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This is to certify that the

thesis entitled

Postemergence Crabgrass Control in
Turfgrass with Dithiopyr plus Adjuvants

presented by

Steven James Keeley

has been accepted towards fulfillment
of the requirements for

M.S. Crop & Soil Sciences

degree in

 

 

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POSTEMERGENCE CRABGRASS CONTROL IN TURFGRASS
WITH DITHIOPYR PLUS ADJUVANTS

By

Steven James Keeley

A THESIS

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

MASTER OF SCIENCE

Department of Crop and Soil Sciences

1991

55o " ~Tilk/(3

ABSTRACT

POSTEMERGENCE CRABGRASS CONTROL IN TURFGRASS
WITH DITHIOPYR PLUS ADJUVANTS

By

Steven James Keeley

Field, greenhouse, and laboratory studies were conducted
to evaluate the efficacy of dithiopyr plus adjuvants for
postemergence crabgrass control. Safety to turfgrasses was
investigated and factors involved “H1 the' adjuvants’
enhancement of dithiopyr activity were studied. Dithiopyr
effectively Controlled untillered crabgrass in the field, but
was ineffective on tillered crabgrass. The primary site of
uptake of dithiopyr was through the foliage; thus, adjuvants
were evaluated for enhancement of activity; Several adjuvants
significantly increased control of 2 to 3- and 3 to 6-tiller
crabgrass when compared with dithiopyr alone. Adjuvants
enhanced activity by increasing herbicide absorption,
translocation, spray retention, and physical placement near
the site of action. The relative importance of any factor
depended on the adjuvant used.

Chewings fescues were more susceptible to dithiopyr
injury than hard or creeping red fescues. Two consecutive
annual dithiopyr applications at 1.12 kg ai/ha did not inhibit
Kentucky bluegrass rooting. Dithiopyr at 0.42 kg ai/ha was
not phytotoxic to Kentucky bluegrass; adjuvants did not

increase phytotoxicity.

to Terri,

my best friend and journey companion

iii

ACKNOWLEDGEMENTS

Sincere appreciation is expressed to Dr. Bruce Branham
for his guidance throughout my program of study. I am
grateful to my committee members, Dr. Donald Penner, Dr. Paul
Rieke, and Dr. Matt Zabik, for their assistance with my
research and for their suggestions in the preparation of this
document.

Thanks is due to the Monsanto Agricultural Company for
their financial support of this project.

Finally, gratitude is extended to my fellow graduate

students, whose friendship has made my study enjoyable.

iv

TABLE OF CONTENTS

LIST OF TABLES ...................
LIST OF FIGURES ....................
INTRODUCTION .....................

Chapter 1: EFFICACY OF DITHIOPYR ALONE AND IN
COMBINATION WITH ADJUVANTS FOR POSTEMERGENCE
CRABGRASS CONTROL ...............
ABSTRACT ....................
INTRODUCTION ..................
MATERIALS AND METHODS .............

1989 Field Study ..............
Greenhouse Adjuvant Screens .........
1990 Field Study ..............
RESULTS AND DISCUSSION .............
1989 Field Study ..............
Greenhouse Adjuvant Screens .........
1990 Field Study ..............
LITERATURE CITED ................

Chapter 2: SAFETY OF DITHIOPYR TO FINE FESCUES AND
KENTUCKY BLUEGRASS AND OF DITHIOPYR-ADJUVANT
COMBINATIONS TO KENTUCKY BLUEGRASS .......
ABSTRACT ....................
INTRODUCTION ..................
MATERIALS AND METHODS .............

Dithiopyr Injury to Fine Fescues ......
Dithiopyr + Adjuvants Phytotoxicity to
Kentucky Bluegrass ...........
Preemergence Herbicide Effect on Rooting .
RESULTS AND DISCUSSION .............
Dithiopyr Injury to Fine Fescues ......

Dithiopyr + Adjuvants Phytotoxicity to
Kentucky Bluegrass ...........
Preemergence Herbicide Effect on Rooting .
LITERATURE CITED ................

Chapter 3: FACTORS INVOLVED IN THE ADJUVANT

ENHANCEMENT OF POSTEMERGENCE CRABGRASS CONTROL
WITH DITHIOPYR .................
ABSTRACT ....................
INTRODUCTION ..................
MATERIALS AND METHODS .............
General procedures for greenhouse
experiments ..............
Site of uptake ...............
Leaf isolation ...............
Absorption and translocation ........
Effect of temperature on 1"C-dithiopyr
absorption ...............
RESULTS AND DISCUSSION .............
Site of uptake ...............
Absorption and translocation with MON-15104 .
Absorption and translocation with MON-15151 .
Leaf isolation ...............
Effect of temperature on 1l’C-dithiopyr
absorption ...............
LITERATURE CITED ................

APPENDIX: INFORMATION ON THE CHEMICAL COMPOSITION OF

SELECTED ADJUVANTS ...............

vi

45
46
52

Chapter 1:
Table 1.

Table 2.

Table 3.

Table 4.
Table 5.

Table 6.

Table 7.

Chapter 2:
Table 1.
Table 2.

Table 3.

Table 4.

LIST OF TABLES

Effect of pre- and postemergence herbicides
on early-postemergence crabgrass control. .

Effect of pre- and postemergence herbicides
on mid-postemergence crabgrass control. .

Effect of pre- and postemergence herbicides
on late-postemergence crabgrass control.

Greenhouse adjuvant screens with dithiopyr.

Early-postemergence crabgrass control with
dithiopyr and adjuvants. ........

Mid-postemergence crabgrass control with
dithiopyr and adjuvants. . .....

Late-postemergence crabgrass control with
dithiopyr and adjuvants.

Dithiopyr injury to fine fescue varieties.

Summary of dithiopyr injury to the fine
fescue subspecies. . . . . ...... . .

Dithiopyr + adjuvants phytotoxicity to
’Midnight’ Kentucky bluegrass. ..... .

Effect of preemergence herbicides on rooting
of Kentucky bluegrass. ........ .

vii

23

24

25
26

29

3O

31

47

49

50

51

Chapter 3:
Table 1.

Table 2.

Table 3.

Table 4.

Table 5.

Table 6.

Table 7.

APPENDIX:
Table A1.

Effect of adjuvants on absorption and
translocation of 1‘C-dithiopyr (MON-15104)-

Experiment 1 .................

Effect of adjuvants on absorption and
translocation of 1"C-dithiopyr (MON-15104)-

Experiment 2 .................

Effect of adjuvants on absorption and
translocation of 1"C-dithiopyr (MON-15151)-

Experiment 3 .................

Treatment of an isolated crabgrass leaf with
dithiopyr (MON-15151) and adjuvants-

Experiment 1 .................

Treatment of an isolated crabgrass leaf with
dithiopyr (MON-15151) and adjuvants-

Experiment 2 .................

Effect of temperature on dithiopyr uptake

with adjuvants ................

Effect of temperature on non-recoverability

of dithiopyr with adjuvants. ........

Chemical composition of the ten adjuvants
used in field, laboratory, and greenhouse
experiments ................

viii

79

80

81

82

83

84

85

96

Figure 1.

Figure 2.

Figure 3.

Figure 4.

LIST OF FIGURES

Effect of site of application of dithiopyr
on large crabgrass control-- Experiment 1.

Effect of site of application of dithiopyr
on large crabgrass control-- Experiment 2.

Effect of temperature on absorption of 14C-
dithiopyr alone and in combination with
adjuvants. .........

Effect of temperature on non-recoverability

of 1"C-dithiopyr alone and in combination
with adjuvants ......

ix

86

88

9O

92

INTRODUCTION

Highly maintained turfgrass is widely recognized as a
valuable commodity. The presence of weeds in turfgrass often
interferes with the turf’s aesthetic or functional purposes.
Crabgrass (Dioitaria spp.) has been a pernicious weed in lawns
in the United States since its introduction as a forage crop
in the 19”‘century. Several species infest the United States,
but smooth crabgrass [D, ischaemum (Schreb.) Muhl.] and large
crabgrass (D. sanguinalis Scop.) are the most common. Many
new herbicides have been developed in the last three decades
in an attempt to control these weeds, yet crabgrass control
continues to be a challenging problem for turfgrass managers.

Dithiopyr [3,5-pyridinedicarbothioic acid,2-
(difluoromethyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-S,S-
dimethylester] , a new herbicide from the Monsanto Agricultural
Company, has excellent preemergence activity on crabgrass.
This product also effectively controls untillered crabgrass
when applied postemergence, but is ineffective on tillered

crabgrass. If the activity of dithiopyr on tillered crabgrass

2

could be increased, the total effectiveness of the herbicide
would be vastly improved.

Adjuvants are often used to enhance the activity of
foliar-applied herbicides; thus, if the site of uptake of
dithiopyr applied postemergence to crabgrass is via the
foliage, then adjuvants merit investigation. 'Turfgrass safety
is a concern, however, as the addition of adjuvants to a spray
solution can increase herbicidal phytotoxicity to desirable
crops.

The objectives of this research were: 1) to evaluate
the efficacy of dithiopyr for postemergence control of
crabgrass, 2) to determine whether adjuvants could be used to
enhance postemergence control, 3) to elucidate the factors
involved in adjuvants’ enhancement of dithiopyr activity, and
4) to evaluate dithiopyr and dithiopyr-adjuvant combinations

for safety on turfgrasses.

Chapter 1

EFFICACY OF DITHIOPYR ALONE AND IN COMBINATION WITH
ADJUVANTS FOR POSTEMERGENCE CRABGRASS CONTROL

ABSTRACT

Field and greenhouse studies were conducted in 1989 and
1990 to evaluate the efficacy of dithiopyr for postemergence
crabgrass control at three growth stages, and to evaluate
adjuvants for enhancement of dithiopyr activity on tillered
crabgrass. In the 1989 field study, various formulations of
dithiopyr gave excellent control of crabgrass when applied at
the 2 to 3-leaf growth stage. Control was longer lasting than
that provided by single applications of fenoxaprop, fenoxaprop
tank-mixed with preemergence herbicides, or quinchlorac. When
applied to tillered crabgrass, however, dithiopyr gave
virtually no control. In 1990, 95 adjuvants were screened in
greenhouse studies in an attempt to identify adjuvants with
high potential for enhancing dithiopyr activity on tillered
crabgrass. Nearty all adjuvants tested irI the greenhouse
increased crabgrass control when compared with dithiopyr
alone. Ten adjuvants were selected from these screens for
evaluation with dithiopyr“ in the 1990 field study. In
comparison with dithiopyr alone, several adjuvants
significantly increased crabgrass control when applied to 2 to

3-tiller or 3 to 6-tiller crabgrass. Adjuvants giving

4

consistent increases in control included Dow Corning X2-5309,
Dow Corning 6955-145, CSY-77715512, Pfizer 14636-181-7,
Activator 90, Agsco Sunit, Herbimax and X-77. Pfizer M and
Dash gave inconsistent control. No adjuvant was clearly
superior to the rest; thus, cost and availability may be the
deciding factors when selecting an adjuvant to use with
dithiopyr. Nomenclature: Dithiopyr, 3,5-
pyridinedicarbothioic acid,2-(difluoromethyl)-4-(2-
methylpropyl)-6-(trifluoromethyl)-S,S-dimethylester;
f'eric>x arar‘o p , ( :_)-2 - [II- [ (€5— Gill 0 r<)-2 -
benzoxazolyl)oxy]phenoxy]propanoic acid; quinchlorac, 3,7-

dichloro-B-quinolinecarboxylic acid; crabgrass, Digitaria spp.

Additional index words. Adjuvant screens, tank-mixes.

5
INTRODUCTION

Crabgrass is a pernicious weed in lawns, gardens and
cultivated fields throughout the temperate and tropical
regions of the world. Thirteen species infest the United
States, but large crabgrass (D, sanguinalis Scop.) and smooth
crabgrass [0, ischaemum (Screb.) Muhl.] are the most common
(12). Control of these weeds continues to be a challenging
problem for turfgrass managers; consequently, the search for
new, more effective herbicides persists.

Dithiopyr is a new preemergence herbicide from the
Monsanto Agricultural Company. This compound provides
outstanding, season-long preemergence crabgrass control at
rates of 0.28 to 0.56 kg ai/ha (1, 5, 6, 7, 8, 13, 18).
Excellent safety on Kentucky bluegrass (Poa pratensis L.),
perennial ryegrass (Lolium perenne L.), creeping bentgrass
(Agrostis palustris Huds.), and zoysiagrass (Zoysia spp.) has
been reported at rates as high as 1.1 kg ai/ha (1, 4, 8, 9).

