STRESS RESPONSES OF KENTUCKY BLUEGRASS VARIETIES IN MONOSTANDS
AND BLENDS
By
Jeffrey Colin Dunne

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE
Crop and Soil Science
2012

ABSTRACT
STRESS RESPONSES OF KENTUCKY BLUEGRASS VARIETIES IN MONOSTANDS
AND BLENDS
By
Jeffrey Colin Dunne
Traditional recommendations for athletic field construction have included the blending of
turfgrass varieties; however, due to recent advancements in breeding technology, single cultivars
bred for generalized disease resistance, aggressive tillering, and herbicide resistance may be used
in place of a blend, which was previously necessary to provide all of these characteristics. Four
separate studies were initiated in East Lansing, MI on 25 September 2009 to measure the validity
of using monostands instead of blends. Two studies were subjected to twelve traffic events (ten
passes per week) with the Brinkman traffic simulator beginning 3 August 2010 and evaluated for
various response variables. One of the studies, established on native soil, showed that the blends
did not out perform all of their constituent varieties in quality, cover, and surface strength
characteristics during traffic applications. In addition to these findings, a comparable experiment
established on native soil but receiving 2.4 cm of high sand-based topdressing prior to traffic
applications, provided similar results over the two years of data collection. Two additional
studies focused on blends and monostands under Sclerotinia homoeocarpa (Dollar Spot) and
Bispyribac-sodium (Velocity) stress. Two resistant and two susceptible varieties were chosen for
blend construction. Two-year results from the dollar spot study consistently showed the resistant
varieties and the blend of the two resistant varieties having fewer dollar spot infection centers
and higher overall quality. Similarly, in the two-year duration, blends of the Velocity study
showed tendencies of intermediate results in Normalized Difference Vegetation Index (NDVI),
quality, and percent blighted tissue when compared to the resistant and sensitive varieties.

DEDICATED
To my parents, Mike and Linda Dunne
and my brothers Ben and Lane,
for their love and support
Thank you

iii

ACKNOWLEDGMENTS
I would like to extend my greatest recognition to Dr. John (Trey) N. Rogers, III for his
belief in my potential, his guidance, and support throughout my experiences at Michigan State
University. It has truly been an incredibly journey to this point and I thank you for this
extraordinary opportunity and the leadership qualities you have instilled in me. Most of all, I
want to thank you for the pushing me to be a better researcher and person. My committee also
deserves special recognition for their guidance, support, and insight throughout my graduate
experience. Dr. James Crum – Thank you for your friendship and advice that I have come to
admire greatest about you since first setting foot on this campus. Dr. Joe Vargas – Thank you for
showing me to think outside of the box and to lead by example. I greatly appreciate your
commitment to believing in your research and ideas.
I would like to thank my friends and research associates, Aaron Hathaway, Dr. Alec
Kowalewski, Paul Giordano, and Rodney Tocco for keeping me on the lighter side of life,
particularly when things would get stressful. It makes the ride more enjoyable when there are
good people in the car! Furthermore, I want to specially thank Mark Collins, Frank Roggenbuck
and the rest of the HTRC crew for their devoted help and friendship in all of my endeavors. You
created such a wonderful working environment, while providing wisdom and a blue-collar
mentality.
Lastly, I would especially like to thank my parent, Mike and Linda, for their
encouragement and love that has driven me to complete my master’s degree. You inspired me at
an early age to set goals and to strive for greatness in everything I do. I hope you are proud of the
person I have become today.

iv

TABLE OF CONTENTS
List of Tables

vii

Introduction

1

Chapter One: Effects of Traffic on Kentucky Bluegrass Varieties in
Monostands and Blends on Native Soil

9

Introduction
Materials and Methods
Results and Discussion
Conclusions
References

9
11
15
23
24

Chapter Two: Effects of Traffic on Kentucky Bluegrass Varieties in
Monostands and Blends with High-Sand Based Topdressing Applications
Over Native Soil
Introduction
Materials and Methods
Results and Discussion
Conclusions
References

26
26
28
32
40
41

Chapter Three: Evaluation of Sclerotinia homoeocarpa (Dollar Spot)
Pressure on Kentucky Bluegrass Varieties in Monostands and Blends
Introduction
Materials and Methods
Results and Discussion
Conclusions
References

43
43
46
50
57
59

Chapter Four: Evaluation of Bispyribac-sodium (Velocity) applications
on Kentucky Bluegrass Varieties in Monostands and Blends
Introduction
Materials and Methods
Results and Discussion
Conclusions
References

61
61
64
68
73
75

Thesis Conclusion

77

v

References

80

Appendix

83

vi

LIST OF TABLES

Table 1

List of treatments for traffic on native soil

14

Table 2

Mean Comparisons of treatments following 6-weeks of traffic on native
soil in 2010, obtained 17 September at HTRC, East Lansing, MI

17

Mean Comparisons of treatments following 12-weeks of traffic on native
soil in 2010, obtained 12 November at HTRC, East Lansing, MI

18

Mean Comparisons of treatments following 6-weeks of traffic on native
soil in 2011, obtained 21 September at HTRC, East Lansing, MI

19

Mean Comparisons of treatments following 12-weeks of traffic on native
soil in 2011, obtained 2 November at HTRC, East Lansing, MI

20

Table 6

List of treatment for traffic on topdressing over native soil

31

Table 7

Mean Comparisons of treatments following 6-weeks of traffic on
topdressing over native soil in 2010, obtained 17 September at HTRC, East
Lansing, MI

34

Mean Comparisons of treatments following 12-weeks of traffic on
topdressing over native soil in 2010, obtained 12 November at HTRC, East
Lansing, MI

35

Mean Comparisons of treatments following 6-weeks of traffic on
topdressing over native soil in 2011, obtained 21 September at HTRC, East
Lansing, MI

36

Table 3
Table 4
Table 5

Table 8

Table 9

Table 10 Mean Comparisons of treatments following 12-weeks of traffic on
topdressing over native soil in 2011, obtained 2 November at HTRC, East
Lansing, MI

37

Table 11 List of treatments for Kentucky bluegrass monostands and blends
under dollar spot pressure

49

Table 12 Mean separation of Kentucky bluegrass monostands and blends for quality,
dollar spot infection centers, and percent dollar spot infected turfgrass cover
on 6 September 2010 at HTRC, East Lansing, MI

51

vii

Table 13 Mean separation of Kentucky bluegrass monostands and blends for quality,
dollar spot infection centers, and percent dollar spot infected turfgrass cover
on 18 September 2011 at HTRC, East Lansing, MI

52

Table 14 Mean separation of Kentucky bluegrass monostands and blends for quality,
dollar spot infection centers, and percent dollar spot infected turfgrass cover on
high, sand-based rootzone mix 15 September 2011 at HTRC, East Lansing, MI

53

Table 15 List of treatments for Kentucky bluegrass monostands and blends
under bispyribac-sodium stress

66

Table 16 Mean separation of Kentucky bluegrass monostands and blends for quality,
Normalized Difference Vegetation Index and percent blighted tissue under
bispyribac-sodium stress on 12 July 2010 at HTRC, East Lansing, MI

69

Table 17 Mean separation of Kentucky bluegrass monostands and blends for quality,
Normalized Difference Vegetation Index and percent blighted tissue under
bispyribac-sodium stress on 21 September 2011 at HTRC, East Lansing, MI

70

Table 18 Analysis of variance (AOV) for percent turfgrass ground cover for traffic on
native soil in 2010, results obtained at HTRC, East Lansing, MI

83

Table 19 Analysis of variance (AOV) for turfgrass quality for traffic on native soil in
2010, results obtained at HTRC, East Lansing, MI

84

Table 20 Analysis of variance (AOV) for Turf Shear Tester for traffic on native soil in
2010, results obtained at HTRC, East Lansing, MI

85

Table 21 Analysis of variance (AOV) for Clegg Hammer for traffic on native soil in
2010, results obtained at HTRC, East Lansing, MI

86

Table 22 Analysis of variance (AOV) for Shear Vane for traffic on native soil in 2010,
results obtained at HTRC, East Lansing, MI

87

Table 23 Analysis of variance (AOV) for percent turfgrass ground cover for traffic on
native soil in 2011, results obtained at HTRC, East Lansing, MI

88

Table 24 Analysis of variance (AOV) for turfgrass quality for traffic on native soil in
2011, results obtained at HTRC, East Lansing, MI

89

Table 25 Analysis of variance (AOV) for Turf Shear Tester for traffic on native soil in
2011, results obtained at HTRC, East Lansing, MI

90

Table 26 Analysis of variance (AOV) for Clegg Hammer for traffic on native soil in
2011, results obtained at HTRC, East Lansing, MI

91

viii

Table 27 Analysis of variance (AOV) for Shear Vane for traffic on native soil in 2011,
results obtained at HTRC, East Lansing, MI

92

Table 28 Analysis of variance (AOV) for percent turfgrass ground cover for traffic on
topdressing over native soil in 2010, results obtained at HTRC, East Lansing,
MI

93

Table 29 Analysis of variance (AOV) for turfgrass quality for traffic on topdressing over
native soil in 2010, results obtained at HTRC, East Lansing, MI

94

Table 30 Analysis of variance (AOV) for Turf Shear Tester for traffic on topdressing
over
native soil in 2010, results obtained at HTRC, East Lansing, MI

95

Table 31 Analysis of variance (AOV) for Clegg Hammer for traffic on topdressing over
native soil in 2010, results obtained at HTRC, East Lansing, MI

96

Table 32 Analysis of variance (AOV) for Shear Vane for traffic on topdressing over
native soil in 2010, results obtained at HTRC, East Lansing, MI

97

Table 33 Analysis of variance (AOV) for percent turfgrass ground cover for traffic
on topdressing over native soil in 2011

98

Table 34 Analysis of variance (AOV) for turfgrass quality for traffic on topdressing
over native soil in 2011, results obtained at HTRC, East Lansing, MI

99

Table 35 Analysis of variance (AOV) for Turf Shear Tester for traffic on topdressing
over native soil in 2011, results obtained at HTRC, East Lansing, MI

100

Table 36 Analysis of variance (AOV) for Clegg Hammer for traffic on topdressing
over native soil in 2011, results obtained at HTRC, East Lansing, MI

101

Table 37 Analysis of variance (AOV) for Shear Vane for traffic on topdressing
over native soil in 2011, results obtained at HTRC, East Lansing, MI

102

Table 38 Analysis of variance (AOV) for turfgrass quality under dollar spot
pressure in 2010, results obtained at HTRC, East Lansing, MI

103

Table 39 Analysis of variance (AOV) for dollar spot infection centers on Kentucky
bluegrass blends and monostands in 2010, results obtained at HTRC, East
Lansing, MI

104

ix

Table 40 Analysis of variance (AOV) for percent dollar spot infected turfgrass cover
of Kentucky bluegrass blends and monostands in 2010, results obtained at
HTRC, East Lansing, MI

105

Table 41 Analysis of variance (AOV) for turfgrass quality under dollar spot
pressure in 2011, results obtained at HTRC, East Lansing, MI

106

Table 42 Analysis of variance (AOV) for dollar spot infection centers on Kentucky
bluegrass blends and monostands in 2011, results obtained at HTRC, East
Lansing, MI

107

Table 43 Analysis of variance (AOV) for percent dollar spot infected turfgrass
cover of Kentucky bluegrass blends and monostands in 2011, results obtained
at HTRC, East Lansing, MI

108

Table 44 Analysis of variance (AOV) for turfgrass quality under dollar spot pressure
on a high, sand-based rootzone in 2011, results obtained at HTRC, East
Lansing, MI

109

Table 45 Analysis of variance (AOV) for dollar spot infection centers on Kentucky
bluegrass blends and monostands on a high, sand-based rootzone in 2011,
results obtained at HTRC, East Lansing, MI

110

Table 46 Analysis of variance (AOV) for percent dollar spot infected turfgrass cover
of Kentucky bluegrass blends and monostands on a high, sand-based
rootzone in 2011, results obtained at HTRC, East Lansing, MI

111

Table 47 Analysis of variance (AOV) for Normalized Difference Vegetation Index on
Kentucky bluegrass blends and monostands under bispyribac-sodium
stress in 2010, results obtained at HTRC, East Lansing, MI

112

Table 48 Analysis of variance (AOV) for turfgrass quality on Kentucky bluegrass
blends and monostands under bispyribac-sodium stress in 2010, results
obtained at HTRC, East Lansing, MI

113

Table 49 Analysis of variance (AOV) for percent blighted tissue on Kentucky
bluegrass blends and monostands under bispyribac-sodium stress in 2010,
results obtained at HTRC, East Lansing, MI

114

Table 50 Analysis of variance (AOV) for Normalized Difference Vegetation Index on
Kentucky bluegrass blends and monostands under bispyribac-sodium stress in
2011, results obtained at HTRC, East Lansing, MI

115

Table 51 Analysis of variance (AOV) for turfgrass quality on Kentucky bluegrass blends
and monostands under bispyribac-sodium stress in 2011, results obtained at
HTRC, East Lansing, MI

116

x

Table 52 Analysis of variance (AOV) for percent blighted tissue on Kentucky
bluegrass blends and monostands under bispyribac-sodium stress in 2011,
results obtained at HTRC, East Lansing, MI

xi

117

INTRODUCTION
Blending turfgrasses often provide advantages over single-variety stands, particularly in
highly stressed situations (Beard, 1973; Turgeon, 2008; Schumann et al, 1992; Vargas, 2005;
Bell, 2011). Variable environments and habitats generally more conducive to a wide range of
disease and insect problems create a favorable platform for blends to succeed over monostands.
In athletic fields, the tendencies for blends to compose the turf stand are undeniable considering
the frequent exposure to traffic, biotic and abiotic stressors, and the lack of genetic diversity of
Kentucky bluegrass (Poa pratensis L.). Kentucky bluegrass is a widely adaptive turfgrass species
used throughout cool, humid and transitional regions of the world (Beard, 1973). However, the
apomictic nature of Kentucky bluegrass has brought about changes in its use, functionality and
adaptability across many situations, including but not limited to athletic fields. Prior to the
introduction of ‘Merion’ Kentucky bluegrass in 1947, common Kentucky bluegrasses were used
in low-maintenance areas but were frequent to abuse by Helminthosporium leaf spot caused by
Helminthosporium vagans Dresch (Schumann et al. 1992). Currently, this disease is known
separately and caused by Dreschsler poae (Melting-out) and Bipolaris sorokiniana (Leaf Spot)
(Vargas, 2005). The release of ‘Merion’ Kentucky bluegrass provided generalized resistance to
Helminthosporium leaf spot; however, this also brought about the onset of other devastating
diseases including Fusarium blight (Fusarium roseum), Gray leaf spot (Piricularia grisea), but
most importantly stripe smut (Ustilago striiformis). The high susceptibility of ‘Merion’
Kentucky bluegrass to strip smut can be directly related to the narrow gene pools and the high
percentage of apomixis associated with this variety (Bruneau et al. 1992). It has been reported
that ‘Merion’ had a level of apomixis of 96% making this variety highly uniform (Meyer 1982;
Burton, 1992; Casler 2003). Although this percentage coincides with stable seed production and

