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FACTORS AFFECTING THE EFFICACY OF TWO TURFGRASS GROWTH
REGULATORS, TRINEXAPAC-ETHYL AND V-10029

By

Matthew James Fagemess

A THESIS

Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Crop and Soil Sciences

1997

ABSTRACT

FACTORS AFFECTING THE EFFICACY OF TWO TURFGRASS GROWTH
REGULATORS, TRINEXAPAC-ETHYL AND V-10029

By

Matthew James Fagerness

Tn'nexapac—ethyl is a foliar absorbed turfgrass growth regulator that inhibits shoot
growth in many turfgrass species. Research initiated in 1995 showed the addition of
Sylgard 309° + 28% urea ammonium nitrate could signiﬁcantly enhance the eﬁcacy of
trinexapac-ethyl on four cool-season turfgrass species. Ammonium sulfate compensated
for reductions in trinexapac-ethyl eﬁcacy when hard water was the carrier and increased
the rainfastness of trinexapac-ethyl for perennial ryegrass. The plant base was determined
to be a preferred site of absorption for "C-trinexapac—ethyl in Kentucky bluegrass while
absorption by the leaf blade could be enhanced by adding Sylgard 309°. Translocation of
“C-trinexapac-ethyl in Kentucky bluegrass was acropetal when the material was absorbed
by the plant base and basipetal when the material was absorbed by the leaf blade. An
experimental turfgrass growth regulator, V-10029, signiﬁcantly suppressed seedhead
formation and shoot growth in ﬁve cool-season turfgrass species but was more injurious

than trinexapac-ethyl, due to its herbicidal mode of action.

INTRODUCTION

Trinexapac-ethyl is a foliar absorbed turfgrass growth regulator that has been
commercially available since 1993. Trinexapac-ethyl inhibits the biosynthesis of gibberellic
acid by inhibiting the 3B-hydroxylation of GA” to 6A,. Compared to the activity of other
turfgrass growth regulators that inlu'bit gibberellin biosynthesis, this inhibition appears very
late in the pathway, occurring immediately prior to biosynthesis of the primary active
gibberellin that stimulates shoot elongation. Compounds such as paclobutrazol and
ﬂurprimidol inhibit gibberellin biosynthesis by blocking an earlier step in the pathway.

The singularity of the mode of action seen with trinesrapac-ethyl, coupled with its
relative market infancy, create a multitude of research areas that need to be addressed with
this compound. Research concerning the physiological eﬁ‘ects of applying turfgrass growth
regulators, especially on a long-term basis, has been limited. Commercially available
products such as trinexapac-ethyl may impact the responses of turfgras species to a variety
of environmental and cultural stresses. The purpose of the research presented in this thesis
was to determine the inﬂuence of several factors related to growth regulator application
on the efﬁcacy of trinexapac—ethyl and of an experimental growth regulator, V-10029,

which has an herbicidal mode of action.

iii

ACKNOWLEDGEMENTS

Therearemanypeoplewhohavebeenofgreat assistaneetomethroughoutmy
career at Michigan State University. The help and guidance ﬁ'orn them all has helped make
my time here both enjoyable and, more importantly, a positive educational experience as I
move on towards my career goals. I would ﬁrst like to thank Dr. Donald Penner, whose
sound adviceandunderstmdinghumsdemecomemappredatethenatureofreseardt
Special thanks also to Frank Roggenbuck who helped teach me how to do research and to
Terry Wright, who perhaps was the only reason I came to Michigan State. I would like to
thank as well Novartis, especially Dr. Joseph Dipaola, for the industry support behind my
thesis project. I must also acknowledge the help I have received ﬁ'om my committee
members as well as the other faculty members and graduate students in both weed science
and in turfgrass science. Perhaps largely unnoticed by many but not by me was the
tremendous amount of time and effort put forth by our undergraduate help, namely Renee
Feldpausch, Susan Redwine, and Caren Schmidt. Thank you all so much. Finally, I must
thank my family, whose love and support over the past couple of years has really helped

me adjust to being so far away ﬁom home.

iv

TABLE OF CONTENTS

LIST OF TABLES ......................................................................................... vii
LIST OF FIGURES ........................................................................................ ix

CHAPTER 1

SPRAY APPLICATION PARAMETERS THAT INFLUENCE THE
GROWTH INHIBITING EFFECTS OF TRINEXAPAC-ETHYL

ABSTRACT ........................................................................ 1
INTRODUCTION .............................................................................. 3
RESULTS AND DISCUSSION 12
LIST OF REFERENCES ................................................................... 18

CHAPTER2

“C-TRINEXAPAC—ETHYL ABSORPTION AND TRANSLOCATION
IN KENTUCKY BLUEGRASS

ABSTRACT ....................................................................... 33
INTRODUCTION ............................................................................. 35
RESULTS AND DISCUSSION W42

LIST OF REFERENCES ..................................................................... 46

CHAPTER3

EVALUATION OF V-10029 AND TRINEXAPAC-ETHYL AS TURFGRASS
GROWTH REGULATORS ON FIVE COOL-SEASON SPECIES

ABSTRACT ........................................................................ 57
INTRODUCTION ............................................................................. 59
LIST OF REFERENCES ..................................................................... 69

CONCLUSIONS ........................................................................................... 82

LIST OF TABLES

CHAPTERI

Table l - Trinexapac-ethyl emcacy on ‘Georgetown’ Kentucky bluegrass:

the eﬁ'ect of application rates and Sylgard 309' + 28%

urea ammonium nitrate ......................................................

Table 2 - Trinexapac-ethyl eﬁcacy on ‘Mondial’ perennial ryegrass:
the eﬂ‘ect of application rates and Sylgard 309' + 28%

urea ammonium nitrate ......................................................

Table 3 - Trinexapac-ethyl eﬁcacy on ‘Putter’ creeping bentgrass:
the eﬂ‘ect of application rates and Sylgard 309‘ + 28%

urea ammonium nitrate ......................................................

Table 4 - Trinexapac-ethyl eﬁcacy on ‘Triathlon’ tall fescue:
the eﬁ‘ect of application rates and Sylgard 309' + 28%

urea ammonium nitrate ......................................................

Table 5 - Eﬂ'ects of hard water cations and ammonium sulfate (AMS)

on trinexapac-ethyl activity in perennial ryegrass ........................

Table 6 - Eﬁ‘ects of hard water cations and ammonium sulfate (AMS)

on sethoxydim activity in perennial ryegrass .............................

Table 7 - Rainfastness characteristics of trinexapac-ethyl applied to

perennial ryegrass............ ............................................................

Table 8 - Rainfastness characteristics of sethoxydim applied to

perennial ryegrass. .......................................................................

Table A1- Speciﬁcations for greenhouse spray carrier
volume treatments...

Table A2 - Speciﬁcations for ﬁeld spray carrier volume

treatments .................................................................................

vii

Ease

...... 21

...... 22

...... 23

...... 24

....... 25

....... 26

........ 27

........ 28

...31

...... 32

CHAPTER2 Baas

Table 1 - Content of absorption study "C treatment solutions ........................ 49
Table 2 - Plant segmentation in translocation studies ................................... 50
Table 3- Translocation of “C trtnertapac-ethyl from three sites of

uptake... 53
Table 4 - Translocation of “C trinexapac-ethyl when rhizomes are present ......... 54
Table Bl - Contents of stock nutrient solutions ......................................... 55
Table B2 - Contents of full strength I-Ioagland’s solution .............................. 56
CHAPTER 3

Table l - Seedhead suppression in tall fescue and perennial ryegrass pots,
as a function ofturfgrass growth regulator treatment....... 71

Table 2 - Growth inhibiting eﬁ‘ects of V-10029 and trinexapac-ethyl
on perennial ryegrass .............................................................. 72

Table 3 - Growth inhibiting eﬁ'ects of V-10029 and trinexapac-ethyl
on Kentucky bluegrass ............................................................ 73

Table 4 - Growth inhibiting eﬁ'ects of V-10029 and trinexapac-ethyl
on tall fescue ....................................................................... 74

Table 5 - Growth inhibiting eﬁ‘ects of V-10029 and trinexapac-ethyl
on creeping bentgrass ............................................................. 75

Table 6 - Growth inhibiting eﬁ‘ects of V-10029 and trinexapac-ethyl
on creeping red fescue ............................................................ 76

LIST OF FIGURES

CHAPTERI 238:

Figure l - Eﬁ‘ects of spray carrier volume and ammonium sulfate
on ‘Mondial’ perermial ryegrass 14 days after treatment ................... 29

Figure 2 - Eﬁ‘ects of spray carrier volume on clipping production
21 days aﬁer treatment for ‘Blacltsburg’ Kentucky

bluegrass mowed at S, 7.5, and 10 cm ....................................... 30
CHAPTER 2
Figure 1 - Chemical structure for 1,2,6-“C-trinexapac-ethyl ......................... 48
Figure 2 - Absorption patterns of l‘C-trinexapac-ethyl over a 24 hour

period ﬁ'om three sites of uptake. The patterns are

represented by the followin regression data:

Roots: Y==0.219x + 0.042 .901

LeafBlade: Y2=1043.1x°°’ + 15.9 r1=.995

Plant Base: Y==0.961nx + 84 82951 ........................................ 51

Figure 3a,b - The eﬁ‘ect of Sylgard 309° on absorption of

"C-trinerrapac-ethyl by the leaf blade (Figure 3a)
and by the plant base (Figure 3b) ......................................... 52

CHAPTER3 m

Figure l -Decreasedpredictabi1ityinthepatternsofgmwth
inhibition over time in Kentucky bluegrass, as a function
of increasing rate of V-10029. LSD”, values for
2, 4, and 6 WAT were 16, 27, and 31, respectivelywhile
R2 values for the depicted curves for growth inhibition
at 2, 4, and 6 WAT were 0.73, 0.47, and 0.25, respectively ............. 77

Figure 2 - Growth inhibiting eﬁ’ects of V-10029 (0.015 kyha)
across four turfgrass species. The LSD“: values for
weeks 1, 2, 3, and 4 were 17, 19, 28, and 24, respectively .............. 78

Figure 3 - Growth inhibiting eﬁ‘ects of V-10029 (0.029 kg/ha)
across four turfgrass species. The LSD”: values for
weeks 1, 2, 3, and 4 were 13, 17, 21, and 29, respectively .............. 79

Figure 4 - Growth inhibiting eﬁ'ects of V-10029 (0.059 kg/ha)
across four turfgrass species. The LSD“, values for
weeks 1, 2, 3, and 4 were 13, 15, 21, and 25, respectively .............. 80

Figure 5 - Growth inhibiting effects of trinexapac-ethyl (0.287 kg/ha
for Kentucky bluegrass; 0.382 kg/ha for perennial ryegrass,
tall fescue, and creeping bentgrass) across four turfgrass
species. The LSD“, values for weeks 1, 2, 3, and 4 were
34, 19, 32, and 34, respectively .............................................. 81

CHAPTERI

SPRAY APPLICATION PARAMETERS THAT INFLUENCE THE GROWTH
INHIBITING EFFECTS OF TRINEXAPAC-ETHYL

SPRAY APPLICATION PARAMETERS THAT INFLUENCE THE GROWTH
INHIBITING EFFECTS OF TRINEXAPAC-ETHYL

Matthew James Fagerness
ABSTRACT

Trinexapac-ethyl is a foliar absorbed cyclohexanedione turfgrass growth regulator
that can inhibit shoot growth in a broad range of turfgrass species. Greenhouse studies
were conducted with trinexapac-ethyl to investigate the eﬂ‘ects of hard water, rainfastness,
photolability, and spray carrier volume on eﬁcacy. Results were compared to those
obtained with the cyclohexanedione herbicide, sethoxydim. Studies with Kentucky
bluegrass, perennial ryegrass, creeping bentgrass, and tall fescue showed that the adjuvant
combination of Sylgard 309' plus 28% urea ammonium nitrate (UAN) could signiﬁcantly
enhance the efﬁcacy of trinexapac-ethyl when applied at or below 0.382 kg ha".
Ammonium sulfate compensated for reductions in both trinexapac-ethyl and sethoxydirn
activity on perermial ryegrass when hard water was the carrier. Ammonium sulfate
increased the rainfastness of trinertapac-ethyl on perennial ryegrass to a greater extent than
did Sylgard 309" while the rainfastness of sethoxydim was only increased by the latter.
Photolabilty of formulated trinexapacoethyl on perennial ryegrass was not observed to be a
liability. Increasing spray carrier volume did not signiﬁcantly inﬂuence the eﬁicacy of
trinexapac-ethyl on perennial ryegrass, although efﬁcacy enhancements observed with
additions of ammonium sulfate were only apparent at low volumes. The impact of
ammonium salts on trinexapac—ethyl activity had a broad range of implications for

applications of this growth regulator. .