In addition to its preemergence activity, dithiopyr
gives superior postemergence crabgrass control at 0.56 kg
ai/ha or less, if applied before the crabgrass has tillered
(1, 4, 6, 8, 9). However, control becomes increasingly more

difficult as the crabgrass matures. At the 1-3 tiller growth

6

stage, rates of 0.84 kg ai/ha or higher are required, while at
the 3 to 6-tiller stage, rates of 1.68 kg ai/ha or higher are
needed (1, 4, 7, 8, 9, 13). Even at these high rates, control
may be marginal.

Improved activity of dithiopyr on tillered crabgrass
would increase the versatility and application window of the
compound. The use of adjuvants in the spray solution is a
potential means of enhancing dithiopyr activity. McWhorter
defines adjuvants as materials that facilitate the action of
a herbicide or that facilitate or modify characteristics of
herbicide formulations or spray solutions (11). Many
researchers have reported enhanced weed control when adjuvants
were added to the spray solution (2, 3, 10, 15, 16). However,
adjuvants do not always increase herbicidal activity; in some
cases, control may even be decreased (14, 17). The
effectiveness of an adjuvant-herbicide combination depends on
the particular adjuvant and herbicide used, and the weed
species involved (15, 17, 19). Therefore, screens must be
conducted to identify the most efficacious adjuvants for each
individual weed control scenario.

The objectives of this research were threefold: 1) to
evaluate dithiopyr for postemergence crabgrass control at

various crabgrass growth stages in Michigan; 2) to identify

7

potentially effective adjuvants for use with dithiopyr in the
field, and 3) to evaluate adjuvant-herbicide combinations for

control of tillered crabgrass in the field.

8
MATERIALS AND METHODS

1 Fi l

A field study was conducted during the summer of 1989
to evaluate the efficacy of dithiopyr and other pre- and
postemergence herbicides for postemergence crabgrass control
at three different growth stages. The research site consisted
of a weedy area with a previous history of crabgrass
infestation at the Hancock Turfgrass Research Center, East
Lansing, Michigan. Glyphosate (1.1 kg ai/ha) was applied in
April of 1989 to kill existing vegetation, and the site was
overseeded with large crabgrass to supplement the natural
population of large and smooth crabgrass. The area was
fertilized with 24 kg N/ha in May. Trimec was applied at 3.5
l/ha on 6/14/89 and 8/21/89 to control broadleaf weeds. The
plots were mowed as needed to maintain the height at 5 cm.
The experimental area was not irrigated, however, rainfall was
plentiful during the application period (late May to early
July). The soil at the site was an Owosso-Marlette sandy loam
complex (Fine-loamy, mixed, mesic, Typic Hapludalfs).

A randomized complete block design was used with three
replications. Individual plots measured 1.2 m x 1.8 m.

Liquid treatments were applied with a four nozzle boom-CO2

9
backpack sprayer delivering 449 L/ha at 0.21 MPa. Granular

treatments were weighed and applied with a shaker bottle. All
early-postemergence treatments were applied at the 2 to 3-leaf
stage on 6/2/89, with the exception of the quinchlorac
treatment (1.12 kg ai/ha applied as a late preemergent on
5/23/89), and the DCPA + fenoxaprop treatment (11.8 kg ai/ha
DCPA applied as a late preemergent on 5/23/89, and 0.28 kg
ai/ha fenoxaprop appliedat the 2 to 4-tiller stage on
6/23/89). The mid-postemergence treatments were applied at
the 2 to 4-tiller stage on 6/23/89. The late-postemergence
treatments were applied at the 4 to 6-tiller stage on 7/7/89.
No rainfall occurred for at least 24 hours after the
application of all treatments.

Percent crabgrass cover was visually estimated at the
time of each treatment application and at two week intervals
following application. Data were converted to percent control
using the formula:

percent control= [(initial% - final%)/initial%]*100
Data were transformed by the arcsin transformation and the
analysis of variance and LSD multiple range test were
performed on the transformed data. Means reported are actual

percent control values.

10

r enh us Ad' v n r n

In April and May of 1990, ninety-five adjuvants were
screened in the greenhouse for enhancement of postemergence
dithiopyr activity on large crabgrass. For practical reasons,
the adjuvants were broken down into subsets of the 95, and
twelve separate screening experiments were performed. Most
adjuvants were tested three times. Two commonly used
adjuvants, X-77 and Herbimax, were included irrlall twelve
experiments as internal standards. Two herbicide-only
treatments and two control treatments were also included in
all twelve experiments to provide a basis for comparison.
Because of a scarcity of material, Dow Corning 8034-150-1 and
8034-150-9 were tested only twice.

A completely randomized design, with four replications
per treatment, was used for all screens. Large crabgrass was
grown from seed in 355-ml styrofoam cups; on the day of
treatment, cups were thinned to one plant each. Plants were
treated at the three-leaf stage in the first two sets of
screens, and at the two-tiller stage in the third set.
Dithiopyr (MON-15151 formulation) was applied to the plants at
a rate of 0.03 kg ai/ha. Preliminary dose-response studies
indicated that this rate would give approximately 50% control

with no adjuvants. Liquid adjuvants were added to the spray

11

solution at a rate of 0.5% V/V, and dry adjuvants were added
at 0.5% W/V. Treatments were applied using a trolley sprayer
delivering 163 l/ha at a pressure of 0.21 MPa. Plants were
placed in the greenhouse under automatic irrigation, however,
no irrigation was applied to the plants for at least 8 hours
following treatment. Supplemental lighting provided by metal-
halide vapor lamps maintained a 16 hour day length. Plants
were fertilized weekly with 50 ml of Peter’s 20-20-20
solution, containing 238 ppm N.

Three weeks after treatment, shoot fresh weights were
taken. Percent control values were calculated based on the
average shoot fresh weights of the control treatments. The
data were transformed by the arcsin transformation and the
analysis of variance and Tukey’s Honestly Significant
Difference multiple range test were performed on the
transformed data. A scoring system was devised in which an
adjuvant received one-half point if: it gave significantly
greater control than one herbicide-alone treatment in its
particular group, and a full point if greater than both. Data
reported are the number of points over the number of times the

adjuvant was tested (Table 4).

12
1 Fi l

A field study was conducted during the spring and
summer of 1990 to evaluate the effect of adjuvants on
postemergence crabgrass control at three different growth
stages with dithiopyr. The research site was in the same
general area as the 1989 field study, but in a section that
was not treated with preemergence herbicides in 1989. The
site was seeded with 49 kg/ha ’Newport’ Kentucky bluegrass
(Poa pratensis L. cv. Newport) in October of 1989 and was 50-
60% established by .April of’ 1990. Large crabgrass was
overseeded into the existing turf’ in April of 1990 to
supplement the natural population of smooth and large
crabgrass. The area was fertilized with 24 kg N/ha in May.
Trimec was applied at 3.5 l/ha on 7/19/90 to control broadleaf
weeds. The plots were mowed once or twice weekly to maintain
the height at 3.8 cm. Supplemental irrigation was applied as
needed to prevent drought stress.

A randomized complete block design was used with three
replications. Plot size and treatment application method were
the same as in the 1989 field study, except that the spray
pressure was increased to 0.28 MPa, giving a spray volume of
533 l/ha. The early-postemergence treatments were applied at

the 2 to 3-leaf stage on 6/14/90, the mid-postemergence

13
treatments at the 2 to 3-tiller stage on 7/10/90, and the

late-postemergence treatments at the 3 to 6-tiller stage on
8/1/90. No rainfall occurred for at least 24 hours after the
application of all treatments.

Percent crabgrass cover was estimated at 4 and 8 weeks
after the early-postemergence treatments, 2, 4 and 9 weeks
after the mid-postemergence treatments, and 2, 4 and 6 weeks
after the late-postemergence treatments. Percent cover was
estimated by placing a 1.2 m x 1.8 m grid, with 112 equally
spaced intersections, over each plot and counting the number
of times a crabgrass plant occurred under an intersection.
Data were converted to percent control based on the average
crabgrass cover in the control plots for each replication.
Data were transformed by the arcsin transformation and the
analysis of variance and LSD multiple range test were
performed on the transformed data. Means reported are actual

percent control values.

14
RESULTS AND DISCUSSION

1 Fi l u

Two emulsifiable concentrate formulations of dithiopyr,
MON-15104 and MON-15151, and two granular formulations, MON-
15111 and MON-15112, provided acceptable (85% or greater)
control of 2 to 3-leaf crabgrass, at rates ranging from 0.42-
0.84 kg ai/ha, by 4 weeksafter treatment (WAT) (Table 1).
MON-15104 at 0.56 kg ai/ha was an exception: it provided only
76% control, as compared with 89% for the 0.42 kg ai/ha rate
of the same formulation. However, this difference was not
statistically significant, and probably'is a reflection of the
somewhat variable crabgrass infestation levels in the plots
early in the season. MON-15175, a granular formulation, did
not give acceptable control at 0.42 or 0.56 kg ai/ha.
Overall, the sprayable formulations gave slightly greater
control than the granular formulations, though differences
were not statistically significant.

Dithiopyr exerted its effect on the crabgrass plants
more slowly than quinchlorac or the fenoxaprop-dinitroaniline
combinations (Table 1). Dithiopyr took 4 weeks to reach peak
control levels, while the other compounds typically reached

maximum control levels within 2 weeks. Control with all

15

treatments, except the sequential quinchlorac applications,
began to drop by'6 WAT due to late germination and/or regrowth
of crabgrass. Single applications of quinchlorac plus
surfactant, and fenoxaprop, gave very little control after 6
weeks. Interestingly, quinchlorac without surfactant, applied
as a late preemergent, provided significantly greater control
after'6 weeks than the single applications of quinchlorac plus
surfactant. Perhaps the surfactant, acting as a wetting
agent, causes increased movement of the active ingredient
through the soil profile, and past the zone of crabgrass
germination. Combining fenoxaprop with pendimethalin [N-(l-
ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] or Team, a
combination of benefin [N-butyl-N-ethyl-2,6-dinitro-4-
(trifluoromethyl)benzenamine] and trifluralin [2,6-dinitro-
N,N-dipropyl-4-(trifluoromethyl)benzenamine], extended control
somewhat over fenoxaprop alone, but control was essentially
gone after 8 weeks.

The dithiopyr treatments, particularly the emulsifiable
concentrate formulations, had a longer residual control than
the other compounds. After 8 weeks, control with the MON-
15104 and MON-15151 treatments ranged from 42-75%, which, in
most cases, was significantly greater than the single

applications of quinchlorac plus surfactant, and the

16

fenoxaprop treatments. It should be noted that 50% control
with these treatments represents fairly low crabgrass levels
since initial crabgrass levels in the plots averaged only
about 10%. The longer residual control given by dithiopyr is
a reflection of its outstanding preemergence activity.

When applied at the 2 to 4-tiller, or the 4 to 6-tiller
crabgrass growth stage, dithiopyr*(MON-15151) gaveressentially
no control at rates of 0.42-0.84 kg ai/ha (Tables 2 and 3).
By contrast, quinchlorac plus surfactant gave outstanding
control of 2 to 4-tiller crabgrass through 8 WAT (Table 2).
Fenoxaprop alone, and in combination with pendimethalin, gave
outstanding control initially; but control gradually'decreased
due to regrowth in the plots. Quinchlorac plus surfactant
also provided outstanding initial control of 4 to 6-tiller
crabgrass, but control decreased over time with regrowth of
the crabgrass (Table 3). Fenoxaprop alone did not produce
acceptable control of 4 to 6-tiller crabgrass. When combined
with pendimethalin, however, 0.39 kg ai/ha of fenoxaprop did
give outstanding control at 4 WAT. MSMA (monosodium salt of
methylarsonic acid) provided poor control of 2-4 and 4 to 6-
tiller crabgrass.

Conclusions drawn from this study are the following:

1) dithiopyr provides effective early-postemergence crabgrass

17

control at rates as low as 0.42 kg ai/ha; 2) control is longer
lasting than that provided by quinchlorac, fenoxaprop, and
fenoxaprop combined with pendimethalin or Team; 3) dithiopyr

does not give acceptable control of tillered crabgrass.

r nh A ' v n r n

The vast majority of the adjuvants tested in the
greenhouse increased crabgrass control dramatically over
dithiopyr alone. For example, if dithiopyr alone gave 30-40%
control, it was not unusual to achieve control levels of
greater than 90% when most adjuvants were added to the spray
solution (data not shown). No adjuvants resulted in
significant decreases in control. Consequently, it was
difficult to separate superior adjuvants from inferior ones
solely on the basis of percent control values, although some
adjuvants did seem to perform consistently better than others
on the basis of visual observation. For this reason, we chose
Tukey’s Honestly Significant Differencelnultiple range test at
p=0.01 for the statistical evaluation, giving us a
conservative range test with a high power for detecting
differences among treatments. Using the statistical
evaluation with the scoring system previously described, we

were able to rank the adjuvants (Table 4).