1

ultimately leading to ‘Merion’ Kentucky bluegrass’ distribution in the 1960’s, the uniformity
lead to complete decimation of entire turfgrass stands by stripe smut, a cultivar specific disease
(Vargas, 1980, Casler, 2003). With this in mind, there was a general lack in cultivated or
improved varieties of Kentucky bluegrass at this time. Conjointly, varieties like ‘Merion’
Kentucky bluegrass were relatively unavailable, and if obtainable, were exceptionally expensive
(Juska and Tyson 1955, Vargas 1980, Vargas 2005). A concept that would provide genetic
diversity to a relatively uniform turf stand soon emerged, suggesting the mixing or blending of
common-type Kentucky bluegrass and cultivated varieties like ‘Merion’ Kentucky bluegrass.
This would introduce disease resistances to Helminthosporium leaf spot from ‘Merion’ and stripe
smut from common-types, while reducing the cost to plant ‘Merion’ as a single-variety stand.
However, blending turfgrass varieties created controversy. Madison (1971) questioned whether
blending standard and dwarf varieties would prove to be an advantage due to the differing
management practices required for each variety to thrive. Madison claimed that the differences in
density between the varieties would cause an increase in density of the stand and would then be
subject to Helminthosporium disease from high humidity produced within the turf canopy.
A traditional recommendation for the blending of turfgrass has been two or more
varieties together with similar leaf texture, growth habit, color, shoot density and vertical growth
rate in order to achieve an acceptable turfgrass stand (Beard, 1973; Vargas, 1980). Selecting
varieties for use in a blend should be in accordance with the following guidelines: 1) Varieties
selected have shown resistance to disease in the geographical area where the blend will be
planted, 2) the varieties should be similar in appearance and competitive ability, and 3) at least
one variety should be select based on adaptation to unique conditions where the blend will be
planted (i.e. shade, soil pH, moisture, traffic, etc.) (Turgeon, 2008). The failure to coordinate the

2

selection of varieties to these recommendations may reduce the efficacy of the blend over time.
Vargas (2005), based on the previous research of Vargas and Turgeon (1980), suggested the
inclusion of susceptible varieties of Kentucky bluegrass planted with improved varieties reduced
the quality of the blend and in some instances drastically reduced the presumed percentage of
stand composition of the susceptible variety to the point of elimination. Furthermore, the
ecological competition that exists between turfgrass varieties or intra-specific competition,
particularly aggressiveness and environmental adaptability, may also reduce the benefits of using
blends (Golembiewski, 1999).
Although not available during the introduction of ‘Merion’ Kentucky bluegrass,
numerous varieties have been separated in to distinct classifications used to relate these growth
characteristics. Work by Rutgers University has divided Kentucky bluegrass varieties into
several classifications (Park, 2005). However, blends are not necessarily advantageous because
of similar growth characteristics alone. According to Funk (2000), Kentucky bluegrass provides
enhanced tolerance to drought, heat, shade, close mowing, excessive wear, acid soils, salinity, as
well as resistance to many of the major turfgrass diseases: all of the characteristics necessary for
an ideal athletic field. However, Funk (2000) continues to suggests that the reason blends are
necessary to promote all of these characteristics can be related to the lack of breeding techniques
that are required to include these characteristics into a single variety. Likewise, Beard (1973)
proclaims a blend cannot provide an advantage if one variety is available with superior resistance
to all the noteworthy pest problems and has superior tolerance to all environmental stresses
within a given habitat. As suggested by Funk, the successful development and breeding of
Kentucky bluegrass varieties to exude all of the aforementioned quality characteristics relies
heavily on an understanding of its apomictic reproductive system (Beard, 1973). The inhibition

3

of the sexual process reduces a breeder’s efforts to produce effective hybridizations. The
development of a superior genotype within an apomictic plant results in fixed hybrid vigor, the
intended goal of plant breeding programs (Casler, 2003). And since the asexual reproduction
results in the production of seeds with out recombination or segregation, high levels of stability
and uniformity can be achieved for seed production efforts and distribution; however, the
problem lies in the sexual recombination (Casler, 2003). Kentucky bluegrass F1 hybrids
segregate drastically and far exceed the parental character values, a process called transgressive
segregation (Casler, 2003). Transgressive segregation develops from traditional breeding
techniques and often makes interpreting quantitative genetic information difficult. Therefore,
identifying a superior genotype is often a daunting task. Traditional breeding programs are
responsible for varieties that, although were developed decades ago, continue to compete with
novel varieties. For instance, Midnight was developed in the 1970’s and continues to show
standards of high quality and traffic tolerance in the most recent National Turfgrass Evaluation
Program (NTEP) results (NTEP 2009, Casler 2003, Meyer 1984).
Marker-assisted selection may provide the means of developing improved varieties by
giving insight into genetic changes of progeny from parental crosses. Markers such as Random
Amplified Polymorphic DNA (RAPD), Restriction Fragment Length Polymorphisms (RFLP),
Simple Sequence Repeats (SSR), and Amplified Fragment Length Polymorphisms (AFLP) are
used in correlation to phenotypic data to locate and identify putative quantitative traits, or QTL
(Quantitative Trait Loci) (Young, 2000; Huff, 2001). All of the previously mentioned markers
locate polymorphisms and track the segregation of the inherited DNA sequences among the
progeny of a genetic cross. This information is collected into a linkage map, which will help
explain which QTL has the greatest effect on the phenotypic traits in question. The linkage map

4

assists breeders in selecting progeny based on the desired traits segregating from the parents.
These new technologies have begun to gain momentum in turfgrass breeding programs. Markerassisted selection will lead to future consideration of mapping built from single nucleotide
polymorphisms (SNPs) and unique micro-arrays designed specifically for turfgrass species.
Research conducted on blends has focused primarily on disease incidence but current
research provides a unique insight into varietal composition and spatial patterns of Kentucky
bluegrass varieties in blends and cost effective approaches through the addition of lowperforming varieties on turfgrass quality when added to high-performing varieties. Juska and
Hanson (1959) began looking at mixtures of Kentucky bluegrass, tall fescue, and colonial
bentgrass for stand composition and weed competition. Interestingly, a blend of ‘Merion’
Kentucky bluegrass and common bluegrass was included and showed average botanical
composition comparable to a stand consisting of 100% ‘Merion’ Kentucky bluegrass and also
showing reduced bare ground percentages. Juska was inclined to prescribe a mixture of perennial
species due to the susceptibility of ‘Merion’ to stripe smut. Funk et al. (1968) would continue the
recommendation by Juska and Hanson by testing the available varieties with stripe smut as the
deciding factor. The work of Juska and Hanson, and Funk generated several new research
approaches including further evaluations of turf quality of blends on disease incidence, variety
trials, and the eventual use of DNA fingerprinting to help explain intra-specific competition.
Vargas and Turgeon (1980) showed intermediate quality ratings of turfgrass blends including
resistance varieties, Merion, Nugget, and Pennstar, and susceptible varieties, Kenblue and Park,
to melting-out. These results do not show improved quality of blends, but suggest a reduction of
disease incidence when compared to the susceptible varieties. Furthermore, Smiley and Fowler
(1986) and Fowler and Hummel (1987) proposed that the benefits of blending Kentucky

5

bluegrass varieties were not observed under Magnaporthe poae (Summer Patch) and
Leptoshaeria korrae (Necrotic Ring Spot). Continuing, Watkins et al. (1981) evaluated 60
Kentucky bluegrass varieties and 24 blends of these varieties against natural stem rust
populations. Watkins presented results of the blends and the associated varieties as means for the
blends and cultivars in pure stand. In this case, the blend accurately reflected a reduction in
natural stem rust populations when compared to the mean of constituent varieties. (Watkins
1981). This also suggested the reduction of disease incidence with the inclusion of more than
one resistant variety in the blend. Prior to the introduction of DNA fingerprinting, an accurate
representation of the ecological competition between turfgrass species was limited. Only the
inference of varying adaptabilities between monocultures could show the potential of a variety to
a specific environment and the possible incorporation of the variety into a blend. The National
Turfgrass Evaluation Program (NTEP) collects and coordinates the distribution of varieties of
most turfgrass species to be evaluated for a wide range of adaptations, including heat, drought,
wear and disease tolerance across several regions of the United States. Using the data compiled,
improved varieties can be selected for blend construction that will provide benefits for a specific
location and environment. Presently, using genetic markers has aided in evaluating competition
among Kentucky bluegrass varieties. Although more research in this area would provide
increased knowledge in the inter-workings of blend composition, current research reflects
changes in blend constitution over time, naturally and under disease stress, spatial patterns of
blends, and the effects of turf quality by introducing low- and high-performance varieties into
blends. Lickfeldt et al. (2002a) used RAPD markers to track changes in blends composed of
‘Blacksburg’, ‘Midnight’, and ‘Unique’ Kentucky bluegrass. Lickfeldt used RAPD markers to
determine spatial arrangements of Kentucky bluegrass in blends under different management

6

practices and locations. From this, the research concluded the spatial arrangement to be
randomized and not clumped, and that the management or location does not determine stand
composition: Rather, the competitive advantages of the varieties determine composition. Later,
Lickfeldt (2002b) used RAPD markers to determine changes over time of seeded blends of the
same varieties used previously. In a three-way blend, a 33.3% blend by weight, resulted in a
dramatic decrease in ‘Blacksburg’, and an increase in ‘Midnight’ from seeding to the time of the
second year of sampling. In two-way blends ‘Blacksburg’ x ‘Unique’ and ‘Blacksburg’ x
‘Midnight’, 50% blends by weight, showed a decrease in ‘Unique’ and an increase in ‘Midnight’
after two years of development, respectively. Data collected shows the competition between
varieties with differences in aggressiveness. However, contrary to the these findings,
Golembiewski et al. (2001) demonstrated, using RAPD markers, that differing disease treatments
had no ill effect on stand composition of ‘Crenshaw’ and ‘Penncross’ creeping bentgrass planted
with a 50:50 ratio. Brede (2004) used molecular markers to determine the effects of varying
performance varieties (low = ‘Huntsville’, medium = ‘NuBlue’, and high = ‘Award’) on the
overall turf quality (TQ) of the blend. Brede shows through segmented regression analysis, that
by adding ‘Huntsville’ to a high-performing variety like ‘Award, the low-performing variety
decreased the TQ of the high performing variety on 71% of rating dates. Likewise, adding
‘NuBlue’ decreased TQ of ‘Award’ on 60% of rating dates. Furthermore, the segmented or
“pivot points” in the regression analysis were significant on 14 rating dates for ‘Huntsville’
suggesting that the introduction of a low-performing variety up to a 50:50 ratio did not bring
down TQ and would reduce the cost of seed.
With the complexity of blend construction and development, variety selection, and the
continual advancements of improved varieties through traditional and molecular techniques,

7

reverting to single-variety stands may prove beneficial. Newer varieties have increased disease
resistances, wear tolerance, and protection from other abiotic and biotic stressors. For disease
control, blends of Kentucky bluegrass that include resistant and susceptible varieties may
increase the susceptibility of the resistant variety (Vargas et al. 1980). Vargas hypothesized that
the decrease in resistance is due to the build up of inoculum surrounding the resistant variety.
From a cultural practices standpoint, managing varieties under a single maintenance program
will prove to be more conducive to a single variety, and due to the competitive nature of
Kentucky bluegrass, the variety growing under optimal conditions may dominate the blend. With
this in mind, the current benefits of using a blend in an athletic field setting are under scrutiny.

8

Chapter One: Effects of Traffic on Kentucky Bluegrass Varieties in Monostands and Blends on
Native Soil
INTRODUCTION
Some varieties of Kentucky bluegrass grow more aggressively and have better
recuperative abilities than others. Tolerant varieties to traffic have been shown to posses higher
lignin content and distribution, total cell wall content, leaf width, and leaf tensile strength
(Shearman et al., 1975; Brosnan et al. 2005, Carrow and Petrovic, 1992). In addition, wear
tolerance in cool-season species has been linked to photosynthetic carbohydrate production,
transpiration, and respiration management (Trenholm et al., 1999). Suggesting, single variety
Kentucky bluegrass stands breed specifically for an aggressive growth habit and rapid
recuperation rates could potentially provide a higher quality-playing surface than a blend
containing traffic intolerant or slow recovering cultivars. Vargas (2005) suggests that blending
improved varieties with a common Kentucky bluegrass may diminish the overall quality, or
resistance to melting-out, of a ‘Merion’ Kentucky bluegrass stand. The same concept can be
applied when considering adding a traffic intolerant variety to a blend intended for use on a high
traffic area, such as an athletic field.
Wear is described as injury to a turfgrass stand from pressure, tearing, and scuffing on the
turfgrass leaf tissue (Carrow and Petrovic, 1992). Turf, particularly on a high traffic area, is
subject to great quantities of traffic throughout playing seasons. Although aggressive cultivars
have a great effect on the wear tolerance, other factors like environment, management, and
compaction greatly influence the adaptability of a turfgrass variety (Bell, 2011). Turgeon (2008)
describes the limiting factor concept, developed from Liebig’s law of minimums, as it applies to
turfgrasses. Liebig’s law of minimum states, “That if one necessary element is deficient and all

9

others are adequate, growth will be limited by the one that is missing (Turgeon, 2008)”. As the
limiting factors progress, excessive soil moisture and a reduction in soil oxygen exchange greatly
affect the turfgrass growth by inhibiting root respiration (Bell, 2011). On athletic fields high in
silt and clay, heavy use and excessive rainfall create severe soil compaction, not to mention the
physical growth reduction caused by the wear (Benson and Daniel, 1990). Furthermore, research
by Kowalewski et al. (2010), although showing an increase in surface shear strength associated
to turfgrass cover on native soil, showed a reduction of turfgrass cover when compared to
treatments receiving subsequent topdressing applications. Applying the law of minimums to a
stand composed of a blend, the reduction in growth associated with wear, compaction (oxygen),
and moisture would lead to diminished quality of a single variety susceptible to any one of these
conditions and also the blend as a whole. Management practices focusing on alleviating
compaction, water movement and infiltration, and wear prevention may help to create a
beneficial environment; however, on native soil, an aggressive Kentucky bluegrass variety with
better recuperative potentials may prove as a viable monostand under high-traffic areas.