2
Abbreviations: UAN - urea ammonium nitrate, E formulation - ernulsiﬁable concentrate

formulation, AMS - ammonium sulfate, UV - ultraviolet, DAT - days aﬁer treatment

INTRODUCTION

Foliar absorbed herbicides provide eﬁ‘ective post-emergence control of a broad
range of agronomic weeds. Uptake by the shoots speeds the arrival of active ingredient at
the target tissue, as compared to root absorbed materials. However, eﬁcacy of foliar
absorbed herbicides is dependent on a greater number of application parameters than for
herbicides applied to the soil. Examples of such parameters are adjuvants, chemical
rainfastness, carrier water quality, chemical photolability, and spray carrier volume.

Trinexapac-ethyl is a foliar absorbed turfgrass growth regulator that can cause
growth inhibition, with maximum eﬁcacy at 14-21 days after treatment, in numerous
turfgrass species (Johnson, 1993; Johnson, 1994). Trinexapac-ethyl falls into the
cyclohexanedione class of herbicide chemistry, having structural similarity to both
sethoxydim and clethodim, two common grarninicides. Spray application parameter eﬁ‘ects
on trinexapaeethyl eﬁcacy may therefore follow the same trends that exist for
sethoxydim and/or clethodim The label for trinexapac-ethyl identiﬁes a broad range of
effective spray carrier volumes (187-1683 1 ha"), achievement of rainfastness within one
hour after application, and no need for an adjuvant to enhance emcacy. There is little
evidence available to either support or discount these stipulations.

Adjuvants may enhance spray droplet coverage on plant leaves and chemical
absorption (Wanarnarta et al., (1989a); Bridges et al., 1991; Bridges et al., 1992). These
eﬁ‘ects may be due to a number of possible mechanisms, including cuticle solubilization
and physical interaction with the herbicide in question (Wanamarta et al., (1989a)).

3

4
Adjuvants can thus be used to increase herbicide eﬁcacy, enhance activity of photolabile

herbicides, or overcome problems with antagonism from other chemicals and/or solution
salts (Campbell and Penner, 1985; Penner, 1989; Hazen and Krebs, 1992; McInnes et al.,
1992). Many adjuvants have been tested for enhancement of eitha' sethoxydim or
clethodim with varying results (Wanamarta et al., (1989a); Bridges et al., 1992; Hazen
and Krebs, 1992; Jordan et al., 1996). Therefore, the choice of adjuvant can be very
critical. Herbicide applications on grasses may show a favorable response to additions of
organosilicone surfactants, oﬂ‘ering potential for these adjuvants to enhance herbicide
eﬂicacy (Field and Bishop, 1988; Roggenbuclt et al., 1990; Sun et al., 1996).

Chemical rainfastness is the time required after a chemical application for enough
absorption to occur so that activity is not diminished by subsequent rainfall removing the
chemical from the leaf surface. Postemergence herbicides with slow rates of foliar
absorption are often susceptible to losses of activity via this mechanism. Thus, the
inﬂuence of adjuvants in enhancing foliar absorption has been a logical area of interest.
Organosilicone surfactants have the potential for increasing the rainfastness and/or eﬁcacy
of some herbicides (Jansen, 1973). However, the mechanism by which such improvements
act is disputed. Field and Bishop (1988) document reduced spray solution surface tension
as a result of organosilicone surfactant action. Accelerated absorption would enhance
rainfastness. They assumed increased absorption was related to herbicide penetration
through the stomatal pore. However, this mechanism doesn’t explain variable eﬁcacy
responses between organosilicone surfactants which similarly reduce spray solution
surface tension. Enhanced cuticular penetration thus appears responsible for the activity

enhancement (Roggenbuck et al., 1990). Sun et al. (1996) document rainfastness as soon

5
as 15 minutes after application of primisulfuron on velvetleaf with an organosilicone

surfactant. The overall potential ofthese mrfactantstoincreaserainfastnessisclearand
warrants invesﬁgaﬁonwithanychemicalwhererainfamsmayneedtobeincreased.

Carrier water quality can aﬁect absorption and/or activity of herbicides due to the
presence of Na", Ca”, Mg“, and Fe“. Glyphosate activity is reduced in the presence of
many soluble cations because it forms a conjugate salt with the inorganic cation (Stahlman
and Phillips, 1979; Nalewaja and Matysiak, 1993; Thelen et al., 1995). This antagonism is
increased with high spray carrier volumes (Sandberg et al., 1978). Antagonism of
clethodim is seen in the presence of sodium bicarbonate but is not seen with a diﬂ'erent
graminicide, quizalofop (McMullan, 1994). Antagonism between sethoxydim and Na-
bentazon, through a similar formation of a Na-sethoxydim conjugate salt is also well
documented (Jordan and York, 1989; Wanarnarta et al., (1989b); Wanarnarta et al., 1993;
Nalewaja et al., 1994; Thelen et al., 1995).

These antagonisms can be overcome with adjuvants. Addition of ammonium salts
eﬂ‘ectively restores herbicide activity by replacing the metal cation portion of the inactive
conjugate salt with ammonium, forming a new conjugate that has higher solubility and
thus is more readily absorbed (Jordan and York, 1989; Wanarnarta et al., 1989; Nalewaja
and Matysiak, 1993; Wanarnarta et al., 1993; Thelen et al., 1995). Other methods such as
replacing tank mixed applications of Na-bentazon and sethoxydim with sequential
applications also overcome this antagonistic eﬂ'ect (Rhodes and Coble, 1983). The speciﬁc
susceptibility of some herbicides, especially the cyclohexanediones, to antagonism with
inorganic metal cations provides a basis for research with other products showing similar

chemistry.

6

Chemical photolability, most commonly due to the eﬂ‘ects of ultraviolet (UV) light,
can reduce the eﬁcacy of some herbicides. Cyclohexanedione grass herbicides are
particularly susceptible to photolability (Zorner et al., 1989; Bridges et al., 1992; Hazen
and Krebs, 1992; McInnes et al., 1992; McMullan, 1994; Nalewaja et al., 1994;
McMullan, 1996). The same researchers suggest a slower rate of foliar uptake than
photodegradation as the reason why herbicide eﬂicacy is reduced, a mechanism that can
be counteracted with an adjuvant. Na+ in the spray solution inhibits cyclohexanedione
foliar absorption and ampliﬁed photolability-induced eﬁcacy reductions (McMullan, 1994;
Nalewaja et al., 1994). Trinexapac-ethyl is also a cyclohexanedione but is labeled as
having rapid foliar absorption and, as such, should be less susceptible to photolability.

The objectives of this research were to test whether spray application parameters
that inﬂuence cyclohexanedione herbicide eﬁcacy also inﬂuence the eﬁcacy of
trinexapac-ethyl. These parameters include adjuvants, carrier water quality, rainfastness,
chemical photolability and spray carrier volume. Successfully identifying if trinexapac-
ethyl applications Should follow the same guidelines as those for other cyclohexanedione
herbicides may provide valuable information necessary in maximizing eﬂicacy of this

turfgrass growth regulator.

MATERIALS AND METHODS

Turfgrass studies involving spray application parameters that impact eﬁcacy of
cyclohexanedione herbicides were initiated with trinexapac-ethyl and, in some cases,
sethoxydim. Studies in the greenhouse were at 25 C +/- 2 C with supplemental lighting
from high-pressure sodium lights providing 1200 umol photons rn‘2 s" during 18 hours of
daylight. All pots were irrigated daily or as needed and received 5 kg nitrogen ha" in the
form of Peters" 20-20-20 fertilizer on a weekly basis.

Unless otherwise indicated, the speciﬁcations for treatment applications were as
follows. Treatments were applied with a continuous link-belt sprayer at 170 kPa and 230 1
ha‘1 spray pressure and carrier volume, respectively, with a nozzle height of 30 cm above
the canopy. Applied rates for trinexapac-ethyl as the IE formulation and sethoxydim as

the 1.531; formulation were 0.191 kg ha" and 0.114 kg ha“, respectively.

WW

Studies were initiated in September, 1995 to evaluate the impact of an activator
organosilicone adjuvant on the eﬁcacy of trinexapac-ethyl, applied to four cool-season
turfgrass species. Plant material studied was ‘Georgetown’ Kentucky bluegrass (Poa
pratensis L.), ‘Mondial’ pereruiial ryegrass (Lo/iron perenne L.), ‘Putter’ creeping
bentgrass (Agrosris palusrris Huds.), and ‘Triathlon’, a blend of three varieties of tall

fescue (Fesruca arundinacea Schreb.). Plugs of 1-year old tall fescue were imported as

sodﬁ'omtheHancockTurfgrassResearchCenterinEastIansing, MItothegreenhouse,
where they were placed into 946-ml pots containing Bacctoo potting media and allowed
to acclimateoveratwoweekperiodbeforebeingsprayed. Theotherturfgrasseswere
established ﬁ'om seed at recommended seeding rates three months prior to the studies.

The study was done twice in September, 1995 with Kentucky bluegrass, creeping
bentgrass, and tall fescue. Perennial ryegrass was sprayed in January, 1996. Treatments for
each species included a control and trinatapac-ethyl at 0.048 kg ha" (tall fescue only),
0.095 kg ha", 0.191 kg ha", 0.382 kg ha", and 0.763 kg ha" (all species but tall fescue).
All treatments were sprayed with or without Sylgard 309' +28% urea ammonium nitrate

(UAN) adjuvant (5.0 ml r' and 10.0 ml r‘, respectively).

arrier Water 01' mi

Studies were initiated in the fall of 1995 to evaluate adjuvants for enhancing both
carrier water quality and chemical rainfastness, with respect to sethoxydim and trinexapac-
ethyl eﬂicacy. Applications were made to 2-month old ‘Mondial’ perennial ryegrass
(Lolium perenne L.), originally seeded into Baccto' potting media in 946-ml pots at 293
kg seed ha”. Pilot studies were conducted to determine rates for sethoxydim and
trinexapac-ethyl which would be less than fully eﬂ'ective, such that eﬂ‘ects of adjuvants
would be detectable.

Carrier water quality studies were sprayed in September and October, 1995 for
both sethoxydim and trinexapac-ethyl treatments. Three carrier solutions were selected:

deionized water, 0.5 mg 1‘1 calcium acetate, and 0.5 mg 1’l magnesium acetate. The pH of

9

each stock solution was determined. Trinexapac-ethyl and sethoxydim treatments were
applied in each carrier solution, with or without ammonium sulfate (AMS) at 5.0 gl".
ForrdnfannusuudiauinexapaeahylandsahoxydimUeaunanswueappﬁed
with each of the following adjuvant combinations: no adjuvant, AMS at 5.0 g 1‘ ‘, Sylgard
309' at 5.0 ml 1", and Sylgard 309' plus AMS. A simulated 1.25 cm ofrainfall was
applied at 303 kPa, 20 cm above the canopy surface in 1.25 mirnltes. Chemical treatments
weregiveneachofthefollowingfourrainfallevents: norainfallevent, arainfallevent
immediately after chemical treatment, and rainfall events either 15 or 30 minutes after

treatment. The experiment had t1uee replications and was repeated.

Chemical Photgﬂiligg

A study was initiated in April, 1996 to evaluate the potential for high intensity UV
light to reduce the eﬁcacy of both sethoxydim and trinexapac-ethyl. The plant material
used was 8-month old ‘Mondial’ pereru'lial ryegrass, originally seeded into Baccto' potting
media at 293 g seed ha".

Chemical treatments included sethoxydim and trinexapac-ethyl, with or without
Sylgard 309° adjuvant at 5.0 ml rl . Uv light exposure for each treatment was for 0, 20,
or 40 minutes aﬁer spray application in a Rayonet’ photochemical reactor containing 12
high intensity UV bulbs around the interior perimeter. Light intensity in the chamber was

15 w m'z.

10
W

Studies were initiated in September, 1996 to determine the eﬂ‘ects of adjuvants and
spmycarﬁavolumeonuinmpaeahyleﬁcacyinthegreenhouseandmdamnmeﬂw
effects of spray carrier volume and mowing height on trinenpac-ethyl eﬁcacy in the ﬁeld.
Plant material was l-yesr old ‘Mondial’ perermial ryegrass, originally seeded into Baccto'
potting media at 293 g seed ha", for the greenhouse study and 3-year old ‘Blacksburg’
Kentuckybluegrass, establishedinanativesandyclayloamsoilattheHancockTurfgrass
Research Center in East Lansing, MI.

Greenhouse treatments included four adjuvant combinations: no adjuvant, Sylgard
309O at 5.0 ml 1", AMS at 5.0 g1", and Sylgard 309' plus AMS; each was applied with or
withouttrinexapac-ethyl. Alltnatmentsincludingtrinmpac-ethyland/oradjuvantwere
sprayed at each ofﬁve spray carrier volumes (187 1 ha", 561 1 ha", 935 I ha", 1309 1 ha",
and 1683 1 ha") which encompassed the range indicated on the trinexapac-ethyl label.

