoysiagrass quality 1-8 weeks after initial treatment (WAIT) in Table 18. Effects of plant growth regulators on Empire zoysiagrass quality 9-16 weeks after initial treatment (WAIT) in Table 19. Effects of plant growth regulators on Empire zoysiagrass quality weeks after initial treatment (WAIT) in Table 20. Effects of plant growth regulators on Empire zoysiagrass injury 1-7 weeks after initial treatment (WAIT) in Table 21. Effects of plant growth regulators on Empire zoysiagrass injury 8-14 weeks after initial treatment (WAIT) in Table 22. Effects of plant growth regulators on Empire zoysiagrass injury weeks after initial treatment (WAIT) in Table 23. Effects of plant growth regulators on Empire zoysiagrass injury 1-7 weeks after initial treatment (WAIT) in Table 24. Effects of plant growth regulators on Empire zoysiagrass injury 8-14 weeks after initial treatment (WAIT) in Table 25. Effects of plant growth regulators on Empire zoysiagrass injury weeks after initial treatment (WAIT) in Table 26. Effects of plant growth regulators on Empire zoysiagrass lateral regrowth 1-4 weeks after initial treatment (WAIT) in Table 27. Effects of plant growth regulators on Empire zoysiagrass lateral regrowth 9-12 weeks after initial treatment (WAIT) in viii

11 Table 28. Effects of plant growth regulators on Empire zoysiagrass lateral regrowth weeks after initial treatment (WAIT) in Table 29. Effects of plant growth regulators on Empire zoysiagrass lateral regrowth 1-4 weeks after initial treatment (WAIT) in Table 30. Effects of plant growth regulators on Empire zoysiagrass lateral regrowth 9-12 weeks after initial treatment (WAIT) in Table 31. Effects of plant growth regulators on Empire zoysiagrass lateral regrowth weeks after initial treatment (WAIT) in Table 32. Residual scalping effects on clipping after each application of Empire zoysiagrass unmowed for 4 weeks in 2012 and ix

12 List of Figures Figure 1. Weekly rainfall totals from 8 May 2012 to 6 October 2012, and 14 May 2013 to 11 October 2013, at the Plant Science Complex, Martin, TN Figure 2. Average weekly temperatures from 8 May 2012 to 6 October 2012, and 14 May 2013 to 11 October 2013, at the Plant Science Complex, Martin, TN x

13 Chapter I Introduction Since their introduction into the United States in 1911, zoysiagrasses have become an ideal turfgrass for golf courses and home lawns (McCarty et al., 2001), especially within the transitional and southern climate zones. Characteristics such as excellent shade and salinity tolerance, unique summer color, and improved winter hardiness contribute to an increase in zoysiagrass use. Empire zoysiagrass (Zoysia japonica Steud.) is a relatively new cultivar with rapidly increasing popularity especially within the southeastern U.S. (Anderson, 2000). Environmental stresses within the southern and transitional climate zones trigger inflorescence development, which reduces aesthetic quality and increases maintenance requirements (Engelke and Anderson, 2003). Schwartz et al. (2009) indicated that the severity of seedhead density was a heritable trait that differed among cultivars. Synthetic plant growth regulators (PGRs) are capable of suppressing inflorescence development in warm- and cool-season grasses; however, the degree of suppression varies considerably due to factors such as the PGR s mode of action, turfgrass cultivar characteristics, application rate and timing, mowing frequency, and environmental influences. Previous research has shown that some of the current PGRs have the ability to suppress seedhead development in some warm-season turfgrasses (Diesburg and Christians, 1989; Johnson, 1989a, 1989b, 1989c, 1990, 1993a, 1993b, 1994; McCarty et al., 2004; Watsche et al., 1995). However, there is little research on suppression of seedheads in the Empire cultivar of zoysiagrass. 1

14 Chapter II Literature Review Zoysiagrass Zoysiagrasses, named to honor 18 th century Australian botanist Karl von Zois, are warmseason grasses native to China, Japan, and other parts of Southeast Asia (Duble, 1996). Zoysia is adapted to transitional climates, between temperate and subtropical climates (Turgeon, 2012). Duble (1996) further indicates that zoysia is adapted to the Atlantic and gulf coasts, as well as the transition zone of the U.S. After the release of the first cultivar, Matrella, in the 1940s, zoysiagrass became popular in the southern United States due to lack of adaptation of other turfgrass species within this region (Engelke and Anderson, 2003; McCarty et al., 2001). Zoysiagrass did not become commercially available until the 1980s. Christians and Engelke (1994) reported roughly 16,293 acres of zoysiagrass planted on golf courses in the United States, 81% in the transition zone and 18% in the southeastern region. Ideal shade and salinity tolerance, improved cold hardiness, and unique color during summer are the essential characteristics of the zoysia species that contribute to their growing importance with respect to golf course use (Beard 2002; McCarty et al., 2001). Conversely, slow establishment and growth rates, genetic variability in seeded cultivars, relatively poor disease and pest resistance, and thatch build up characteristics limit zoysiagrass use (Busey and Myers, 1979; Sladek et al., 2009). Morphological features of zoysiagrasses include prostrate growth of stolons and rhizomes, stiff leaves and stems, adventitious root system, and short, compact racemes with spikelets on appressed pedicels (Anderson, 2000; Beard, 1973, 2002). 2

15 Zoysia Species There are 11 species within the Zoysia genus; the genus is native to areas from New Zealand to Japan and from Polynesia to Mauritius (Anderson, 2000). Beard (1973) notes the following three species with turfgrass characteristics: Z. japonica Steud., known as Japanese or Korean lawngrass; Z. matrella (L.) Merr., known as manilagrass; and Z. tenuifolia Willd, known as mascarenegrass. These species vary extensively in color, texture, adaptation, and growth rates. Z. japonica was introduced into the United States from Japan in 1902 (Busey and Myers, 1979), and later as seed from Kokai, North Korea in 1930 through efforts of botanist Frank N. Meyer (Engelke and Anderson, 2003). Its coarse texture and fast growth rate makes this species the most winter hardy and wear tolerant of warm-season grasses grown in the U.S. (Anderson, 2000; McCarty et al., 2001). The ideal climate for this species is found in the transition zone, where Z. japonica has a competitive advantage over cool season grasses susceptible to humid summers and bermudagrass (Cynodon dactylon L. Pers.), which is susceptible to cold winters (Duble, 1996). The essential difference from other Zoysia species is seed propagation capability in certain cultivars. Z. matrella was introduced into the United States in 1912 from Manila, Philippines, hence the common name manilagrass (Anderson, 2000; Engelke and Anderson, 2003). Anderson (2000), Beard (1973), and Duble (1996) all state that this species has finer and denser turf than Z. japonica but is less cold tolerant. Manilagrass texture, color, quality, and maintenance level resemble bermudagrass; but the species has a considerably slower establishment rate, which is also lower than that of Z. japonica (Beard, 1973; Duble 1996). Unlike Z. japonica, Z. matrella can only be propagated vegetatively. 3