10

MATERIALS AND METHODS
The study was initiated on 15 September 2009 at the Hancock Turfgrass Research Center
2

at Michigan State University in East Lansing, MI, USA. Plots, 2.32-m in size, of Kentucky
bluegrass (Poa pratensis L.) varieties and blends (Table 1) were established from seed on 25
September 2009 on a Colwood-Brookston Loam/Aubbeenaubee Capac Sandy Loam (NRCS,
2009). Lebanon Country Club 13-25-12 Starter fertilizer (Lebanon Seaboard Corp., Lebanon PA)
-2

-2

was applied at a rate of 4.88-g P2O5 m . Each plot was seeded at a rate of 7.32-g m . Prior to
covering the experimental area with a 95% light transmitted germination and insect AgroFabric
(A.M. Leonard, Piqua, OH) on 25 September 2009, one application of mesotrione
-2

(Tenacity)(Syngenta, Wilmington, DE) at a rate of 0.043-ml m was applied to prevent
broadleaf weeds and annual bluegrass germination. All treatments, excluding the treatments
containing the variety ‘Kenblue’, were established on 25 September 2009 (Table 1). Treatments
containing the variety ‘Kenblue’ were seeded on 29 September 2009. Since the germination
AgroFabric was laid prior to the inclusion of these treatments, the plot areas were clearly marked
until the treatments could be planted. The germination blanket was cut on three sides of the
AgroFabric and pulled away from the plot area. The seed was spread using a hand shaker and
sewn into the soil with a spring rake similar to the other treatments planted on 25 September
2009. The seams of AgroFabric was then stitched back together using 15.24 x 2.54 cm anchor
pins.
An irrigation program was developed for the germination process of the experimental
-1

area providing 0.508-cm day and was reduced to an as needed basis following the removal of
the germination AgroFabric on 7 and 11 October 2009 for the early-seeded treatments and the

11

‘Kenblue’ treatments, respectively. The germination AgroFabric provided an adequate 12-day
germination period for all treatments, except for ‘Barzan’ showing minimal germination. A
second starter fertilizer application was applied on 11 October 2009 applied at a rate of 4.88-g P
-2

m with a supplemental application of 46-0-0 Urea (The Andersons, Inc., Maumee, Ohio) at a
-2

rate of 2.44-g N m . In 2010, applications of 46-0-0 Urea (The Andersons, Inc., Maumee,
-2

Ohio) at a rate of 2.44-g N m and 42-0-0 Polyon (Harrell’s, Lakeland, Florida) at a rate of 4.88
-2

-2

g N m were applied cumulating 24.4 g N m for the year. In 2011, fertility followed the
application program developed and used in the previous year. In both years of the study, twelve
weekly traffic applications were initiated on 9 August 2010 and 8 August 2011. Traffic was
implemented with the Brinkman Traffic Simulator and ten passes were made weekly to simulate
five events, which depicts a practice field in terms of applied traffic (Cockerham et al, 1990;
Vannini et al. 2007). The experimental area was mowed two times weekly at 6.35 cm and
maintained throughout the two-year duration of the study. Following the completion of the traffic
applications in 2010, core cultivation was performed using 2.77 cm hollow tines on 5.08 cm
centers at a 5.08 cm depth. The cores were incorporated back into the soil using hand rakes to
-2

prevent contamination. Furthermore, all plots were reseeded at a 7.32-g m rate on 6 May 2011
to properly restore plots to full turfgrass coverage and mimic an interseeded athletic field
situation.
Weekly ratings of visual assessment for color, quality, and percent turfgrass cover were
collected beginning 27 July 2010 and 5 August 2011. Turfgrass color and quality were rated
using a 1-9 scale, with 1 being inferior, 9 being superior and 6 being acceptable (NTEP, 2009).
Percent turfgrass cover was also assessed visually. Ratings for turf shear (divoting), shear vane

12

(pivoting), and surface hardness were taken bi-weekly throughout the duration of traffic
applications for assessment of surface strength characteristics. All evaluations began with initial
ratings on 27 July 2010 and 5 August 2011.
The study was established as a Randomized Complete Block Design (RCBD) with three
replications. A single factor [Varieties (Table 1)] included 24 total treatments; however, for the
purposes of the study, 10 treatments were compared following the analysis of all treatments in
the study. Therefore, differences in least significant means were developed to compare between
individual treatment means. The Proc UNIVARIATE (SAS Institute, Cary, NC) procedure was
used to test the normality of homogeneity of variances and residuals. Mean separations obtained
using Proc MIXED specifying all pairwise comparisons.

13

Table 1. List of treatments for traffic on native soil
Treatments
Midnight
Right
Prosperity
North Star
Moonshine
Jump Start
Avalanche
PST 103-585
PST 102-158
PST 102-45
Kenblue
TS Blend (25% Jump Start, 25% Avalanche, 25%
Thermal Blue, 25% Moonshine)
TS Blend (25% Right, 25% Prosperity, 25% Midnight II,
25% Moonlight SLT)
Bar VV 0709
Barrister
Barimpala
Barduke
Barrari
Barzan
B Blend (33% Barrari, 33% Barimpala, 33% Bar VV
0709)
B Blend (25% Barrari, 25% Barimpala, 25% Bar VV
0709, 25% Barrister)
B Blend (33.3% Barrister, 33.3% Bar VV 0709, 33.3%
Barrari)
TS Blend (33.3 % Midnight, 33.3% Prosperity, 33.3%
Avalanche)
Kenblue Blend (33.3% Midnight, 33.3% Barrister,
33.3% Kenblue)

14

Sponsor
Turf Seed Company
Turf Seed Company
Turf Seed Company
Turf Seed Company
Turf Seed Company
Turf Seed Company
Turf Seed Company
Turf Seed Company
Turf Seed Company
Turf Seed Company
Common-Type Standard Entry
Turf Seed Company
Turf Seed Company
Barenbrug, USA
Barenbrug, USA
Barenbrug, USA
Barenbrug, USA
Barenbrug, USA
Barenbrug, USA
Barenbrug, USA
Barenbrug, USA
Barenbrug, USA
Turf Seed Company
Manufactured Blend

RESULTS AND DISCUSSION
Percent Ground Cover
All of the turf varieties included in the study (Table 1) were evaluated for percent living
ground cover on a weekly basis. Statistical analysis of the twelve, weekly ratings showed
significance among treatments 6 times in 2010. Pair-wise comparisons between only 7 varieties
and 3 blends were included for the purpose of this study. Furthermore, provided data reflects
mean ground cover following 6 weeks of traffic applications (Table 2) and 12 weeks of traffic
(Table 3) in 2010. After 6 weeks of traffic, mean comparisons revealed no differences between
each of the blends and the associated varieties within the blends. The varieties ‘Barrister’ and
‘Midnight’ provided a slight increase in percent ground cover to the associated blend except for
the blend when the two varieties were included together. Furthermore, ‘Kenblue’, a common
Kentucky bluegrass variety that was included to show the potential reduction in blend capability
provided the lowest percent ground cover at 92.0% following the 6 weeks of traffic events in
2010. Following 12 weeks of traffic events, no significant differences were shown with the blend
including ‘Barrister’, ‘Bar VV 0709’, and ‘Barrari’. Contrasting, differences were observed
between the varieties ‘Prosperity’ and ‘Kenblue’ to their associated varieties; however the
difference could not be discerned between the other two varieties included in the blend with
‘Prosperity’ and ‘Kenblue’ as monostands. Similar to 2010, statistical analysis of the twelve,
weekly ratings showed significance among treatments 6 times in 2011. Mean ground cover
comparisons after 6 weeks of traffic events in 2011 showed statistical differences but not
necessarily biological significance between ‘Midnight’ and ‘Prosperity’ and ‘Barrister’ and the
blend including ‘Barrister’, ‘Midnight’, and ‘Kenblue’ (Table 4). After 12 weeks of traffic, there
were no statistical differences between the blends and the associated varieties but ‘Barrister’ did

15

maintain a higher percent ground cover compared to the blend consisting of ‘Barrister’,
‘Midnight’, and ‘Kenblue’ (Table 5).
Quality
All of the turf varieties included in the study were evaluated for visual turfgrass quality
on a weekly basis. Statistical analysis of the twelve, weekly ratings showed significance among
treatments 8 times in 2010. Pair-wise comparisons between only 7 varieties and 3 blends were
included for the purpose of this study. Furthermore, provided data reflects turfgrass quality
following 6-weeks (Table 2) and 12 weeks of traffic applications (Table 3) in 2010. After 6weeks of traffic, differences were only noticed among the blend containing ‘Midnight’,
‘Avalanche’, and ‘Prosperity’. The variety ‘Midnight’ produced quality less than the variety
‘Prosperity’; however, ‘Midnight’ did not significantly differ from ‘Avalanche’ and the blend.
After 12-weeks of traffic, ‘Prosperity’ had a significantly lower quality than ‘Avalanche’,
‘Midnight’, and the blend containing the three varieties. Similar to the 6-week quality ratings,
there were no differences in the blends containing ‘Barrister’, ‘Bar VV 0709’ and ‘Barrari and
the blend containing ‘Midnight’, ‘Barrister’, and ‘Kenblue’. Data collection in 2011 revealed
significance among treatments 8 times, similar to 2010. Six-week traffic data showed no
significance among all blends and their associated varieties (Table 4). The absence of differences
was also reflected following 12-weeks of traffic events (Table 5). The variety ‘Barrister’ had a
higher turfgrass quality rating than the blend containing ‘Barrister’, ‘Midnight’, and ‘Kenblue’,
although not significant.

16

Table 2. Mean comparisons of treatments following 6-weeks of traffic on native soil in 2010,
obtained 17 September at HTRC, East Lansing, MI
Percent
Clegg
Turf Shear
Shear Vane
Treatment
Ground
Quality ‡
Hammer
Tester (Nm)
(Nm)
Cover
(Gmax)
Barrister
97.3 a†
6.7 a
85.0 a
16.7 a
59.7 a
Bar VV 0709
96.3 a
7.3 a
88.3 a
13.0 a
60.7 a
Barrari
96.3 a
7.0 a
83.7 a
14.7 a
59.0 a
*
Blend
96.7 a
7.3 a
85.0 a
16.0 a
52.7 a
Midnight
Avalanche
Prosperity
Blend

97.0 a
94.0 a
94.7 a
94.7 a

6.3 b
6.7 ab
7.0 a
6.7 ab

83.3 ab
80.3 ab
72.7 b
90.3 a

16.7 a
15.3 a
15.0 a
16.7 a

60.3 a
59.7 a
54.3 a
61.7 a

Midnight
97.0 a
6.3 a
83.3 ab
16.7 a
60.3 a
Barrister
97.3 a
6.7 a
85.0 ab
16.7 a
59.7 a
Kenblue
92.0 a
6.3 a
81.7 b
14.0 a
54.7 a
Blend
99.0 a
6.7 a
92.0 a
14.0 a
57.0 a
* Blends comprised of three constituents located directly above treatment
† Means in same column and blend grouping followed by the same letter are not significantly
different according to (p=0.05)
‡ Quality: 1= Poor, 5 = Acceptable, and 9 = Excellent

17

Table 3. Mean comparisons of treatments following 12-weeks of traffic on native soil in 2010, ,
obtained 12 November at HTRC, East Lansing, MI
Percent
Clegg
Turf Shear
Shear Vane
Treatment
Ground
Quality ‡
Hammer
Tester (Nm)
(Nm)
Cover
(Gmax)
Barrister
68.3 a†
4.7 a
84.5 a
18.7 a
103.0 a
Bar VV 0709
75.0 a
5.0 a
82.3 a
21.0 a
109.0 a
Barrari
70.0 a
5.3 a
71.0 a
19.3 a
100.0 a
*
Blend
71.7 a
5.0 a
86.0 a
21.3 a
91.0 a
Midnight
Avalanche
Prosperity
Blend

61.7 ab
62.3 ab
50.0 b
70.0 a

4.7 ab
5.0 a
4.0 b
5.3 a

73.7 a
77.0 a
75.7 a
84.0 a

18.7 a
19.0 a
18.0 a
17.3 a

92.0 a
105.0 a
94.0 a
96.0 a

Midnight
61.7 a
4.7 a
73.7 a
18.7 a
92.0 a
Barrister
68.3 a
4.7 a
84.5 a
18.7 a
103.0 a
Kenblue
48.3 b
4.3 a
86.7 a
19.0 a
104.0 a
Blend
61.7 a
4.3 a
79.0 a
17.3 a
104.0 a
* Blends comprised of three constituents located directly above treatment
† Means in same column and blend grouping followed by the same letter are not significantly
different according to (p=0.05)
‡ Quality: 1= Poor, 5 = Acceptable, and 9 = Excellent

18

Table 4. Mean comparisons of treatments following 6-weeks of traffic on native soil in 2011,
obtained 21 September at HTRC, East Lansing, MI
Percent
Clegg
Turf Shear
Shear Vane
Treatment
Ground
Quality ‡
Hammer
Tester (Nm)
(Nm)
Cover
(Gmax)
Barrister
99.0 a†
7.0 a
68.0 a
14.0 b
61.0 a
Bar VV 0709
99.0 a
7.3 a
67.0 a
14.0 b
57.3 a
Barrari
99.3 a
7.7 a
70.7 a
15.3 ab
51.0 a
*
Blend
99.0 a
7.0 a
71.0 a
16.7 a
55.3 a
Midnight
Avalanche
Prosperity
Blend

95.0 b
98.0 ab
98.3 a
97.0 ab

7.0 a
6.7 a
6.7 a
6.7 a

65.0 a
65.3 a
56.3 a
62.3 a

14.0 a
15.3 a
14.3 a
14.7 a

56.0 a
59.3 a
51.3 a
54.3 a

Midnight
95.0 b
7.0 a
65.0 a
14.0 ab
56.0 a
Barrister
99.0 a
7.0 a
68.0 a
14.0 ab
61.0 a
Kenblue
95.0 b
6.3 a
68.0 a
12.7 b
55.0 a
Blend
95.3 b
6.3 a
66.7 a
15.0 a
54.3 a
* Blends comprised of three constituents located directly above treatment
† Means in same column and blend grouping followed by the same letter are not significantly
different according to (p=0.05)
‡ Quality: 1= Poor, 5 = Acceptable, and 9 = Excellent

19

Table 5. Mean comparisons of treatments following 12-weeks of traffic on native soil in 2011,
obtained 2 November at HTRC, East Lansing, MI
Percent
Clegg
Turf Shear
Shear Vane
Treatment
Ground
Quality ‡
Hammer
Tester (Nm)
(Nm)
Cover
(Gmax)
Barrister
82.0 a†
5.7 a
70.7 a
14.7 a
63.7 a
Bar VV 0709
81.0 a
5.7 a
74.0 a
14.3 a
63.7 a
Barrari
80.3 a
5.7 a
74.7 a
15.7 a
63.0 a
*
Blend
81.0 a
5.7 a
78.7 a
14.3 a
63.0 a
Midnight
Avalanche
Prosperity
Blend

76.0 a
74.0 a
77.0 a
79.0 a

5.0 a
5.0 a
5.0 a
5.3 a

69.7 a
63.3 a
66.0 a
66.7 a

14.3 a
14.7 a
14.3 a
15.7 a

61.7 a
63.7 a
61.7 a
65.3 a

Midnight
76.0 a
5.0 a
69.7 a
14.3 a
61.7 a
Barrister
82.0 a
5.7 a
70.7 a
14.7 a
63.7 a
Kenblue
75.3 a
5.0 a
68.3 a
15.3 a
62.3 a
Blend
76.0 a
5.0 a
70.7 a
15.0 a
64.7 a
* Blends comprised of three constituents located directly above treatment
† Means in same column and blend grouping followed by the same letter are not significantly
different according to (p=0.05)
‡ Quality: 1= Poor, 5 = Acceptable, and 9 = Excellent

20

Surface Strength Characteristics
Surface strength characteristics were taken to evaluate the surface performance of the
field during consistent applications of traffic and to potentially assess the playability of a field
during a traffic event at a particular point of a 12-week season. In 2010, evaluations of surface
strength characteristics were taken every 3-weeks succeeding initial ratings on 30 July 2010. The
turf shear tester ratings for 18 October 2010 were not available due to necessary maintenance on
the equipment. In 2010, analysis of turf shear tester ratings reflected significance on half of the
rating dates. Six-week traffic events revealed differences in resistance to divoting among blends
containing ‘Midnight’, ‘Avalanche’, and ‘Prosperity’ and ‘Midnight’, ‘Barrister’, and ‘Kenblue’.
The varieties ‘Prosperity’ and ‘Kenblue’ produced turf shear tester ratings lower than their
respective blends. Following 12-weeks of traffic events there were no significant differences
between the blends and their constituent varieties. Analysis of shear vane data showed
significance among treatment means only initially on 30 July 2010 and produced no significant
differences between blends and their associated varieties following 6-weeks and 12-weeks of
traffic events. Similarly, Clegg hammer data, or surface hardness, did not show significance
throughout the 12-weeks of traffic applications in 2010 (Table 2 and 3).
In 2011, evaluations of surface strength characteristics were taken biweekly after the initial
ratings on 5 August. Analysis of turf shear tester ratings produced one rating date showing
significance; however, differences among the blends and the associated varieties were not
observed. Shear vane data analysis revealed significance 2-times throughout the traffic
applications, initially on 5 August and on 21 September 2011. The blend containing ‘Barrister’,
‘Bar VV 0709’, and ‘Barrari’ was significantly higher than ‘Barrister’ and ‘Bar VV 0709’ but
not ‘Barrari’. Furthermore, the blend containing ‘Midnight’, ‘Barrister’, and ‘Kenblue’,

21

‘Barrister’ alone, and ‘Midnight’ alone were significantly greater than ‘Kenblue’ as a monostand.
Lastly, Clegg hammer data analysis showed significance after 4-weeks of traffic simulation. The
data did not show significance among the blends and the varieties contained with in the blends
Tables 4 and 5).