A 7.32 m by 14.64 m ﬁeld plot was staked out and split into three equal-Sized 4.88
mby 7.32 m areas. Eachoftheseareaswasmowed atadiﬂ‘erent cutting height (5, 7.5,
and 10 cm). Single treatment plot area was 1.22 m by 2.44 m. All plots were irrigated
daily or as needed and received 25 kg N ha'1 in the form of urea (46-0-0) on a biweekly
basis.

The study was initiated in September, 1996 in the early morning. Air temperature
was 19 C and wind speed was negligible. Each mowing height block received three
chemical treatments plus an untreated control treatment. Trinexapac-ethyl as the IE
formulation was applied with a backpack sprayer at a rate of 0.287 kg ha'1 for each of the

three spray carrier volumes (187 I ha", 561 1 ha", and 1683 1 ha"). Clippings were

11

collected at 7, 14, 21, and 28 days after treatment. Clippings were oven-dried for 48 hours
and then weighed. The study was a 3 by 4 randomized complete block design and all
treatments had three replications.
Themrfgmssesinthegreuulousepotsweremaintainedata4anmtﬁngheight
(2 cm for creeping bentgrass) before studies were sprayed and mowed back to this height
when data was collected. Evaluation of trinexapac-ethyl growth inhibition was determined
by production of clipping ﬁesh weight. Clipping weights were determined at 7, 14, and 21
days after treatment. The multiple species study had an additional clipping harvest at 28
DAT. Eﬂicacy of sethoxydim treatments was based on visual injury ratings (0-10 scale:
0=a1ninjured, 10=complete bumdown) taken at 12, 16, and 20 days after treatment. All
greenhouse studies were completely randomized designs, had four replications per
treatment, and were repeated, unless otherwise indicated. Data reﬂect combined means
ﬁom both runs of repeated studies. Statistical analyses were based on factorial analysis of
variance, with signiﬁcance set at the 5% level. In the carrier volume study, the percent of

control data were transformed to the arcsine for analysis of variance and mean separation.

RESULTS AND DISCUSSION

 

The magnitude of growth inhibition by trinexapac-ethyl differed for the diﬂ‘erent
species in this study. Maximum growth inhibition of trinexapac-ethyl occurred at either
two to three weeks after treatment with all of the species, supporting speciﬁcations given
on the chemical label.

All trinexapac-ethyl treatments, with or without Sylgard 3090 plus 28% UAN,
signiﬁcantly reduced clipping production in Kentucky bluegrass 7 days alter treatment
(DAT). The adjuvant signiﬁcantly enhanced the performance of tnnexapac-ethyl at 0.095
kg ha'1 7 DAT (Table 1). Trinexapac-ethyl eﬁcacy, at the lower two rates, was enhanced
by the adjuvant 14, 21, and 28 DAT. Trinerrapac-ethyl at 0.382 kg ha" and at 0.753 kg ha"
performed equally well for the ﬁrst two weeks of the study but trinexapac-ethyl at the
higher rate caused greater growth inhibition over the last two weeks. Trinexapac-ethyl at
all rates, with the adjuvant, was still inlubiting growth 28 DAT.

Trinexapac-ethyl, at all rates, inhibited growth of perennial ryegrass 7 DAT.
However, among trinexapac-ethyl treatments, little signiﬁcance was observed (Table 2). A
notable exception at 7 DAT was the enhancement of growth inhibition caused by the
adjuvant at the 0.095 kg ha" rate. A similar enhancement was observed 14 DAT. High
variation between treatment replicates at 28 DAT resulted in a lack of signiﬁcant growth

inhibition in almost all treatments.

12

13
Trinexapac-ethyl, at all rates, inhibited the growth of creeping bentgrass 7 DAT

but no diﬂ‘erences between treatments were observed. The adjuvant signiﬁcantly enhanced
trinexapac-ethyl at both 0095 kg ha" and at 0.191 kg ha" 14 DAT (Table 3). A similar
enhancement occurred 21 DAT.

Trinexapac-ethyl at 0.048 kg ha" was included exclusively with tall fescue and it
did not inhibit growth throughout the study. Trinexapac-ethyl did not have a signiﬁcant
overall impact on tall fescue as few treatments mecessﬂilly inhibited shoot growth (Table
4). The adjuvant enhanced trinexapac-ethyl at 0.095 kg ha" 14 DAT but other
enhancements were not observed.

Growth of creeping bentgrass was the most inhibited by trinexapac-ethyl whereas
grth of tall fescue was the least inhibited, due to diﬂ‘erences in maturity level between
the two species. Growth of Kentucky bluegrass and perennial ryegrass was inhibited to a
similar extent. Trinexapac-ethyl at 0.763 kg ha" was generally the most eﬂ‘ective treatment
applied. However, trinexapac-ethyl at this rate was at least twice the recommended rate
for all the Species and was often seen to cause both visual injury and discoloration
unacceptable to turfgrass managers.

The selected Sylgard 309' plus 28% UAN adjuvant combination was eﬂ‘ective in
enhancing the eﬁcacy of trinerrapac-ethyl. Growth inhibition in tall fescue was usually
unaffected by the addition of the adjuvants. However, growth of all other species was
generally more inhibited by trinexapac-ethyl with the adjuvant than without it. The
adjuvant oﬂen reduced the necessary application rate of trinexapac-ethyl for a given
response level. The exact mechanism for such an enhancement was not explored in this

study but probably was a function of both of the constituents in the adjuvant.

l4

 

Perennialryegrasswassensiﬁvetotheeﬂ‘ectsofbothuinetapac-ethyland
sethoxydim. Seven DAT, the potentially antagonistic impact of calcium and magnesium in
the water carrier on trinexapac-ethyl eﬁcacy was not yet evident and AMS did not impact
eﬂicacy (Table 5). However, at 14 DAT, trinexapac-ethyl applied in calcium and
magnesium carrier solutions without AMS had clipping production equal to that for the
untreated control. Trinexapac-ethyl applied in calcium and magnesium carrier solutions
with AMS, conversely, signiﬁcantly decreased clipping production. This eﬂ‘ect diminished
by 21 DAT.

Sethoxydirn injury was signiﬁcantly enhanced by the addition of AMS to both the
calcium and magnesium carrier solutions at both 12 and 16 DAT (Table 6). Twenty DAT,
the level of injury in all treatments was greater than 60% and no signiﬁcant differences
among treatments were observed.

The pH values for the calcium and magnesium canier solutions were 7.1 and 7.5,
respectively. The inﬂuence of pH on the results appeared negligible. Although signiﬁcant
differences were observed between treatments for both chemicals, the results may have
reﬂected the low 5.0 gl" level of AMS that was used. AMS levels of 10 g1" and 20 g 1'1
are commonly used in many herbicide applications. The potential for AMS to oﬂ‘set the
antagonistic effects of hard water cations is clear and AMS may have had even a greater
positive impact in these studies had the level included been greater.

Clipping production was signiﬁcantly reduced by all trinexapac-ethyl treatments in

rainfastness studies. Rainfastness of trinexapac-ethyl was also signiﬁcantly increased by

15

the three adjuvants selected for these studies. Seven DAT, AMS seemed to play an
important role in enhancing eﬁcacy as only treatments containing AMS produced
sigrﬁﬁcanﬂyfewercﬂppingsﬂunmnnansmadjuvunsformyofthewuhoﬂ‘
times (Table 7).

Fourteen DAT, all trinexapac-ethyl treatments containing Sylgard 309° and most
containing AMS showed enhanced eﬁcacy, as compared to treatments without an
adjuvant, at allthreewashoﬂ'times (Table 7). Lossoftrinexapac-ethylactivitydueto
washoﬂ‘ was observed with washes at both 0 and 15 minutes after application. Compared
to their unwashed counterparts, only trinuapac-ethyl with Sylgard 309° plus AMS at the
0 minute washoﬂ‘ and trinexapac-ethyl with AMS at the 15 minute washoﬂ‘ had no loss of
activity due to the washoﬂ‘s. By 30 minutes alter treatment, washoﬂ‘had no signiﬁcant
impact on trinexapac-ethyl activity.

Twenty-one DAT, the positive impact of AMS on trinexapac-ethyl rainfastness
had disappeared. Loss of trinexapac—ethyl activity due to washoﬁ‘ occurred with AMS and
with Sylgard 309‘ plus AMS at the 0 minute washoﬂ‘time and with AMS at the 30 minute
washoﬂ‘ time (Table 7). Trinexapac-ethyl with Sylgard 309' suﬂ‘ered no loss of activity at
any of the washoﬂ‘ times.

All sethoxydim treatments showed signiﬁcantly greater injury than untreated
controls over the duration of the study. None of the adjuvants enhanced sethoxydim
activity in the unwashed treatments. However, signiﬁcant losses of activity were observed
with all washoff treatments. Sylgard 309' was the only adjuvant that restored activity lost

due to washoﬂ‘ (Table 8).

16

Overall, trinexapac-ethyl seemed to be more rainfast than was sethoxydim. The
label for trinexapac-ethyl indicates rainfastness within one hour of application. Results
fromthesestudies suggestedrainfastnesswasmorerapidthanthat, especiallywhenan
adjuvant was included. AMS, with or without Sylgard 309°, signiﬁcantly increased the
rainfaﬁnessoftﬁnexapaedhylwhﬂehhadmhpaﬂonﬂwrdMusofsﬂhoxydim.

Sylgard 309° increased the rainfastness of both cyclohexanediones.

chemical Ehotolabilim
Neither sethoxydim nor trinexapac-ethyl treatments suﬂ‘ered any loss of activity

ﬁ'om the effects of UV light exposure. Sethoxydirn was expected to lose activity under
such conditions while the impact on trinexapac-ethyl was unknown (Zorner et al., 1989;
Hazen and Krebs, 1992; McInnes et al., 1992; Nalewaja et al., 1994; McMullan, 1996).
Newer formulations of sethoxydim contain additives inhibitory to UV photodegradation. It
does not appear that trinexapac-ethyl, applied as the IE formulation, is susceptible to loss

of activity due to photolability.

We
AMS enhanced trinexapac-ethyl eﬁcacy in the greenhouse at 187 1 ha‘1 but

insigniﬁcantly or negatively impacted eﬁcacy at higher volumes 14 DAT (Figure 1). The
observed enhancement supported results seen in the carrier water quality study. However,
the lack of enhancement seen at 561 l ha'l or greater was probably related to the low AMS
concentration, 5.0 gl". At high spray volumes, the ratio of ammonium to Ca++ and Mg”

in the hard water may have been insuﬁcient to oﬂ‘set the negative impact of hard water

l7

cations on uptake. AMS has the potential to enhance trinexapac-ethyl eﬁcacy across a
broad range of spray carrier volumes but it is recommended that a higher level of AMS be
included at higher volumes to adequately account for hard water cations.

A signiﬁcant interaction between mowing height and spray carrier volume was
observed at 21 DAT. Results were not conclusive at 7, 14, or 28 DAT. Carrier volume
signiﬁcantly impacted trinatapac-ethyl eﬁcacy at the 5 cm and 10 cm mowing heights
(PiguresZand3). Adensercanopystinmlatedbylateralgrowthandahighercanopywith
more leaf tissue may necessitate higher spray carrier volumes for applications to the 5 cm
and 10 cm mowing heights, respectively. Treatments mowed at 7.5 cm, with
predominance of neither lateral development nor excess leaf matter, responded equally
well to trinexapac-ethyl at all spray carrier volumes (Figure 4). Because a signiﬁcant
interaction occurred when trinexapac-ethyl exhibited maximum eﬁcacy at 21 DAT, an
interaction between cutting height and spray carrier volume may have signiﬁcant
implications for ﬁeld applied trinexapac-ethyl.

It is suggested, based on results ﬁ'om greenhouse studies, that adjuvants have a
beneﬁcial impact on trinexapac-ethyl eﬁcacy, rainfastness, and activity in hard water,
especially at lower spray carrier volumes. The role of AMS in overcoming hard water
problems with trinexapac-ethyl is likely a key factor in explaining increased rainfastness
and enhanced emcacy observed with trinexapac-ethyl treatments containing AMS. Uptake

of trinexapac-ethyl seemed to be inherently more rapid than absorption of sethoxydim.

LIST OF REFERENCES

Bridges, D.C., AE. Smith, and LN. Falb. 1991. Eﬂ'ect of adjuvant on foliar absorption
and activity of clethodim and polar degradation products of clethodim. Weed Sci.
39:543-547.

Bridges, D.C., L.N. Falb, and AE. Smith 1992. Stability and activity of clethodim as
inﬂuenced by pH, UV light, and adjuvant. p. 215-222. In C.L. Foy (ed.) Adjuvants
for Agrichernicals. CRC Press, Boca Raton, FL.

Campbell, J .R and D. Penner. 1985. Abiotic transformations of sethoxydim. Weed Sci.
33:435-439.

Field, RJ. and N. G. Bishop. 1988. Promotion of stomatal inﬁltration of glyphosate by an
organosilicone surfactant reduces the critical rainfall period. Pestic. Sci. 24:55-62.