 

18

Very slight differences in the sizes of the treated
plants between groups resulted in differences in the amount of
control provided by the herbicide alone; thus, all adjuvants
were not subjected to equally stringent tests. With this in
mind, we decided to combine the statistical evaluation with
visual observations in order to identify the most efficacious
adjuvants.

Our objective was to identify 10 adjuvants, out of the
95 tested, that had high potential for increasing dithiopyr
activity on tillered crabgrass in the field, and that included
representatives from the various sources at our disposal. A
wide representation of adjuvant types was desired because
different types may perform dissimilarly under varying
environmental conditions. The ten selected for field
evaluation (with Table 4 scores in parentheses) were Pfizer
14636-181-7 (3/3), Dash (3/3), Agsco Sunit (3/3), Dow Corning
X2-5309 (2.5/3), Dow Corning 6955-145 (2.5/3), CSY-77715512
(2.5/3), Activator 90 (2/3), Pfizer M (2/3), X-77 (7.5/12) and
Herbimax (7/12). The first six adjuvants listed were selected
due to excellent performance and representation from different
sources. Activator 90 and Pfizer M warranted selection
despite scoring only 2/3, because they were noticeably

superior to other adjuvants in their first two groups.

19

Herbimax and X-77 are widely used adjuvants, and so were

included as standard treatments.

1 Fi l

The spring and summer of 1990 were cooler than normal;
consequently, it was not a favorable year for crabgrass
growth. The resulting lack of crabgrass pressure led to
greater control with all compounds than in 1989. Particularly
notable is the increased control achieved with dithiopyr on
tillered crabgrass in 1990 (Tables 6 and 7).

Adding adjuvants to the spray solution did not result
in increased crabgrass control with dithiopyr at the 1 to 3-
leaf growth stage (TabTe 5). Dithiopyr alone, at 0.42 kg
ai/ha, gave 90% control by four WAT. This result was not
unexpected since the/early'postemergence activity'of dithiopyr
is well established. All adjuvants, in combination with
dithiopyr at the 0.42 kg ai/ha rate, provided 87-90% control,
with the exception of Pfizer M, which resulted in only 57%
control. This adjuvant seemed to become more effective as the
crabgrass matured (Tables 6 and 7).

The level of control provided by the dithiopyr/adjuvant
treatments at 4 WAT was similar to that given by fenoxaprop

(0.13 and 0.20 kg ai/ha) and fenoxaprop tank-mixed with

20
pendimethalin (0.09 + 1.68 kg ai/ha). Pendimethalin alone

gave poor control (Table 5). Newly germinated crabgrass
plants in the plots where fenoxaprop alone was applied caused
a decrease in control by 8 WAT, whereas control remained
fairly constant with all other treatments, except for the 0.14
kg ai/ha rate of dithiopyr plus Activator 90. For single
applications, then, dithiopyr is clearly superior to strictly
postemergence products for extended early-postemergence
control due to its preemergence activity.

When applied at the 2 to 3-tiller growth stage, several
adjuvants, in combination with dithiopyr, gave significantly
greater control at 4 WAT than dithiopyr alone (Table 6).
These included Dow'Corning 6955-145, Dow Corning X2-5309, CSY-
77715512, X-77 and Activator 90. Other adjuvants performing
well were Agsco Sunit, Herbimax, and Pfizer 14636-181-7.
Combining Dash with dithiopyr decreased control slightly in
comparison with the herbicide alone, though the difference was
not statistically significant. Control with dithiopyr plus
the more efficacious adjuvants was similar to that obtained
with fenoxaprop (0.20 kg ai/ha) and the sequential MSMA
treatment (2.24 + 2.24 kg ai/ha at a 4 week interval). A
single application of MSMA resulted in poor control. Ratings

taken at the end of the season (9 WAT) revealed that all

21

treatments had maintained fairly even control, except for
fenoxaprop, which decreased from 96% at 4 WAT to 77% at 9 WAT,
indicating some regrowth or regermination had occurred in
those plots.

The higher crabgrass growth pressure at the 3 to 6-
tiller stage resulted in more typical, slow-developing
dithiopyr control, taking four weeks to reach maximum control
levels (Table'7). All dithiopyr/adjuvant.combinations, except
dithiopyr at the lower rates of 0.14 and 0.28 kg ai/ha plus
Activator 90, gave greater control at 4 WAT than dithiopyr
alone; however the differences were not statistically
significant. Control with dithiopyr alone dropped from 74% at
4 WAT to 49% at 6 WAT, due to regrowth in those plots.
Meanwhile, control with the {dithiopyr/adjuvant treatments
remained constant, leading to significantly increased control
with Dow Corning X2-5309, Pfizer 14636-181-7, CSY-77715512,
Herbimax and Dash. Other adjuvants performing well were
Pfizer M, Dow Corning 6955-145 and Activator 90.

Lowering the rate of dithiopyr to 0.28 and 0.14 kg
ai/ha, in combination with Activator 90, resulted in slight
decreases in early-postemergence control compared with the
0.42 kg ai/ha rate» of’ dithiopyr alone (Table 5). 'The

differences in control were more pronounced at 8 WAT,

22

especially with the lowest rate. However, when applied mid-
or late-postemergence, Activator 90 plus dithiopyr at 0.28 kg
ai/ha provided greater control (though not statistically
different) than dithiopyr alone at 0.42 kg ai/ha. This
suggests that a lower rate of dithiopyr, in combination with
adjuvants, is probably sufficient to control emerged 1 to 3-
leaf plants, but does not provide the residual preemergence
activity needed to achieve extended control at the early-
postemergence timing.

In summary, this research indicates that effective
control of tillered crabgrass is achievable by adding
adjuvants 1x) the dithiopyr spray solution. No benefit is
gained by using adjuvants in combination with dithiopyr for
early-postemergence crabgrass control. All adjuvants
performed well, with the exceptions of Pfizer M and Dash,
which gave inconsistent control at different growth stages.
Based on this research, any of the remaining adjuvants would
be a suitable choice for use with dithiopyr on tillered
crabgrass. Cost and availability of the compounds may be the
determining factor when considering which adjuvant to use.
The apparent safety of dithiopyr/adjuvant combinations
(discussed in Chapter 2) should make this control strategy a

valuable alternative to currently available products.

23

Table 1. Effect of pre- and postemergence herbicides on
early-postemergence crabgrass control.

 

Growth Stage= 2 to 3-leef X Crabgrass Controla

 

 

Treatment Rate (k9 81/158) 2 HAT 4 HAT 6WAT 8 WAT
HON-15104 0.84 57 d-g 100 a 90 ab 75 ab
MON-15151 0.42 48 f-h 98 ab 82 a-e 65 a-c
Fenoxaprop + Team 0.13 + 2.24 98 ab 98 ab 72 a-e 10 de
Quinchlorac + BASO90° 0.84 + 2.3 l/ha 100 a 97 ab 97 a 97 a
Quinchlorac + BASO90 0.84 + 2.3 l/ha 98 ab 94 ab 7 hi 0 e
MON-15151 0.56 76 a-f 93 ab 67 a-f 60 a-d
Quinchloracb 1.12 91 a-d 93 ab 86 a'd 54 a-d
Fenoxaprop + Team 0.09 + 2.24 100 a 91 ab 33 e-i 0 e
Fenoxaprop + Pendimethalin 0.09 + 1.68 83 a-e 90 ab 47 b-h 7 de
Fenoxaprop + Pendimethalin 0.13 + 1.68 93 a-c 90 ab 47 c-h 0 e
DCPAb + Fenoxapropd 11.8 + 0.23 90 a-d 89 ab 41 b-h 27 de
MON-15112 0.84 58 d-g 89 ab 76 a-e 51 a-d
MON-15104 0.42 78 a-f 89 ab 61 a-g 56 b-d
HON'15111 0.42 60 c-g 87 ab 44 c-h 31 c-e
MON-15112 0.56 45 e-h 85 ab 72 a-e 27 de
Quinchlorac + BASO90° 1.12 + 2.3 l/ha 100 a so ab 87 a-c 87 ab
Quinchlorac + BASO90 1.12 + 2.3 l/ha 100 a 85 a-c 35 e-i 0 e
Fenoxaprop 0.13 73 b-g 80 a-c 20 f-i 0 e
MON-15104 0.56 54 d-g 76 a-c 72 a-e 42 b-e
Fenoxaprop 0.20 53 e-h 73 be 0 i 0 e
HON-15175 0.56 17 hi 50 cd 40 d-i 23 de
MON-15175 0.42 33 g-i 33 d 22 g-i 22 de
MSMA 2.24 38 f-h 17 de 0 i 0 e
HSMA‘ 2.24 o i o e o i o e
CONTROL 0 i 0 e 0 i 0 e
CONTROL 0 i 0 e 0 i 0 e

 

‘Means followed by the same letter are not significantly different by LSD at p=0.05

bApplied as a late-preemergent on 5/23/89

cTreatment repeated after 4 weeks

dApplied at z to 4-tiller stage on 6/23/89

24

Table 2. Effect of pre- and postemergence herbicides on
mid-postemergence crabgrass control.

 

Growth Sta9e= 2 to 4-tillers

X Crabgrass Controla

 

 

Treatment Rate (kg ai/ha) 2 HAT 4 HAT 6 WAT 8 WAT
Quinchlorac + BASO90 0.84 + 2.3 l/ha 98 a 95 a 93 a 88 a
Quinchlorac + BASO90 1.12 + 2.3 l/ha 97 a 93 a 92 a 90 a
Fenoxaprop + Pendimethalin 0.28 + 1.68 93 a 70 ab 50 b 7 b
Fenoxaprop 0.28 93 ab 68 ab 8 cd 0 c
Fenoxaprop + Pendimethalin 0.13 + 1.68 90 ab 47 abc 11 cd 0 c
Fenoxaprop + Pendimethalin 0.20 + 1.68 88 ab 53 bed 27 c 0 c
Fenoxaprop 0.20 86 ab 20 cde 0 d 0 c
MOW-15151 0.84 10 b 10 e 0 d 0 c
MSMAb 2.24 6 b o e o a o c
MSMA 2.24 6 b 0 e 0 d 0 c
MON-15151 0.56 0 b 0 e 0 d 0 c
MON-15151 0.42 0 b 0 e 0 d 0 c
CONTROL 0 b 0 e 0 d 0 c
CONTROL 0 b 0 e 0 d 0 c

 

‘Means followed by the same letter are not significantly different by LSD at p=0.05

bTreatment repeated after 4 weeks

 

25

Table 3. Effect of pre- and postemergence herbicides on
late-postemergence crabgrass control.

 

 

 

Growth Stage= 4 to 6-tiller X Crabgrass Controla

Treatment Rate (kg ai/ha) 2 HAT 4 HAT 6 HAT 8 HAT
Fenoxaprop + Pendimethalin 0.39 + 1.12 70 c 96 a 70 a 67 a
Fenoxaprop + Pendimethalin 0.20 + 1.68 76 be 82 a 54 a 47 ab
Quinchlorac + BASO90 0.84 + 2.3 l/ha 95 a 81 a 65 a 61 a
Fenoxaprop 0.28 59 c 79 a 52 a 29 abc
Fenoxaprop + Pendimethalin 0.28 + 1.12 72 c 78 a 49 a 33 abc
Fenoxaprop 0.20 70 c 77 a 34 ab 22 abc
Quinchlorac + BASO90 1.12 + 2.3 l/ha 96 ab 74 a 61 a 58 ab
MON-15151 0.84 0 d 26 b 6 be 8 bc
MSMA 2.24 53 c 18 b 0 c 0 c
HON-15151 0.42 0 d 12 be 0 c 0 c
MSMAb 2.24 20 d o c o c o c
HON-15151 0.56 0 d 0 c 0 c 24 bc
CONTROL 2 d 0 c 0 c 0 c
CONTROL 0 d 0 c 0 c 11 be

 

aMeans followed by same letter are not significantly different by LSD at p=0.05

bTreatment repeated after 4 weeks

 

Table 3.

25

late-postemergence crabgrass control.