16 Z. tenuifolia, or mascarenegrass, produces the finest textured turf but is the least cold hardy species of the current zoysiagrasses (Duble, 1996; Engelke and Anderson, 2003). Due to its cold sensitivity, this species is adapted to subtropical and tropical climates (Beard, 2002; Duble, 1996). Although it has good wear tolerance, high thatch accumulation and slow recuperation are negative characteristics of Z. tenuifolia associated with its exceptionally slow growth rate (Engelke and Anderson, 2003; Turgeon, 2012). Like Z. matrella, propagation of Z. tenuifolia can only be done vegetatively. Empire Zoysiagrass Empire zoysiagrass, a cultivar of the Z. japonica species, was discovered by Minoru Ito and Roberto Gurgel on a turf farm in São Paolo, Brazil (Ito and Gurgel, 2000). Distinctive characteristics are prostrate growth habit, wide leaf blades, rapid establishment, good fall color retention, and massive, deep root systems (Ito and Gurgel, 2000). Inflorescences are single, greyish purple racemes at the top of the stems (Engelke and Anderson, 2003; Ito and Gurgel, 2000). Empire has a high seedhead density compared to other zoysiagrass cultivars. High seedhead density coupled with their greyish purple color can significantly reduce aesthetic quality, requiring additional maintenance for seedhead removal. Plant Growth Hormones Plants contain the endogenous growth promoting hormones, auxins, cytokinins, and gibberellins, and the growth inhibiting hormones abscisic acid (ABA) and ethylene (Nickell, 1982; Roberts and Hooley, 1988). Indole-3-acetic acid (IAA), phenyl acetic acid, naphthalene acetic acid (NAA), and 2, 4-dichlorophenoxy acetic acid (2, 4-D) are auxins produced in the meristematic region for growth promotion by cell elongation (Butler, 2006; Roberts and Hooley, 4

17 1988). Numerous gibberellins promote cell elongation and division. According to Kaufmann (1994) and Freeborg (1983), cytokinin hormones promote cytokinesis in root tips, cambium, vegetative apices, and undeveloped leaves. Inhibitory hormones, such as ABA, promote senescence, abscission, and dormancy by disturbing protein synthesis (Nickell, 1982; Freeborg, 1983). Ethylene hormones retard root growth; ethylene gas is released as methionine and is degraded within the shoots (Roberts and Hooley, 1988). Synthetic Plant Growth Regulators Synthetic chemical retardants that act as plant growth regulators (PGRs), were originally developed in the late 1940s to reduce mowing requirements along roadsides (Beard, 1973; Ervin and Zhang, 2008; Watschke et al., 1992). Increased use of PGRs on turfgrasses can be attributed to hundreds of studies that show PGRs reduce vegetative growth, which lowers mowing frequencies, suppresses inflorescence formation, controls the undesirable grass species annual bluegrass (Poa annua L.), and enhances turfgrass quality (Elkins et al., 1977). Chemical retardants inhibit growth by altering the functions performed by endogenous plant compounds (Kaufmann, 1994; Fermanian et al., 2003). The mode of action (MOA), binding site, and site of absorption (SOA) of PGRs differ significantly. Butler (2006), Branham (1994), Christians (2011), Kaufmann (1994), and Murphy et al. (2001) all classify PGRs into three distinct groups based on their MOA: mitotic inhibitors (Type I), gibberellic acid (GA) biosynthesis inhibitors (Type II), and herbicidal Type I inhibitors. Ervin and Zhang (2008) proposed further classification of PGRs into six classes to include new PGRs; these six classes were defined as: (A) late GA biosynthesis inhibitors, (B) early GA biosynthesis inhibitors, (C) mitotic inhibitors, (D) herbicides, (E) hormonal compounds, and (F) natural-source PGRs. 5

18 Class A and B GA biosynthesis suppression results in the cyclization interference of geranylgeranyl pyrophosphate into copalylphosphate (Freeborg, 1983; Nickell, 1982; Roberts and Hooley, 1998). Butler (2006) indicates that PGRs with GA biosynthesis interference do not inhibit vegetative growth, but suppress the overall size of the plant. Disruption of GA biosynthesis can occur either early or late in the pathway. Trinexapac-ethyl [4-(cyclopropyl-a-hydroxymethylene)-3,5-dioxocyclohexanecarboxylic acid ethylester], the only Class A PGR labeled for turfgrass use, is absorbed by leaves; it disrupts the final form of GA that affects cell elongation by blocking 3βhydroxylation of GA₂ₒ to GA₁ (Ervin and Zhang, 2008; McCarty, 2001; Nickell, 1982). Previous studies show that trinexapac-ethyl can enhance turf color, reduce vegetative growth, and increase root mass and tiller development (Ervin and Ok, 2001; Johnson, 1993b, 1994; Totten et al., 2006). Flurprimidol [α-(1-methylethyl)-α-[4-(trifluourmethoxy)phenyl]-5-pyrimidinemethanol] is a root-absorbed Class B inhibitor that disrupts the pathway of cytochrome P-450-dependent reactions, blocking oxidation of ent-kaurene to ent-kaurenol (Nickell, 1982; Roberts and Hooley, 1988). This early disruption occurs prior to the first GA compound production, preventing construction of all GA compounds (Dernoeden, 1984). Flurprimidol has been found to enhance turf color and reduce vegetative growth (Dernoeden, 1984; Freeborg, 1983; Totten et al., 2006), but the ability to inhibit inflorescence development has varied depending on application rate and timing, mowing frequency, and turfgrass species (Johnson, 1993a, 1993b, 1994). 6