22

CONCLUSIONS
The analysis of the native soil data in 2010 and 2011 produced a consistent occurrence
following 6-weeks and 12-weeks of traffic events with the Brinkman traffic simulator. The
blends did not outperform all of the monostands of the associated varieties within the blends in
percent turfgrass ground cover, turfgrass quality, Turf Shear Tester ratings, shear vane ratings,
and Clegg hammer ratings. Furthermore, traffic simulation on native soil reflected the ability of
the individual varieties to compete against the continual traffic applications and the potential for
increased compaction and a reduction of oxygen available for respiration. That is, this
experiment showed how the varieties would react in unfavorable growing conditions as
suggested by law of minimums previously suggested. Varieties showing poor adaptability to
these conditions were ‘Kenblue’ and ‘Prosperity’. ‘Kenblue’, a common-type Kentucky
bluegrass variety with low tolerance to traffic (NTEP), represents a variety that would not
commonly be included among improved varieties like ‘Barrister’ and ‘Midnight’. However, even
when ‘Kenblue’ produced a reduction in turfgrass cover and Turf Shear Tester in 2010, the
effects with in the blend were not observed. This suggests that the other varieties included may
have compensated for the susceptibility. Likewise in 2010, ‘Prosperity’ also showed a significant
reduction in turfgrass cover, quality, and Turf Shear Tester but did not have an ill effect on the
blend as shown by the blend compared to the other varieties included, ‘Midnight’ and
‘Avalanche’. The development of these varieties within the blend could have been offsetting
producing a lower percentage of ‘Prosperity’ with in the turf stand initially. Therefore, a
reduction of ‘Prosperity’ with in the blend may not have been substantial.

23

REFERENCES

24

REFERENCES
Bell, G. E. 2011. Turfgrass Physiology and Ecology. Cambridge, MA. CAB International. P. 7273, 170-178, 193-195.
Benson, C.H. and D.E. Daniel. 1990. Influence of Clods on the Hydraulic Conductivity of
Compacted Clay. Journal of Geotechnology Engineering Division. 116:1231–1248.
Brosnan, J.T., J. S. Ebdon, and W. M. Dest. 2005. Characteristics in Diverse Wear Tolerant
Genotypes of Kentucky Bluegrass. Crop Science. 45: 1917-1926
Carrow, R. N. and A. N. Petrovic. 1992. In: Waddington, D. V., Carrow, R. N., and Shearman,
R. C., eds. Turfgrass. 32. Madison, WI: ASA, CSSA, & SSSA. P. 285-325.
Cockerham, S. T, V. A. Gibault, J. Van Dam and J. K. Leonard. 1990. Tolerance of Several Cool
Season Turfgrasses to Simulated Sport Traffic. In natural and artificial playing fields, Schmidt.
American Society for Testing and Materials. ASTM STP. 1073: 85-95.
Kowalewski, A.R., J. R. Crum, J. N. Rogers III, J. C. Dunne. 2011. Improving Native Soil
Athletic Fields with Intercept Drain Tile Installation and Subsequent Sand Topdressing
Applications. Soil Science. March. 176(3): 143-149.
NTEP. 2009. A guide to NTEP turfgrass ratings. Retrieved Aug 20, 2009.
(http://www.ntep.org/reports/ratings.htm)
Shearman, R. C. and J. B. Beard. 1975. Turfgrass Wear Tolerance Mechanisms II. Effects of
Cell Wall Constituents on Turfgrass Wear Tolerance. Agronomy Journal. 67: 211-215.
Trenholm, L. E., R. R. Duncan, and R. N. Carrow. 1999. Wear tolerance, Shoot Performance,
and Spectral Reflectance of Seashore Paspalum and Bermudagrass. Crop Science. 39: 11471152.
Turgeon, A. J. 2008. Turfgrass Management. Boston: Prentice Hall. 8th Edition. P. 122, 332-334,
366-367.
Vanini, J.T., J.J. Henderson, J.C. Sorochan, and J.N. Rogers, III. 2007. Evaluating Traffic Stress
by the Brinkman Traffic Simulator and Cady Traffic Simulator on a Kentucky Bluegrass Stand.
Crop Science. 47:780–784.
Vargas, J. M. 2005. Management of turfgrass diseases. Hoboken, N.J: J. Wiley. P. 86-89, 181185.

25

Chapter Two: Effects of Traffic on Kentucky Bluegrass Varieties in Monostands and Blends
with High-Sand Based Topdressing Applications Over Native Soil
INTRODUCTION
Sand topdressing on an athletic field will provide a number of advantages. Higher sand
content will reduce the compaction in a high trafficked area, prevent an accumulation of thatch,
and improve drainage or water movement through the root zone of the turf (Vavrek, 1993).
Recent research conducted by Kowalewski et al. (2010) and Miller (2008) has shown that sand
topdressing can improve the wear tolerance, turfgrass cover, density and surface strength, of a
variety of turfgrass stands, including Kentucky bluegrass. Further research conducted by
Kowalewski et al. (2011) shows sand topdressing to provide improved surface drainage and
decreases in surface water runoff; all important factors for providing a dry, stable playing
surface. With this in mind, Kentucky bluegrass varieties with more aggressive tillering will tend
to accept more frequent and heavier topdressing programs and will provide a better, more
uniform playing surface than blends containing cultivars with a weak or slow growth habit.
Areas that receive excessive use and intense traffic often include soil modifications to
reduce the effects of wear and ultimately compaction on native soils high in silt and clay. On
athletic fields, the inclusion of sand topdressing programs has become a increasingly used
management practice and soil amendment. The relatively high macropore volume and low
inclusion of silt and clay allows for the inherent ability to maintain air movement, water
infiltration, and resistance to compaction, making this amendment desired in an athletic field
setting (Bingaman and Kohnski, 1970, Henderson et al., 2005, Carrow and Petrovic, 1992).
Research by Samaranayake et al. (2008), suggested wear on creeping bentgrass (Agrostis
palustris) and velvet bentgrass (Agrostis canina) caused more damage than the resulting soil
compaction. This study was performed on a sandy loam soil and offers inference into the
26

importance of sand as a soil modification. With this in mind, the reliability placed on selecting
wear tolerant species is more beneficial than alleviating poor soil conditions when sand
topdressing or sand as a soil modification is used. The additions of wear intolerant varieties of
Kentucky bluegrass into a blend may result in more aggressive varieties leaning out the number
of varieties originally included in the blend. Therefore, aggressively growing-wear tolerant
varieties may provide evidence to the single-variety plantings for athletic field use.

27

MATERIALS AND METHODS
The study was initiated on 15 September 2009 at the Hancock Turfgrass Research Center
2

at Michigan State University in East Lansing, MI, USA. Plots, 2.32-m in size, of Kentucky
bluegrass (Poa pratensis L.) varieties and blends (Table 6) were established from seed on 25
September 2009 on a Colwood-Brookston Loam/Aubbeenaubee Capac Sandy Loam (NRCS,
2009). Lebanon Country Club 13-25-12 Starter fertilizer (Lebanon Seaboard Corp., Lebanon PA)
-2

-2

was applied at a rate of 4.88-g P m . Each plot was seeded at a rate of 7.32-g m . Prior to
covering the experimental area with a 95% light transmitted germination and insect AgroFabric
(A.M. Leonard, Piqua, OH) on 25 September 2009, one application of mesotrione
-2

(Tenacity)(Syngenta, Wilmington, DE) at a rate of 0.043-ml m was applied to prevent
broadleaf weeds and annual bluegrass germination. All treatments, excluding the treatments
containing variety ‘Kenblue’, were established on 25 September 2009 (Table 6). Treatments
containing the variety ‘Kenblue’ were seeded on 29 September 2009. Since the germination
AgroFabric was laid prior to the inclusion of these treatments, the plot areas were clearly marked
until the treatments could be planted. The germination blanket was cut on three sides of the
AgroFabric and pulled away from the plot area. The seed was spread using a hand shaker and
sewn into the soil with a spring rake similar to the other treatments planted on 25 September
2009. The seams of AgroFabric was then stitched back together using 15.24 x 2.54 cm anchor
pins.
An irrigation program was developed for the germination process of the experimental
-1

area providing 0.508-cm day and was reduced to an as needed basis following the removal of
the germination AgroFabric on 7 and 11 October 2009 for the early-seeded treatments and the

28

‘Kenblue’ treatments, respectively. The germination AgroFabric provided an adequate 12-day
germination period for all treatments, except for ‘Barzan’ showing minimal germination. A
second starter fertilizer application was applied on 11 October 2009 applied at a rate of 4.88-g P
-2

m with a supplemental application of 46-0-0 Urea (The Andersons, Inc., Maumee, Ohio) at a
-2

rate of 2.44-g N m . In 2010, applications of 46-0-0 Urea (The Andersons, Inc., Maumee,
-2

Ohio) at a rate of 2.44-g N m and 42-0-0 Polyon (Harrell’s, Lakeland, Florida) at a rate of 4.88
-2

-2

g N m were applied cumulating 24.4 g N m for the year. In 2011, fertility followed the
application program developed and used in the previous year. Four weekly applications of a
well-graded, high-sand-content topdressing were initiated on 10 June 2010 and 15 June 2011 to
provide 2.54-cm and 5.08-cm, respectively. The applications would be similar to topdressing
applications on an athletic field and would provide improved infiltration, shoot density, and
surface shear strength (Kowalewski et al. 2010). The root-zone mixture used as the sand
topdressing, (90.0% sand, 7.0% silt, and 3.0% clay) developed for athletic field construction
(ASTM International, 2006; Henderson et al. 2005), was applied at a 0.635-cm depth to achieve
the aforementioned depths for each year.
During the two years of the study, twelve weekly traffic applications were initiated on 9
August 2010 and 8 August 2011. Traffic was implemented with the Brinkman Traffic Simulator
and ten passes were made weekly to simulate five events, which depicts a practice field in terms
of applied traffic (Cockerham et al. 1990; Vannini et al. 2007). The experimental area was
mowed two times weekly at 6.35 cm and maintained throughout the two-year duration of the
study. Following the completion of the traffic applications in 2010, core cultivation was
performed using 2.77 cm hollow tines on 5.08 cm centers at a 5.08 depth. The cores were

29

incorporated back into the soil using hand rakes to prevent contamination. Furthermore, all plots
-2

were reseeded at a 7.32-g m rate on 6 May 2011 to properly restore plots to full turfgrass
coverage and mimic an interseeded athletic field situation.
Weekly ratings of visual assessment for color, quality, and percent turfgrass cover were
collected beginning 27 July 2010 and 5 August 2011. Turfgrass color and quality were rated
using a 1-9 scale, with 1 being inferior, 9 being superior and 6 being acceptable (NTEP, 2009).
Percent turfgrass cover was also assessed visually. Ratings for turf shear (divoting), shear vane
(pivoting) and surface hardness were taken bi-weekly throughout the duration of traffic
applications for assessment of surface strength characteristics. All evaluations began with initial
ratings on 27 July 2010 and 5 August 2011.
The study was established as a Randomized Complete Block Design (RCBD) with three
replications. A single factor [Varieties (Table 6)] included 24 total treatments; however, for the
purposes of the study, 10 treatments were compared following the analysis of all treatments in
the study. Therefore, differences in least significant means were developed to compare between
individual treatments. The Proc UNIVARIATE (SAS Institute, Cary, NC) procedure was used to
test the normality of homogeneity of variances and residuals. Mean separations obtained using
Proc MIXED specifying all pair-wise comparisons.

30

Table 6. List of treatments for traffic on topdressing over native soil
Treatments
Sponsor
Midnight
Turf Seed Company
Right
Turf Seed Company
Prosperity
Turf Seed Company
North Star
Turf Seed Company
Moonshine
Turf Seed Company
Jump Start
Turf Seed Company
Avalanche
Turf Seed Company
PST 103-585
Turf Seed Company
PST 102-158
Turf Seed Company
PST 102-45
Turf Seed Company
Kenblue
Common-Type Standard Entry
TS Blend (25% Jump Start, 25% Avalanche, 25%
Turf Seed Company
Thermal Blue, 25% Moonshine)
TS Blend (25% Right, 25% Prosperity, 25% Midnight II,
Turf Seed Company
25% Moonlight SLT)
Bar VV 0709
Barenbrug, USA
Barrister
Barenbrug, USA
Barimpala
Barenbrug, USA
Barduke
Barenbrug, USA
Barrari
Barenbrug, USA
Barzan
Barenbrug, USA
B Blend (33% Barrari, 33% Barimpala, 33% Bar VV
Barenbrug, USA
0709)
B Blend (25% Barrari, 25% Barimpala, 25% Bar VV
Barenbrug, USA
0709, 25% Barrister)
B Blend (33.3% Barrister, 33.3% Bar VV 0709, 33.3%
Barenbrug, USA
Barrari)
TS Blend (33.3 % Midnight, 33.3% Prosperity, 33.3%
Turf Seed Company
Avalanche)
Kenblue Blend (33.3% Midnight, 33.3% Barrister,
Manufactured Blend
33.3% Kenblue)

31

RESULTS AND DISCUSSION
Percent Ground Cover
All of the turf varieties included in the study (Table 6) were evaluated for percent living
ground cover on a weekly basis. Statistical analysis of the twelve, weekly ratings showed
significance among treatments 10 times in 2010. Pair-wise comparisons between only 7 varieties
and 3 blends were included for the purpose of this study. Therefore, provided data reflects mean
ground cover following 6 weeks of traffic applications (Table 7) and 12 weeks of traffic (Table
8) in 2010. After 6 weeks of traffic, mean comparisons revealed differences between monostands
of ‘Midnight’, ‘Barrister’, and ‘Kenblue’ and the blend containing these varieties. Although not
biologically significant, ‘Kenblue’ produced turfgrass ground cover lower than ‘Midnight’ alone,
‘Barrister’ alone, and the blend. Following 12-weeks of traffic applications, several differences
were observed. The variety ‘Prosperity’ had significant reduction in turfgrass cover compared to
‘Midnight’, ‘Avalanche’ and the blend containing these varieties. Furthermore, the blend
containing ‘Barrister’, ‘Bar VV 0709’, and ‘Barrari’ and ‘Barrister’ alone showed significant
reduction in turfgrass ground cover compared to ‘Bar VV 0709’. Statistical analysis of the
twelve, weekly ratings showed significance among treatments 5 times in 2011. Again, pair-wise
comparisons between only 7 varieties and 3 blends were included for the purpose of this study.
Following 6-weeks of traffic applications, no difference among treatment means were observed
(Table 9). Mean ground cover comparisons after 12-weeks of traffic events in 2011 produced
significance among the blend containing the varieties ‘Midnight’, ‘Avalanche’, and ‘Prosperity’
and the blend containing ‘Midnight’, ‘Barrister’, and ‘Kenblue’ (Table 10). The variety
‘Prosperity’ showed a significant reduction in percent ground cover compared to ‘Midnight’ and
the blend, but not ‘Avalanche’. Furthermore, the variety ‘Kenblue’ in monostand had a

32

significant reduction in turfgrass ground cover compared to ‘Midnight’ alone, ‘Barrister’ alone,
and the blend containing the varieties.