Hazen, J .L. and P.J. Krebs. 1992. Photodegradation and absorption of sethoxydim as
adjuvant-inﬂuenced surface eﬂ'ects. p. 195-203. In C.L. Foy (ed.) Adjuvants for
Agrichemicals. CRC Press, Boca Raton, FL.

Jansen, L.L. Enhancement of herbicides by silicone surfactants. Weed Sci. 21:130-135.

Johnson, B.J. 1993. Frequency of plant growth regulator and mowing treatments: eﬂ‘ects
on injury and suppression of centipedegrass. Agron. J. 85:276-280.

Johnson, B.J. 1994. Inﬂuence ofplarrt growth regulators and mowing on two
bermudagrasses. Agron. J. 86:805-810.

Jordan, D.L. and AC. York 1989. Eﬂ‘ects of ammonium fertilizers and BCH 81508 S on
antagonism with sethoxydim phrs bentazon mixtures. Weed Technol. 32450-454.

Jordan, D.L., PR Vidrine, J.L. Griﬁn, and DB. Reynolds. 1996. Inﬂuence of adjuvants
on eﬁcacy of clethodim. Weed Technol. 10:738-743.

McInnes, D., K.N. Harker, RE. Blackshaw, and W.H VandenBorn. 1992. The inﬂuence
of ultraviolet light on the phytotoxicity of sethoxydim tank mixtures with various
adjuvants. p. 205-213. In C.L. Foy (ed.) Adjuvants for Agrichernicals. CRC
Press, Boca Raton, FL.

McMullan, PM. 1994. Eﬂ‘ect of sodium bicarbonate on clethodim or quizalofop eﬁcacy
and the role of ultraviolet light. Weed Technol. 8:572-575.

18

19

McMullan, PM. 1996. Grass herbicide eﬁcacy as inﬂuenced by adjuvant, spray solution
pH, and ultraviolet light. Weed Technol. 10:72-77.

Nalewaja, JD. and R Matysiak. 1993. Optimizing adjuvants to overcome glyphosate
antagonistic salts. Weed Technol. 7:337-342.

Nalewaja, J .D., R Matysiala and E. Szelezniak. 1994. Sethoxydirn response to spray
carrier chemical properties and environment. Weed Technol. 8:591-597.

Penner, D. 1989. The impact of adjuvants on herbicide antagonism. Weed Technol.
3 :227-23 1.

Rhodes, G.N., Jr. and HD. Coble. 1984. Inﬂuence of application variables on antagonism
between sethoxydim and bentazon. Weed Sci. 32:436-441.

Roggenbuck, F .C., L. Rowe, D. Penner, L. Petroﬂ‘, and R Burow. 1990. Increasing
postemergence herbicide eﬁcacy and rainfastness with silicone adjuvants. Weed
Technol. 42576-580.

Sandberg, C.L., W.F. Meggitt, and D. Penner. 1978. Effect of diluent volume and
calcium on glyphosate phytotoxicity. Weed Sci. 26:476-479.

Stahlman, P.W. and W.M. Phillips. 1979. Eﬂ‘ects of water quality and spray volume on
glyphosate phytotoxicity. Weed Sci. 27:38-41.

Sun, 1., CL. Foy, and BL. Witt. 1996. Effect of organosilicone surfactants on the
rainfastness of primisulﬁrron in velvetleaf (Abnn'lon rheophrasn). Weed Technol.
10:263-267.

Thelen, K.D., E.P. Jackson, and D. Penner. 1995. Characterizing the sethoxydim-
bentazon interaction with proton nuclear magnetic resonance spectrometry. Weed
Sci. 43:337-341.

Wanarnarta, G., D. Penner, and 1.]. Kells. 1989 (a). Identiﬁcation of eﬂ'rcacious
adjuvants for sethoxydim and bentazon. Weed Technol. 3:60-66.

Wanarnarta, G., D. Penner, and J .J . Kells. 1989 (b). The basis of bentazon antagonism on
sethoxydim absorption and activity. Weed Sci. 37:400-404.

Wanamarta, G., U. Kells, and D. Penner. 1993. Overcoming antagonistic effects of Na-
bentazon on sethoxydim absorption. Weed Technol. 7:322-325.

20
Zorner, P., J. Hazen, R Evans, D. Gourd, and T. Fitzgerald. 1989. The inﬂuence of
DASH adjuvant in limiting photodegradation of sethoxydim on leaf surfaces. p.
83. In Weed Sci. Soc. Amer. Abstracts. WSSA, Charnpaign, IL.

21

Table 1: Trinexapac-ethyl efﬁcacy on ‘Georgetown’ Kentucky bluegrass: the effect

of application rates and Sylgard 309' plus 28% urea ammonium nitrate.

 

 

 

 

 

 

Time after application (days)
7 14 21 28
Trinexapac-
ethyl rate -adj. +adj. -adj. +adj. -adj. +adj. -adj. +adj.
kg ha“ Clipping production (96 of control}

0 100 89 100 107 100 111 100 106
(1095 76 53 88 60 90 78 101 78
0.191 60 45 56 31 70 47 75 66
0.3 82 49 36 36 23 51 19 70 45
0.763 31 28 21 15 16 10 37 24

LSD”, ' ---18-—- ---18-—— ---l7-—-- ---18-—-

 

Table 2: Trinexapac-ethyl efﬁcacy on ‘Mondial’ perennial ryegrass:
the effect of application rates and Sylgard 309’ plus 28%

urea ammonium nitrate.

 

 

 

 

 

 

Time after application (days)
7 14 21
Trinexapac-
ethyl rate -adj. +adj. -adj. +adj.

kg ha" Clipping production (96 of control}
0 100 89 100 88 100 82
0.095 62 38 51 27 85 57
0. 191 46 41 30 20 54 37
0.382 59 38 39 23 55 27
0.763 39 29 19 10 27 17

LSDo,05 ---24-—- —--23—— —--29—--

 

Table 3: Trinexapac-ethyl efﬁcacy on ‘Putter’ creeping bentgrass:
the effect of application rates and Sylgard 309' plus 28%

urea ammonium nitrate.

 

 

 

 

 

 

Time alter application (days)
7 14 21
Trinexapac-
ethyl rate -adj. +adj. -adj. +adj. -adj. +adj.
kg ha-1 Clippingtlodnctiar(%ofcontrol}

0 100 104 100 95 100 119
0.095 55 38 35 17 60 41
0.191 51 38 31 13 60 22
0-332 34 38 14 12 24 14
0-763 33 32 15 6 12 10

LSD”, --—-30—— -—-15-— -——-35—-—

 

24

Table 4: Trinexapac-ethyl efficacy on ‘Triathlon’ tall fescue: the effect of application

rates and Sylgard 309' plus 28% urea ammonium nitrate.

 

 

 

 

 

 

Time after application (days)
7 14 21 28
Trinexapac-

ethyl rate -adj. +adj. -adj. +adj. -adj. +adj. -adj. +adj.

kg ha" Clipping prudtrcdon (96 ofcontrol‘r
0 100 102 100 101 100 118 100 106
0.043 91 76 93 79 109 93 105 103
0.095 85 63 82 50 104 74 95 82
0.191 75 60 65 44 90 68 78 68
0.382 62 57 39 38 52 52 66 57

LSDoos ---25—-—- --—-22-—— ---34-—- ---25-—-

 

25

Table 5: Effects of hard water cations and ammonium sulfate (AMS) on

trinexapac-ethyl activity in perennial ryegrass.

 

 

 

 

 

 

Time after application (days)
7 14 21
Treatment - AMS + AMS - AMS + AMS - AMS + AMS
Clipping plantation (96 ofcontrol)
90m”! 100 121 100 141 100 121

Twahvlin 63 66 38 50 12 37
deromzedwater

'l‘n'11133751111119«ethylin 5-0 71 82 55 43 38 38
gl ealcrum acetate

Terence-tarmac 80 69 78 36 53 33
gl magnesrumacetate

13130.05 —--39—-— —47--- -—-29---

 

26

Table 6: Effects of hard water cations and ammonium sulfate (AMS) on

sethoxydim activity in perennial ryegrass.

 

 

 

 

Time after application (days)
12 16 20
Treatment -AMS +AMS -AMS +AMS -AMS +AMS
4% injury ’0
Control 0 0 0 0 0 0
sethoxydim 41 48 68 79 74 83
deromzed water
schoxydiminwtr' 34 49 61 77 68 83
calcium acetate
sahoxydiminwsr' 34 42 59 73 64 77
magnesrum acetate
LSD”, ---8-—- --ll-—— -——17---

 

 

 

t %injmyvalueswu'econvutedﬁumnaigina10-10mungsmlewhae0-1minjmed, 10-dead

27

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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8. 8. 8. 8. 8. 8. 8. 8. 8. 8. 8. 8. 0.82 .880
985835833... 39...... 8......a
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23. .555. .553...
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A933 528.3% .3... 2......

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28

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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on mm on 3 2. z. X. we 3 mm on co 282 5.5.2.3
o o c c o c c c c c c o 0:62 .2230
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983 .593 m2... 982 .53 253 ms... 982 ...-.3 25...... ms... 982 been? .558;
53.6.4. 5.5.5.. 53.5.4.
on o. N.
A933 5.56.39. .3... 2:3.

 

 

6229.0. 35.9.2— 3 3:1...— 5.1.3223... 3.8.8.6223 82.3555— 8 933—.

29

 

1

 

r

 

6

Clipplngprodlsctlonﬁolcontrol)
8

 

 

Figure 1: Effects of spray carrier volume and ammonium sulfate on ‘Mondial’

perennial ryegrass 14 days after treatment.

 

_n

 

 

 

 

 

88888388

Clipplngproductlonﬁofcontrot)

.-
O
.L

 

 

O
1

 

Figure 2: Effects of spray carrier volume on clipping production 21 days after

treatment for ‘Blacksburg’ Kentucky bluegrass mowed at 5, 7.5, and 10 cm.

APPENDIX A

31

Table A1: Specifications for greenhouse spray carrier volume treatments
Spray Carrier Volurneaha") t SprayPressurthPa) Tee-Jet5 Nozzle Tm Used

 

187 p 68 8001B (100 mesh screen)
561 265 80015 (100 mesh screen)
935 136 8004VS (50 mesh screen)
1309 224 8004VS (50 mesh screen)
1683 272 888005 (50 mesh screen)

 

tAﬂWapphcaﬁmwuemdewiﬁanmlehdﬂuofmcmmmemopymﬁce

32

Table A2: Speciﬁcations for field spray carrier volume treatments.

 

 

 

Spray Carrier Volume SprayPressure Walking Speed Tee-Jet“ Nozzle Type
aha") t (kPa) (erns‘) Used
187 177 152.40 8002 (50 mesh screen)
561 258 60.96 8002 (50 mesh screen)
1683 252 30.48 8006 (50 mesh M)

 

tAnmmappﬁmﬁmswuemndewithsnonleheigmoﬂOunabovemecnopymfnce

CHAPTER2

"C-TRINEXAPAC-ETHYL ABSORPTION AND TRANSLOCATION IN
KENTUCKY BLUEGRASS

“C-TRINEXAPAC-ETHYL ABSORPTION AND TRANSLOCATION IN
KENTUCKY BLUEGRASS

Matthew James Fagerness
ABSTRACT

Trinexapac-ethyl is a foliar-applied growth regulator for turfgrass that can reduce
mowing ﬁ'equency, clipping production, and enhance turfgrass color. l‘C-Trinexapac-ethyl
was used to evaluate absorption and subsequent l‘C-trinesrapac-ethyl translocation in
hydroponically grown ‘Blacksburg’ Kentucky bluegrass (Pan pratensr's L.). The
magnitude and rate of 1‘C trinexapac-ethyl absorption by various organs was as follows:
plant base > leaf blade > roots. Over the time period of 0 to 24 hours, mardmum
absorption by the plant base was obtained in 8 hours and by the leaf blade in 24 hours.
Absorption by the roots was negligible. Addition of an activator organosilicone adjuvant,
Sylgard 309°, signiﬁcantly enhanced l‘C-tlinertapac-ethyl absorption by the leaf blade one
hour aﬂer application but did not enhance absorption by the plant base. Of the “C-
trinexapac-ethyl absorbed by the plant base, over 50% was translocated to the plant
foliage after 24 hours. Of the l‘C-trinexapac-ethyl absorbed by the leaf blade, one-third
was translocated after 24 hours; the direction of movement was predominantly basipetal.
Less than 5% of absorbed l‘C-trinerltapac-ethyl ﬁ'orn either site was translocated to roots
or to rhizomes with daughter plants, explaining the lack of inhibition of lateral turfgrass
growth. Combined eﬂ‘ects of enhanced leaf blade absorption, basipetal translocation ﬁorn
the leaf blade, and acropetal translocation from the plant base of I‘C-tlinexapac-ethyl
helped explain the positive impact of Sylgard 309‘ on efﬁcacy and rainfastness of

trinexapac-ethyl.