Effect of pre- and postemergence herbicides on

 

Growth Stage= 4 to 6-tiller

X Crabgrass Controla

 

 

Treatment Rate (kg ai/ha) 2 HAT 4 HAT 6 HAT 8 HAT
Fenoxaprop + Pendimethalin 0.39 + 1.12 70 c 96 a 70 a 67 a
Fenoxaprop + Pendimethalin 0.20 + 1.68 76 be 82 a 54 a 47 ab
Quinchlorac + BASO90 0.84 + 2.3 l/ha 95 a 81 a 65 a 61 a
Fenoxaprop 0.28 59 c 79 a 52 a 29 abc
Fenoxaprop + Pendimethalin 0.28 + 1.12 72 c 78 a 49 a 33 abc
Fenoxaprop 0.20 70 c 77 a 34 ab 22 abc
Quinchlorac + BASO90 1.12 + 2.3 l/ha 96 ab 74 a 61 a 58 ab
MON-15151 0.84 0 d 26 b 6 be 8 bc
MSMA 2.24 53 c 18 b 0 c 0 c
MON-15151 0.42 0 d 12 be 0 c 0 c
MSMAb 2.24 20 d o c o c o c
MON-15151 0.56 0 d 0 c 0 c 24 bc
CONTROL 2 d 0 c 0 c 0 c
CONTROL 0 d 0 c 0 c 11 be

 

aMeans followed by same letter are not significantly different by LSD at p=0.05

bTreatment repeated after 4 weeks

 

 

26

Table 4. Greenhouse adjuvant screens with dithiopyr.

 

 

Adjuvant Times betteraltimes tested
Pfizer 14636-181-7 3/3
Dash 3/3
Agsco Sunit 3/3
Frigate 3/3
Dow Corning 8687-12-1 3/3
Dow Corning x2-5309 2.5/3
Dow Corning 6955-145 2.5/3
Dow Corning X2-5177-B 2.5/3
Dow Corning 6736-99 2.5/3
Dow Corning 8687-12-3 2.5/3
Dow Corning 8687-12-9 2.5/3
Dow Corning 8034-150-2 2.5/3
CSY-77715510 2.5/3
CSY-77715512 2.5/3
CSY-77715514 2.5/3
CSY-7771552 2.5/3
CST-7771553 2.5/3
Dow Corning 8034-150-1 1.5/2
Activator 90 2/3
Pfizer A 2/3
Pfizer B 2/3
Pfizer O 2/3
Pfizer N 2/3
Pfizer 14636-181-2 2/3
Pfizer 14636-181-3 2/3
Pfizer 14636-181-4 2/3
Pfizer 14636-181-6 2/3
Pfizer 14636-181-9 2/3
Dow Corning A 2/3
Dow Corning x2-5177-A 2/3
Dow Corning X2-5152 2/3

Dow Corning x2-5211 2/3

 

27

Table 4 (cont'd.).

Adjuvant

Times bettera/times tested

 

Dow Corning 6584-14
CST-77715515
CSY-77715516
CST-7771551
CSY-7771554
CSY-7771559

Dow Corning 8687-12-2
Dow Corning 8687-12-8
Dow Corning 8034-150-3
Dow Corning 8034-150-6
X-77

Herbimax

Pfizer C

Pfizer E

Pfizer L

Pfizer 14636-181-1
Pfizer 14636-181-8
Pfizer 14636-181-11
Dow Corning 8

Dow Corning 6584-109
Dow Corning 6584-17
CST-77715511

Dow Corning 8687-12-7
Dow Corning 8034-150-10
Dow Corning 8034-150-11
Pfizer H

Pfizer I

Dow Corning 6584-151
Dow Corning 6736-30
Dow Corning 6736-110
Dow Corning 6736-108
Dow Corning 8687-12-4

2/3
2/3
2/3
2/3
2/3
2/3
2/3
2/3
2/3
2/3
7.5/12
7/12
1.5/3
1.5/3
1.5/3
1.5/3
1.5/3
1.5/3
1.5/3
1.5/3
1.5/3
1.5/3
1.5/3
1.5/3
1.5/3
1/3
1/3
1/3
1/3
1/3
1/3
1/3

 

28

Table 4 (cont'd.).

 

Adjuvant Times better‘ltimes tested
Dow Corning 8687-12-5 1/3
Dow Corning 8687-12-6 1/3
Dow Corning 8034-150-4 1/3
Dow Corning 8034—150-5 1/3
Dow Corning 8034-150-7 1/3
Dow Corning 8034-150-12 1/3
Dow Corning 8034-40 1/3
Dow Corning 8687-25-7 1/3
Dow Corning 8034-150-14 1/4
Pfizer 14636-181-5 0.5/3
Triton x-114 0.5/3
Dow Corning 6955-7 0.5/3
Dow Corning 8034-150-15 0.5/3
Dow Corning 8034-85 0.5/3
Dow Corning 8687-25-5 0.5/3
Dow Corning 8034-150-9 0/2
Pfizer F 0/3
Pfizer G 0/3
Pfizer J 0/3
Pfizer K 0/3
Dow Corning 6584-16 0/3
Dow Corning 8034-150-8 0/3
Dow Corning 8034-150-13 0/3
Dow Corning 8687-25-3 0/3
Dow Corning 8687-25-6 0/3
Dow Corning 8687-25-8 0/3
Dow Corning 8687-25-9 0/3
LI700 0/3
Bond 0/3

 

‘Significantly better than dithiopyr alone by Tukey's Honestly

Significant Difference test at p=0.01

29

Table 5. Early-postemergence crabgrass control with

dithiopyr and adjuvants.

 

Growth Stage= 1 to 3-leaf

X Crabgrass Controla

 

 

Treatment Rate (kg ai/ha) 4 HAT 8 HAT
Fenoxaprop + Pendimethalin 0.09 + 1.68 97 a 95 a
MON-15104 0.42 90 ab 94 a
MON-15104 + Activator 90 0.42 + 0.5% v/v 90 ab 86 abc
MON-15104 + CSY-77715512 0.42 + 0.5% v/v 90 ab 88 abc
MON-15104 + Dow Corning 6955-145 0.42 + 0.5% v/v 90 ab 90 abc
MON-15104 + Herbimax 0.42 + 0.5% v/v 90 ab 91 abc
NON-15104 + Dash 0.42 + 0.5% v/v 87 ab 95 ab
NON-15104 + x-77 0.42 + 0.5% v/v 87 ab 88 abc
MON-15104 + Agsco Sunit 0.42 + 0.5% v/v 87 ab 94 ab
Fenoxaprop 0.20 87 ab 51 be
NON-15104 + Pfizer 14636-181-7 0.42 + 0.5% v/v 87 ab 92 ab
MON-15104 + Dow Corning X2-5309 0.42 + 0.5% v/v 87 ab 82 abc
MON-15104 + Activator 90 0.28 + 0.5% v/v 84 ab 75 abc
fenoxaprop 0.13 82 ab 65 abc
NON-15104 * Activator 90 0.14 + 0.5% v/v 79 ab 50 bc
Pendimethalin 1.68 58 b 50 c
NON-15104 + Pfizer N 0.42 f 0.5% v/v 57 b 62 abc
CONTROL 0 c 0

 

'Means followed by the same letter are not significantly different by LSD at p=0.05

30

Table 6. Mid—postemergence crabgrass control with dithiopyr
and adjuvants.

 

 

 

Growth Stage: 2 to 3-tillers X Crabgrass Controla
Treatment Rate (kg ai/ha) 2 HAT 4 HAT 9 WAT
MON-15104 + Dow Corning 6955-145 0.42 + 0.5% v/v 96 ab 97 a 93 abc
Fenoxaprop 0.20 98 a 96 ab 77 bed
MON-15104 + CSY-77715512 0.42 + 0.5% v/v 86 abcd 96 ab 98 ab
MON-15104 + Dow Corning X2-S309 0.42 + 0.5% v/v 98 a 96 ab 100 a
MON-15104 + X-77 0.42 + 0.5% v/v 89 abc 94 ab 93 abc
MON-15104 + Activator 90 0.42 + 0.5% v/v 89 ab 92 ab 93 abc
MSMA 2.24 + 2.24 92 ab 93 abc 88 abcd
MON-15104 + Agsco Sunit 0.42 + 0.5% v/v 96 ab 92 abc 95 ab
MON-15104 + Herbimax 0.42 + 0.5% v/v 94 ab 91 abc 87 abcd
NON-15104 + Pfizer 14636-181-7 0.42 + 0.5% v/v 92 ab 89 abc 98 ab
MON-15104 + Activator 90 0.28 + 0.5% v/v 90 ab 86 abcd 84 abc
MON-15104 + Pfizer M 0.42 + 0.5% v/v 94 ab 81 bcd 76 abcd
MON-15104 0.42 73 bed 72 cd 82 abcd
MON-15104 + Dash 0.42 + 0.5% v/v 61 cd 65 de 59 d
MON-15104 + Activator 90 0.14 + 0.5% v/v 70 bed 64 de 63 cd
MSMA 2.24 58 d 45 e 64 cd
CONTROL 0 e O f 0 e

 

aMeans followed by the same letter are not significantly different by LSD at p=0.05

Table 7.

Late-postemergence crabgrass control with
dithiopyr and adjuvants.

31

 

Growth Stage: 3 to 6-tillers

X Crabgrass Controla

 

 

Treatment Rate (kg ai/ha) 2 HAT 4 HAT 6 HAT
FenoxaprOp 0.28 93 a 97 a 98 a
NON-15104 + Dow Corning X2-5309 0.42 + 0.5% v/v 56 abc 90 ab 93 a
MON-15104 + Dash 0.42 + 0.5% v/v 51 abc 83 ab 92 a
HON-15104 + CSY-77715512 0.42 + 0.5% v/v 60 abc 85 ab 90 ab
NON-15104 + Herbimax 0.42 + 0.5% v/v 64 ab 89 ab 90 ab
NON-15104 + Pfizer 14636-181-7 0.42 + 0.5% v/v 63 abc 86 ab 86 ab
MON-15104 + Pfizer M 0.42 + 0.5% v/v 69 ab 90 ab 87 abc
MON-15104 + Dow Corning 6955-145 0.42 + 0.5% v/v 54 abc 88 ab 87 abc
MON-15104 + Activator 90 0.42 + 0.5% v/v 46 abc 83 ab 85 abc
MON-15104 + X-77 0.42 + 0.5% v/v 59 abc 89 ab 80 abc
MON-15104 + Agsco Sunit 0.42 + 0.5% v/v 46 abc 90 ab 80 abc
MON-15104 + Activator 90 0.28 + 0.5% v/v 40 be 74 DC 74 abc
MON-15104 + Activator 90 0.14 + 0.5% v/v 24 cd 51 c 57 be
NON-15104 0.42 31 bed 74 bc 49 c
CONTROL 0 d 0 d 0

 

aMeans followed by the same letter are not significantly different by LSD at

p=0.05

10.

LITERATURE CITED

Bhowmik, P.C. and B.M. Bahnson. 1989. Pre- and
postemergence smooth crabgrass control with MON-15151 in
cool season turfgrass. Proc. Northeastern Weed Sci. Soc.
43:110.

Brooks, R.L., M.G. Merkle, and J.M. Chandler. 1985.
Efficacy of glyphosate/adjuvant combinations for
johnsongrass control. Proc. Southern Weed Sci. Soc. 38:46.

Croon, K.A., M.G. Merkle, and K.R. Norton. 1985. Activity
of fluazifop-butyl/adjuvant combination against
johnsongrass. Proc. Southern Weed Sci. Soc. 38:45.

Dernoeden, P.H. and D.B. Davis. 1989. Herbicide tank mixes
for postemergence control of smooth crabgrass in turf.
Proc. Northeastern Weed Sci. Soc. 43:85-86.

Dernoeden, P.H. and D.B. Davis. 1989. Preemergence control
of smooth crabgrass and goosegrass in Maryland in 1988.
Proc. Northeastern Weed Sci. Soc. 43:93-94.

Dernoeden, P.H. and J.M. Krouse. 1990. Maryland smooth
crabgrass evaluations for 1989. Proc. Northeastern Weed
Sci. Soc. 44:141-142.

Harrison, S.A. and T.L. Watschke. 1989. Pre- and
postemergence herbicide combinations for smooth crabgrass
control in turf. Proc. Northeastern Weed Sci. Soc. 43:90-

91.

Hurto, K.A. and L. Schaber. 1989. Preemergence activity of
MON-15151 for smooth crabgrass control in Kentucky
bluegrass turf. Proc. Northeastern Weed Sci. Soc. 43:104.

Jagschitz, J.A. and C.D. Sawyer. 1989. Preemergence
control of crabgrass, spurge and oxalis and pre-post, post
control of crabgrass in turf. Proc. Northeastern Weed Sci.
Soc. 43:96-97.

Kells, J. J. and G. Wanamarta. 1987. Effect of adjuvant
and spray volume on quackgrass (Aoroovron repens) control

32

 

11.

12.
13.

14.

15.

16.

17.

18.

19.

33

with selective postemergence herbicides. Weed Technol.
2:129-132.

McWhorter, 0.6. 1982. The use of adjuvants. p. 10-25 in
Adjuvants for Herbicides. Weed Sci. Soc. Am. Champaign,
IL.