19 Class C A mitotic inhibiting MOA interrupts cellular division within the meristematic region of root tips and vegetative apices, providing temporary suppression of inflorescence development and cell elongation (Butler, 2006; Turgeon, 2012). Mefluidide [N-2,4-dimethyl- 5(trifluoromethyl)-sulfonyl-aminophenylacetamide] is an example of a foliar absorbed Type I PGR designed for the suppression of low-maintenance roadside vegetation by inducing radical cell division within reproductive apices, thus disrupting seedhead development (Kaufman, 1994). The precise MOA is not completely defined because of differing inhibitory effects depending on concentration level. Low concentrations of mefluidide inhibit only cell elongation, not cell division; cell division is inhibited at higher mefluidide concentrations (Elkins, 1974). Prior research has indicated excellent seedhead suppression in tall fescue (Festuca arundinacea) and common bermudagrass (Cynodon dactylon), but severe phototoxicity and reduced root and shoot development were also observed (Johnson, 1989a, 1989c; McCarty et al., 1985). Class D Most herbicidal growth regulators have postemergent activity and have been shown to inhibit the growth of turfgrass at sub-lethal rates (Watschke et al., 1992). Atrazine [2-chloro-4- (ethylamino)-6-(isopropylamino)-s-triazine] is the most common herbicide used for turfgrass growth regulation in the U.S (McCarty et al., 2001). Derived from the triazine herbicide group, atrazine inhibits growth by disrupting the normal binding of the D₁ protein and plastoquinone in the electron transport chain during photosynthesis, known as the Hill reaction (Penner, 1994). 7

20 Class E Ervin and Zhang (2008) define Class E PGRs as consisting of endogenous hormones or hormones that imitate the actions of endogenous plant growth regulators. Hormonal compounds are capable of promoting or inhibiting plant growth depending on the MOA of the PGR. Ethephon [(2-cholroethylphosponic acid], a Class E PGR, is a synthetic form of ethylene; it inhibits vegetative growth by increasing natural ethylene levels in plants creating ethylene gas, which decreases cell size (Kaufmann, 1994; Nickell, 1982). The effect of ethephon applications depends on factors such as application timing, number of applications, and concentration. Spring applications of high concentrations of ethephon have been shown to significantly reduce the presence of annual bluegrass inflorescences (Gelernter and Stowell, 2001), but research by McCullough et al. (2005) and Shatters et al. (1998) indicate an unacceptable phototoxicity when high concentrations of ethephon were applied to bermudagrass cultivars. High concentrations of ethylene, from 5,000 to 10,000 ppm, after multiple applications has been shown to promote growth and stimulate inflorescences in bluegrass (Poa pratentis L. Sydsport ) and wheat (Triticum aestivum L. Waldron ) (Poovaiah and Leopold, 1973). Class F Natural-source PGRs consist of processed organic compounds from animals, algae, and other plants (Ervin and Zhang, 2008). Humic acid and seaweed extracts are the most common compounds in Class F PGRs. These compounds have been shown to promote plant growth and increase the availability of auxins and cytokinins (Zhang and Ervin, 2004). Because applications of natural-source PGRs to turfgrasses are a relatively new concept, further research is needed to fully understand the effects of current Class F PGRs. 8

21 Research Objectives McCarty et al. (1985), Freeborg (1983), and Elkins (1974) describe how the suppression or complete inhibition of seedhead development would eliminate the need for additional mowing requirements and reduce fuel and labor costs. Extensive research identifies effective seedhead suppression of annual bluegrass and many other warm and cool-season turfgrasses, yet there still remains lack of research regarding seedhead suppression on several zoysia cultivars. This research focuses on evaluating the efficacy of various PGRs for seedhead suppression in Empire zoysiagrass, as well as their subsidiary effects on (1) turf quality and injury, (2) lateral regrowth, and (3) residual scalping. 9

22 Chapter III Materials and Methods Research was conducted from 8 May to 10 October, 2012 and 13 May to 11 October 2013, at the Plant Science Complex at The University of Tennessee at Martin. Empire zoysiagrass was established in 2009 on native, silt loam soil. Turfgrass was irrigated and fertilized to maintain nutritional status. The experimental design was a randomized complete block with four replications, with a plot size of 1.5 x 2 meters. Plots were mowed and debris cleared before each application, then remained unmowed during the four week application duration. Treatments were applied every four weeks throughout the growing season, for a total of five applications each year. Treatments consisted of Atrazine 4L, Proxy, and Embark T&O applied alone and combined at 1.0, 3.5, and 0.6 kg a.i./ha, respectively; as well as, combinations of Atrazine 4L plus Cutless 50WP at 1.0 and 0.5 kg a.i./ha; Proxy plus Primo Maxx at 3.5 and 0.04 kg a.i./ha and Embark T&O plus Primo Maxx at 0.6 and 0.04 kg a.i./ha (Table 1). Table 1. List of trade names, active ingredients, and manufacturers of the plant growth regulators used in the study. Trade Name Active Ingredient Manufacture Atrazine 4L atrazine Drexel Proxy ethephon Bayer Cutless 50WP flurprimidol SePRO Embark T&O mefluidide PBI/Gordon Primo Maxx trinexapac-ethyl Syngenta 10

23 Applications were delivered using a CO₂ backpack sprayer with 8003 flat iron nozzles calibrated at 187 kg/ha. Irrigation was applied to all plots three times a week at a rate of 3.2 cm each time. Seedhead populations, seedhead height, turfgrass quality, and turfgrass injury measurements were rated every 7 days for 4 weeks after each application. Seedhead populations were rated by counting seedheads present within a 15.2 cm² frame made of 1.3 cm PVC pipe. The frame was dropped at random twice per plot. The two counts were then averaged. Seedhead height was determined by measuring heights (cm) of ten seedheads at random per plot and then calculating the mean per plot. Turfgrass quality was visually assessed on scale of 1 to 9, where 1 = brown, dead turfgrass and 9 = dark green, uniform turfgrass; > 7 is the minimum acceptable threshold. Turfgrass injury was also assessed visually on a scale of 0 to 100%, where 0% = dark green, healthy turfgrass and 100% = brown, dead turfgrass; > 30% is the minimum acceptable threshold. Percent lateral regrowth measurements were taken during the first, third, and fifth applications over backfilled holes where root samples were removed. Two measurements were taken by placing a wire mesh screen over the backfilled holes and counting the squares filled with regrowth (Totten et. al, 2006). The mesh screen contains 230 uniform squares. Percent lateral growth was calculated by: Number of squares filled X 100 Total squares (230) 11