33

34
Abbreviations: HAT - hours alter treatment

INTRODUCTION

The use of “C-labeled xenobiotics is a common tool for evaluating absorption and
translocation patterns of these compounds. Trinexapac-ethyl is a foliar absorbed
cyclohexanedione plant growth regulator. Speciﬁcity for uptake of trinexapac-ethyl among
foliar sites is unknown for trinerapac-ethyl although leaf blades come into more direct
contact with the spray droplets than do other tissues. Barrett and Bartuska (1982) found
the Stern, as compared to the leaves, to be a preferred site of uptake for an experimental
growth retardant, PP333. Speed of absorption of foliar applied chemicals can be important
in both emcacy and chemical rainfastness. Results ﬁom Al-Khatib et al. (1992) suggest
that most herbicide absorption occurs within 24 hours of application. Trinexapac-ethyl,
labeled as being rainfast within one hour of application, should conform to this pattern.

The absorption pattern of a given herbicide can be aﬂ‘ected positively by adjuvants
or negatively by antagonistic chemicals and/or ions. The absorption of sethoxydim by
leaves was dramatically reduced in the presence of bentazon (Rhodes and Coble, 1984).
Ammonium salts were able to counteract this antagonism (Wanarnarta et al., 1993) and
were able to increase leaf absorption of picloram (Moxness and Lym, 1989). Crop oil
concentrate adjuvants increase the absorption of ﬂuazifop, quizalofop, and sethoxydim in
cats (Manthey et al., 1992). Organosilicone surfactants enhance the eﬂicacy of many
herbicides and can be excellent surface wetting agents (Jansen, 1973; Roggenbuck et al.,
1990). The optimal adjuvants for enhancing trinexapac-ethyl eﬂicacy have not been
determined.

35

36
Systemic herbicide translocation from the site of uptake to the meristerns can be as

important a factor in determining eﬁcacy as absorption for herbicides aﬂ’ecting
meristematic activity. Phloem transport can be slow (Derr et al., 1985; Peregoy et al.,
1990; Camacho et al., 1991). Instances where plants transclocate herbicides basipetally
through phloem more rapidly may relate to observed patterns of emcacy (Hart and
Penner, 1993). Response to ﬂuazifop was dependent on translocation (Derr et al., 1985).
When slow basipetal translocation does not coincide with observed patterns of herbicide
efﬁcacy, alternate sites of uptake and translocation patterns may contribute to activity
(Achhireddy et al., 1985). Dicamba, for example, is translocated acropetally in several
Species, the mechanism for which may or may not be phloem transport (Al-Khatib et al.,
1992). Translocation of the cyclohexanedione herbicide, sethoxydim, is both acropetal and
basipetal (\Vrlls, 1984). Potential impact of trinexapac-ethyl on lateral turf growth was
addressed by Calhoun (1996), who reported divot closure rates in creeping bentgrass
treated with trinexapac-ethyl to be equal to or higher than those for untreated controls.
The translocation pattern for trinexapac-ethyl is not known but may be largely dependent
on the preferred site of absorption.

The objectives of this research were to (i) determine the preferred site of
absorption for “C-trinexapac—ethyl, (ii) determine the effect of an organosilicone
surfactant on absorption of l‘C-trinexapac-ethyl, and (iii) determine the translocation
patterns of "C-trinexapac-ethyl over a 24 hour period ﬁom three sites of uptake. The goal
was to increase the understanding of foliar absorption and translocation patterns for

trinexapac-ethyl such that eﬁcacy may be maximized.

MATERIALS AND METHODS

Plant material for all studies was 2-year old ‘Blacksburg’ Kentucky bluegrass (Poa
prarensis L.), originally obtained as sod ﬁ'orn the Hancock Turfgrass Research Center in
EastLansing, MI. Sodpieceswereplacedinto25 cmby50cmﬂatscontainingacoarse
soil (23% gravel, 77% sand)inthegreenhouseandallowedtlueeweekstoestablish. The
soiltypewaschosensothattheplantscouldlaterberemovedﬁ'omthesoilwithaminimal
amount of root damage. The greenhouse was at 25 C +/- 2 C with supplemental lighting
from high-pressure sodium lights providing 1200 umol photons rn'2 s'1 of light during 18
hours of daylight. All ﬂats were irrigated regularly and received 10 kg nitrogen ha" per
week. The rate of nitrogen application was higher than normal for maintenance of
greenhouse plants because the soil used was coarse and leached readily.

Plants were established hydroponically prior to the l‘C-trinexapac-ethyl absorption
and translocation studies. The hydroponic solution used was a modiﬁed Hoagland’s
solution derived for hydroponic establislunent of creeping bentgrass. Aliquots of this
solution were made using six stock nutrient solutions, each containing one or more
essential nutrients (Menu and McBee, 1970). Deionized water was the carrier for stock
solutions and the Hoagland’s nutrient solution. One-half and one-quarter Strength versions
of the same Hoagland’s solution were used in some instances. Treatment solutions were
made using 1,2,6-“c-1abeled trinexapac-ethyl with 94.8% purity and a speciﬁc activity of

1,139,600 Bq mg’l (Figure 1).

37

38
mm

Individual plants were established in full strength Hoagland’s solution by
removingthemfromthe soil, rinsingthemfreeofdebris, andwrappingthebaseofthe
plant with a slit cut foam plug. Plugs were then inserted through small holes in a colored
plastic lid so the roots could suspend ﬁeely in the solution below. The solution was
aerated using an air stone attached to an electric air pump. Plants studied were selected for
both health and size-based uniformity. Experiments were conducted with individual plants
wrapped in a foam plug and suspended into 120 ml jars containing 100 ml of one-half
strength Hoagland’s solution. A one-quarter strength solution was used for root
absorption experiments to minimize solute interference with l"C-trir'rexapac-ethyl uptake.
All jars were wrapped with aluminum foil.

The speciﬁcations for 200 ul treatment stock solutions differed according to the
type of experiment (Table 1). Absorption experiments for the roots, the leaf blade, and the
plant base were conducted over a three week period in May and June of 1996, while those
involving the adjuvant were conducted in November, 1996. Leaf blades and plant bases
were treated with a 2 pl droplet of treatment stock solution containing a quantity of
trinexapac-ethyl based on a 0.191 kg ha‘1 rate (Table 1); delivery was with a 10 111
Harnilton° syringe. 4 ul droplets were placed in the rootzone solution for the root
absorption experiment. Treated plant parts were washed for 45 seconds with a 1:1
methanolzwater solvent at 0, l, 4, 8, or 24 hours after treatment (HAT). (The 8 HAT
wash was excluded in the adjuvant study). The choice of solvent and duration of wash
were based on solubility of trinexapac-ethyl, previous work with cyclohexanedione

herbicides, and a time threshold, beyond which the solvent could extract absorbed material

39
(Devine et al., 1984; Wills, 1984). Each combination of treated plant site and washoﬂ‘ time

had four replications.

Rinsateswere collectedin20mlliquid scintillationvials, eachcontaining3 mlof
1:1 methanolzwater. Two 2-ml aliquots ﬁom each rootzone solution which had directly
received l‘C-trinexapac-ethyl for the root absorption experiment were similarly collected.
The solutions were then diluted to a total volume of 15 ml with Safety Solve. liquid
scintillation cocktail and analyzed in a liquid scintillation counter. Diﬂ‘erences in
radioactivity between the applied droplets and the collected rinsates were presumed to be
the amounts of 1‘C taken up by each plant. “C in 2 ml aliquots taken ﬁ'om each rootzone
solution was determined to evaluate the amount of “C in root absorption experiments that

was not absorbed.

T ranslocag’on Studies

Studies were initiated in June, 1996 to measure translocation of "C-trinexapac-
ethyl from three sites of uptake. A similar study evaluating two sites of uptake with plants
that had rhizomes with daughter plants was initiated in September, 1996. Plants for the
June study were established and selected as for absorption studies. Plants for the
September study were planted into a coarse sand and allowed to generate rhizomes with
daughter plants. The parent and daughter plants were subsequently transferred to a one-
half strength Hoagland’s solution. The colored lid for pots was prepared with a 0.5 cm by
7. 5 cm slit so both the parent and daughter shoots could be equally supported above the

solution.

40
Treatments were applied ﬁom a stock solution containing the following: 50 ul

“C-tlinexapac-ethyl, 118.85 111 formulation blank (taken ﬂour a 1:100 stock solution), and
31.15 ul deionized water. Sites ofuptakewerethe leafblade, the plant base, and the roots
for the June study, which had six replications per treatment. The September study had four
replications per treatment and did not evaluate roots as a site of uptake. Two 2-ul droplets
containing 3700 Bq of 1‘C were applied to the leaf blade or the plant base and in one 4-ul
droplet to the rootzone solution A ten-fold increase in radioactivity, as compared to
absorption studies, was used to ensure traceability of the l‘C as it was translocated.
Twenty four hours after treatment, treated plant parts were rinsed with 1:1
methanol:water", rinsates and aliquots ﬁom directly treated rootzone solutions were
analyzed for 1‘C.

Plants were segmented based on the original site of 1‘C uptake (Table 2).
Segments were kept at -10 C until they were oxidized in a biological oxidizer. Eﬁciency
of the oxidizer was greater than 95% and was determined by oxidizing a known quantity
of 1‘C placed on a piece of paper towel and then calculating the percent recovery. 1‘CO;
from oxidized samples was trapped in a 2:1 Safety Solve°:CarbosorbII° cocktail. Each
sample was then radioassayed in a liquid scintillation spectrometer. Combined
radioactivity ﬁ'om rinsates and all plant segments was used to determine the percent
recovery of 1‘C for each site of uptake. Percent recoveries of “C were 96%, 75%, and
82% for “C-trinexapac-ethyl applied to the roots, base of the plant, and leaf blade,
respectively, in June, 1996. Percent recoveries of "C were 76% and 79% for l‘C-
trinexapac-ethyl applied to the base of the plant and leaf blade, respectively, in September,

1996. The foam plugs that supported the plant bases accounted for a portion of the

41
unrecovered “C. Distributions of translocated l‘C-trinexapac-ethyl were expressed as

percentages of absorbed “C.
All studies were completely randomized designs and were repeated. Data reﬂect
combined means ﬁom two experiments. Statistical analyses were based on analysis of

variance and/or simple linear regression with signiﬁcance set at the 5% level.

RESULTS AND DISCUSSION

W

There were marked diﬂ‘erencesbetweentheleafblade, theplantbase, andthe
roots, in terms of both rate and total absorption of 1‘C- trinexapwethyl (Figure 2). The
leaf blade absorbed only 4% of applied l‘c-trinernrpnc-ethyl before the immediate washorr
but had absorbed 31% by one HAT. Absorption increased consistently over the next three
washoﬂ‘ periods, culminating in maximum absorption of 70% by 24 HAT. The base of the
plant absorbed 29% of applied l‘C- trinexapac-ethyl before the immediate washoﬂ' and had
absorbed 80% by one HAT. At this point, the absorption rate slowed down, reaching a
maximum by 8 HAT and a level of 94% 24 HAT. The roots absorbed little l‘C-trinexapac-
ethyl, taking up only 5% of applied material after 24 hours. Commercially, trinexapac-
ethyl is foliar applied so the results ﬁom the root absorption experiment were not
surprising. The plant base was the preferred Site of absorption for l‘C-trinertapac-ethyl.
Thus, the amount of trinexapac-ethyl reaching the plant base may be a major factor in
determining eﬁicacy.

The organosilicone surfactant, Sylgard 309°, is an activator adjuvant that was
determined to be capable of enhancing trinexapac-ethyl eﬁcacy (data not presented).
Absorption studies with “C-trinexapac-ethyl plus Sylgard 309' were conducted with the
intent of determining whether enhanced absorption, surface movement to a preferred site
of absorption such as the plant base, or both were involved in the observed enhancement
of trinexapac-ethyl eﬂicacy.

42

43
Absorption of "C-trinatapac-ethyl by the plant base was unaﬂ‘ected by the

addition of Sylgard 309' at any of the washoff times (Figure 3b). Absorption of 1‘C-
trinexapac-ethyl bythe leafbladewasunaﬂ‘ectedbytheaddition ofSylgard 309°at 0, 4,
and 24 HAT. However, signiﬁcant enhancement of absorption with Sylgard 309' occurred
1 HAT, the increase being ﬁom 21% to 51% (Figure 3a). Absorption of l‘C-trinexapac-
ethyl was so rapid that a measurable amount of absorption occurred in less than the 45
seconds it took to wash the “C-trinexapac-ethyl of of either the leaf blade or the plant
base for the zero time treatment.

Enhanced early absorption of 1‘C trinexapac-ethyl by leaf blades when Sylgard
309’ was included could provide greater trinexapac-ethyl rainfastness. Absorption by both
the leafblade and plant base was greater than 50% aaer one hour when Sylgard 309' was
added to the treatment solution. The reduction of surface tension of spray droplets with
Sylgard 309° allow more of the spray solution to move on the surface of the plant to the

base of the plant, which is the preferred site of absorption.