Mitich, L. W. 1988. Crabgrass. Weed Technol. 2:114-115.

Rossi, F.S., J.C. Neal, and A.F. Senesac. 1989. Effect of
crabgrass growth stage on efficacy of MON-15151. Proc.
Northeastern Weed Sci. Soc. 43:95.

Schreiber, M.M., G.F. Warren, and P.L. Orwick. 1979.
Effects of wetting agent, stage of growth, and species on
the selectivity of diclofop. Weed Sci. 27:679-683.

Swietlik, D. 1989. Adjuvants affect the efficacy of
glyphosate on selected perennial weeds. HortScience
24:470-472.

Thompson, D.A. 1986. Use of frigate with glyphosate. Can.
J. Plant Sci. 66:203.

Wanamarta, G., D. Penner, and J.J. Kells. 1989.
Identification of efficacious adj uvants for sethoxydim and
bentazon. Weed Tech. 3:60-66.

Watschke, T.L., G. Hamilton, and S. Harrison. 1989.
Preemergence control of smooth crabgrass in a mixed cool

season turf in 1988. Proc. Northeastern Weed Sci. Soc.
43:111-112.

York, A.C., D.L. Jordan, and J.W. Wilcut. 1990. Effects of
(NH,.)ZSO,, and BCH 81508 S on efficacy of sethoxydim. Weed
Technol. 4:76-80.

 

 

Chapter 2

SAFETY OF DITHIOPYR TO FINE FESCUES AND KENTUCKY BLUEGRASS
AND OF DITHIOPYR-ADJUVANT COMBINATIONS TO
KENTUCKY BLUEGRASS

ABSTRACT

Forty-two varieties, representing three fine fescue
subspecies, were treated with dithiopyr at rates of 0, 0.42
and 0.84 kg ai/ha in a May 1989 field study. Unacceptable
injury occurred only with the high rate. While there were
some significant differences in injury among ‘varieties of the
same species, dithiopyr was more phytotoxic to the Chewings
fescues than to the hard or creeping red fescues. In a 1990
field study, Kentucky bluegrass was treated with dithiopyr, at
0.42 kg ai/ha, in combination with ten different adjuvants.
Fenoxaprop at 0.20 kg ai/ha was included as a comparison
treatment. None of the dithiopyr/adjuvant combinations
injured the Kentucky bluegrass, while fenoxaprop resulted in
unacceptable injury. In a field study initiated in 1989 on a
Kentucky bluegrass turf, two consecutive annual applications
of dithiopyr at 0.42, 0.84 and 1.12 kg ai/ha, prodiamine at
0.84 kg ai/ha, pendimethalin at 3.36 kg ai/ha, and oxadiazon
at 2.24 and 4.48 kg ai/ha, resulted in no significant
reduction of Kentucky bluegrass root dry weight.
Nomenclature: Dithiopyr, 3,5-pyridinedicarbothioic acid,2-
(difluoromethyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-S,S-

34

35

dimethylester; fenoxaprop, (:)-2-[4-[(6-chloro-2-
benzoxazolyl)oxy]phenoxy]propanoic acid; prodiamine, 2,6-
dinitro-N’,N’,-dipropyl-6-(trifluoromethyl)-1,3-
benzenediamine; pendimethalin, N-(l-ethylpropyl)-3,4-dimethyl-
2,6-dinitrobenzenamine; oxadiazon, 3-[2,4-dichloro-5-(1-
methylethoxy)phenyl]-5-(1,l-dimethylethyl)-1,3,4-oxadiazol-2-
(3H)-one; fine fescue, Festuca spp.; Chewings fescue, Festuca
rubra_L. ssp. commutata Gaud.; hard fescue, Festuca lonqifolia
Thuill.; creeping red fescue, Festuca rubra L.; Kentucky
bluegrass, Pga pratensis L.

Additional index words. Herbicide injury, tolerance,

crabgrass control, Diqitaria spp.

 

36
INTRODUCTION

Safety to desirable turfgrasses is an integral component
of successful crabgrass control with pre- or postemergence
herbicides. Injury caused by a particular herbicide may be a
function of herbicide rate, turfgrass species, spray
additives, or a combination of the above. Consequently,
safety of a new herbicide to desirable species must be
evaluated over a range of conditions.

Dithiopyr is a new herbicide from the Monsanto
Agricultural Company with excellent preemergence and early
postemergence crabgrass (Digitaria spp.) activity at rates of
0.28 to 0.56 kg ai/ha (1, 6, 7). Parrish et al. (16) reported

no foliar injury from dithiopyr at rates as high as 4.48 kg

ai/ha to bermudagrass [Cynodon dagtylon (L.)Pers.], St.
Augustinegrass [Stenotaphrum secundatum (Walt.)Ktze.],
centipedegrass [Eremgchlga ophiurgides (Munro.)Hack.],
carpetgrass (Axongpgs affinis Chase), zoysiagrass (lgysia
spp.), tall fescue (Festuca arundinacea Schreb.), Kentucky

bluegrass, perennial ryegrass (Loligm perenne L.), and
creeping bentgrass (Agrostis palustris Huds.). However,

Brauen et al. (3) observed darkening and thinning of creeping

bentgrass when treated with dithiopyr at 2.24 and 4.48 kg

37
ai/ha. At more typical use rates of 0.28 and 0.56 kg ai/ha,

these researchers observed no injury. Other researchers have
reported safety on creeping bentgrass (1) and zoysiagrass (6)
at 1.12 kg ai/ha, and perennial ryegrass (1) and Kentucky
bluegrass (10) at 0.84 kg ai/ha. Thinning of the turfs at
higher rates was generally the first injury symptom reported.
No published information on dithiopyr phytotoxicity to the
fine fescues is available. This represents a significant gap
in the knowledge base, because these grasses are prone to
injury from other pre- and postemergence crabgrass herbicides
(5, 11, 17, 21).

Differences sometimes exist in herbicide tolerance among
cultivars of a particular species. Bensulide [Q,Q-bis(1-
methylethyl)S—[Z-[(phenylsulfonyl)amino]
ethyl]phosphorodithioate] and simazine (6-chloro-N,N’-diethyl -
1,3,5-triazine-2,4-diamine) reduced root weight of ’Belair’
zoysiagrass (Zoysia japonica Steud.) Inn: not ’Meyer’ (9).
Bingham (2) reported inhibition of ’Tifgreen’ bermudagrass (C;
dactylgn L. x C, transvaalensis Davy. ’Tifgreen’) rooting by
siduron [N—(Z-methylcyclohexyl)-N’-phenylurea], bensulide,
benefin [N-butyl-N-ethyl-2,6-dinitro-4-
(trifluoromethyl)benzenamine] and DCPA (dimethyl 2,3,5,6-

tetrachloro-l,4-benzenedicarboxylate); yet Dernoeden et al.

 

38

(8) found no inhibition of ’Midiron’ bermudagrass by the same
herbicides at similar rates. In cases such as these, varietal
tests for herbicide tolerance become necessary.

Adding adjuvants to the spray solution can change the
selectivity characteristics of a herbicide. While the
addition of an adjuvant may increase activity on the target
weed, heightened injury to desirable species can be an
unwanted side effect. Torello and Jagschitz (19) observed
increased injury to desirable turf when surfactants were
combined with DCPA” Jagschitz and Sawyer (12) noted injury in
one of four Kentucky bluegrass lawns when X-77, a surfactant,
was added to 0.84 kg ai/ha dithiopyr. Hurto and Schaber,
using the same dithiopyr rate without surfactant, observed no
injury to Kentucky bluegrass (10).

Because dithiopyr is a new herbicide, little is known
concerning its long term effects on turfgrasses. Research
with other preemergence herbicides suggests that long term
effects depend on the herbicide and turfgrass species used.
Callahan (4) applied siduron, DCPA, bensulide, benefin,
bandane (polychlorodicyclopentadiene) and terbutol (2,6-di-
tent-butyl-p-tolyl methylcarbamate) to creeping bentgrass for
three consecutive years and found increased injury the third

year in comparison with the first. Turgeon et al. (20)

39

reported increased thatch, decreased root growth, greater leaf
spot incidence and higher wilting tendency of Kentucky
bluegrass after four consecutive annual applications of
calcium arsenate and bandane. Bensulide reduced verdure
slightly, while DCPA, benefin and siduron had no ill effects.
Johnson (13) reported that zoysiagrass rooting was not
inhibited by consecutive annual applications of oxadiazon,
bensulide or benefin. In a separate study, he concluded that
three consecutive annual applications of bensulide, DCPA,
benefin and oxadiazon did not affect the quality of Kentucky
bluegrass or bermudagrass (14). Murray et al. (15) observed
a decrease in Kentucky bluegrass quality following eight
consecutive annual applications of DSMA (disodium salt of
methylarsonic acid), but not DCPA, benefin, bensulide, and
siduron.

The objectives of this research were threefold: 1)
evaluate dithiopyr phytotoxicity on fine fescue types and
varieties, 2) determine the effect of adjuvants on dithiopyr
phytotoxicity to Kentucky bluegrass, and 3) ascertain whether
consecutive annual applications of dithiopyr, prodiamine,
pendimethalin or oxadiazon have a deleterious effect on

Kentucky bluegrass rooting.

40
MATERIALS AND METHODS

Three field studies were conducted at the Hancock
Turfgrass Research Center, East Lansing, Michigan. The soil
at the site is an Owosso-Marlette sandy loam complex (Fine-
loamy, mixed, mesic, Typic Hapludalfs). The area was
fertilized with 164 kg N/ha in 1989 and 146 kg N/ha in 1990.
The turf height was maintained at 4.4 cm. Supplemental
irrigation was applied as needed to maintain a high quality
turf.

Dithiopyr Injury to Fine Fescues

The fine fescue variety study was initiated on 5/11/89,
on a five-year: old fine fescue variety trial. The 42
varieties evaluated included 21 chewings, 13 creeping red, and
8 hard fescues. A split plot design with three replications
was used, with fine fescue varieties as the main plots,
arranged in a randomized complete block design, and dithiopyr
rate as the sub plots. The main plots measured 1.2 by 1.8 m,
and the sub plots 1.2 by 0.6 m. Dithiopyr, as the MON-15151
formulation, was applied at 0, 0.42 and 0.84 kg ai/ha, using
a single-nozzle boom C02 backpack sprayer delivering 243 l/ha

at 0.21 MPa. The treatments were watered in after 16 hours.

 

41 ‘

Dithiopyr injury was visually rated at 8 and 12 weeks
after treatment (WAT) using a scale of 1-9, with 1 indicating
no injury, and 9 indicating complete kill (Table 1). The data
were subjected to analysis of variance and means were
separated by the Least Significant Difference (LSD) multiple
range test. Differences in dithiopyr injury among the three
fine fescue subspecies were evaluated by performing orthogonal
contrasts (Table 2).

Dithiepyr + Adjgvente Phytgtgxigity t9 Kentucky Bluegrass

The dithiopyr + adjuvants phytotoxicity study was
initiated on 6/14/90, on a three year old stand of ’Midnight’
Kentucky bluegrass. The experiment was designed as a
randomized complete block with three replications. Individual
plots measured 1.2 by 1.8 m. Treatments (Table 3) were
applied with a four-nozzle boom C02 backpack sprayer
delivering 533 l/ha at 0.28 MPa. The study received no
rainfall or irrigation for at least 24 hours following
treatment.

Herbicide injury was rated at 17 and 28 days after
treatment (DAT) using a scale of 1-9, with 1 indicating no
injury, and 9 indicating complete kill (Table 3). The data
were subjected to analysis of variance and treatment means

were separated by the LS0 multiple range test.

 

42

P m r n H r i i ff n R in

This study was initiated on 5/5/89 on an eight year old
Kentucky bluegrass sod blend. The study was designed as a
randomized complete block with four replications. Individual
plots measured 1.2 by 1.8 m. Treatments (Table 4) were
applied on 5/5/89 and 5/9/90, except for the 1990 oxadiazon
treatments, which were applied on 5/8/90. The oxadiazon
treatments were applied with a shaker bottle; all others were
applied with a four-nozzle boom C02 backpack sprayer,
delivering 449 l/ha at 0.21 MPa in 1989, and 533 l/ha at 0.28
MPa in 1990. The treatments were watered in within 48 hours
of application.

Root samples were collected from the plots on 6/13 and
6/14/90. A hydraulic coring device was used to remove three
randomly chosen samples, each 4 cm in diameter, from each
plot. The top 3 cm of the cores was considered the thatch/mat
layer and was discarded. The 0-5 cm depths of the remaining
cores were then placed in freezer bags and frozen until
analysis. Samples were thawed and divided into four
subsamples prior to washing the soil from the roots. Initial
washing using a hydropneumatic elutriation method (18) removed
the bulk of the soil and other debris. The samples were

stored in 10% methanol and refrigerated until final washing.