Quality
All of the turf varieties included in the study were evaluated for turfgrass quality on a
weekly basis. Statistical analysis of the twelve, weekly ratings showed significance among
treatments 11 times in 2010. Pair-wise comparisons between only 7 varieties and 3 blends were
included for the purpose of this study. Therefore, provided data reflects turfgrass quality
following 6-weeks (Table 7) and 12 weeks of traffic applications (Table 8) in 2010. After 6weeks of traffic, although the treatment means were significant, the blends that were evaluated
did not significantly differ than the associated varieties. Following 12-weeks of traffic
applications, several differences were observed. The variety ‘Avalanche’ had a significantly
higher turfgrass quality rating compared to ‘Prosperity’; however, ‘Midnight’ and the blend
containing ‘Midnight’, ‘Avalanche’, and ‘Prosperity’, did not significantly differ to either
‘Avalanche’ or ‘Prosperity’. Furthermore, the variety ‘Bar VV 0709’ was significantly greater
than the blend containing ‘Barrister’, ‘Bar VV 0709’, and ‘Barrari’ in turfgrass quality. Although
not significant, ‘Barrari’ had greater turfgrass quality than the associated blend and all treatments
were significantly greater than ‘Barrister’ in monostand. Data collection in 2011 revealed
significance among treatments 5 times, greatly reduced from 2010. After six-weeks of traffic
applications, there were no significant differences among the evaluated blends and their
associated varieties (Table 9). Similar to the 6-week ratings, there were no differences between
the evaluated blends and their constituent varieties (Table 10).

33

Table 7. Mean comparisons of treatments following 6-weeks of traffic on topdressing over native
soil in 2010, obtained 17 September at HTRC, East Lansing, MI
Percent
Clegg
Turf Shear
Shear Vane
Treatment
Ground
Quality ‡
Hammer
Tester (Nm)
(Nm)
Cover
(Gmax)
†
Barrister
99.7 a
8.0 a
73.7 a
11.3 a
51.0 a
Bar VV 0709

99.3 a

8.3 a

74.3 a

11.3 a

51.0 a

Barrari

98.0 a

8.0 a

72.3 a

10.3 a

59.0 a

*

99.0 a

7.7 a

71.7 a

9.7 a

51.0 a

Midnight

100.0 a

8.3 a

75.0 a

10.0 a

49.0 a

Avalanche

99.3 a

8.0 a

68.3 a

11.0 a

51.0 a

Prosperity

100.0 a

8.0 a

70.0 a

9.7 a

50.0 a

Blend

99.7 a

8.0 a

70.0 a

10.7 a

54.0 a

Midnight

100.0 a

8.3 a

75.0 a

10.0 a

49.0 a

Barrister

99.7 a

8.0 a

73.7 a

11.3 a

51.0 a

Kenblue

97.0 b

7.3 a

70.3 a

9.3 a

51.0 a

Blend

99.0 a

8.0 a

67.0 a

11.7 a

48.0 a

Blend

* Blends comprised of three constituents located directly above treatment
† Means in same column and blend grouping followed by the same letter are not significantly
different according to (p=0.05)
‡ Quality: 1= Poor, 5 = Acceptable, and 9 = Excellent

34

Table 8. Mean comparisons of treatments following 12-weeks of traffic on topdressing over
native soil in 2010, obtained 12 November at HTRC, East Lansing, MI
Percent
Clegg
Turf Shear
Shear Vane
Treatment
Ground
Quality ‡
Hammer
Tester (Nm)
(Nm)
Cover
(Gmax)
†
Barrister
56.7 b
4.0 c
52.3 a
10.3 b
78.0 a
Bar VV 0709

90.0 a

6.7 a

46.0 a

14.7 a

80.0 a

Barrari

87.3 ab

6.3 ab

49.0 a

11.3 b

87.0 a

71.7 b

5.3 b

55.0 a

11.0 b

75.7 a

Midnight
Avalanche
Prosperity
Blend

58.3 a
75.7 a
48.3 b
70.0 a

4.3 ab
5.3 a
4.0 b
5.0 ab

49.7 a
50.3 a
53.3 a
52.7 a

9.7 a
9.7 a
8.0 a
8.7 a

83.0 a
77.7 a
82.0 a
74.3 a

Midnight
Barrister
Kenblue
Blend

58.3 a
56.7 a
72.7 a
68.3 a

4.3 a
4.0 a
5.0 a
5.0 a

49.7 a
52.3 a
49.3 a
51.7 a

9.7 a
10.3 a
9.3 a
9.0 a

83.0 a
78.0 a
89.7 a
73.0 a

*

Blend

* Blends comprised of three constituents located directly above treatment
† Means in same column and blend grouping followed by the same letter are not significantly
different according to (p=0.05)
‡ Quality: 1= Poor, 5 = Acceptable, and 9 = Excellent

35

Table 9. Mean comparisons of treatments following 6-weeks of traffic on topdressing over native
soil in 2011, obtained 21 September at HTRC, East Lansing, MI
Percent
Clegg
Turf Shear
Shear Vane
Treatment
Ground
Quality ‡
Hammer
Tester (Nm)
(Nm)
Cover
(Gmax)
Barrister
100.0 a†
7.7 a
52.3 a
12.7 a
53.7 a
Bar VV 0709
99.3 a
7.7 a
46.0 a
14.3 a
53.7 a
Barrari
99.7 a
8.0 a
49.0 a
12.3 a
50.3 a
*
Blend
99.3 a
7.7 a
55.0 a
12.3 a
53.0 a
Midnight
Avalanche
Prosperity
Blend

100.0 a
100.0 a
99.3 a
100.0 a

8.3 a
8.3 a
8.0 a
7.7 a

49.7 a
50.3 a
53.3 a
52.7 a

11.3 a
13.7 a
11.0 a
12.3 a

57.3 a
57.3 a
51.7 a
51.7 a

Midnight
100.0 a
8.3 a
49.7 a
11.3 a
57.3 a
Barrister
100.0 a
7.7 a
52.3 a
12.7 a
53.7 a
Kenblue
98.0 a
7.7 a
49.3 a
12.7 a
55.0 a
Blend
100.0 a
8.0 a
51.7 a
12.3 a
55.0 a
* Blends comprised of three associated varieties located directly above treatment
† Means in same column and blend grouping followed by the same letter are not significantly
different according to (p=0.05)
‡ Quality: 1= Poor, 5 = Acceptable, and 9 = Excellent

36

Table 10. Mean comparisons of treatments following 12-weeks of traffic on topdressing over
native soil in 2011, obtained 2 November at HTRC, East Lansing, MI
Percent
Clegg
Turf Shear
Shear Vane
Treatment
Ground
Quality ‡
Hammer
Tester (Nm)
(Nm)
Cover
(Gmax)
Barrister
88.3 a†
6.3 a
46.0 a
11.7 a
55.7 a
Bar VV 0709
90.0 a
6.7 a
56.3 a
11.0 a
57.7 a
Barrari
91.7 a
6.7 a
44.0 a
12.3 a
57.7 a
*
Blend
91.3 a
7.0 a
45.3 a
11.0 a
59.7 a
Midnight
Avalanche
Prosperity
Blend

90.0 a
86.0 ab
81.7 b
89.0 a

6.7 a
6.3 a
5.7 a
6.7 a

42.7 a
44.7 a
41.7 a
45.3 a

10.7 a
11.7 a
9.7 a
10.0 a

59.3 a
60.7 a
55.3 a
52.7 a

Midnight
90.0 a
6.7 a
42.7 a
10.7 a
Barrister
88.3 a
6.3 a
46.0 a
11.7 a
Kenblue
81.7 b
6.0 a
49.0 a
9.7 a
Blend
88.3 a
6.3 a
44.3 a
11.3 a
* Blends comprised of three constituents located directly above treatment

59.3 a
55.7 a
55.3 a
58.0 a

† Means in same column and blend grouping followed by the same letter are not significantly
different according to (p=0.05)
‡ Quality: 1= Poor, 5 = Acceptable, and 9 = Excellent

37

Surface Strength Characteristics
Surface strength characteristics were taken to evaluate the surface performance of the
field during consistent applications of traffic and to potentially assess the playability of a field
during a traffic event at a particular point of a 12-week season. In 2010, similar to the study on
native soil, evaluations of surface strength characteristics were taken every 3-weeks succeeding
initial ratings on 30 July 2010. The turf shear tester ratings for 18 October 2010 were not
available due to necessary maintenance on the equipment. In 2010, analysis of Turf Shear Tester
ratings reflected significance on only one of the rating dates. Six-week traffic events revealed no
differences in resistance to divoting among blends and their associated varieties (Table 7).
Following 12-weeks of traffic applications, analysis of treatment means showed significance but
there were no observed differences between the blends and their constituent varieties evaluated
for this study (Table 8). Analysis of shear vane data, showed significance among treatment
means on 4 rating dates in 2010. Although the analysis of treatments means showed significant
differences, there were no differences among the blends and the associated varieties following 6weeks of traffic applications. Contrasting, the analysis of treatment means after 12-weeks of
traffic applications did reveal differences in resistance to pivoting. The variety ‘Bar VV 0709’
was significantly higher in the shear vane ratings than the blend containing ‘Barrister’, ‘Bar VV
0709’, and ‘Barrari’, ‘Barrister’ alone, and ‘Barrari’ alone. Surface hardness evaluations, did not
show significance throughout the 12-weeks of traffic applications in 2010.
In 2011, evaluations of surface strength characteristics were taken biweekly after the
initial ratings on 5 August. Analysis of turf shear tester ratings produced one rating date showing
significance; however, differences among the blends and the associated varieties were not
observed. Shear vane data analysis revealed significance 2-times throughout the traffic

38

applications, on 23 August and on 26 October 2011. On these rating dates, the blends did not
outperform all of their associated varieties. Furthermore, there were no significant differences
between treatment means after 6-weeks and 12-weeks of traffic applications (Tables 9 and 10).
Analysis of Clegg hammer data showed significance on only one rating day in 2011. Although
significant, the blends did not out perform all of the associated varieties in monostands.
Furthermore, after 6-weeks and 12-weeks of simulated traffic, there were no difference between
the blends and the associated varieties.

39

CONCLUSIONS
Topdressing provides numerous advantages to a turfgrass stand including wear tolerance,
resistance to compaction, increased infiltration and surface drainage, and overall turfgrass cover
(Kowalewski et al, 2011; Vavrek, 1993; Miller, 2008). Although the studies cannot be compared,
the topdressing did provide higher turfgrass ground cover percentages, turfgrass quality, and a
reduction in surface hardness than the native soil alone. Similar to the native soil, a consistent
occurrence following 6-week and 12-week traffic applications emerged. The blends did not
outperform the monostands of the associated varieties of the blends in percent turfgrass ground
cover, turfgrass quality, and surface strength characteristics. In fact, after 12-weeks of traffic
applications, the variety ‘Bar VV 0709’ had significantly higher percent turfgrass ground cover,
turfgrass quality, and resistance to pivoting than the blend containing ‘Barrister’, ‘Bar VV 0709’,
and ‘Barrari’. The variety ‘Barrister’ had drastic reduction in percent turfgrass ground cover and
turfgrass quality after the 6-weeks of traffic applications, which may have had a direct effect on
the performance of the blend. In addition, ‘Prosperity’ had a lower percent turfgrass ground
cover and quality after 12-weeks of traffic in 2010 and both ‘Prosperity’ and ‘Kenblue’ had
significantly less percent turfgrass cover in 2011. Since ‘Barrister’ was also included in the blend
with ‘Kenblue’, and the resulting ‘Kenblue’ did not affect the blend including ‘Midnight’,
‘Barrister’, and ‘Kenblue’ then suggesting ‘Barrister’ had a direct affect on the blend including
‘Barrister’, ‘Bar VV 0709’, and ‘Barrari’ seems accurate, although the reduction in performance
of ‘Barrister’ and ‘Kenblue’ happened in separate years. If anything this should suggest the
importance of using a blend: the ability of one variety covering for another seems inevitable.
With this being said, using a monostand of a high performing improved variety does show
advantages.

40

REFERENCES

41

REFERENCES
ASTM International. 2006. Standard practice for classification of soils for engineering purposes
(unified soil classification system). ASTM International. ASTM International, West
Conshohocken, PA. 2487-06:1-11
Bingaman, D.E. and H. Kohnke. 1970. Evaluating Sand for Athletic Turf. Agronomy Journal.
62:464–467.
Carrow, R. N. and A. N. Petrovic. 1992. In: Waddington, D. V., Carrow, R. N., and Shearman,
R. C., eds. Turfgrass. 32. Madison, WI: ASA, CSSA, & SSSA. P. 285-325.
Cockerham, S. T., V. A. Gibeault, J. Van Dam, and M. K. Leonard. 1990. Tolerance of several
coolseason turf grasses to simulated sports traffic. In R. C. Schmidt, E. F. Hoerner, E. M. Milner
and C. A. Morehouse (eds.). Natural and Artificial Playing Fields: Characteristics and Safety
Features. ASTM STP 1073. American Society for Testing and Materials. Philadelphia, PA. P.
85-89.
Henderson, J.J., J.R. Crum, T.F. Wolf, and J.N. Rogers. 2005. Effects of Particle Size
Distribution and Water Content at Compaction on Saturated Hydraulic Conductivity and
Strength of High Sand Content Root Zone Materials. Soil Science. 170: 315–324.
Kowalewski, A. R., J. N. Rogers III, J. R. Crum, J. C. Dunne. 2010. Sand Topdressing
Applications Improve Shear Strength and Turfgrass Density on Trafficked Athletic Fields. Hort
Technology. October. 20(5): 867-872.
Kowalewski, A.R., J. R. Crum, J. N. Rogers III, J. C. Dunne. 2011. Improving Native Soil
Athletic Fields with Intercept Drain Tile Installation and Subsequent Sand Topdressing
Applications. Soil Science. March. 176(3): 143-149.
Miller, G. L. 2008. An Evaluation of Crumb Rubber and Calcined Clay for Topdressing Sports
Fields. Acta Horticulturae (ISHS). 783:381-390.
NTEP. 2009. A guide to NTEP turfgrass ratings. Retrieved Aug 20, 2009.
(http://www.ntep.org/reports/ratings.htm)
Samaranayake, H., T. J. Lawson, and J. A. Murphy. 2008. Traffic Stress Effects on Bentgrass
Putting Green and Fairway Turf. Crop Science. 48(3): 1193-1202.
Vanini, J.T., J.J. Henderson, J.C. Sorochan, and J.N. Rogers, III. 2007. Evaluating Traffic Stress
by the Brinkman Traffic Simulator and Cady Traffic Simulator on a Kentucky Bluegrass Stand.
Crop Science. 47:780–784.
Vavrek Jr., Robert C. A Successful Topdressing Program Requires Consistency,
Commitment and Communication. USGA Green Section Record. May, 1993.

42

Chapter Three: Evaluation of Sclerotinia homoeocarpa (Dollar Spot )Pressure on Kentucky
Bluegrass Varieties in Monostands and Blends
INTRODUCTION
One of the purposes of planting a blend instead of a single cultivar in an athletic field
setting is to protect against a major disease causing severe deterioration of the entire turf stand
(Vargas et al., 1980). Traditionally, a blend of two or more improved Kentucky bluegrass
cultivars was necessary to prevent diseases such as melting out, and stripe smut from completely
desiccating a stand. But improved varieties, with multiple disease resistance, may suggest
otherwise. Turfgrass’ have two types of resistance, specific (vertical) and generalized
(horizontal). Specific resistance is characterized by a variety having resistance to a specific race
of the pathogen and is associated with pathogens lacking a sexual reproductive stage.
Generalized resistance is characterized by a variety having resistance to all existing races for a
particular pathogen and is not limited by sexual or asexual reproduction, which provides durable
resistance (Vargas, 2005). Common Kentucky bluegrass was severely susceptible to melting out.
The identification and development of Merion Kentucky bluegrass is a traditional example of
horizontal resistance because Merion maintained resistance across all races for nearly 50 years
(Vargas, 2005). Although Merion has generalized resistance against melting out, it does not
have resistance against stripe smut, a variety specific disease (Vargas et al, 1980). Therefore,
breeding efforts have strived to incorporate specific resistance genes, most likely pyramided, to
maintain resistance. However, as more and more Kentucky bluegrass cultivars are breed for
resistance to these particular diseases, other diseases, such as Ophinosphaerlla korrae (necrotic
ring spot), Magnaporthe poae (summer patch), and Sclerotinia homoeocarpa (dollar spot),
become prevalent, suggesting that blends may still be necessary for broad-spectrum disease
resistance.