Translocation Studies
The direction and extent of ”C-trinexapac-ethyl translocation was dependent on

the site of uptake. The base of the plant absorbed 96% of applied "C-trinexapac-ethyl
while the leaf blade absorbed 70% of applied "C-trinexapac—ethyl in 24 hours. Roots
absorbed 2% of applied l‘C-trinexapac-ethyl in 24 hours and translocated acropetally 50%
of what was absorbed (Table 3).

The leaf blade retained greater than 60% of the 1‘c it absorbed after 24 hours

(Table 3). One percent of absorbed “C moved acropetally while 32% moved basipetally

44
and accumulated in a variety of tissues. The plant base accumulated 11% of absorbed "C.

Roots accumulated 5% ofthe absorbed “c.

Greater than 75% of"C absorbed by the base ofthe plant was translocated
acropetally to the plant foliage over 24 hours. Roots accumulated less than 5% of
absorbed 1‘C while the other 18% remained in the base of the plant (Table 3).

The leaf blade and the plant base were the two sites of absorption evaluated in
translocation studies involving rhizomes/daughter plants. Greater than 70% of the “c-
trinexapac—ethyl applied to the leaf blade was absorbed while the plant base absorbed
greater than 85% of applied “C-trinexapac-ethyl.

Translocation of absorbed 1‘C from the leaf blade was as follows: 36%
translocated to other foliar tissues, 4% translocated to the roots, and 3% translocated to
the rhizome/daughter plant after 24 hours (Table 4). The other 57% remained in the leaf
blade.

Translocation of 1‘C absorbed by the base of the plant was as follows: 61%
translocated acropetally, 3% translocated to the roots, and 3% translocated to the
rhizome/daughter plant after 24 hours (Table 4). The other 33% remained in the base of
the plant.

Acropetal translocation of 1‘C from the plant base and basipetal translocation of
1“c from the leafblade observed in both studies appeared related to the activity of
trinexapac-ethyl observed in turfgrasses. Preferred directional translocation ﬁ'om both sites
of uptake would result in a convergence of the active ingredient at the intercalary
meristems, which are the primary sites of growth inhibition for trinexapac-ethyl. The leaf

blade retained more 1‘C after 24 hours than did the plant base. The rinsate from the leaf

45
blade washoﬂ‘ after 24 hours also contained more “C than that from the plant base. These

results were again indicative of the plant base being the preferred site of absorption for
trinexapac-ethyl and the potential for an adjuvant to increase leaf blade absorption. The
lack of signiﬁcant “c translocation to the roots suggested that any eﬂ'ects trinexapac-ethyl
mayhave onthe rootsareaﬁlnctionofitseﬁ‘ectson shootgrowth. Thesimilarlackof
signiﬁcant translocation to rhizome tissues suggested that trinexapac-ethyl has little impact

on lateral development of rhizomatous turfgrass species such as Kentucky bluegrass.

LIST OF REFERENCES

Achireddy, NR, RC. Kirkwood, and W.W. Fletcher. 1985. Foliar absorption and
translocation of isoproturon, and its action on photosynthesis in wheat (Tritium
aestr’vum) and slender foxtail (Alopecms myowroides). Weed Sci. 33:762-765.

Al-Khatib, K., R Parker, and E.P. Fuerst. 1992. Foliar absorption and translocation of
herbicides from aqueous solution and treated soil. Weed Sci. 40:281-287.

Al-Khatib, K., R Parker, and E.P. Fuerst. 1992. Foliar absorption and translocation of
dicamba from aqueous solution and dicamba-treated soil deposits. Weed Technol.
6:57-61.

Barrett, J.E. and CA. Bartuska 1982. PP333 eﬂ‘ects on stem elongation dependent on
site of application. Hort. Sci. 17(5):737-73 8.

Calhoun, RN. 1996. Eﬁ‘ect of three plant growth regulators and two nitrogen regimes on
grth and performance of creeping bentgrass. MS. thesis. Michigan State Univ.,
East Lansing. 57 p.

Camacho, RF. and LJ. Moshier. 1991. Absorption, translocation, and activity of CGA-
136872, DPX-V93 60, and glyphosate in rhizome johnsongrass (Sorghum
halepense). Weed Sci. 39:354-357.

Derr, 11“., TJ. Monaco, and T.J. Sheets. 1985. Uptake and translocation of ﬂuazifop by
three annual grasses. Weed Sci. 33:612-617.

Devine, M.D., H.D. Bestman, C. Hall, and W11 Vandenbom. 1984. Leafwash
techniques for estimation of foliar absorption of herbicides. Weed Sci. 32:418-
425.

Hart, SE. and D. Penner. 1993. Atrazine reduces primisulﬁlron transport to meristems of
giant foxtail (Setan'afaben) and velvetleaf (Abutr’lon theophrastr). Weed Sci.
4 1 :28-3 3.

Jansen, LL. 1973. Enhancement of herbicides by silicone surfactants. Weed Sci. 21:130-
135.

47

Manthey, EA, E.F. Szelezniak, ZM. Anyszka, and JD. Nalewaja. 1992. Foliar
absorption and phytotoxicity of quizalofop with lipid compounds. Wad Sci.
40:558-562.

Menn, W.G. and 6.6. McBee. 1970. A study of certain mstritional requirements for
Tifgreen bermudagrass (WMIMXC. tram-miendsLJusinga
hydroponic system. Agron. J. 62:192-195.

Moxness, KB. and RG. Lyln 1989. Environment and spray additive eﬂ‘ects on picloram
absorption and translocation in leafy spurge (Eupharbia esula). Weed Sci.
37: 181-186.

Peregoy, RS, L.M. Kitchen, P.W. Jordan, and J.L. Griﬁn. 1990. Moisture stress effects
on the absorption, translocation, and metabolism of haloxyfop in johnsongrass
(Sorghum halepense) and large crabgrass (Digital-ta swrgm'nalis). Weed Sci.

3 8:33 1-337.

Rhodes, G.N., Jr. and H.D. Coble. 1984. Inﬂuence of bentazon on absorption and
translocation of sethoxydim in goosegrass (Eleusine indica). Weed Sci. 32:595-
597.

Roggenbuck, F.C., L. Rowe, D. Penner, L. Petroﬂ, and R Burow. 1990. Increasing
postemergence herbicide eﬁcacy and rainfastness with silicone adjuvants. Weed
Technol. 4:576-580.

Wanarnarta, G., J. J. Kells, and D. Penner. 1993. Overcoming antagonistic eﬁ‘ects of Na-
bentazon on sethoxydim absorption. Weed Technol. 72322-325.

Wills, GD. 1984. Toxicity and translocation of sethoxydim in bermudagrass (Cymdon
dacrylon) as aﬂ‘ected by environment. Weed Sci. 32:20-24.

 

Figure 1: Chemical structure for 1,2,6-"C-trinexapac-ethyl.

49

Table 1: Content of absorption study “C tr'eatlnent solutions.

 

 

 

Absorption Deionized 320 Cold trinexapac- ‘Y: W Form Adqu 3
gm, ethyl t ethyl Hulk 1’
“I
W 57.43 108.8 10 (370 Bq) 23.77 none
Plant base '
W13!“ base 7.43 108.8 10 (370 Bq) 23.77 50
with Adjuvant

 

fAmomtslistedtakenfrunaldOOmcezdeioniudmsolution.
:Ammthstedtakenrrornal:503ylpnrd309‘:deioniaedmaoluuon

Table 2: Plant segmentation in translocation studies

Site of Uptake Segments
Plant base Roots t

 

 

Plantbase
Treatedleart
Leaverabovethetreatedlear
Stemoftreatedleaf
Sheathorueatedlear
Rhizomerwithdmghterplantt
Otherroliaget

‘lApplicabletotheSeptanber, l996studybutnotthe1me, 1996M.
$Segnentsana1yzedintheltme, 1996andinthe8qstemba’,1996mldies.

 

51

 

 

 

 

 

 

 

 

100
so i
so
it -i

- so

3
so
40

l +Roota
3° ‘ +Laarslada
so +Plantaaaa
10 _
o
0 t l
4 s 12 to so 24

.‘.
0

mm

Figure 2: Absorption patterns of “C-trinexapac-ethyl over a 24 hour period from
three sites of uptake. The patterns are represented by the following regression data:
Roots: Y-0.219x + .042 r’-.901
Lear Blade: Y’-lo43.1x“ + 15.9 r‘-.995
Plant Base: Y-o.9olnx + as r’-.951

52

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3a
so
so
70 2!
so
i 50
g 40
I!)
Z) +m ad“!
10 +M
0 t t :
-10 ' 16 Z) 24
Tina Ms)
3b
+no adlumu
+adlmara
8 12 to 20 24
Tina 0101“)

Figure 3a,b: The effect of Sylgard 309' on absorption of "C-trinexapac-ethyl by the

leaf blade (Figure 3a) and by the plant base (Figure 3b).

53

Table 3: Translocation of “C-trinexapae-ethyl from three sites of uptake.

 

 

 

 

 

Site of “C-trinexapac—ethyl uptake
Site of Analysis LeafBlade Plant Base Roots
% of abaubed "C
Roots 5 b s 4 c 50 a
Foliage t N/A 78 a 25 a
Plant Base 11b 18 b 25 a
Treated Leaf 67 a N/A N/A
Leaf Sheath for 5 b N/A N/A
Treated Leaf
Stem of Treated 6 b N/A N/A
Leaf
Leaves Above 1 b N/A N/A
Treated Leaf
Other Tillers 5 b N/A N/A

 

tReferstoallfoliartissueothertbantheplantbase.
tNumbers foﬂowedbydiﬂ‘auuleuusinechrespecdvewhmmmﬁsﬁaﬂydiﬂ'amtattbe5% level.

Table 4: Translocation patterns of l‘C-tr'iuexapae-ethyl when rh'nomes were

 

 

 

 

 

present.
Site of uptake
Site of Analysis Leafblade Plant base
% of abaubed "C
Foliage t 36 b t 61 a
Treated Plant Part 57 a 33 b
Roots 4 c 3 d
Rhizome/Daughter Plant 3 c 2 d

 

tReferstoallfoliartismeotherthanthetreatedplantpart.
tNumbers foﬂowedbydiﬂ'amtleuusineachrespeeﬁvecolmmsnﬁsﬁaﬂydiﬁ‘amtuthe5%level.

APPENDIX B

55

Table Bl: Contents of stock nutrient solutions.

 

 

Chamwaeasan Quuiﬁtylsr‘)
ICNO; 101.1
ca(NOa)2 236.2
NHtHzPOa 1 15.1
MgSOax 7H20 246.5
SequestreneO 1 1.2
KCl t 3.7
H3303 t . 1.5
MnSOa x H20 t 0.3
ZnSOa x 7HzO t 0.6
CuSOa x 5H20 t 0.1
H2M004 t 0.1

 

tDenotesreagentswhoseammmtswereallcombinedinasingleliterofmicronuuientstocksolution.

Table B2: Contents of full strength Hoagland’s solution.

 

 

Nutrient Stock Solution Amount (ml 101")
KNO: 60
030103): 40
NHJ'12P04 20
MgSOa x 71-120 10
Sequestrene" 10
Micronutrients t 10

 

1' Containedall sixreagents highlightedinTable l.