 

43

The final washing was performed in the laboratory by agitating
the sample, allowing soil particles to settle while removing
floating debris with tweezers, then decanting the suspended
roots into a fine mesh screen. The root samples were placed
in aluminum weigh boats, dried overnight in a convection oven,
and dry weights were taken (Table 4). The analysis of

variance was then performed on the data.

 

 

44
RESULTS AND DISCUSSION

Dithiuuyr Injury tu Eine Fescues

Thermagnitude of dithiopyr injury to the fine fescues was
dependent on both the dithiopyr rate and the fine fescue
variety. A rating of 3 or greater, on a scale of 1-9, was
judged to be unacceptable injury. All 42 varieties had an
injury rating of less than 3 at both 8 and 12 WAT, when the
dithiopyr rate was 0 or 0.42 kg ai/ha (Table 1). However, at
a dithiopyr rate of 0.84 kg ai/ha, 13 varieties showed
unacceptable injury 8 WAT. Notably, 12 of the 13 varieties
were chewings fescues; the lone non-chewings variety was
’Pennlawn’ creeping red fescue. Four varieties, all chewings
fescues, still exhibited unacceptable injury 12 WAT.

Orthogonal contrasts confirmed that the chewings fescues
were significantly more susceptible to dithiopyr injury
through 8 WAT (Table 2). After 12 weeks the turfs had
recovered sufficiently so that there were no significant
differences among the types. Although an examination of Table
1 seems to suggest that hard fescues are more susceptible to
dithiopyr injury than creeping red fescues, the differences

were not significant by the LS0 multiple range test, and the

45

contrast indicates no significant difference between the two
types (Table 2).

This research suggests that turfgrass managers should
refrain from applying dithiopyr to chewings fescues at rates
above 0.42 kg ai/ha.

Dithiupyr + Adjuvants Phytutuxieity tu Kentueky Bluegrass

This study was conducted on a high quality stand of
’Midnight’ Kentucky bluegrass; accordingly, an injury rating
of greater' than 2, on scale of 1-9, was judged to be
unacceptable. None of the dithiopyr/adjuvant treated plots
showed any visible injury at 17 or 28 DAT. By contrast, plots
treated with fenoxaprop at 0.20 kg ai/ha showed unacceptable
injury at both timings.

In conclusion, the dithiopyr/adjuvant combinations and
rates used in this study (Table 3), are not phytotoxic to
’Midnight’ Kentucky bluegrass. When using these combinations
on other Kentucky bluegrass varieties, testing of’a small area
before full scale usage would be prudent, because of possible
varietal differences in dithiopyr phytotoxicity similar to

those found with the fine fescues.

46
Preemergenee Herbieide Effeet un Reuting

The F-test for treatment effects in the analysis of
variance was not significant; thus, two consecutive annual
applications of dithiopyr, prodiamine, pendimethalin and
oxadiazon at the rates used (Table 4) had no apparent
inhibitory effect on Kentucky bluegrass rooting. Despite the
lack of significance, it is interesting to note that the
control treatment had the highest root dry weight. This study
will be continued over the next several years, and it is
possible that continued application of these herbicides will

result in significant inhibition of rooting.

47

Table I. Dithiopyr injury to fine fescue varieties.

 

Injury (1 -9)‘

 

 

 

 

3 HAT 12 HAT -------------
--------- Rate (kg ai/ha)-------- ----------Rate (kg ai/ha)--------
Variety Type 0 0.42 0.84 0 0.42 0.84
Heekend Chewings 1.0 1.3 6.3 1.7 1.7 6.0
Mary Chewings 2.0 2.0 4.7 2.0 1.0 3.3
Banner Chewings 1.7 2.7 4.7 1.0 1.7 2.7
Atlanta Chewings 1.3 1.7 4.3 1.0 2.0 3.7
Magenta Chewings 1.7 2.3 3.7 1.7 1.3 2.3
Enjoy Chewings 1.0 1.7 3.7 1.3 1.7 2.7
lvalo Chewings 1.7 1.7 3.7 1.3 1.3 1.0
Hilma Chewings 1.3 1.7 3.3 1.3 1.0 1.0
Tamara Chewings 1.3 1.3 3.3 1.7 1.3 2.3
Pennlawn Creeping 1.7 1.3 3.3 1.0 1.0 1.7
Highlight Chewings 1.3 1.3 3.0 1.0 1.0 1.0
Tatjana Chewings 1.3 1.7 3.0 1.0 1.0 1.0
Victory Chewings 1.7 2.0 3.0 1.3 1.0 1.0
Koket Chewings 1.3 2.0 2.7 1.0 1.0 1.0
Haldorf Chewings 1.7 1.3 2.7 1.0 1.3 2.3
Center Chewings 2.3 2.0 2.7 1.0 1.3 1.0
Aurora Hard 1.7 2.0 2.7 1.0 1.3 1.0
Biljart Hard 1.3 1.7 2.7 1.0 1.3 1.7
Scaldis Hard 1.3 1.3 2.3 1.7 1.0 2.3
Checker Chewings 2.0 2.0 2.3 1.0 1.0 1.0
Haldina Hard 1.7 1.7 2.3 1.0 1.0 1.0
Barfo 81-225 Hard 2.0 1.3 2.3 1.0 1.0 1.0
Shadow Chewings 2.0 1.3 2.3 1.0 1.0 1.0
Lovisa Creeping 2.3 2.3 2.0 1.0 2.3 1.0
Valda Hard 2.0 2.0 2.0 1.0 1.0 1.0
Wintergreen Creeping 1.7 2.0 2.0 1.7 2.0 1.3
Jamestown Chewings 1.0 2.3 2.0 1.0 1.0 1.0
SR3000 Hard 1.7 2.3 2.0 1.0 1.3 1.0

430 CR Creeping 2.0 1.3 2.0 1.7 1.3 1.0

 

Table 1 (cont'd.).

 

Injury (1-9)‘

 

 

 

------------- 8 HAT-------------- --------------12 HAT-------------

--------- Rate (kg ai/ha)-------- ----------Rate (kg ai/ha)--------
Variety Type 0 0.42 0.84 0 0.42 0.84
Longfellow Chewings 2.3 1.0 2.0 1.0 1.0 1.3
Beauty Chewings 1.7 1.7 2.0 1.3 1.3 3.0
Commodore Creeping 1.0 1.0 1.7 1.0 1.0 1.0
Reliant Hard 1.7 1.7 1.7 1.0 1.0 1.0
Ensylva Creeping 1.0 1.0 1.3 1.0 1.3 1.7
Pernille Creeping 1.3 1.3 1.3 1.0 1.0 1.0
Ceres Creeping 2.0 2.0 1.3 1.0 1.0 1.0
Flyer Creeping 1.3 1.3 1.3 1.0 1.0 1.0
Estica Creeping 1.3 1.0 1.3 1.0 1.7 1.3
Ruby Creeping 1.3 1.3 1.0 1.0 1.0 1.0
Boreal Creeping 1.0 1.0 1.0 1.0 1.0 1.0
Robot Creeping 1.3 1.0 1.0 1.0 1.0 1.0
Epsom Chewings 1.0 1.0 1.0 1.0 1.0 1.0
LSD.“ as us 1.8 us us 1.5

a1=no injury 9=complete kill; A rating of 3 or greater was considered to be unacceptable injury.

 

49

Table 2. Summary of dithiopyr

injury to the fine fescue

 

 

 

 

subspecies.
Injury (1-9)a

-------------- 8 HAT--------------- --------------12 HAT----------""

---------- Rate (kg ai/A)---------- ----------Rate (kg ai/A)----------
Type O 0.42 0.84 0 0.42 0.84
Chewings 1.6 1.7 3.2 1.2 1.2 1.9
Creeping 1.5 1.4 1.5 1.1 1.3 1.2
Hard 1.7 1.7 2.2 1.1 1.1 1.2
Contrast 8 HAT 12 HAT
Chewings vs. others ** NS
Creeping vs. Hard NS NS

 

**Denotes significance at p=0.01

a1=no injury 9=complete kill; A rating of 3 or greater was considered to be unacceptable injury.

50

Table 3. Dithiopyr + adjuvants phytotoxicity to ’Midnight’
Kentucky bluegrass.

 

Injury (1-9)8

 

 

 

Treatment Rate (kg ai/A) 17 DATb 28 DATb
non-15104 + x-77 0.42 4 0.5% v/v 1.0 1.0
MON-15104 + Herbimax 0.42 + 0.5% v/v 1.0 1.0
MON-15104 + CSY-77715512 0.42 + 0.5% v/v 1.0 1.0
MON-15104 + Agsco Sunit 0.42 + 0.5% v/v 1.0 1.0
MON-15104 + Dow Corning 6955-145 0.42 + 0.5% v/v 1.0 1.0
MON-15104 0.42 1.0 1.0
MON-15104 + Pfizer M 0.42 + 0.5% v/v 1.0 1.3
MON-15104 + Activator 90 0.42 + 0.5% v/v 1.0 1.3
MON-15104 + Dow Corning X2-5309 0.42 + 0.5% v/v 1.0 1.3
MON-15104 + Pfizer 14636-181-7 0.42 + 0.5% v/v 1.0 1.3
CONTROL 1.0 1.3
MON-15104 + Dash 0.42 + 0.5% v/v 1.3 1.3
Fenoxaprop 0.20 2.7 3.0
LSD.05: 0.8 0.8
a1=no injury 9=complete kill; A rating of greater than 2 was considered to be unacceptable

bDays after treatment

 

51

Table 4. Effect of preemergence herbicides on rooting of
Kentucky bluegrass.

 

 

Herbicide Rate (kg ai/A) Root dry weight (grams)
CONTROL 1 .17
MON-15151 1EC 0.84 1.13
MON-15151 1EC 0.42 1.10
Prodiamine 65HDG 0.84 1.09
MON-15151 1EC 1.12 1.08
Pendimethalin 65HDG 3.36 1.00
Oxadiazon ZG 4.48 0.99
Oxadiazon 26 2.24 0.98

 

Lsofls: us

 

 

10.

LITERATURE CITED

Bhomik, P. C. and B. M. Bahnson. 1989. Pre- and
postemergence smooth crabgrass control with MON-15151 in
cool-season turfgrass. Proc. Northeastern Weed Sci. Soc.
43:110.

Bingham, S. W. 1974. Influence of selected herbicides on
rooting of turfgrass sod. Proc. Intl. Turf. Res. Conf.
2:372-377.

Brauen, S. E., R. Crockett, S. K. Parrish, and R. L. Goss.
1988. Efficacy of MON 15100 on annual bluegrass control in
mixed colonial and creeping bentgrass turf. Agron. Abs.
p.148. .

Callahan, L. M. 1972. Phytotoxicity of herbicides to a
’Penncross’ bentgrass green. Weed Sci. 20:387-391.

Cisar, J. L. and J. A. Jagschitz. 1984. Turfgrass
tolerance to post- and preemergence herbicides. Proc.
Northeastern Weed Sci. Soc. 38:298-302.

Dernoeden, P. H. and D. B. Davis. 1989. Herbicide tank
mixes for postemergence control of smooth crabgrass in
turf. Proc. Northeastern Weed Sci. Soc. 43:85-86.

Dernoeden, P. H. and D. B. Davis. 1989. Preemergence
control of smooth crabgrass and goosegrass in Maryland in
1988. Proc. Northeastern Weed Sci. Soc. 43:93-94.

Dernoeden, P. H., D. B. Davis, and J. 0. Fry. 1988.
Rooting and cover of three turf species as influenced by
preemergence herbicides. Proc. Northeastern Weed Sci. Soc.

42:169-173.

Fry, J. 0., P. H. Dernoeden, and J.J. Murray. 1986.
Establishment and rooting of zoysiagrass (Zovsia .iaponica)
as affected by preemergence herbicides. Weed Sci. 34:413-
418.

Hurto, K. A. and L. Schaber. 1989. Preemergence activity
of MON 15151 for smooth crabgrass control in Kentucky
bluegrass turf. Proc. Northeastern Weed Sci. Soc. 43:104.

52

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

53

Jagschitz, J. A. and C. D. Sawyer. 1987. Effect of
herbicides applied during annual grass emergence in turf.
Proc. Northeastern Weed Sci. Soc. 41:213-214.

Jagschitz, J. A. and C. D. Sawyer. 1989. Preemergence
control of crabgrass, spurge and oxalis and pre-post, post
control of crabgrass in turf. Proc. Northeastern Weed Sci.
Soc. 43:96-97.