43

Dollar spot, caused by Sclerotinia homoeocarpa, is a fungal pathogen that has been
gaining momentum in recent years. The disease is characterized by necrotic lesions on turfgrass
leaf blades and result in sunken areas in the turf ranging from the size of a quarter to the size of a
silver dollar (Vargas, 2005). Individual spots may coalesce and destroy the turf in large, distinct
areas (Vargas, 2005). Mainly transplanting mycelium of an infected area by mowers and other
maintenance equipment can help circulate the pathogen and dollar spot can become prevalent
across an entire turf stand, if the appropriate management is not taken. Presumably, blends
provide greater disease resistance than monostands and recent data suggests that this can be the
case across several turfgrass species. Golembiewski et al. (2001) suggested planting Crenshaw
and Penncross together, a 50:50 blend by weight, provided a reduction of dollar spot incidence
and the development of the disease than the susceptible variety (Crenshaw) alone. Green and
Burpee (1997), showed there was a decrease in the progression of Rhizoctonia blight, caused by
Rhizoctonia solani Kuhn, on blends of tall fescue (Festuca arundinecea Schreb.) when
proportions of the resistant varieties were increased. Furthermore, Vargas and Turgeon (1980)
reported intermediate resistance of blends of ‘Merion’ and common-type Kentucky bluegrass to
melting-out (Drechslera poae Drech.) and Fusarium blight (Fusarium roseum). Abernathy et al.
(2001) showed that two- and three-way blends of ‘Penn A-4’, ‘Crenshaw’, ‘L-93’, ‘Mariner’,
and ‘Penncross’ creeping bentgrass, when compared to monostands, indicated that the level of
activity of dollar spot was a compromise between resistance levels of individual cultivars. All of
these suggest that there is an improved sense of resistance associated with using a blend;
however, the resistance is shown only when being compared to the susceptible variety alone. The
advancements in breeding, traditional and molecular, since the introduction of ‘Merion’
Kentucky bluegrass as the first cultivated variety have been integral in producing the vast

44

majority of varieties that include a wide-range of disease resistances. The prevalence of the
dollar spot disease on athletic fields is potentially reduced by recurring traffic; therefore,
selecting varieties with resistance to diseases common to the location will provide relevance to
using monostands instead of blends.

45

MATERIALS AND METHODS
The study was initiated on 15 September 2009 at the Hancock Turfgrass Research Center
at Michigan State University in East Lansing, MI, USA. Kentucky bluegrass varieties with
2

known resistance and susceptibility were selected (NTEP 2009) Plots, 4.64-m in size, of the
Kentucky bluegrass (Poa pratensis L.) varieties and blends (Table 11) were established from seed
on 25 September 2009 on a Colwood-Brookston Loam/Aubbeenaubee Capac Sandy Loam
(NRCS, 2009). Lebanon Country Club 13-25-12 Starter fertilizer (Lebanon Seaboard Corp.,
-2

-2

Lebanon PA) was applied at a rate of 4.88-g P m . Each plot was seeded at a rate of 7.32-g m .
Prior to covering the experimental area with a 95% light transmitted germination and insect
AgroFabric (A.M. Leonard, Piqua, OH), one application of mesotrione (Tenacity)(Syngenta,
-2

Wilmington, DE) at a rate of 0.043-ml m was applied to prevent broadleaf weeds and annual
bluegrass germination.
An irrigation program was developed for the germination process of the experimental
-1

area providing 0.508-cm day and was reduced to an as needed basis following the removal of
the germination AgroFabric on 7 October 2009. The germination AgroFabric provided an
adequate 12-day germination period for all treatments. A second starter fertilizer application was
-2

applied on 11 October 2009 applied at a rate of 4.88-g P m with a supplemental application of
-2

46-0-0 Urea (The Andersons, Inc., Maumee, Ohio) at a rate of 2.44-g N m . In 2010,
-2

applications of 46-0-0 Urea (The Andersons, Inc., Maumee, Ohio) at a rate of 2.44-g N m and
42-0-0 Polyon

46

-2

-2

(Harrell’s, Lakeland, Florida) at a rate of 4.88 g N m were applied accumulating 14.6 g N m
for the year. In 2011, fertility followed the application program developed and used in the
previous year. The experimental area was inoculated with a sand-cornmeal based inoculum of

Sclerotinia homoeoecarpa vegetative compatibility group (VCG)-B (Table 11) on 17 June 2010
and again on 7 July 2011. Fertilizer applications were halted following the inoculation of the
experimental area to encourage disease development and persistence on nutrient deprived turf.
Irrigation was also stopped to further influence dollar spot disease incidence.
Weekly ratings of visual assessment for quality, dollar spot lesion counts, and percent
dollar spot infected area were collected beginning 19 July 2010 and 25 July 2011. Turfgrass
quality were rated using a 1-9 scale, with 1 being inferior, 9 being superior and 6 being
acceptable (NTEP, 2009). Dollar spot infection centers were counted individually and percent
dollar spot infected area was assessed visually.
The study was analyzed as a Completely Randomized Design (CRD) with three
replications. A single factor [Varieties (Table 11)] included 14 total treatments and were
examined using Proc UNIVARIATE procedure to test the normality of homogeneity of variances
and residuals. Means separations were determined from selected analysis of Fisher’s least
significant difference at a 0.05 level of probability.
In 2010, a second study to examine the effects of dollar spot on the same treatments
(Table 11) was established on 15.24-cm of a well-graded, high-sand-content root-zone mix
[90.0% sand, 7.0% silt, and 3.0% clay (ASTM 2006, Henderson et al. 2005)]. The study was
initiated on 29 September 2010 and adhered to the same protocol for establishment as the
previous study. As with the previous study, prior to covering the experimental area with a 95%
light transmitted germination and insect AgroFabric (A.M. Leonard, Piqua, OH), one application

47

-2

of mesotrione (Tenacity)(Syngenta, Wilmington, DE) at a rate of 1.9-ml m was applied to
prevent broadleaf weeds and annual bluegrass germination. Weekly ratings of visual assessment
for quality, dollar spot lesion counts, and percent dollar spot infected area were collected
beginning 25 July 2011 following the inoculation on 7 July 2011. Turfgrass quality were rated
using a 1-9 scale, with 1 being inferior, 9 being superior and 6 being acceptable (NTEP, 2009).
Dollar spot infection centers were counted individually and percent dollar spot infected area was
assessed visually. The study was analyzed as a Randomized Complete Block Design (CRD)
with three replications. The single factor was examined using Proc UNIVARIATE procedure to
test the normality of homogeneity of variances and residuals. Means separations were
determined from selected analysis of Fisher’s least significant difference at a 0.05 level of
probability.

48

Table 11. List of treatments for
Kentucky bluegrass monostands and
blends under dollar spot pressure
Treatments
Barrister [B]
Midnight [T]
North Star [S1]
Barrari [S2]
B+T
B + S1
B + S2
T + S1
T + S2
B + T + S1
B + T + S2
B + S1 + S2
T + S1 + S2
B + T + S1 + S2

49

RESULTS AND DISCUSSION
Quality
Following inoculation of the study, all treatments (Table 11) were evaluated for turfgrass
quality across 7 rating dates. Analysis of turfgrass quality revealed significant differences among
the treatment means 2 times, 21 Aug and 6 September 2010. Mean comparisons on 6 September
2010 show the resistant varieties, ‘Barrister’ and ‘Midnight’ having greater turfgrass quality than
the susceptible varieties, ‘North Star’ and ‘Barrari’; however, ‘Midnight’ was significantly better
in quality than ‘Barrister’ and the susceptible varieties (Table 12). Of the blends that were
created, the blend of the two resistant varieties (B + T) and the blend of the two resistant
varieties with ‘North Star’ (B + T + S1) were significantly greater than the resistant variety
‘Barrister’ but no differences between these blends and the resistant variety ‘Midnight’. Two Poa
annua (annual bluegrass) ratings were taken 17 May and 11 June 2010. Although not significant
among treatments, the ‘Barrister’ treatment had a greater percent Poa annua than all other
treatments for both rating dates. The resistant variety ‘Midnight’ was significantly greater in
turfgrass quality than 80% of the blends created. In 2011, analysis for turfgrass quality produced
significance 2-times, on 7 September and 18 September. Mean separation on 18 September 2011
showed the resistant varieties ‘Barrister’ and ‘Midnight’ statistically greater in turfgrass quality
than the susceptible varieties ‘North Star’ and ‘Barrari’ (Table 13). The resistant variety
‘Barrister’ was statistically greater than only one blend composed of ‘Barrister’ and the
susceptible variety ‘Barrari’ (B + S2). The resistant variety ‘Midnight’ was statistically greater in
turfgrass quality than 3 of the created blends, ‘Barrister’ and ‘Barrari’ (B + S2), ‘Barrister’,
‘Midnight’ and ‘North Star’ (B + T + S1), and ‘Midnight’, ‘North Star’ and ‘Barrari’ (T + S1 +

50

Table 12. Mean separation of Kentucky bluegrass monostands and blends for quality, dollar spot
infection centers, and percent dollar spot infected turfgrass cover on 6 September 2010 at HTRC,
East Lansing, MI
Percent Dollar Spot
Dollar Spot Infection
Treatments
Quality†
Infected Turfgrass
Centers
Cover
Barrister [B]
7.3
48.0
8.3
Midnight [T]
8.0
33.0
6.0
North Star [S1]
7.0
85.0
14.0
Barrari [S2]
7.0
78.0
12.0
B+T
8.0
31.0
5.0
B + S1
7.0
53.0
9.3
B + S2
7.3
40.0
9.0
T + S1
7.3
56.0
9.0
T + S2
7.0
69.0
11.3
B + T + S1
8.0
38.0
6.5
B + T + S2
7.3
39.0
5.7
B + S1 + S2
7.0
80.0
13.5
T + S1 + S2
7.0
72.0
12.7
B + T + S1 + S2
7.3
68.0
11.0
LSD (0.05)
0.6
31.4
5.5
† Quality: 1= Poor, 5 = Acceptable, and 9 = Excellent

51

Table 13. Mean separation of Kentucky bluegrass monostands and blends for quality, dollar spot
infection centers, and percent dollar spot infected turfgrass cover on 18 September 2011 at
HTRC, East Lansing, MI
Percent Dollar Spot
Dollar Spot Infection
Treatments
Quality†
Infected Turfgrass
Centers
Cover
Barrister [B]
8.0
25.3
3.0
Midnight [T]
8.3
24.7
3.7
North Star [S1]
7.0
62.0
10.3
Barrari [S2]
6.7
86.0
13.7
B+T
8.0
34.0
4.3
B + S1
8.3
26.0
3.7
B + S2
7.3
67.3
9.7
T + S1
8.0
37.0
4.7
T + S2
8.0
35.0
4.7
B + T + S1
8.0
40.3
5.7
B + T + S2
7.7
29.0
3.7
B + S1 + S2
8.0
34.3
5.3
T + S1 + S2
7.7
33.7
5.0
B + T + S1 + S2
8.0
39.7
5.3
LSD (0.05)
0.6
24.7
3.8
† Quality: 1= Poor, 5 = Acceptable, and 9 = Excellent

52

Table 14. Mean separation of Kentucky bluegrass monostands and blends for quality, dollar spot
infection centers, and percent dollar spot infected turfgrass cover on high, sand-based rootzone
on 15 September 2011, at HTRC, East Lansing, MI
Percent Dollar Spot
Dollar Spot Infection
Treatments
Quality†
Infected Turfgrass
Centers
Cover
Barrister [B]
8.0
14.0
3.0
Midnight [T]
8.0
10.0
1.7
North Star [S1]
6.7
44.0
8.0
Barrari [S2]
6.7
49.0
9.3
B+T
8.0
8.0
1.7
B + S1
7.3
16.0
3.0
B + S2
7.0
40.0
7.7
T + S1
7.0
34.0
5.7
T + S2
8.0
17.0
2.7
B + T + S1
7.7
28.3
5.0
B + T + S2
8.0
24.7
4.0
B + S1 + S2
7.3
32.0
5.3
T + S1 + S2
7.7
27.3
4.7
B + T + S1 + S2
7.7
25.0
4.7
LSD (0.05)
1.0
15.3
3.5
† Quality: 1= Poor, 5 = Acceptable, and 9 = Excellent

53

S2). Also in 2011, analysis for the replicated study on 6-inches of high, sand-based rootzone mix
produced significance among 3 of the rating dates, 18 August, 30 August, and 15 September
2011. Again, mean separation on 15 September 2011 showed both of the resistant varieties
having greater turfgrass quality than the two susceptible varieties (Table 14). In this instance, the
two resistant varieties were greater in turfgrass quality than two blends, ‘Barrister’ and ‘Barrari’
(B + S2), and ‘Midnight’ and ‘North Star’ (T + S1). In all years and studies, the top-performing
blend was consistently the blend of the two resistant varieties.

Dollar Spot Infection Centers
Similar to turfgrass quality, counts for dollar spot infection centers per plot were recorded
following the inoculation of the study. In 2010, analysis of the dollar spot infection centers count
was significant on only one of the rating dates, 6 September 2010. Mean separation on 6
September revealed significant differences between the both resistant varieties, ‘Barrister’ and
‘Midnight’ to one susceptible variety, ‘North Star’ (Table 12). Furthermore, the variety
‘Midnight’ was also statistically lower in dollar spot infection centers than the other susceptible
variety, ‘Barrari’. Of the blends that were created, ‘Barrister’ was only significantly lower in
dollar spot infection centers than one blend, ‘Barrister’, ‘North Star’, and ‘Barrari’ (B + S1 +
S2). On the other hand, ‘Midnight’ produced fewer dollar spot infection centers than 4 of the
created blends including the 4-way blend, ‘Midnight’, ‘North Star’, and ‘Barrari’ (T + S1 + S20,
‘Barrister’, ‘North Star’, and ‘Barrari’ (B + S1 + S2), and ‘Midnight’ and ‘Barrari’ (T + S2). In
2011, analysis of dollar spot infection centers produced significant ratings on 7 September and
18 September. Mean separation on 18 September 2011 showed the resistant varieties
significantly lower in infection centers when compared to the susceptible varieties (Table 13).