24 At the end of each four week treatment period, the turf in each plot was mowed at a height of 1.9 cm. Residual scalping ratings of each plot were recorded after mowing. Assessments were made visually on a scale of 0 to 100%, where 0% = no scalping present and 100% = entire area scalped. Data was subjected to analysis of variance (ANOVA) using Statistical Analysis System (SAS v. 9.3); statistical significance of main and interaction effects was determined using α = Treatment means were separated using Fisher s LSD test. For all measurements except residual scalping, results are presented by year due to detection of significant treatment by year interaction. 12

25 Chapter IV Results Precipitation The amount and distribution of precipitation differed considerably for each year, causing treatment by year analyses to be significant for all measurements except residual scalping. Consistent amounts of heavy rainfall uncharacteristic to our region occurred in 2013 (Figure 1). Rainfall totals 7-14 weeks after initial treatment (WAIT) depicts the considerable differences in drought presence (Figure 1). Drought conditions were more prominent in 2012, especially 5-14 WAIT, and cooler than normal temperatures for this climate zone were present 6-13 WAIT during 2013 (Figure 2) Precipitation (cm) Weeks After Initial Treatment Figure 1. Weekly rainfall totals from 8 May 2012 to 6 October 2012, and 14 May 2013 to 11 October 2013, at the Plant Science Complex, Martin, TN. 13

26 35 30 Temperature ( C) Weeks After Initial Treatment Figure 2. Average weekly temperatures from 8 May 2012 to 6 October 2012, and 14 May 2013 to 11 October 2013, at the Plant Science Complex, Martin, TN. Seedhead Populations In 2012, atrazine applied alone to zoysiagrass plots produces seedhead populations similar to untreated grass plots for all rating dates except 7 and WAIT (Tables 2-4). Ethephon applied alone and coupled with trinexapac-ethyl produced significant seedhead suppression 5-6 and 1-8 WAIT, respectively. However, during some time periods both treatments had significantly higher seedhead populations than the untreated control; ethephon produced 76.6 and 61.7% more seedheads than the control and WAIT (Tables 3-4). Ethephon coupled with trinexapac-ethyl increased seedhead populations by 51.2% compared to the control at 16 and 18 WAIT (Tables 3-4). Mefluidide applied alone and combined with trinexapac-ethyl had the greatest seedhead suppression efficacy with significantly lower 14

27 seedhead numbers than untreated zoysiagrass 3-8 and WAIT (Tables 2-4). No seedheads were observed on all dates after 10 WAIT in plots treated with mefluidide + trinexapac-ethyl (Tables 3-4). Turfgrass treated with ethephon + mefluidide showed the greatest seedhead suppression during the second application, averaging 53% reduction (Tables 2-3), but also significantly reduced seedheads 12, 13, 16, and WAIT (Tables 3-4). Atrazine + trinexapac-ethyl produced significant seedhead reductions of 48.7% at 2-4 WAIT, as well as significant seedhead reductions and WAIT (Tables 2-4); there were no seedheads 13 WAIT (Table 3). Atrazine + ethephon and atrazine + flurprimidol both produced significant seedhead suppression 3, 5-8, and WAIT (Tables 2-4). Table 2. Effects of plant growth regulators on Empire zoysiagrass seedhead populations 1-6 weeks after initial treatment (WAIT) in Seedhead Populations (WAIT) Treatment Initial Untreated 72.3a 35.5a 53.9a 67.1a 96.6a 12.1a 22.2a ATR 54.1a 25.4ab 39.8ab 62.9a 82.9ab 9.3abc 14.1abc ETH 55.4a 25.8ab 40.4ab 60.0ab 87.5a 6.3bcd 12.9bc MEF 46.5a 25.4ab 35.9ab 26.0d 29.0d 1.8d 3.4de ATR + ETH 46.9a 23.1ab 34.9ab 40.6bcd 70.9abc 3.9cd 5.4cde ATR + FLU 63.6a 24.6ab 44.3ab 63.3a 83.6ab 4.8bcd 11.9bcd ATR + TE 40.9a 22.4ab 31.6b 34.3cd 55.8bcd 10.1ab 17.3ab ETH + MEF 65.1a 24.8ab 44.9ab 50.1abc 67.8abc 5.0bcd 9.1bcde ETH + TE 49.6a 12.1b 30.9b 31.9cd 46.3cd 4.8bcd 7.6cde MEF + TE 64.3a 22.9ab 43.5ab 20.5d 29.0d 1.8d 2.5e *Two counts taken within a 15.2 cm² frame placed randomly per plot and averaged together. Treatment means with the same letter are not significantly different at α = 0.05, according to Fisher s LSD test. 15