Johnson, B. J. 1980. Rootgrowth of southern turf cultivars
as affected by herbicides. Weed Sci. 28:526-528.

Johnson, B. J. 1982. Frequency of herbicide treatments for
summer and winter weed control in turfgrasses. Weed Sci.
30:116-124.

Murray, J. J., D. L. Klingman, R. G. Nash, and E. A.
Woolson. 1983. Eight years of herbicide and nitrogen
fertilizer treatments on Kentucky bluegrass (Bee
pratensis) turf. Weed Sci. 31:825-831.

Parrish, S. K., R. J. Thompson, S. J. Stehling, D. E.
Schafer, and J. E. Kaufmann. 1987. Discovery and early
development of MON-15100 for crabgrass (Digitaria spp.)
control in turfgrass. Agron. Abs. p.137.

Sawyer, C. D. and J. A” Jagschitz. 1987. Postemergence
crabgrass control in turf - 1985 and 1986. Proc.
Northeastern Weed Sci. Soc. 41:220-221.

Smucker, A. J. M., S. L. McBurney, and A. K. Srivastava.
1982. Quantitative separation of roots from compacted soil
profiles by the hydropneumatic elutriation system. Agron.
J. 74:500-503.

Torello, W. A. and J. A. Jagschitz. 1979. Crabgrass
control in turf using preemergent herbicides and
surfactants. Proc. Northeastern Weed Sci. Soc. 33:297-302

Turgeon, A. J., R. P. Freeborg, and W. N. Bruce. 1975.
Thatch development and other effects of preemergence
herbicides in Kentucky bluegrass turf. Agron. J. 67:563-
565.

 

21.

54

Watschke, T. L. and J. M. Duich. 1978. Control of
crabgrass in Kentucky bluegrass and red fescue turf using

preemergence herbicides. Proc. Northeastern Weed Sci. Soc.
32:303-307.

 

Chapter 3

FACTORS INVOLVED IN THE ADJUVANT ENHANCEMENT OF
POSTEMERGENCE CRABGRASS CONTROL WITH DITHIOPYR

ABSTRACT

A greenhouse study was conducted to determine the site of
uptake of dithiopyr applied postemergence to large crabgrass.
Using barriers to isolate the foliage and the soil, the
primary site of uptake was found to be via the foliage. Based
on this result, adjuvants were evaluated for enhancement of
postemergence crabgrass control with dithiopyr. Imnpreviously
reported studies, several adjuvants significantly increased
control in the field and greenhouse. Further laboratory and
greenhouse studies were conducted to elucidate the factors
involved in the enhancement of dithiopyr control by nine of
these adjuvants. Experiments with 1‘C-dithiopyr revealed that
only two adjuvants significantly increased absorption with the
MON-15104 formulation of dithiopyr, giving increases of 5.0-
5.4% over the herbicide alone. Seven adjuvants significantly
increased absorption with the MON-15151 formulation, giving
increases of 6.2-15.2%. Despite the differences in
absorption, no adjuvants resulted in increased translocation
of the applied herbicide out of the treated leaf, with less
than 1% translocated in all cases. However, because of the

very low levels of radioactivity detected outside the treated

55

 

56

leaf, these studies may not have been sensitive enough to
detect true adjuvant effects on translocation. A greenhouse
study in which a single, isolated large crabgrass leaf was
treated, indicated that enhancement of dithiopyr activity by
adjuvants did involve an effect on translocation, as well as
on spray retention, and on the external movement of the spray
solution to the apical meristem. Enhancement seems to involve
a combination of these three factors plus absorption, with the
relative importance of any one factor depending on the
particular adjuvant used. A. temperature study revealed
decreasing absorption, and increasing non-recoverability of
dithiopyr, with each 10° C increase in temperature. The
percent non-recoverable dithiopyr, believed to represent
volatilized herbicide, ranged from 46-55% at 5° C, to 92-95%
at 35°C; Volatility losses of this magnitude mitigate any
positive adjuvant effects on absorption of dithiopyr.
Nomenclature: dithiopyr, 3,5-pyridinedicarbothioic acid,2-
(difluoromethyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-§,S-
dimethylester; large crabgrass, Digitaria sanguinalis (L.)
Scop. #‘ DIGSA.

Additional index words. Site of uptake, surfactants,

volatility.

 

1Letters following this symbol are a WSSA-approved computer
code from. Composite List. of ‘Weeds, Weed Sci. 32, Suppl. 2.
Available from WSSA, 309 West Clark St., Champaign, IL 61820.

 

57
INTRODUCTION

Dithiopyr is a new preemergence herbicide from the
Monsanto Agricultural Company. This product also effectively
controls untillered crabgrass ‘when applied postemergence.
Little is known concerning the route of entry of dithiopyr
into the crabgrass plant when applied postemergence» Once the
route of entry is known, strategies can be explored for
enhancing the postemergence activity of dithiopyr.

Herbicides can be taken up by plants through root or
shoot tissue (2). If the plant foliage is the primary site of
absorption, adjuvants can be used to enhance herbicidal
activity. Adjuvants used in postemergence applications to
increase the activity of herbicides are classified as
activator adjuvants, and include surfactants and oils (6).

According to Holly (3), surfactants may influence
herbicidal efficacy by increasing leaf wettability, increasing
spray retention, increasing droplet spread, decreasing surface
and interfacial tensions, acting as a humectant or co-solvent,
or acting as a cuticle solubilizer. Sands and Bachelard (8)
found that surfactants increased herbicide uptakerbylaffecting
wetting of the leaf surface and dissolving the epicuticular

wax. The hydrophilic-Iipophilic balance of an adjuvant may

58

also determine its effectiveness in enhancing herbicidal
activity (5).

Many researchers have reported increased absorption of
1"C-labeled herbicides when adjuvants were added to the spray
solution (1, 8, 9, 11, 12). Adjuvants can also increase the
translocation of herbicides (3, 6). McWhorter noted that the
most effective surfactants in increasing absorption were not
always best in increasing herbicide translocation away from
the treated area (6).

Immediately after application, herbicides begin to
disappear from the target area through a variety of physical
or chemical processes (10). Clearly, a high rate of loss from
any process will diminish the positive effects adjuvants may
otherwise have on absorption. Volatilization is one process
by which herbicides are dissipated. No published information
is available regarding losses of dithiopyr by volatilization.
According to Nash (7), volatilization losses are influenced by
the herbicide vapor pressure, application method, formulation,
temperature, relative humidity, wind velocity and target
surface roughness. Under unfavorable conditions, losses of
herbicide residues may approach 80-90%‘within a few days (10).

The objectives of this research were: 1) to determine

the site of uptake of dithiopyr applied postemergence to

 

 

59

crabgrass, and 2) to evaluate the factors involved in adjuvant
enhancement of dithiopyr activity on this weed. The latter
objective was pursued by examining adjuvant effects on
dithiopyr: absorption and translocation, investigating the
factors necessary for whole plant control with dithiopyr and
adjuvants, and examining the effect of temperature on

dithiopyr absorption with adjuvants.

60
MATERIALS AND METHODS

n r r r f r nh im n
Large crabgrass was grown from seed in 355 ml styrofoam
cups. On the day of treatment, cups were thinned to one plant
each. Dithiopyr and adjuvant treatments were applied with a
trolley Sprayer delivering 163 l/ha at 0.21 MPa. Following
treatment, plants were placed in the greenhouse under
automatic irrigation. Supplemental lighting from metal-halide
vapor lamps provided a 16 hour day length. Greenhouse
temperature was maintained at 22 1 2° C. and relative humidity
at 40-75%.
i f k
A two factor randomized complete block design was used
with six replications. 'The factors were dithiopyr (MON-15151)
rate and site of application. Crabgrass plants were at the
three-leaf stage when treated. The soil in the styrofoam cups
was a Spinks sandy loam (mixed, mesic Psammentic Hapludalfs).
Dithiopyr rates were 0.01, 0.02, 0.04 and 0.07 kg ai/ha in
experiment 1. Two additional rates, 0.14 and 0.28 kg ai/ha,
were included in experiment 2. The two experiments were

identical in all other respects.

 

61

The foliar and soil sites of application were isolated
using barriers. A sheet of aluminum foil, placed over the
soil and fitted carefully around the base of the crabgrass
plant, was used to isolate the foliage. The soil was isolated
by carefully folding the crabgrass leaves upwards, along the
axis of the stem, and wrapping the plant with a small strip of
parafilm. A normally applied treatment (no barriers) was
included for comparison purposes, along with two sets of
untreated controls. The barriers were removed immediately
after treatment and the soil-applied treatments were covered
with a 0.5 cm layer of fresh soil to minimize volatilization
of the herbicide.

The pots were placed in the greenhouse and irrigation was
withheld for eight hours following treatment. After two
weeks, shoot fresh weights were taken and the percent of
control shoot fresh weight for each treatment was calculated
based on the untreated controls. The data were subjected to
analysis of variance and the effects of the foliar and soil
sites were evaluated by performing orthogonal contrasts.
Leaf isulatiun

A completely randomized design with six replications was

used for these experiments. The large crabgrass plants were

 

62

grown in Baccto2 potting media and were at the three-leaf
growth stage when treated.

The second leaf (youngest fully expanded) was isolated
for treatment by placing a small, adhesive paper strip, folded
at a 90° angle, at the base of the leaf blade. A slit was
then cut in a lightweight plastic bag, the leaf was pulled
through the slit, and the bag was taped in place. The purpose
of the bag was to ensure that only the isolated leaf was
contacted by herbicide when sprayed; the purpose of the
adhesive paper strip was to prevent the herbicide from running
off the treated leaf onto the rest of the plant.

The dithiopyr/adjuvant treatments (Table 4) were applied
in the trolley sprayer. The dithiopyr rate was 0.03 kg ai/ha
and adjuvants were added at 0.5% v/v. The leaves were allowed
to dry before removing the bag, and the plants were placed in
the greenhouse. Shoot fresh weights were taken after two
weeks, and percent control was calculated based on the shoot
fresh weights of the untreated controls. The data were
transformed by the arcsin transformation and the analysis of

variance and LSD multiple range test were performed on the

 

zBaccto is a product of Michigan Peat Company, P.o. Box
980129, Houston, TX. 77098.

 

63

transformed data. Means reported are the actual percent
control values (Tables 4 and 5).

r i n n r n l i n

Large crabgrass was grown from seed as described above.
Plants were at the four-leaf stage when treated. We
encountered great difficulty in forming a:stable emulsion with
the 1‘C-dithiopyr; therefore, to accurately determine the
radioactivity applied per leaf, it was necessary to prepare a
separate spotting solution for each plant. The spotting
solutions were made by adding 1"C-dithiopyr (specific activity
29.24» mCi/mmole, uniformly ring labeled) to commercially
formulated dithiopyr, distilled water and adjuvants, to give
a final volume of 10 ul. The dithiopyr formulation was MON-
15104 in experiments 1 and 2, and MON-15151 in experiment 3.
Each solution contained 12.1 ug dithiopyr, 1.3% of which was
1‘C-dithiopyr. The effect of adjuvants was examined by adding
them to the spotting solution at 0.5% v/v (Tables 1,2 and 3).
The spotting solution was equivalent to a dithiopyr spray
solution containing 0.28 kg ai/ha at a spray volume of 234
l/ha.

Two microliters of the spotting solution were applied to
the center of the adaxial surface, between thernidrib and leaf

edge, of the youngest fully expanded leaf. The remaining

 

 

64

spotting solution was then transferred into a scintillation
vial with five-0.1 ml hexane rinses, covered with 12 ml
scintillation cocktail, and radioassayed by liquid
scintillation spectrometry. The radioactivity added to the
spotting solution, minus the radioactivity in the hexane
rinsate, equalled the radioactivity applied to the leaf, and
was typically around 0.003 uCi.

The treated plants were placed under fluorescent lighting
in the laboratory for 24 h. The laboratory temperature was
2112° C. The plants were then separated into the treated
leaf, parts above, and parts below the treated leaf, excluding
roots. After separation, the treated leaf was rinsed with 10
ml acetone to remove any unabsorbed I"C-dithiopyr. Preliminary
studies revealed that the 24 h time period allowed maximum
absorption and translocation of the herbicide, and that the 10
ml acetone rinse would remove all surface radioactivity. The
acetone rinsate was evaporated for 36 h to near dryness, and
radioassayed as previously described. Plant parts were frozen
until combusted to 1"C02 in a biological oxidizer, and the
combusted samples were radioassayed.

Percent 1"C-dithiopyr absorption was calculated based on
the total radioactivity' recovered in 'the plant, and the

initial amount applied to the leaf; Percent translocation was

65

calculated based on the radioactivity recovered in plant parts
away from the treated leaf, and the initial amount applied to
the leaf. No significant difference occurred in translocation
to plant parts above or below the treated leaf, so the data
were combined for reporting purposes. Percent 1"'C-dithiopyr
not recovered was calculated based on the radioactivity
recovered in the plant plus the acetone rinsate, and the
initial amount applied.