54

Furthermore, the resistant varieties were only statistically lower in infection centers to a single
blend created with ‘Barrister’ and ‘Barrari’ (B + S2). Also in 2011, analysis of the replicated
study on high, sand-based rootzone mix produced significant mean separation on 23 August and
15 September. Data collected on 15 September 2011 continued to show the resistant varieties
lower in dollar spot infection centers compared to the susceptible varieties in monostands (Table
14). The variety ‘Barrister’ produced significantly lower infection centers than the blend
containing ‘Midnight’ and ‘North Star’ (T + S1), the blend with ‘Barrister’ and ‘Barrari’ (B +
S2), and also the blend with ‘Barrister’, ‘North Star’, and ‘Barrari’ (B + S1 + S2). The variety
‘Midnight’ showed significantly reduced dollar spot infection centers compared to 50% of the
blends that were created.
Percent Dollar Spot Infected Turfgrass
Percentages for dollar spot infection centers per plot were recorded following the
inoculation of the study. In 2010, analysis of percent dollar spot infected turfgrass cover was
significant on three of the rating dates, 19 July, 6 September, and 17 September. Mean separation
on 6 September revealed significant differences between ‘Midnight’ and both susceptible
varieties, but ‘Barrister’ was only lower in percent dollar spot infected turfgrass cover than
‘North Star’ (Table 12). The variety ‘Barrister’ was not statistically greater in percent dollar spot
infected turfgrass cover. The blend ‘Barrister’, ‘North Star’, and ‘Barrari’ (B + S1 + S2), and the
blend ‘Midnight’, ‘North Star’, and ‘Barrari’ (T + S1 + S2), were greater in percent infected
turfgrass cover than ‘Midnight’, in monostand. In 2011, analysis of dollar spot infected turfgrass
cover produced significant ratings on 30 August, 7 September and 18 September. Mean
separation on 18 September 2011 showed the resistant varieties significantly lower in infected
turfgrass cover when compared to the susceptible varieties (Table 13). Furthermore, the resistant

55

varieties were only statistically lower in infection centers to a single blend created with
‘Barrister’ and ‘Barrari’ (B + S2). Also in 2011, analysis of the replicated study on high, sandbased rootzone mix produced significant mean separation on 23 August and 15 September. Data
collected on 15 September 2011 continued to show the resistant varieties lower in dollar spot
infected turfgrass cover compared to the susceptible varieties in monostands (Table 14). The
variety ‘Barrister’ produced significantly lower infected turfgrass cover than the blend
containing ‘Barrister’ and ‘Barrari’ (B + S2). The variety ‘Midnight’ showed significantly
reduced dollar spot infection centers compared to 30% of the blends that were created.

56

CONCLUSIONS
After reviewing the data collected across the two years of the study and also
incorporating the replicated study on high, sand-based rootzone mix, evidence suggests that the
blends, in most cases, were amid the ratings for the resistant varieties, ‘Barrister’ and ‘Midnight’,
and the susceptible varieties, ‘North Star’ and ‘Barrari’. The blends that did not necessarily
follow suit included ‘Barrister’, ‘Midnight’, and ‘North Star’ (B + T + S1), ‘Barrister’,
‘Midnight’, and ‘Barrari’ (B + T + S2), and also the blend of the two resistant varieties together,
were among the top-performing blends, consistently. Blends including higher percentages of the
susceptible varieties often exhibited higher dollar spot infection centers, percent infected
turfgrass cover, and in turn, lower turfgrass quality. These findings were congruent with the
original findings of blend construction by Vargas and Turgeon (1980) that showed lower disease
ratings for melting out, Fusarium blight, and stripe smut when including a resistant and
susceptible variety together compared to the susceptible variety in a monostand. Furthermore, by
planting resistant varieties in monostands, the ability of inoculum to build-up and eventually
reduce the efficacy of the resistant variety to oppose Sclerotinia homoeocarpa pathogenicity is
not present because susceptible varieties are not included. Therefore, the incompatibility
associated with the resistant variety to the pathogen may prolong life of the turf stand. Since it is
not known if the dollar spot resistance in these Kentucky bluegrass varieties is specific (vertical)
or generalized (horizontal) it is difficult to know whether the resistance will last. However, based
on this study the resistance appears to be similar to generalized resistance to melting-out in
Kentucky bluegrass (Vargas 1980). If this is the case, the cultivars should retain their resistance
to dollar spot with reduced chances of a new strain of the pathogen developing that could

57

overcome the resistance. This evidence is strongly supported by the duration of dollar spot
resistance in ‘Midnight’ Kentucky bluegrass since the release of the variety decades ago.

58

REFERENCES

59

REFERENCES
Abernathy, S. D., R. H. White, P. F. Colbaugh, M. C. Engelke, G. R. Taylor II, T. C. and Hale.
2001. Dollar Spot Resistance Among Blends of Creeping Bentgrass Cultivars. Crop Science. 41:
806-809.
ASTM International. 2006. Standard practice for classification of soils for engineering purposes
(unified soil classification system). ASTM International. ASTM International, West
Conshohocken, PA. 2487-06:1-11
Golembiewski, R. C., T. K. Danneberger, and P. M. Sweeney. 2001. Lack of dollar spot
(Sclerotinia homoeocarpa F.T. Bennett) influence on changing the cultivar composition of a
stand of creeping bentgrass. International Turfgrass Society Research Journal. 9: 665-668.
Green, D.E., and L.L. Burpee. 1997. Modeling the Effects of Host Resistance on the Progress of
Rhizoctonia Blight in Tall Fescue (Festuca arundinacea Schreb.). International Turfgrass
Society Research Journal. 8:883–892.
Henderson, J.J., J.R. Crum, T.F. Wolf, and J.N. Rogers. 2005. Effects of Particle Size
Distribution and Water Content at Compaction on Saturated Hydraulic Conductivity and
Strength of High Sand Content Root Zone Materials. Soil Science. 170: 315–324.
Vargas, J. M. 2005. Management of turfgrass diseases. Hoboken, N.J: J. Wiley. P. 86-89, 181185.
Vargas, J. M. Jr., and A. J. Turgeon. 1980. Proceeding of the Third International Turfgrass
Research Conference. p. 45-52.

60

Chapter Four: Evaluation of Bispyribac-sodium (Velocity) applications on Kentucky Bluegrass
Varieties in Monostands and Blends
INTRODUCTION
Improved varieties of Kentucky bluegrass selected for Velocity tolerance may provide
field managers with another means to suppress annual bluegrass (Poa annua L.) invasion.
Because of Kentucky bluegrass’s genetic similarities to annual bluegrass, it is the most sensitive
turfgrass species to Bispyribac-sodium (Velocity) applications for annual bluegrass control.
Therefore, consecutive applications of Velocity to a blend containing one or more varieties that
are susceptible to the herbicide could be a critical error.
Although found in every continent of the world as a cultivated turfgrass for performance
turf, annual bluegrass is typically classified as a weed. Annual bluegrass can become the
dominant turf under irrigated, closely mowed, intensely fertilized turfgrass conditions which are
apparent on most golf courses and athletic fields (Beard, 1973). In the field, annual bluegrass
attracts attention because of the dissimilar light green coloration and the great contrast between
varieties of Kentucky bluegrass’ dark green appearance. The eradication of annual bluegrass
from a Kentucky bluegrass stand has proven to be a daunting task due to the adaptability of the
turfgrass. Annual bluegrass tolerates compacted soils, full sun, shade and close mowing heights
and also exists as biotypes ranging between short-lived annuals to long-lived perennials
(Gibeault, 1972; Slavens, 2010). These characteristics and the adaptability make annual
bluegrass extremely competitive.
Chemical controls, although limited in number, have developed to combat annual
bluegrass invasion in Kentucky bluegrass. Research by Reicher et al. (2011), studied the fall
application of mesotrione (Tenacity) on annual bluegrass control in Kentucky bluegrass.

61

Researchers showed in some of the experiments that span the 6-years of the study, that greater
than 80% control of annual bluegrass could be achieved; however, inconsistencies across all of
the studies were observed and marginal control was obtained depending on location and year.
The use of mesotrione for control of annual bluegrass in Kentucky bluegrass seems promising
but not overly impressive. The low sensitivity of Kentucky bluegrass to mesotrione makes the
herbicide intriguing. Contrary to mesotrione, ethofumesate (Prograss) has shown minimal control
-1

-1

to no control of annual bluegrass at rates ≤10.2 kg ha , and at high rates of 20.2 kg ha up to
62% control was observed (Meyer and Branham, 2006). However injury associated with
Kentucky bluegrass varied by variety. ‘Moonlight’ and ‘America’ never showed injury
associated with ethofumesate applications; However, ‘North Star’, and ‘Total Eclipse’ showed
severe damage. Like ethofumesate, Kentucky bluegrass sensitivity to Bispyribac-sodium
(Velocity) is more drastic than mesotrione (Lycan and Hart, 2005). Bispyribac-sodium, an ALS
(acetolactate synthase) inhibiting herbicide, has been used to control annual bluegrass in
creeping bentgrass putting greens (McCullough and Hart, 2008, 2010; Lycan and Hart, 2006;
Park et al. 2002). McCullough and Hart (2010) observed 90% control of annual bluegrass with
-1

acceptable creeping bentgrass discoloration after 8-weeks following 24.6 g ha regimen.
Furthermore, McCullough and Hart (2008) used spray adjuvants to increase the efficacy and
reduce the amount of Bispyribac-sodium used. Spraying with crop oil concentrate, nonionic
surfactant and methylated seed oil increased foliar absorption of bispyribac-sodium 45, 46, and
75%, respectively. Studies by Lycan and Hart (2005, 2006) assessed the severity of bispyribacsodium applications across several turfgrass species. Single applications ranging from 37 to 296
-1

g ha were applied to Kentucky bluegrass (Poa pratensis), perennial ryegrass (Lolium perenne

62

L.), tall fescue (Festuca arundinacea [L.] Schreb.), and chewings fine fescue (Festuca rubra L.
subsp. Commutata Gaud.) and evaluated for injury. Kentucky bluegrass was least tolerant to
bispyribac-sodium with up to 28% injury at the highest rate. Injury on the other species was
determined to be more chlorotic with Kentucky bluegrass experiencing severe stunting and
thinning. Kentucky bluegrass also had the most minimal, incomplete recover of the four turfgrass
species evaluated. Lycan and Hart (2006) investigated the responses of creeping bentgrass
(Agrostis palustris), annual bluegrass (Poa annua L.), Kentucky bluegrass (Poa pratensis L.), and
rough bluegrass (Poa trivialis L.) to foliar, soil, and foliar plus soil applied bispyribac-sodium
absorption and translocation. The study exhibited an intermediate absorption and translocation of
14

C-bispyribac in Kentucky bluegrass compared to creeping bentgrass (tolerant) and annual or

rough bluegrass (sensitive) contributing to the greater tolerance of creeping bentgrass to
bispyribac-sodium. This also suggests that Kentucky bluegrass shows slightly better tolerance to
bispyribac-sodium than annual bluegrass and varying tolerances among Kentucky bluegrass
varieties may attribute to using bispyribac-sodium for removal of annual bluegrass in Kentucky
bluegrass. Shortell et al. (2008) assessed 55 varieties of Kentucky bluegrass for bispyribacsodium tolerance. Injury during the two year evaluation of the varieties showed injury ranging
between 8% and 93% 8 weeks following the initial treatment. Shortell et al. (2008) indicates the
potential for the development of varieties with improved bispyribac-sodium tolerance.

63

MATERIALS AND METHODS
The study was initiated on 15 September 2009 at the Hancock Turfgrass Research Center
at Michigan State University in East Lansing, MI, USA. Kentucky bluegrass varieties were
2

selected based on sensitivity to Bispyribac-sodium applications. Plots, 4.64-m in size, of the
Kentucky bluegrass (Poa pratensis L.) varieties and blends (Table 15) were established from seed
on 25 September 2009 on a Colwood-Brookston Loam/Aubbeenaubee Capac Sandy Loam
(NRCS, 2009). Lebanon Country Club 13-25-12 Starter fertilizer (Lebanon Seaboard Corp.,
-2

-2

Lebanon PA) was applied at a rate of 4.88-g P m . Each plot was seeded at a rate of 7.32-g m .
Prior to covering the experimental area with a 95% light transmitted germination and insect
AgroFabric (A.M. Leonard, Piqua, OH), one application of mesotrione (Tenacity)(Syngenta,
-2

Wilmington, DE) at a rate of 1.9-ml m was applied to prevent broadleaf weeds and annual
bluegrass germination.
An irrigation program was developed for the germination process of the experimental
-1

area providing 0.508-cm day and was reduced to an as needed basis following the removal of
the germination AgroFabric on 7 October 2009. The germination AgroFabric provided an
adequate 12-day germination period for all treatments, except treatments including ‘Barzan’ as
previously noted in experiments 1 and 2 (Table 15). A second starter fertilizer application was
-2

applied on 11 October 2009 applied at a rate of 4.88-g P m with a supplemental application of
-2

46-0-0 Urea (The Andersons, Inc., Maumee, Ohio) at a rate of 2.44-g N m . In 2010,
-2

applications of 46-0-0 Urea (The Andersons, Inc., Maumee, Ohio) at a rate of 2.44-g N m and

64

-2

42-0-0 Polyon (Harrell’s, Lakeland, Florida) at a rate of 4.88 g N m were applied cumulating
-2

19.5-g N m for the year. Four applications of Bispyribac-sodium [17 DG Formulation (Valent,
-1

inc. Walnut Creek, CA) at a rate of 37.1 g ha were applied over a two-week period beginning
15 June 2010.
Weekly ratings of visual assessment for quality and percent blighted tissue were collected
beginning on the initial application date, 15 June 2010. Turfgrass quality were rated using a 1-9
scale, with 1 being inferior, 9 being superior and 6 being acceptable (NTEP, 2009). Percent
blighted tissue was assessed visually as a percent of injured turf over the plot area. Also,
Normalized Difference Vegetation Index (NDVI) ratings were taken weekly with the Field Scout
TCM 500 turf color meter (Spectrum Technologies, Inc. Plainfield, IL).
The study was analyzed as a Completely Randomized Design (CRD) with three
replications. A single factor [Varieties (Table 15)] included 14 total treatments and 42 total plots
were examined using Proc UNIVARIATE procedure to test the normality of homogeneity of
variances and residuals. Due to the exclusion of treatments including ‘Barzan’, contrasts for
mean separation were obtained using Proc MIXED of the remaining treatments.
In 2010, a second study to examine the effects of Bispyribac-sodium on the same
treatments (Figure 15), were established on 15.24-cm of a well-graded, high-sand-content rootzone mix [90.0% sand, 7.0% silt, and 3.0% clay (ASTM 2006, Henderson et al. 2005)]. The
study was initiated on 29 September 2010 and adhered to the same protocol for establishment as
2

the previous study. Plot sizes were reduced to 1.67-m . The variety ‘Barzan’ was replaced with
‘Barrister’ and also included in all blends associated with ‘Barzan’. Weekly ratings of visual
assessment for quality and percent blighted tissue were collected beginning on the initial

65

Table 15. List of treatments for Kentucky bluegrass monostands and blends under bispyribacsodium stress
Treatments (2010)
Treatments (2011)
Barzan [B]
Barrister [B]
Moonshine [T]
Moonshine [T]
North Star [S1]
North Star [S1]
Avalanche [S2]
Avalanche [S2]
B+T
B+T
B + S1
B + S1
B + S2
B + S2
T + S1
T + S1
T + S2
T + S2
B + T + S1
B + T + S1
B + T + S2
B + T + S2
B + S1 + S2
B + S1 + S2
T + S1 + S2
T + S1 + S2
B + T + S1 + S2
B + T + S1 + S2

66

application date. Again, four applications of Bispyribac-sodium [17 DG Formulation (Valent,
-1

inc. Walnut Creek, CA) at a rate of 37.1 g ha were applied over a two-week period beginning
30 August 2011. Turfgrass quality were rated using a 1-9 scale, with 1 being inferior, 9 being
superior and 6 being acceptable (NTEP, 2009). Percent blighted tissue was assessed visually as a
percent of injured turf over the plot area. Also, Normalized Difference Vegetation Index (NDVI)
ratings were taken weekly with the Field Scout TCM 500 turf color meter (Spectrum
Technologies, Inc. Plainfield, IL). The study was analyzed as a Randomized Complete Block
Design (CRD) with three replications. The single factor was examined using Proc
UNIVARIATE procedure to test the normality of homogeneity of variances and residuals.
Means separations were determined using Proc GLM from selected analysis of Fisher’s least
significant difference at a 0.05 level of probability.