28 Table 3. Effects of plant growth regulators on Empire zoysiagrass seedhead populations 7-13 weeks after initial treatment (WAIT) in Seedhead Populations (WAIT) Treatment Untreated 25.6a 36.3a 4.5abc 17.3bc 41.9b 62.1ab 6.8ab ATR 16.8bcd 25.5ab 2.6bc 17.8bc 34.9bc 55.8bc 3.1bcd ETH 18.9abc 24.4bc 8.1a 42.8a 64.4a 78.5a 9.1a MEF 1.3e 1.5d 0.3c 0.3d 0.3d 0.0d 0.0d ATR + ETH 10.3d 14.4c 2.8bc 25.8b 37.1b 52.5bc 3.8bcd ATR + FLU 14.3bcd 17.1bc 2.0bc 19.4b 43.0b 54.4bc 4.1bcd ATR + TE 20.1ab 23.0bc 0.3c 5.5cd 15.0cd 18.4d 0.0d ETH + MEF 11.1cd 15.5bc 6.5ab 24.8b 30.5bc 39.6c 1.9cd ETH + TE 12.3bcd 16.0bc 4.5abc 23.8b 40.1b 47.6bc 5.6abc MEF + TE 2.0e 1.5d 0.1c 0.0d 0.0d 0.0d 0.0d *Two counts taken within a 15.2cm² frame placed randomly per plot and averaged together. Treatment means with the same letter are not significantly different at α = 0.05, according to Fisher s LSD test. Table 4. Effects of plant growth regulators on Empire zoysiagrass seedhead populations weeks after initial treatment (WAIT) in Seedhead Populations (WAIT) Treatment Untreated 13.9ab 23.4bc 33.8b 2.7b 8.5b 14.5a 17.0ab ATR 7.8bc 15.4cd 21.0bc 0.6b 2.1c 3.9b 5.8c ETH 20.5a 35.5a 54.9a 1.8b 8.6b 12.9a 12.6b MEF 0.0c 0.0e 0.0d 0.0b 0.5c 0.9b 0.5c ATR + ETH 10.5b 17.9c 32.4b 0.5b 3.5c 5.3b 4.9c ATR + FLU 14.1ab 22.6bc 34.0b 0.3b 0.6c 1.1b 0.0c ATR + TE 2.3c 3.9de 16.0c 0.5b 0.4c 2.1b 0.6c ETH + MEF 7.4bc 12.9cd 14.1cd 1.3b 0.9c 0.8b 0.0c ETH + TE 13.5ab 29.8ab 49.1a 8.0a 14.0a 17.4a 18.9a MEF + TE 0.0c 0.0e 0.0d 0.4b 0.0c 0.0b 0.0c *Two counts taken within a 6in² frame placed randomly per plot and averaged together. Treatment means with the same letter are not significantly different at α = 0.05, according to Fisher s LSD test. 16

29 In 2013, atrazine applied alone to plots produced seedhead populations similar to the untreated control except 7-8 and WAIT (Tables 5-7). Ethephon alone and combined with trinexapac-ethyl again initially suppressed seedheads before yielding seedhead populations significantly higher than the untreated control, averaging 25% more at WAIT for ethephon (Table 6) and 102% more at WAIT for ethephon + trinexapac-ethyl (Tables 6-7). Mefluidide applied alone and combined with trinexapac-ethyl had significant seedhead suppression efficacy for all rating dates except the initial rating (Tables 5-7). The absence of seedheads was detected 7-11, 13-17, and 20 WAIT with mefluidide + trinexapac-ethyl, as well as 10, 13, 14, 17, and 20 WAIT with mefluidide (Tables 6-7). Similar to 2012, atrazine + flurprimidol significantly reduced seedhead populations 5-8 WAIT (Tables 5-6), but remained similar to the untreated plots throughout the remainder of the year. Atrazine + ethephon initially showed significant suppression averaging 30% 1-8 WAIT (Tables 5-6), but resulted in seedhead populations similar to the untreated control for the remaining rating dates except 13 and WAIT (Tables 6-7). Atrazine + trinexapac-ethyl significantly reduced seedheads an average of 57% 9-13 WAIT and 68% at WAIT (Tables 6-7). Seedhead suppression efficacy for ethephon + mefluidide was sporadic with significant reductions 3-8, 11, 13, and WAIT (Tables 5-7). Seedhead Height Similar to seedhead populations, seedhead heights were generally higher in 2012 than in Grass plots treated with atrazine had heights similar to the untreated plots except 1, 8 and 20 WAIT (Tables 8-10). Even though ethephon treatments significantly suppressed seedhead 17

30 Table 5. Effects of plant growth regulators on Empire zoysiagrass seedhead populations 1-6 weeks after initial treatment (WAIT) in Seedhead Populations (WAIT) Treatment Initial Untreated 1.6bc 25.4ab 54.6a 90.3a 105.1a 8.9ab 21.1a ATR 0.9bc 16.9bcd 45.1a 78.4ab 96.1ab 9.3a 14.4bc ETH 2.6b 12.0cd 39.8ab 60.9bc 85.8abc 6.4bc 15.5bc MEF 0.0c 0.0e 0.4c 1.1e 0.9d 1.4d 1.6fg ATR + ETH 0.9bc 0.1e 25.0b 37.9d 67.8c 5.1c 6.0ef ATR + FLU 0.8bc 16.1bcd 47.1a 70.1abc 91.8abc 5.4c 12.3cd ATR + TE 0.5bc 27.0a 44.4a 60.3bc 72.6bc 9.0ab 17.8ab ETH + MEF 0.0c 20.1abc 36.1ab 54.0cd 66.8c 5.6c 9.1de ETH + TE 5.6a 21.1abc 36.8ab 60.5bc 82.3abc 6.8abc 11.4cd MEF + TE 0.0c 0.1e 0.1c 0.6e 0.5d 1.3d 0.4g *Two counts taken within a 15.2cm² frame placed randomly per plot and averaged together. Treatment means with the same letter are not significantly different at α = 0.05, according to Fisher s LSD test. Table 6. Effects of plant growth regulators on Empire zoysiagrass seedhead populations 7-13 weeks after initial treatment (WAIT) in Seedhead Populations (WAIT) Treatment Untreated 24.6a 30.0a 4.8ab 18.5ab 32.6b 41.5b 3.9b ATR 18.0bc 21.9b 4.0b 14.1b 29.9bc 38.1b 3.6bc ETH 20.8ab 23.6ab 6.9a 24.4a 43.6a 55.4a 4.6b MEF 1.3d 0.1d 0.1de 0.0d 0.4e 0.5d 0.0e ATR + ETH 11.9d 17.9bc 3.6bc 14.3b 28.0bc 37.5b 1.9cde ATR + FLU 12.5d 17.5bc 3.4bc 19.8ab 30.3bc 38.8b 2.9bcd ATR + TE 21.1ab 22.6b 0.9cde 7.9c 15.3d 23.0c 0.5e ETH + MEF 11.3d 13.6c 4.3b 13.8bc 22.5cd 33.6bc 1.5de ETH + TE 14.1cd 18.5bc 2.6bcd 14.5b 28.8bc 43.1b 7.3a MEF + TE 0.0e 0.0d 0.0e 0.0d 0.0e 0.1d 0.0e *Two counts taken within a 6in² frame placed randomly per plot and averaged together. Treatment means with the same letter are not significantly different at α = 0.05, according to Fisher s LSD test. 18