CHAPTER3

EVALUATION OF V-10029 AND TRINEXAPAC-ETHYL AS TURFGRASS
GROWTH REGULATORS ON FIVE COOL-SEASON SPECIES

EVALUATION OF V-10029 AND TRINEXAPAC-ETHYL AS TURFGRASS
GROWTH REGULATORS ON FIVE COOL-SEASON SPECIES

Matthew James Fagerness
ABSTRACT
An experimental turfgrass growth regulator, V-10029, was compared with
trinexapac-ethyl to evaluate growth inhibition patterns and suppression of seedhead
formation; the latterwas evaluated forturfgrass speciesand forthe infestingweed species,
annualbluegrass. Tall fescue, creepingredfesweKentuckybluegrass, pererulialryegrass,
and creeping bentgrass were transferred ﬁ'orn the ﬁeld into the greenhouse. V-10029, at
three rates (0.015 kg/ha, 0.029 kg/ha, and 0.059 kg/ha), was compared to an untreated
control and trinexapac-ethyl at the label rate. Of the eight replications for each treatment,
four were not mowed for the purpose of evaluating suppression of seedhead formation
and four were used for weekly clipping collection to evaluate growth inhibition. Compared
to the untreated control, V-10029 at all three applied rates caused signiﬁcant suppression
of seedhead formation in both tall fescue and perennial ryegrass pots. Trinexapac-ethyl
was not as eﬁ‘ective. V-10029 caused discoloration in all turfgrass species depending on
the rate of application. Patterns of growth inhibition for tall fescue, Kentucky bluegrass,
and perennial ryegrass, in response to V-10029 at all rates and to trinexapac-ethyl, were
similar on a percent of control basis. Growth of creeping bentgrass was only inhibited by
V-10029 at high rates. In contrast, creeping red fescue was signiﬁcantly injured by V-
10029. The greatest growth inhibition, in response to all treatments, occurred 2 to 3

weeks after application. The eﬁ‘ect of trinexapaeethyl faded after 4 weeks while V-10029

57

58
was eﬁcacious slightly longer. Observed eﬁ‘ects of V-10029 support its known activity as

an ALS inhibiting herbicide and therefore as a Class D turfgrass growth regulator.
1552mm: V-10029 {sodium 2.6-bis[(4.6-dimethoxypyﬁnﬁdin-2-yl)oxy]bmzoate}.
“imam-ethyl {Hcydopmvyl-a-hydmxy-methylweH.S-dioxocyclohmwcarboxyﬁc
acid ethyl ester}, annual bluegrass (Paa m L. ), tall fescue (Fesnroa mordirroceo
Schreb.), creeping red fescue (Fesnrca rubra L.) , Kentucky bluegrass (Paa prutensis L.),
perminl ryegrass (Laﬁmmw L). creepins banal!” (WWW Hinds.)
mandamus: growth inhibition, suppression of seedhead formation,

discoloration, clipping collection

INTRODUCTION

Plant growth regulators (PGRs) in turfgrass systems are commonly used to reduce
vegetative growth, production of seedheads, or both. Watschke (1985) discussed the
impact of plant growth regulators that inhibit mitosis, as compared to plant growth
retardants that disrupt cell division and elongation through impact on gibberellin
biosynthesis. This breakdown of PGR mode of action was later used to classify PGRs as
Type I or Type II (Watschke et al. 1992). Type I PGR’s, such as maleic hydrazide {1,2-
dihydro-3,6-pylidazinedione} and meﬂuidide {N-[2,4-dimethyl-5-[[(triﬁuoromethyl)
sulfonyl]amino]phenyl]acetamide}, cause excellent seedhead formation suppression and
growth inhibition in turfgrasses but are also injurious (Schott et al. 1980, McCarty et al.
1985, Diesburg and Christians 1989, Johnson 1989, Spak et al. 1993). Type II PGRs, such
as paclobutrazol {(+/-)-(R",R')-B-[(4-chlorophenyl)methyl]-a—(1,l-dirnethylethyl)—1H-
1,2,4-triazole-l-ethanol}, ﬂurprimidol {a-(l-methylethylya-[4-(triﬂuoro-
methoxy)phenyl]-5-pyrimidine-ethanol}, and trinexapac-ethyl, are less injurious but are
also less effective in seedhead formation suppression.

Watschke and DiPaola (1995) reclassiﬁed Type II PGRs, based on the site of
uptake and the site of inhibition in the gibberellin (GA) biosynthesis pathway. Trinexapac-
ethyl is foliar absorbed, inhibits GA biosynthesis late in the pathway, and is classiﬁed as a
Class A PGR Paclobutrazol and ﬁurprimidol are root absorbed, inhibit GA biosynthesis
earlier, and are thus classiﬁed as Class B PGRs. Mitotis inhibiting PGRs that previously

were classiﬁed as Type I are now Class C. A ﬁnal class of PGRs, Class D, includes

59

60
chemicals with herbicidal activity applied at non-lethal rates. V-10029 is a member of this

group, showing ALS inhibiting activity (Hopkins 1994, Lirn et al. 1997). Proper
classiﬁcation of both current and future plant growth regulators is essential for proper
selection of a PGR to use for speciﬁc management needs.

Evaluation ofnew plant growth regulators is a function ofseveral factors that,
collectively, determine PGR eﬁcacy. Growth inhibition, seedhead formation suppression,
visual quality, anddensityintlu'fgrassesarecommonlyevaluatedinPGRstudies.
Evaluation of experimental PGRs using a range of applied rates is also common. Schott et
al. (1980) tested meﬂuidide at ﬁve rates and at diﬁ‘erent timings of application to evaluate
the eﬁ‘ects of meﬂuidide on shoot growth, seedhead initiation, and turfgrass quality.
Johnson (1992) evaluated the persistence of trinexapac-ethyl eﬁcacy in bermudagrass.
Many studies with new compounds also include a commercial PGR as a tool for
comparison (Hoﬁ'man and Ilnicki 1989, Johnson 1989, Sawyer and Jagschitz 1989).

Plant grth regulators have been tested on both cool and warm season
turfgrasses. Most of these individual studies concentrate on a limited number of species
and/or PGRs. Conversely, few studies directly compare the effects of a given PGR across
multiple species. Such studies could lead to more ﬂexible uses for PGRs and be useful in
instances where multiple species are aﬁ‘ected by a single application.

The objectives of this study were to (a) evaluate the ability of V-10029 to inhibit
growth and/or suppress seedhead formation, as compared to trinexapac-ethyl, (b)
recommend a chemical rate of V-10029 that, when applied, causes growth inhibition

without negatively impacting turfgrass color and quality, and (c) compare ﬁve cool-season

61
turfgrass species, with respect to patterns of growth inlu'bition over time, as impacted by

V-10029 at three rates and trinexapac-ethyl

MATERIALS AND METHODS

StudieswereinitiatedinApril, 1996toevaluatethegrowthinhibitingand
seedhead formation suppressing abilities of the experimental V-10029 turfgrass grth
regulator, as compared to trinexapac-ethyl. Plant material was ‘Penncross’ creeping
bentgrass, ‘Viva/Columbia’ Kentucky bluegrass, ‘BrightstarManhattanlDimension’
perennial ryegrass, ‘Triathlon’ tall fescue, and ‘Hector’ creeping red fescue. All species
wereirnportedassod plugs 10cmindiameterﬁ'omtheI-IancockTurfgrassResearch
Center in East Lansing, MI to the greenhouse, where they were placed into 946 ml pots
containing professional potting medial and allowed to acclimate over a two week period
before treatments were applied. The greenhouse was at 25 C +/- 2 C with supplemental
lighting ﬁ'om high-pressure sodium lights providing 1200 uEJm’ls of light during 18 hours
of daylight. All pots were irrigated as needed and received nitrogen at 5 kyha weekly
throughout establishment and the duration of the study.

Treatments were applied using a continuous link-belt sprayer at 170 kPa and 230
W spray pressure and carrier volume, respectively, on May 8 and May 9, 1996. V-
100292 as the 80W formulation was applied to each species at three rates: 0.015 kg/ha,

0.029 kyha, and 0.059 kyha. Trinexapac-ethyl’ was applied as the 1E formulation at a

‘Bacctoo isaproductoflldidlingeatCompany,Houston,'lX

2v.10029 isaproductofValentUSACorp.,WalnutCreek,CA

1‘I‘rintrxapllc-ethyl, sold as PrimoO, Ciba-Geigy Caporation, Greensboro, NC

62

63
label rate of 0.382 kg/ha for perennial ryegrass and 0.287 kg/ha for the other four species.

A 0.25% v/v level ofx-77“ nonionic surfactant was included in all treatments but the
untreated controls. Each treatment had eight replications: four were used to evaluate
seedhead formation suppression and four were used to evaluate growth inhibition.

Replications evaluated for growth inhibition were maintained at a 4 cm (2 cm for
creeping bentgrass) cutting height before chemical applications. Evaluation of growth
suppression was a function of clipping ﬁ'esh weight, with clippings harvested weekly for
seven weeks after treatment. Replications for seedhead formation suppression were
unmowed throughout the course of the study and were evaluated through counts of
numbers of seedheads per pot at 3 and 6 weeks aﬁer treatment. Subjective assessment of
turfquality was conducted throughout the course ofthe study.

The study was a completely randomized design and was repeated. Data reﬂect
combined means from two experiments. All data were analyzed using analysis of variance

and/or simple linear regression with signiﬁcance set at the 5% level.

‘xmo, Valent USA Corp., Walnut Creelt. CA

RESULTS AND DISCUSSION

S E l E i' 51 .
Seedhead initiation was insigniﬁcant in Kentucky bluegrass, creeping red fescue,
andcreepingbentgrass. Tallfescuepotshadasigniﬁcantmimberofseedheads, allof
which were annual bluegrass. Only perennial ryegrass produced enough ofits own
seedheads to be measurable. Long day light conditions allowed for seedhead formation in
perennial ryegrass. Compared to the untreated control, V-10029 at all three rates caused
signiﬁcant suppression of annual bluegrass seedhead formation in tall fescue pots and of
perennial ryegrass seedhead formation. Trinexapac-ethyl was not as eﬁ'ective in seedhead

formation suppression as V-10029 (Table 1).

Growth Inhibig'on

V-10029 and trinexapac-ethyl were eﬁ'ective in inhibiting growth in all of the
turfgrass species (Tables 2 to 6). The pattern of growth inhibition, as evaluated across
PGR treatments, diﬁ‘ered ﬁom species to species, both in terms of magnitude and
persistence of inhibition. Growth of perennial ryegrass, Kentucky bluegrass, and tall fescue
was similarly inhibited by all PGR treatments.

V-10029 inhibited growth of perennial ryegrass, Kentucky bluegrass, and tall
fescue in a rate dependent manner (Tables 2 to 4). The pattern of growth inhibition for
trinexapac-ethyl in these species was most analogous to V-10029 at the 0.029 W rate.
The growth inhibiting eﬁ‘ects of trinexapac-ethyl and V-10029, at all three rates, were less

64

65
pronounced in creeping bentgrass than in the other species, perhaps due to the tendency

for creeping bentgrass to grow laterally when mature (Table 5). Growth of creeping red
fescue was inhibited by V-10029 but injury to the turf was largely responsible for this
eﬁ‘ect and caused huge variation among treatment replications (Table 6). Trinexapac-ethyl
did not injure creeping red fescue but caused little, ifany, growth inhibition.

ThegreatestgrowthhuubiﬁoninaﬂueannentsguleraﬂyocwnedaroundZoH
weeks after treatment (WAT). The eﬁ‘ects of trinexapac-ethyl faded by 4 WAT; however,
V-10029, at the 0.029 kg/ha and 0.059 kg/ha rates, was eﬁicacious for a longer period of
time. V-10029 at the 0.015 kyha rate was the least persistent treatment across species
with eﬁ'ects lasting only 2 to 3 weeks. V-10029 at the 0.059 kg/ha rate still caused
signiﬁcant growth inhibition in some species when the study concluded 7 WAT but much
of this was attributable to unacceptable injury it caused in the turf. Seven WAT,
trinexapac-ethyl, V-10029 at 0.015 kg/ha, and V-10029 at 0.029 kg/ha treatments had no
longer reduced clipping yield, compared to the untreated control. The predictability of
growth inhibition of Kentucky bluegrass by V-10029, as a function of increasing rate,
diminished as the study progressed (Figure 1).

V-10029 caused signiﬁcant discoloration in all the turfgrass species at all three
rates of application. The speciﬁc extent of discoloration was not rated but was
characterized by a yellowing of the turf that appeared within a week of application and
persisted until 2 to 3 weeks after application. The extent of discoloration increased as the
application rate of V-10029 increased. Trinexapac-ethyl treatments did not cause
discoloration in any species and the turfgrasses actually assumed a darker green color as

soon as 2 weeks after application.

66
Visible injury to the turfgrass species occurred with V-10029 at both the 0.029

kg/ha and 0.059 kg/ha rates. V-10029 at 0.029 kg/ha caused injury but the turfgrass was
ableto recoverby4to 5WAT.TheturfgrassinjuredbyV-10029at0.059kglhadidnot
ﬁrllyrecoverby7WATinatleast 50% ofthetreatrnents. Amongtheﬁvespecies,
creeping bentgrass showed the greatest recovery ﬁom injury caused by V-10029 at 0.059
kg/ha. Injuryobservedwasleaftipburnandreducedmrfdensityperpot. Theextentof
injuryobserved seemedtobeproportionaltoamnralbhiegrasspmhferationwithinthepot.
Observations made during the study suggested that armual bluegrass, as a weed
species, appeared most abundantly in tall fescue and creeping red fescue pots. The
creeping red fescue exhibited the least growth among the ﬁve species. Annual bluegrass
becmnepronunentinsomepouofaeepingredfeswemdcataiMyhnpaaedthedm
Annual bluegrass appeared less ﬁ‘equently in pots treated with V-10029 than in control
pots or those treated with trinexapac-ethyl. Arumal bluegrass was observed in some of the
tall fescue pots but wasn’t abundant enough to have any impact on collected data
V-10029 at 0.029 kg/ha and 0.059 kg/ha caused signiﬁcant growth inhibition but,
in many cases, also caused unacceptable discoloration and/or injury to the turf. Therefore,
these rateswere detenninedtobetoohighforacceptableturfgrassgromh regulation in
the greenhouse. V-10029 at 0.015 kg/ha was the least eﬁ’ective growth regulator
treatment, both in terms of extent of growth inhibition and persistence. V-10029, at this
rate, however, caused little or no injury to the turf and discoloration was only slight. V-
10029, at an intermediate rate between 0.015 kg/ha and 0.029 kg/ha, would have the
greatest potential to combine good growth inhibition with maintenance of acceptable

turfgrass quality. A suitable range of application rates that is this narrow would reduce the

67
practicality of V-10029 as a turfgrass growth regulator used for intensively managed

turfgrass systems.