67

RESULTS AND DISCUSSION
Quality
Following the initial applications of bispyribac-sodium on 15 June 2010 and 30 August
2011, weekly ratings were taken on turfgrass quality. In 2010, analysis of treatment means
produced significance 6 times occurring on 29 June, 2 July, 6 July, 12 July, 19 July and 23 July.
However, only 5 treatments were analyzed due to an unanticipated poor germination of the
variety ‘Barzan’. Therefore, all treatments including the variety ‘Barzan’ were not included in
the analysis of 2010 rating dates. Mean separation on 12 July showed drastic differences between
the remaining bispyribac-sodium tolerant variety ‘Moonshine’, the sensitive varieties ‘North
Star’ and ‘Avalanche’ and the blends created between the three varieties (Table 16). The variety
‘Moonshine’ showed the highest quality rating and was statistically greater than all other
treatments. Of the sensitive varieties ‘North Star’ was statistically greater than ‘Avalanche’ in
monostands. Of the blends that were created between the three varieties, all were statistically
greater in quality than ‘Avalanche’ alone and no differences were observed between the blends
and ‘North Star’. The top-performing blend included ‘Moonshine’ and ‘North Star’ (T + S1),
which was an expected result. Analysis in 2011, after the study was replicated on high, sandbased rootzone mix and ‘Barzan’ replaced with ‘Barrister’ as a bispyribac-sodium tolerant
variety, treatment means revealed significance on only one of the rating dates occurring on 21
September. Mean separation on 21 September produced significant differences between the
tolerant varieties ‘Barrister’ and ‘Moonshine’ and the sensitive varieties ‘North Star’ and
‘Avalanche’ (Table 17). Furthermore, both tolerant varieties were greater in turfgrass quality
than all blends except the four-way blend.

68

Table 16. Mean separation of Kentucky bluegrass monostands and blends for quality,
Normalized Difference Vegetation Index and percent blighted tissue under bispyribac-sodium
stress on 12 July 2010 at HTRC, East Lansing, MI
Normalized
Percent Blighted
Treatments
Quality†
Difference Vegetation
Tissue
Index
Midnight [T]
8.0
0.697
3.0
North Star [S1]
6.0
0.656
21.0
Barrari [S2]
5.0
0.607
36.7
T + S1
7.0
0.689
10.0
T + S2
6.0
0.667
16.7
T + S1 + S2
5.7
0.656
15.7
LSD (0.05)
0.4
0.050
9.9
† Quality: 1= Poor, 5 = Acceptable, and 9 = Excellent

69

Table 17. Mean separation of Kentucky bluegrass monostands and blends for quality,
Normalized Difference Vegetation Index and percent blighted tissue under bispyribac-sodium
stress on 21 September 2011 at HTRC, East Lansing, MI
Normalized
Percent Blighted
Treatments
Quality†
Difference Vegetation
Tissue
Index
Barrister [B]
8.3
0.700
4.0
Moonshine [T]
8.3
0.686
3.0
North Star [S1]
5.3
0.611
31.7
Avalanche [S2]
5.3
0.630
26.6
B+T
7.7
0.666
6.7
B + S1
7.0
0.668
11.7
B + S2
7.0
0.667
12.7
T + S1
6.3
0.650
18.3
T + S2
7.0
0.638
16.0
B + T + S1
7.3
0.673
9.3
B + T + S2
7.0
0.653
8.3
B + S1 + S2
6.3
0.650
17.3
T + S1 + S2
6.3
0.640
19.3
B + T + S1 + S2
7.3
0.674
9.0
LSD (0.05)
1.3
0.031
12.5
† Quality: 1= Poor, 5 = Acceptable, and 9 = Excellent

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Normalized Difference Vegetation Index
Following the initial applications of bispyribac-sodium on 15 June 2010 and 30 August
2011, weekly ratings were taken on Normalized Difference Vegetation Index (NDVI). In 2010,
analysis of treatment means produced significance 5 times occurring on 29 June, 2 July, 6 July,
12 July and 19 July. However, only 5 treatments were analyzed due to an unanticipated poor
germination of the variety ‘Barzan’. On 12 July 2010, the tolerant variety ‘Moonshine’ was only
statistically greater in NDVI compared to the sensitive variety ‘Avalanche’. Additionally, there
were no differences between ‘Moonshine’ and the created blends; however, the 3-way blend was
not statistically different than the sensitive variety ‘Avalanche’ (Table 16). In 2011, analysis of
the treatment means from the replicated study on high, sand-based rootzone mix with ‘Barzan’
replaced with ‘Barrister’ as a bispyribac-sodium tolerant variety provided significance on 2 of
the ratings dates, happening on 15 September and 21 September. Treatment means on 21
September showed the tolerant varieties having higher NDVI ratings than the sensitive varieties
(Table 17). The varieties ‘Barrister’ and ‘Moonshine’ in monostands showed higher NDVI
ratings than 70% and 50% of the blends, respectively. ‘Moonshine’ proved to be significantly
indifferent to the ‘Barrister’ and ‘Moonshine’ (B + T) blend and ‘Barrister’ and ‘Avalanche’ (B
+ S2) Blend.
Percent Blighted Turfgrass Tissue Cover
Weekly percent blighted turfgrass tissue cover was also taken weekly following the initial
application of bispyribac-sodium on 15 June 2010 and 30 August 2011. In 2010, analysis of
treatment means for percent blighted turfgrass tissue showed significance 6 times, occurring on
29 June, 2 July, 6 July, 12 July, 19 July and 23 July. Similar to turfgrass quality and NDVI,
analysis of percent blighted turfgrass tissue cover excluded all treatments including the variety

71

‘Barzan’. Mean separation of percent blighted turfgrass tissue cover yielded significant
differences between the tolerant variety ‘Moonshine’ and the sensitive varieties ‘North Star’ and
‘Avalanche’ (Table 16). Furthermore, ‘Avalanche’ had significantly greater percent blighted
tissue cover compared to ‘North Star’. When measured against the created blends, ‘Moonshine’
was statistically lower in percent blighted turfgrass tissue cover than the blend ‘Moonshine’ and
‘Avalanche’ (T + S2) and the 3-way blend but not the blend ‘Moonshine’ and ‘North Star’. This
is justified by the decrease in percent blighted tissue cover of the variety ‘North Star’ from
‘Avalanche’ in monostands. In 2011, analysis of percent blighted turfgrass tissue cover exposed
only one rating date with significance among treatment means on 21 September. To reiterate,
changes were made between 2010 and 2011 to the study to include ‘Barrister’ instead of
‘Barzan’ and was established on high, sand-based rootzone mix. On 21 September 2011, the
trend continued with both tolerant varieties having a significant reduction in percent blighted
tissue cover when compared to the sensitive varieties in monostands (Table 17). The variety
‘Barrister’ produced lower percentages of blighted tissue cover than the blend containing
‘Moonshine’ and ‘North Star’ (T + S1), the blend with ‘Barrister’, ‘North Star’ and, ‘Avalanche’
(B + S1 + S2), and the blend including ‘Moonshine’, ‘North Star’, and ‘Avalanche’ (T + S1 +
S2). In addition to these blends, the variety ‘Moonshine’ provided lower percent blighted tissue
cover compared to the blend ‘Moonshine’ and ‘Avalanche’ (T + S2), also.

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CONCLUSIONS
With bispyribac-sodium providing another means for Poa annua (annual bluegrass)
suppression, varieties that are tolerant to the herbicide will provide a weed free field. Research
by Shortell et al. (2008) has provided ranges in sensitivities of Kentucky bluegrass varieties to
bispyribac-sodium applications. The inclusion of one or more of the varieties least tolerant to
consecutive applications of bispyribac-sodium may prove detrimental as shown by this research.
Although changes from the 2010 to the 2011 in design and set-up may have changed the study
entirely, strong evidence regarding the plausibility of using monostands or blends of all tolerant
varieties for continual applications of bispyribac-sodium are conclusive. In both years of the
study, regardless if on native soil or a high, sand-based rootzone mix, the tolerant varieties were
higher in turfgrass quality and NDVI and lower in percent blighted tissue cover than the sensitive
varieties in monostand. In addition, ‘Moonshine’ and ‘Barrister’, although not always significant,
were higher in turfgrass quality and NDVI and lower in percent blighted tissue cover than all
blends that were created. Similar to the dollar spot, the blends that were created were always
intermediate in turfgrass quality, NDVI and percent blighted tissue cover as compared to the
tolerant and sensitive varieties in monostands. Furthermore, differences in turfgrass quality,
NDVI and percent blighted tissue cover between the two tolerant varieties, ‘Moonshine’ and
‘Barrister’ (2011 only), and the sensitive varieties, ‘North Star’ and ‘Avalanche’, in monostands
provided a predictor for the performance of each blend. For instance, the combination of
‘Moonshine’ and ‘North Star’ (T + S1) was higher in turfgrass quality, NDVI, and lower in
percent blighted tissue cover compared to the blend between ‘Moonshine’ and ‘Avalanche’ (T +
S2), provided that ‘North Star’ was greater in performance under these ratings than ‘Avalanche’.
The same held true in 2011; however, the role of ‘Avalanche’ in blends on the sand-based

73

system was more beneficial in this year compared to ‘North Star’. Lastly, 3-way blends
consisting of higher percentages of sensitive varieties, generally had lower turfgrass quality,
NDVI ratings, and higher percent blighted tissue cover compared to all other blends, which
suggests the importance of using tolerant varieties to bispyribac-sodium if the herbicide is to be
used as a means to suppress annual bluegrass invasion in athletic field situations.

74

REFERENCES

75

REFERENCES
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(unified soil classification system). ASTM International. ASTM International, West
Conshohocken, PA. 2487-06:1-11
Beard, J. B. 1973. Turfgrass: Science and culture. Prentice-Hall, Inc., Englewood Cliffs,
N.J. P. 166-175, 368-372.
Gibeault, V. A and N. R. Goetze. 1972. Annual Meadow-Grass. The Journal of the Sports Turf
Research Institute. 48: 9-19.
Henderson, J.J., J.R. Crum, T.F. Wolf, and J.N. Rogers. 2005. Effects of Particle Size
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Strength of High Sand Content Root Zone Materials. Soil Science. 170: 315–324.
Lycan, D. W. and S. E. Hart. 2005. Cool-Season Turfgrass Response to Bispyribac-Sodium.
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Lycan, D. W. and S. E. Hart. 2006. Foliar and root absorption and translocation of bispyribacsodium in cool-season turfgrass. Weed Technology 20(4):1015-1022.
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Ethofumesate. Weed Technology 20:1, 123-129
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(http://www.ntep.org/reports/ratings.htm)
Park, N. I., Y. Suto, Y. Miura, N. Nakatani, S. I. Iori, and M. Ogasawara. 2002. Annual
Bluegrass (Poa annua L.) Control in Bentgrass (Agrostis palustris Huds.) Green with Sequential
Applications of Bispyribac-Sodium Combined with Dinitroanilines. Weed Biology and
Management. 2:159-162.
Reicher, Z. J., D. V. Weisenberger, D. E. Morton, B. E. Branham, and W. Sharp. 2011. Fall
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Shortell, R. R., S. E. Hart, and S. A. Bonos. 2008. Response of Kentucky bluegrass cultivars and
selections to bispyribac-sodium herbicide. Hort Science. 43(7) 2252-2255.
Slavens, M. R., P. G. Johnson, and B. Bugbee. 2011. Irrigation Frequency Differentially Alters
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314-322.

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THESIS CONCLUSION
Evaluation of the Kentucky bluegrass varieties in monostands and blends under traffic,
dollar spot, and bispyribac-sodium stress has presented plausibility of using monostands of
improved varieties to replace blends. In both traffic studies, results suggest that using varieties
with increased traffic tolerance, recuperative potential, and aggressiveness showed, in some
cases, to have increases in percent ground cover, quality, and surface strength characteristics
compared to a blend where the variety was included (‘Bar VV 0709’). Likewise, monostands of
resistant varieties under dollar spot and bispyribac-sodium stress provided an increase in
turfgrass quality, a reduction in dollar spot infection centers, and a reduction in percent blighted
turfgrass tissue when compared to blends created from resistant and susceptible varieties.
Having said this, the use of these improved varieties in monostands may be limited to highly
maintained turfgrass stands. The safety blanket associated with diversity of disease resistances
and growth characteristics among Kentucky bluegrass varieties in a blend may allow low
maintenance municipalities to maintain turfgrass cover and quality without the potential threat of
complete decimation by a variety specific disease, like stripe smut. Furthermore, a blend
consisting of varieties tolerant to bispyribac-sodium will still provide field managers a means to
suppress annual bluegrass.
The evolution of monostands has already begun. Now and in the immediate future, the
use of herbicide tolerant varieties of turfgrass species, particularly glyphosate tolerant, will
require monostands. Nandula et al. (2008) began screening varieties of Italian ryegrass (Lolium
multiflorum) populations for glyphosate tolerances. In their investigations, varieties ‘Tribbett’
and ‘Fratesi’ showed a threefold increase based on dose required to cause a 50% reduction in
plant growth when compared to a glyphosate susceptible variety, ‘Elizabeth’. Hart et al. (2005),

77

through a recurrent selection-breeding program, identified glyphosate tolerance in ‘Aurora
Gold’, a variety of hard fescue. The experiment showed single rate applications of 0.6 to 0.8 kg
-1

ha could be applied to ‘Aurora Gold’ with minimal injury or stand thinning. Furthermore,
-1

multiple applications of glyphosate at 0.4 to 0.6 kg ha showed similar reduced injury. Hart
described the hard fescue variety ‘Aurora Gold’ as an ideal variety for golf course roughs,
vineyards, orchards, and landscapes and would incorporate glyphosate into a weed management
program.
Breeding programs are attempting to generate herbicide tolerance into turfgrass;
however, the use of genetically modified (GM) turfgrass could be the next breakthrough in
monostand implementation. The ecological impacts of GM turfgrasses, biosafety, gene flow and
intellectual property (IP) rights, remains a concern; in spite of this, genetic engineering for
herbicide resistance would provide complete protection from products such as glyphosate and
other herbicides for grasses (Spillane et al., 2004). The creation of glyphosate resistant creeping
bentgrass is both encouraging due to the potential in weed management programs yet imposes
negative ecological impacts. Reichman et al. (2006) showed transgene flow of transgenic
herbicide-resistant creeping bentgrass (Agrostis stolonifera L.) to compatible wild species, which
could establish and resist direct applications of glyphosate. The problem with most turfgrass
species is the ability to cross-pollinate. However, Kentucky bluegrass reproduces asexually by
apomixis. The fixed hybrid vigor and low recombination potential associated with an apomictic
plant may limit gene flow and increase potential to develop transgenic varieties for commercial
release (Spillane et al., 2004). Johnson et al. (2006) showed an overall hybrid frequency of
0.048% and hybrid frequency at 0-m distance of 0.53% of Kentucky bluegrass hybrids when
measuring pollen mediated gene flow of intra- and inter-specific turfgrass species. Johnson

78

suggests that apomixis in receptor plants and pollen competition most likely reduced the number
of hybrids; however, gene flow did occur but at low frequencies and over short distances. The
use of Kentucky bluegrass to include genetic modifications due to its asexual nature may
produce advanced hybrids with increased disease and herbicide resistances and would demand
further investigation into the potential of monostands.

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