31 Table 7. Effects of plant growth regulators on Empire zoysiagrass seedhead populations weeks after initial treatment (WAIT) in Seedhead Populations (WAIT) Treatment Untreated 7.4bcd 16.1b 29.1bc 4.4a 12.9a 18.9a 24.5a ATR 8.3bc 14.4bc 24.5bcd 2.5abcd 6.3bcd 11.6b 17.5b ETH 9.9b 18.3b 33.1b 4.1ab 11.4a 19.5a 27.9a MEF 0.0e 0.5de 0.3f 0.0e 0.3e 0.3c 0.0c ATR + ETH 8.4bc 13.8bc 24.3bcd 2.0abcde 7.3bc 10.5b 16.9b ATR + FLU 6.1bcd 13.1bc 21.9cde 1.9bcde 6.5bcd 10.3b 15.7b ATR + TE 3.4de 7.9cde 16.9de 1.1cde 3.4de 9.0b 12.8b ETH + MEF 4.8cd 8.0cd 12.4e 0.5de 3.6cde 8.5b 12.0b ETH + TE 17.3a 37.3a 52.1a 3.4abc 9.9ab 16.6a 25.9a MEF + TE 0.0e 0.0e 0.0f 0.0e 0.1e 0.4c 0.0c *Two counts taken within a 15.2cm² frame placed randomly per plot and averaged together. Treatment means with the same letter are not significantly different at α = 0.05, according to Fisher s LSD test. heights for all dates during the first application period, suppression was generally not significant for sequential applications (Table 8). All treatments containing mefluidide and ethephon + trinexapac-ethyl had the greatest reductions in seedhead height (Tables 8-10). Mefluidide applied to turfgrass alone and combined with trinexapac-ethyl significantly lowered seedhead heights for all rating dates except 9 WAIT (Table 9), with mefluidide treated turfgrass having a height of 0.0 cm WAIT and mefluidide + trinexapac-ethyl treated plots having 0.0 cm height WAIT (Tables 9-10). Atrazine combined with trinexapac-ethyl also produced significant seedhead height suppression for all rating dates except 1 and 5 WAIT (Table 8-10), and a seedhead height of 0.0 cm 13 WAIT (Table 9). Atrazine coupled with ethephon significantly reduced height 18 and 29%, 2-4 and 6-8 WAIT; and 22, 12, and 13% at 12, 15, and 16 WAIT, respectively (Tables 8-9). Turfgrass treated with atrazine coupled with flurprimidol 19

32 Table 8. Effects of plant growth regulators on Empire zoysiagrass seedhead height 1-6 weeks after initial treatment (WAIT) in Seedhead Height (cm) (WAIT) Treatment Initial Untreated 8.0a 5.3abc 7.5a 10.2a 11.4a 5.3a 7.6a ATR 6.9b 5.6a 6.7b 10.4a 9.8b 5.2ab 6.8ab ETH 7.1ab 4.8bcd 6.5b 8.5bc 8.8b 4.7abc 6.4bc MEF 6.7b 5.2abc 5.7cd 6.4de 6.6c 4.2bc 4.5de ATR + ETH 6.6b 5.2abc 6.7b 7.9cd 9.1b 4.7abc 5.4cd ATR + FLU 7.0b 5.2abc 6.9ab 9.8ab 10.1ab 4.6abc 7.0ab ATR + TE 6.6b 4.8cd 5.7d 7.2cde 6.9c 4.3abc 4.3de ETH + MEF 7.4ab 5.3ab 6.3bc 7.8cd 9.0b 4.9ab 6.1bc ETH + TE 7.2ab 4.5d 5.3d 6.3de 6.4c 3.8cd 3.8e MEF + TE 7.1ab 4.8cd 5.1d 5.7e 6.2c 2.8d 4.0e *Ten heights were taken per plot and averaged together. Treatment means with the same letter are not significantly different at α = 0.05, according to Fisher s LSD test. Table 9. Effects of plant growth regulators on Empire zoysiagrass seedhead height 7-13 weeks after initial treatment (WAIT) in Seedhead Height (cm) (WAIT) Treatment Untreated 9.1a 10.6a 5.9a 9.4a 12.0a 13.9a 3.9a ATR 7.6abc 8.2bc 6.2a 9.5a 11.1a 12.7ab 3.7a ETH 7.1bc 7.5cd 6.0a 8.9a 10.2a 11.6b 5.1a MEF 5.1e 3.7e 4.1ab 2.0c 2.1c 0.0d 0.0b ATR + ETH 6.8bcd 7.1cd 4.4ab 8.3a 10.1a 10.9b 3.5a ATR + FLU 8.4ab 9.7ab 5.7a 8.6a 11.6a 12.4ab 5.3a ATR + TE 5.3de 5.6de 2.2bc 5.3b 6.6b 6.9c 0.0b ETH + MEF 6.7cd 7.2cd 6.2a 9.1a 10.5a 11.9ab 3.5a ETH + TE 4.6ef 4.7e 4.8a 5.4b 6.0b 6.4c 3.0a MEF + TE 3.4f 3.5e 0.9c 0.0c 0.0c 0.0d 0.0b *Ten heights were taken per plot and averaged together. Treatment means with the same letter are not significantly different at α = 0.05, according to Fisher s LSD test. 20