The extent of seedhead formation suppression caused by V-10029, coupled with
its potential to injure turfgrass at higher rates, were useful in supporting the classiﬁcation
ofV-10029asaPGR ClassAandClassBPGRsarenotinjuriousandarenoteﬁ‘ectivein
suppressing seedhead formation (Watschke and DiPaola 1995). Conversely, Class C and
Class D PGRs, such as meﬂuidide and glyphosate (N-(phosphonomethyl)glycine), can be
injurious and are very effective in seedhead formation suppression. The known activity of
V-10029 as an ALS inhibitor conﬁrms its place as a Class D PGR

An alternate method of evaluating PGR eﬁcacy was employed by directly
comparing the growth suppression patterns for all ﬁve species, as inﬂuenced by a single
PGR treatment (Figures 2 to 5). Perennial ryegrass, Kentucky bluegrass, and tall fescue
clipping production, on a percent of control basis, responded similarly to V-10029 at each
of the three rates and in response to trinexapac-ethyl at the label rate. Creeping bentgrass
was less sensitive to V-10029 than the perermial ryegrass, Kentucky bluegrass, or tall
fescue. Creeping red fescue and creeping bentgrass responded similarly to trinexapac-ethyl
at the label rate. The injury caused by V-10029, at all rates, to creeping red fescue,
however, discounts the merit of including this species in such an evaluation. Ranking the
species responses by treatment, would therefore be as follows:

V-10029 (all three rates): Kentucky bluegrass == perennial ryegrass = tall fescue >

creeping bentgrass

Trinertapac-ethyl (label rate): Kentucky bluegrass = perennial ryegrass = tall

fescue > creeping red fescue = creeping bentgrass

68
These results may be useful not only in determination of a proper PGR application rate but

also in predicting response patterns of diﬂ‘erent turfgrasses to a given PGR application,
especiaﬂymmstanceswherenmlﬁplespedesmaycoedumaﬁxedmanaganausyuan
(Johnson and Murphy 1996).

LIST OF REFERENCES

Diesburg, KL. and NE. Cluistians. 1989. Seasonal application of ethephon, ﬂurprimidol,
meﬂuidide, paclobutrazol, and amidochlor as they aﬂ‘ect Kentucky bluegrass
shoot morphogenesis. Crop Sci. 29:841-847.

Hoﬁnan, K. G. and RD. Ilnicki. 1989. Triasulfuron in combination with some growth
regulators in turf. Proc. Northeast Weed Sci. Soc. 43:76.

Hopkins, W.L. 1994. P.80. Global Herbicide Directory. Ag Chem Information Services,
Indianapolis, IN.

Johnson, B.J. 1989. Response of tall fescue (Fes1uca amndinacea) to plant growth
regulators and mowing ﬁequency. Weed Technol. 3:54-59.

Johnson, B.J. 1989. Response of tall fescue (Festuca mmdinacea) to plant growth
regulator application dates. Weed Technol. 3:408-413.

Johnson, B.J. 1992. Response of bermudagrass (Cynodon spp.) to CGA 163935. Wad
Technol. 6:577-582.

Johnson, B.J. and TR Murphy. 1996. Suppression of a perennial subspecies of annual

bluegrass (Poo annua spp. reptans) in a creeping bentgrass (Agrostr‘s stolom’fera)
green with plant growth regulators. Weed Technol. 10:705-709.

Lim, J.S., Y.T. Bae, 111 Lee, and SJ. Koo. 1997. Mode of acetolactate synthase
inhibition of the new herbicide LGC-40863. Abstr. Weed Sci. Soc. Amer. 37:169.

McCarty, L.B., J.M. DiPaola, W.M Lewis, and W.B. Gilbert. 1985. Tall fescue response
to plant growth retardants and fertilizer sources. Agron. J. 77:476-480.

Sawyer, OD. and 1A Jagschitz. 1989. Evaluation of ACP-21 10 as a turfgrass growth
regulator. Proc. Northeast Weed Sci. Soc. 43:98-99.

Schott, P.E., H. Will, and H.H~ Nolle. 1980. Turfgrass growth reduction by means of a
new plant growth regulator. p. 325-328. In 13. Beard(ed.) Proc. 3rd Int.
Turfgrass Res. Conf., Munich, Germany. Amer. Soc. of Agron., Madison, WI.

Spak D.R., J .M. DiPaola, W.L. Lewis, and CE. Anderson. 1993. Tall fescue sward
dynamics: 11. Inﬂuence of four plant growth regulators. Crop Sci. 33:304-310.

69

70

Watschke, TL. 1985. Turfgrass weed control and growth regulation. p. 63-80. In F.
Lemaire(ed.) Proc. 5th Int. Turfgrass Res. Conf., Avignon, France. 1-5 July. Inst.
Natl. de la Recherche Agron., Paris.

Watschke, T.L., MG. Prinster, and J.M. Brueninger. 1992. Plant growth regulators and
turfgrass management. p. 557-588 In D.V. Waddington et al. (ed.) Turfgrass
Science. Agron. Monogr. 32 ASA, CSSA, and SSSA, Madison, WI

Watschke, TL. and J .M. DiPaola. 1995. Plant growth regulators. Golf Course Man.
64(3):59-62.

71

Table l: Seedhead formation suppression in tall fescue and perennial ryegrass pots,
as a function of turfgrass growth regulator treatment.
Tall fescue and Perennial Tall fescue and Perennial
Treatment annual bluesms W883 m hm W888

 

 

 

 

3 WAT‘ 3 WAT 6 WAT 6 WAT
lumber ofseorﬂleads per pot
003m“ 6.0 10.9 12.4 25.0
V-loo29 0.5 6.0 1.1 12.9
(0.015 kg/ha)
v-10029 0.4 4,4 1.0 6.6
(0.029 kg/ha)
moon 0 3.0 o 5.0
(0.059 kg/ha)
Trinexapac-ethyl 1.9 8.5 6.9 15.8
(0.382 kg/ha)
15130.05 2.8 5.5

 

 

 

 

‘WATswuksaﬂertreatrnent

72

Table 2: Growth inhibiting effects of V-10029 and trinexapae-ethyl on perennial

 

 

 

 

 

WW
Time after application (weeks)
Treatment 1 2 3 4 5 5 7
clipping puductim (9s ofcontrol}

"Comm“ 100 100 100 100 100 100 100

(0.3333,) 57 59 73 79 85 109 111

(03:03:) 47 46 62 73 74 96 99

($30,338) 35 20 22 32 39 59 63

mm”. «11le ' 58 42 60 85 92 1 14 128
(0.382 kyha)

LSDo.os 9 13 17 20 16 34 29

 

Table 3: Growth inhibiting effects of V-10029 and trinexapae-ethyl on Kentucky

 

 

 

 

 

bluegrass.
Time aﬁer application (weeks)
Jilipping poductiar (% of castrol}

Um 100 100 100 100 100 100 100

(0.313%) 68 6O 98 97 88 103 93

(01333;) 50 32 57 67 59 81 73

(075303;) 39 23 31 46 58 65 70

WW, - 74 46 61 82 86 101 108
(0.287kg/ha)

LSD0.05 18 16 23 27 23 31 33

 

74

Table 4: Growth inhibiting effects of V-10029 and trinexapae-ethyl on tall fescue.

 

Time after application (weeks)
Treatment 1 2 3 4 5 5 7

 

 

 

 

Clippingpoduction(%ofcontrol}
mm 100 100 100 100 100 100 100

Control

(0:30:33) 55 53 91 82 102 l 15 102

(0.3330333) 44 25 57 81 86 88 88

(0.0390333) 3 8 l3 3 1 41 5 3 6O 60

“mm, - 69 40 57 74 95 103 107
(0.3821ryha)

LSDo.os l4 8 l8 17 20 149 29

 

75

Table 5: Growth inhibiting effects of V-10029 and trinexapac-ethyl on creeping

 

 

 

bentgrass.
Time after application (weeks)
Treatment 1 2 3 4 5 6 7
Clipping poduction (% of clnrtrolrP

 

 

mm 100 100 100 100 100 100 100

Control

(03:02:13) 95 105 96 100 97 88 100

(03:03:13) 80 89 102 1 17 106 101 100

(03;;0282’18) 54 59 67 94 91 85 87

“$1,“. 64 69 100 103 1 12 120 120
(0.382 kglha)

LSDooa l4 14 22 29 24 20 25

 

76

Table 6: Growth inhibiting effects of V-10029 and trinexapac-ethyl on creeping red

 

 

fescue.
Time after application (weeks)
Treatment 1 2 3 4 5 6 7
Clipping poductim (% of control)

 

 

 

 

”DWI 100 100 100 100 100 100 100

(033033“) 137 88 99 71 71 74 75

(0.979033%) 126 74 69 43 37 38 49

(0059033111) 85 64 76 42 48 48 56

TW‘ 109 75 98 109 113 127 117
(0.382 lrg/ha)

LSDo.05 71 36 67 44 46 56 42

 

 

 

 

 

 

 

 

rur- olV-lssas Mn)

Figure l: Decreased predictability in the patterns of growth inhibition over time in
Kentucky bluegrass, as a function of increasing rate of V-10029. LSD.”
values for 2, 4, and 6 war were 16, 27, and 31, respectively while 11’ values
for the depicted curves for growth inhibition at 2, 4, and 6 WAT were 0.73,

0.47, and 0.25, respectively.

. O
,¢,-.--.' .r H o -— o H e' :.‘.‘.L'. ..

 

 

 

 

 

 

 

 

 

‘0 ---Parnnnﬂryngnaa
- --Knntl.lcllybnlaunas
20" Tituscua
------ emu-rou-
0 1 4
t 2 3 4

M‘wwm

Figure 2: Growth inhibiting effects of V-10029 (0.015 kg/ha) across four turfgrass
species. The LSD“; values for weeks 1, 2, 3, and 4 were 17, 19, 28, and 24,

respectively.

79

 

 

 

 

 

 

 

Thunderwnonaks)

Figure 3: Growth inhibiting effects of V-10029 (0.029 kg/ha) across four turfgrass

respectively.

‘

 

 

 

 

l l I A L A 1 J.
U I V I I V I

emprutluoaonaoroornron

 

‘
O
1

Y

 

O
J

 

.a
N
a l-
&

Figure 4: Growth inhibiting effects of V-10029 (0.059 kg/ha) across four turfgrass

species. The LSD”; values for weeks 1, 2, 3, and 4 were 13, 15, 21, and 25,

respectively.

81

1” -.

 

 

 

 

 

 

 

Figure 5: Growth inhibiting effects of trinexapac-ethyl (0.287 kglha for Kentucky
bluegrass; 0.382 kg/ha for perennial ryegrass, tall fescue, and creeping
bentgrass) across four turfgrass species. The LSD.” values for weeks 1, 2, 3,

and 4 were 34, 19, 32, and 34, respectively.

CONCLUSIONS

The spectrumoftheresearchdetailedinthisthesiswasdiverse. Assuch, valuable
information regarding the performance of turfgrass growth regulators was obtained, using
techniques not conﬁned to a speciﬁc discipline. Research investigating spray application
parameters that may aﬁ‘ecttheperformance oftrinexapac-ethyl illustratedthe multi-
faceted beneﬁts of adjuvants, as pertains to eﬂicacy, rainfastness, and activity in a hard
water carrier of trinexapac-ethyl.

The potential beneﬁt of adjuvants was ﬁlrther explored using "C-labeled
trinexapac-ethyl. The direct role of adjuvants in enhancing absorption and the ancillary
role of promoting surface movement to alternate sites of absorption are believed to be
very crucial in obtaining a good understanding of how trinexapac-ethyl exerts its activity
and how eﬂicacy may be enhanced. Patterns of absorption and translocation for
trinexapac-ethyl seem to correspond with activity at the intercalary meristems in turfgrass
plants.

V-10029 was compared with trinexapac-ethyl as a turfgrass growth regulator and
was superior in terms of suppressing seedhead formation. However, levels of growth
inhibition were comparable between the two PGRs and more injury was seen with V-
10029 than with trinexapac-ethyl, due to the activity ofV-10029 as an ALS inlubiting
herbicide. Species comparisons showed tall fescue, perennial ryegrass, and Kentucky
bluegrass to respond similarly to both trinexapac-ethyl and V-10029, oﬂ'ering some

usefulness in growth inhibition predictability where multiple species coexist.

82

I“11301117121110.3031“11100I