33 Table 10. Effects of plant growth regulators on Empire zoysiagrass seedhead height weeks after initial treatment (WAIT) in Seedhead Height (cm) (WAIT) Treatment Untreated 7.8ab 10.2a 12.5a 4.4ab 6.5a 8.1a 9.5a ATR 7.4ab 10.0a 11.3abc 2.6abc 4.4ab 5.0ab 6.1b ETH 7.7ab 9.6ab 10.8bc 2.4abc 5.3ab 5.7ab 6.0b MEF 0.0d 0.0d 0.0e 0.0c 2.6bc 0.9de 1.0de ATR + ETH 7.7ab 9.0b 10.9bc 1.0c 4.2ab 3.1bcde 2.9cd ATR + FLU 8.1a 10.4a 12.1ab 1.1c 3.0bc 1.7cde 0.0e ATR + TE 4.4c 6.1c 7.1d 1.5c 2.3bc 3.4bcd 1.0de ETH + MEF 7.1b 8.9b 10.6c 4.6a 3.9ab 3.6bcd 0.0e ETH + TE 4.8c 5.9c 6.4d 2.6abc 4.4ab 4.6bc 5.0bc MEF + TE 0.0d 0.0d 0.0e 0.0c 0.0c 0.0e 0.0e *Ten heights were taken per plot and averaged together. Treatment means with the same letter are not significantly different at α = 0.05, according to Fisher s LSD test. had heights similar to untreated turf for all rating dates except WAIT. Ethephon mixed with trinexapac ethyl produced significant reductions of seedhead height, averaging 41% for the first two applications, as well as 49 and 43% and WAIT, respectively (Tables 9-10). Seedhead heights in 2013 (Tables 11-13) differed from the results found in Atrazine applied alone to plots and coupled with flurprimidol reduced seedhead height at only a few rating dates; atrazine alone at 8 WAIT (Table 12) and atrazine + flurprimidol at 3, 4, and 7 WAIT (Tables 11-12). Ethephon applied to turfgrass alone and combined with atrazine and mefluidide maintained seedhead height suppression 6-8 WAIT (Tables 11-12), and the mixtures of ethephon + atrazine and ethephon + mefluidide also had significant height reductions both at 15 WAIT, and 16 and 17 WAIT, respectively (Table 13). Mefluidide and mefluidide + trinexapac-ethyl significantly suppressed seedhead height for all rating dates in

34 Table 11. Effects of plant growth regulators on Empire zoysiagrass seedhead height 1-6 weeks after initial treatment (WAIT) in Seedhead Height (cm) (WAIT) Treatment Initial Untreated 4.6a 6.8a 9.4a 11.3a 13.1a 5.5a 7.7a ATR 4.1ab 4.9ab 7.9ab 9.9ab 11.9ab 5.2a 7.1ab ETH 4.4ab 2.8bcd 4.9c 6.9cde 8.0de 5.1ab 6.4b MEF 0.0c 2.3bcd 1.2d 3.4g 3.7g 4.2cd 4.3d ATR + ETH 2.8abc 4.1abc 6.6bc 7.7cd 9.6cd 5.1ab 6.0bc ATR + FLU 4.1ab 2.9bcd 7.2abc 8.7bc 10.2bc 5.1ab 7.8a ATR + TE 1.3bc 5.2ab 6.4bc 7.6cde 8.9cde 4.6bc 5.0cd ETH + MEF 0.0c 0.0d 1.4d 6.0de 7.4ef 5.2ab 6.4b ETH + TE 5.3a 4.4abc 5.1c 5.6ef 5.8fg 3.9d 4.1d MEF + TE 0.0c 1.3cd 1.2d 3.7fg 3.8g 3.8d 2.8e *Ten heights were taken per plot then averaged together. Treatment means with the same letter are not significantly different at α = 0.05, according to Fisher s LSD test. Table 12. Effects of plant growth regulators on Empire zoysiagrass seedhead height 7-13 weeks after initial treatment (WAIT) in Seedhead Height (cm) (WAIT) Treatment Untreated 9.8a 11.1a 6.1a 9.4a 11.9a 13.8a 5.6a ATR 8.4ab 9.4bc 6.2a 9.5a 11.1a 12.5a 5.2a ETH 7.6b 8.3c 6.1a 9.0a 10.2a 11.5a 5.7a MEF 3.3d 1.1e 1.1cd 0.0c 2.4c 1.4c 0.0b ATR + ETH 7.3b 8.1c 5.8a 8.3a 10.1a 11.3a 3.7a ATR + FLU 9.5a 10.5ab 5.6a 8.6a 11.6a 12.5a 5.6a ATR + TE 5.6c 6.0d 2.1bc 5.4b 6.7b 6.9b 1.0b ETH + MEF 7.7b 8.5c 6.1a 9.2a 10.6a 11.9a 3.9a ETH + TE 4.8c 5.1d 3.5b 5.6b 6.0b 6.4b 4.3a MEF + TE 0.0e 0.0e 0.0d 0.0c 0.0d 0.9c 0.0b *Ten heights were taken per plot then averaged together. Treatment means with the same letter are not significantly different at α = 0.05, according to Fisher s LSD test. 22

35 Table 13. Effects of plant growth regulators on Empire zoysiagrass seedhead height weeks after initial treatment (WAIT) in Seedhead Height (cm) (WAIT) Treatment Untreated 8.0ab 10.6a 12.6a 5.2a 6.8a 8.4a 9.6a ATR 7.6ab 10.0abc 11.5ab 3.7abc 6.3a 7.4a 8.9a ETH 8.1ab 10.0abc 11.1ab 2.5abcd 6.0ab 8.0a 8.5a MEF 0.0d 1.8e 1.0d 0.0d 0.8d 0.9c 0.0d ATR + ETH 7.8ab 9.1c 10.6b 2.6abcd 6.2a 7.5a 8.5a ATR + FLU 8.3a 10.6ab 12.2a 4.7ab 6.4a 7.8a 8.6a ATR + TE 4.5c 6.0d 7.1c 1.7cd 3.3c 5.0b 4.2c ETH + MEF 7.2b 9.2bc 11.3ab 1.2cd 5.8ab 7.3a 8.3a ETH + TE 5.0c 5.9d 6.2c 2.0bcd 4.5bc 5.7b 5.9b MEF + TE 0.0d 0.0f 0.0d 0.0d 0.8d 1.0c 0.0d *Ten heights were taken per plot then averaged together. Treatment means with the same letter are not significantly different at α = 0.05, according to Fisher s LSD test. (Tables 11-13). Turfgrass treated with mefluidide had seedhead heights of 0.0 cm initially and 10, 13-14, 17 and 20 WAIT (Tables 11-13). Mefluidide + trinexapac-ethyl also produced seedhead heights of 0.0 cm initially and 7-11 and WAIT (Tables 11-13). Tank mixtures of atrazine + trinexapac-ethyl and ethephon + trinexapac-ethyl also produced significant height suppression for all rating dates after 1 WAIT except for ethephon + trinexapac-ethyl at 13 WAIT (Table 13). All other treatments containing ethephon had significant height suppression for all dates in the first application (Table 11), but lost efficacy with sequential applications. Turfgrass Quality In 2012, quality ratings for all treatments including the untreated plots (Tables 14-16) decreased 19 and 20 WAIT due to the turfgrass entering dormancy (Table 16). Atrazine alone and coupled with trinexapac-ethyl resulted in quality ratings similar to untreated plots for all 23

36 Table 14. Effects of plant growth regulators on Empire zoysiagrass quality 1-8 weeks after initial treatment (WAIT) in Turf Quality (WAIT) Treatment Untreated 7.6a 7.9a 7.9a 7.9a 7.9a 7.9a 7.9a 7.9a ATR 7.5ab 7.8ab 7.6ab 7.8ab 7.6ab 8.0a 8.0a 7.8a ETH 7.4ab 7.8ab 7.9a 7.8ab 7.6ab 7.9a 8.0a 7.9a MEF 7.1abc 7.5ab 7.0c 7.3c 6.6c 6.5c 6.6c 6.4b ATR + ETH 7.5ab 7.5ab 7.6ab 7.8ab 7.6ab 7.9a 7.8ab 7.6a ATR + FLU 7.4ab 7.8ab 7.6ab 7.5abc 7.8ab 7.9a 7.9ab 7.9a ATR + TE 7.4ab 7.4ab 7.5abc 7.6abc 7.6ab 7.6ab 7.8ab 7.8a ETH + MEF 6.6c 7.4ab 7.3bc 7.3c 7.3b 7.6ab 7.6ab 7.6a ETH + TE 7.5ab 7.5ab 7.3bc 7.4bc 7.3b 7.3b 7.5b 7.5a MEF + TE 7.0bc 7.3b 7.1bc 7.3c 6.5c 6.4c 6.4c 6.1b *Visual rating on a scale of 1-9 with 1=brown, dead turfgrass and 9=dark green, uniform turfgrass with >7 being minimum acceptable. Treatment means with the same letter are not significantly different at α = 0.05, according to Fisher s LSD test. Table 15. Effects of plant growth regulators on Empire zoysiagrass quality 9-16 weeks after initial treatment (WAIT) in Turf Quality (WAIT) Treatment Untreated 8.0a 7.9a 7.9a 8.0a 7.3ab 7.8ab 8.0a 8.0a ATR 7.9a 8.0a 8.0a 8.0a 7.3ab 7.8ab 7.9ab 8.0a ETH 8.0a 7.8a 7.9a 7.8a 7.4ab 7.8ab 7.6ab 7.6ab MEF 6.8b 6.5b 6.6b 6.6b 7.5ab 7.0c 6.8d 7.0c ATR + ETH 7.9a 7.8a 7.8a 7.9a 7.0b 7.8a 7.5ab 7.4bc ATR + FLU 7.9a 7.8a 7.8a 7.9a 7.6ab 7.9ab 8.0a 8.0a ATR + TE 7.8a 7.6a 7.8a 7.8a 7.9ab 7.8ab 7.6ab 7.5bc ETH + MEF 7.9a 7.6a 7.6a 7.8a 7.4ab 7.6ab 6.9cd 7.3bc ETH + TE 7.8a 7.6a 7.8a 7.9a 8.0a 7.8ab 7.4bc 7.3bc MEF + TE 6.5b 6.3b 6.5b 6.6b 7.8ab 7.3bc 6.9cd 7.0c *Visual rating on a scale of 1-9 with 1=brown, dead turfgrass and 9=dark green, uniform turfgrass with >7 being minimum acceptable. Treatment means with the same letter are not significantly different at α = 0.05, according to Fisher s LSD test. 24

37 Table 16. Effects of plant growth regulators on Empire zoysiagrass quality weeks after initial treatment (WAIT) in Turf Quality* (WAIT) Treatment Untreated 8.0a 8.0a 7.8a 7.5a ATR 7.5bcd 8.0a 7.6ab 7.3ab ETH 7.8ab 8.0a 7.4ab 6.9bc MEF 7.3cd 6.9c 6.5cd 6.1de ATR + ETH 7.5bcd 7.9a 6.8c 6.5cd ATR + FLU 7.6abc 8.0a 7.3b 6.9bc ATR + TE 7.8ab 8.0a 7.5ab 7.1ab ETH + MEF 7.5bcd 7.5b 6.3d 5.9e ETH + TE 7.8ab 8.0a 7.4ab 7.1ab MEF + TE 7.1d 7.1c 6.5cd 6.4d *Visual rating on a scale of 1-9 with 1=brown, dead turfgrass and 9=dark green, uniform turfgrass with >7 being minimum acceptable. Treatment means with the same letter are not significantly different at α = 0.05, according to Fisher s LSD test. dates except 17 and 16 WAIT, respectively (Table 16). Mefluidide applied alone and tank mixed with trinexapac-ethyl significiantlly reduced turfgrass quality at all dates except 1 and 2 WAIT for mefluidide, resulting in unacceptable quality ratings (< 7) 5-12, 15, and WAIT for mefluidide and mefluidide + trinexapac-ethyl treatments, also 18 WAIT for mefluidide applied alone (Tables 15-16). Ethephon + mefluidide reduced quality during the first application and WAIT (Tables 14-16), with unacceptable ratings of 6.6 and and 15 WAIT (Tables 14-15). Ethephon + trinexapac-ethyl lowered quality 4-7 and WAIT (Tables 14-15). Atrazine + ethephon and atrazine + trinexapac-ethyl both reduced quality 16 WAIT (Table 14), also at 17 WAIT for atrazine + trinexapac-ethyl (Table 16). Atrazine + ethephon, atrazine + flurprimidol, and all treatments containing mefluidide had unacceptable quality WAIT (Table 16). 25