A randomized complete block design was used with four
replications. The data were transformed by the arcsin
transformation and the analysis of variance and LSD multiple
range tests were performed on the transformed data. Means
reported are the untransformed data.

Aside from the different dithiopyr formulation used in
experiment 3, all three experiments were identical, except
that the experiment 1 plants were kept on the laboratory bench
for the 24 h absorption period, while the experiment 2 and 3
plants were kept in a modified fume hood, because of
volatility concerns. The fume hood was modified by plugging
all lower vents, so that the laboratory air entered the hood
only from the front, and was exhausted only at the top of the
hood. In this manner, air flow over the treated plants was

minimized.

66

Eff f m r r n “ - i hi r i n

A two factor randomized complete block design was used
with four replications. The factors were post-treatment
temperature and adjuvant treatment. Procedures were the same
as in the absorption/translocation experiments, except that
translocation was not examined, so the treated plant was not
separated prior to combustion. Adjuvants used are listed in
Table 6. Immediately following treatment, the plants were
placed in a growth chamber for the 24 h absorption period.
Post-treatment temperatures investigated were 5, 15, 25 and
35° C. Relative humidity in the chamber was maintained at 75
i 5%. The experiment was repeated, and the data from the two
experiments were combined. The arcsin transformation was
performed on the data, and the transformed data were subjected
to analysis of variance. Means were separated by the LSD

multiple range test.

67
RESULTS AND DISCUSSION

Site 9f uptake

The herbicidal effect from the foliar-applied treatments
closely approximated the effect given by the normally applied
treatments, with increasing control as the dithiopyr rate was
increased (Figures 1 and 2). By contrast, the soil-applied
treatments provided minimal control at all dithiopyr rates.

Orthogonal contrasts between the foliar and soil-applied
treatments at each rate revealed highly significant
differences at the two high rates, 0.04 and 0.07 kg ai/ha, in
experiment 1 (Figure 1). The lowest rate, 0.01 kg ai/ha, was
significantly different between the treatments, but this
result had little interpretive value because of the varying
response to the herbicide at the lowest rates (Figures 1 and
2).

In experiment 2, the overall level of control was lower,
possibly because the crabgrass plants were slightly larger
when treated. Despite this fact, results were similar to
those obtained in experiment 1. Orthogonal contrasts revealed
highly significant differences between the foliar and soil-
applied treatments at the two highest rates, 0.14 and 0.28 kg
ai/ha (Figure 2). The 0.04 kg ai/ha rate was significantly

 

68
different between the two treatments, but the 0.07 kg ai/ha

rate was not. The lack of significance at the 0.07 kg ai/ha
rate was due to a 25% increase in control over the 0.04 kg
ai/ha rate by the soil-applied treatments, while the foliar-
applied treatments, though still giving far greater control,
increased by only 10% over the 0.04 kg ai/ha rate.

These experiments indicate that the primary site of
uptake of dithiopyr, applied postemergence to crabgrass, is
through the foliage.

A r i n n r n l i n wi h M -1 1 4

In experiment 1, only Dow Corning X2-5309 significantly
increased absorption over dithiopyr alone (Table 1), and in
experiment 2, only X-77 significantly increased absorption
(Table 2). Activator 90, while not significantly different
from the herbicide alone, was the only adjuvant to increase
absorption by more than 3% in both experiments. No adjuvant
significantly decreased absorption in either experiment.
Previous field studies, in which the adjuvants were combined
with the MON-15104 formulation of dithiopyr, revealed
significant increases in crabgrass control with several of the
adjuvants, and non-statistically significant increases with
the remaining ones (see chapter 1). Therefore, the increased

control with adjuvants cannot be explained by an effect on

 

69

absorption, with the possible exceptions of Dow Corning X2-
5309, X-77 and Activator 90.

Translocation of dithiopyr out of the treated leaf was
less than 1% of the applied herbicide in all cases, and was
not significantly increased with any of the adjuvant
treatments (Tables 1 and 2). This suggests that adjuvants do
not affect translocation of dithiopyr in the plant; however,
this may be a premature conclusion, because the amount of
radioactivity detected outside the treated leaf was nearly
always less than twice the background levels. Thus, these
experiments may not have been sensitive enough to detect true
differences in translocation with the adjuvants.

The percent of the applied herbicide that was not
recovered ranged from 65-77% in experiment 1 (Table 1), and
64-78% in experiment 2 (Table 2). This almost certainly
represents loss by volatilization, because the root system is
the only other possible sink for the non-recovered herbicide,
and translocation out of the treated leaf was less than 1%.
Volatility losses of this magnitude in 24 h will certainly
mitigate any adjuvant effects on absorption. The decreased
absorption effect of Dow Corning X2-5309 in experiment 2 may

be related to increased volatility of this adjuvant/herbicide

 

7O

combination in the fume hood versus on the laboratory bench
(Tables 1 and 2).
Absurptiun end trenslueatiun with MON-15151

When added to the MON-15151 formulation of dithiopyr, all
adjuvants except Agsco Sunit and Dash significantly increased
absorption over MON-15151 alone (Table 3). Notably, the MOM-
15104 formulation also significantly increased absorption over
MON-15151.

Despite the increased absorption, none of the adjuvants
had a significant effect on the amount of herbicide
translocated out of the treated leaf, which was less than 1%
in all cases (Table 3). It is important to note that, as with
the MON-15104 formulation, the radioactivity detected outside
the treated leaf’ was nearly always less than twice the
background levels. Thus, this experiment may not have been
sensitive enough to detect true differences in translocation
with adjuvants, and the conclusion that adjuvants have no
effect on translocation may be premature. P r e v i o u 5
greenhouse studies, in which these adjuvants were added to the
MON-15151 formulation, resulted in significantly increased
control with all the adjuvants (see chapter 1). The fact that
Agsco Sunit and Dash did not significantly increase absorption

of 1"'C-dithiopyrsuggests that other factors besides absorption

71

are involved in the adjuvants’ enhancement of dithiopyr
activity in the greenhouse.

The percent of the applied herbicide that was not
recovered ranged from 52-78% (Table 3). It is interesting to
note that a lower value here (meaning greater recovery) did
not always relate to greater absorption. Some of the
adjuvants seemed to decrease volatilization of the herbicide,
but rather than leading to greater absorption, much of the
herbicide simply remained on the leaf surface. This
particularly seems to be the case with Pfizer 14636-181-7,
Agsco Sunit and Dash.

Leaf isulatiun

The site of action of dithiopyr is believed to be the
apical meristem, where it functions as a mitotic inhibitor3.
Therefore, dithiopyr must reach the apical meristem in toxic
quantities for effective control to occur. This experiment
was designed to test the hypothesis that adjuvants enhance
crabgrass control by increasing the external movement of the
spray solution down the plant, so that the active ingredient

is placed near the apical meristem.

 

3.1T. 8. Kaufman, Monsanto Agricultural Co., personal
communication.

 

72

Because the spray solution was prevented from moving off
the treated leaf externally, the achievement of control levels
as high as 77% in experiment 1 (Table 4), and 61% in
experiment 2 (Table 5), indicates that, with some adjuvants,
enough herbicide is being translocated to the apical meristem
to exert a toxic effect on the plant. In light of the fact
that less than 1% of the applied herbicide was translocated
out of the treated leaf in the absorption/translocation
experiments, it seems that very low levels of dithiopyr at the
site of action are necessary to exert a toxic effect.

Several of the adjuvants increased control significantly
over dithiopyr alone (MON-15151 formulation) in experiment 1
(Table 4). Interestingly, these were not necessarily the same
adjuvants that were most effective in increasing absorption in
absorption/translocation experiment 3, in which the MON-15151
formulation of dithiopyr was also used. This suggests that
there may be differences in spray retention among treatments,
because any adjuvant effects on spray retention in the
absorption/translocation experiments were effectively bypassed
by placing the spray solution on the leaf with alnicrosyringe.

Even with differences in spray retention among adjuvants,
however, it seems probable that adjuvant effects on

translocation are more important in achieving control. Pfizer

 

 

73
M, Pfizer 14636-181-7 and Agsco Sunit gave the best control in

both leaf isolation experiments (Tables 4 and 5), yet were
among the poorest adjuvants in increasing absorption (Table
3). Even if an effect on spray retention caused a 50%
increase in absorption with these adjuvants, they still would
not equal the absorption achieved with X-77 and Activator 90
(Table 3). It is quite possible that some adjuvants are
enhancing dithiopyr absorption into the cuticle, but are
causing the herbicide molecules to be bound there, preventing
further penetration into the symplast.

Several of the adjuvants, particularly the two Dow
Corning products, gave no greater control than dithiopyr alone
(Table 4), despite dramatically increasing control in previous
greenhouse experiments where the whole plant was treated (see
chapter 1). This result confirmed our hypothesis that these
adjuvants were enhancing control by increasingimovement of the
spray solution down the plant so the active ingredient was
physically placed near the apical meristem. EXperience in
working with the two Dow Corning adjuvants, both organo-
silicone based compounds, showed that they decreased the
surface tension of the spray solution more than any other

adjuvant, as judged by the droplet spread on the leaf.

 

 

74

None of the adjuvants were significantly different from
dithiopyr alone in experiment 2 (Table 5), though the trend
was similar to experiment 1, in that the same three adjuvants
gave the best control, and the two Dow Corning adjuvants gave
the worst. For reasons that are not clear, the crabgrass
plants grew less vigorously in experiment 2, resulting in
control plants nearly half the size of those in experiment 1,
and, consequently, less separation of the treatments.
However, the results of this experiment further confirm the
physical placement hypothesis.

In summary, these experiments indicate that the adjuvant
enhancement of dithiopyr activity on crabgrass is related to
effects on absorption, translocation, spray retention and the
physical placement of the active ingredient near the apical
meristem. Enhancement seems to be a combination of the four
factors, and the importance of any one factor depends on the
particular adjuvant used.

The conclusion that adjuvants affect dithiopyr
translocation contradicts the results from the 1"(i-dithiopyr
absorption/translocation experiments in which no differences
in translocation were found. As stated previously, very
little dithiopyr is apparently needed at the site of action;

consequently, the 1"C-dithiopyr translocation experiments were

 

75

probably not sensitive enough to detect true differences in
translocation. Because of their apparent ability to detect
translocation differences, the leaf isolation experiments
would seem to be superior to 1"C-dithiopyr screens for
selecting adjuvants toienhance dithiopyr control of crabgrass.
However, the leaf isolation experiments are tedious to
perform, and their exclusive use for adjuvant selection would
preclude selection of adjuvants which increase control
primarily by enhancing physical placement of dithiopyr near
the apical meristem, such as Dow Corning X2-5309 and Dow
Corning 6955-145. Consequently, the most reliable screening
method for selecting superior adjuvants, as well as the least
expensive, appears to be greenhouse screens with whole
crabgrass plants. This screening method needs to be made more
stringent, however, to facilitate separation of superior
adjuvants from inferior ones. A more stringent test could be
achieved by treating larger, tillered crabgrass plants, or by
simulating an actual turf situation, perhaps by mixing
perennial ryegrass (Lulium perenne L.) with crabgrass, in
which the turf foliage would intercept some herbicide that

might otherwise reach the crabgrass apical meristem.

 

76

Eff f m r r n “ - i hi r r i n

The regression equation for the relationship between
dithiopyr absorption and temperature was significant at
p=0.001, and the association was strong, as indicated by the
r2 value of 0.87 (Figure 3). The mean absorption was 32.4,
20.1, 11.6 and 5.1% at 5, 15, 25 and 35° C, respectively.
Similarly, the regression equation for the relationship
between non-recoverability of dithiopyr and temperature was
significant at p=0.001 and the association was strong, with an
r2 value of 0.92 (Figure 4). The mean percent not recovered
was 50, 71, 86 and 94% at 5, 15, 25 and 35° C, respectively.

Non-recoverable dithiopyr, as stated previously, almost
certainly represents volatilized herbicide, and this
supposition is strengthened by the increasing loss at higher
temperatures.

As shown by the orthogonal contrast in table 6, Dow
Corning X2-5309 significantly increased absorption over the
other adjuvants and dithiopyr alone. Though the Dow Corning
X2-5309 treatment had the highest absorption at each
temperature, the effect was decreased at 25 and 35°C, leading
to a significant interaction between the adjuvant effect and
temperature in the analysis of variance (not shown). This

decreased effect at higher temperatures can be directly

 

 

77

attributed to the increased volatility of the herbicide,
thereby giving the adjuvant less opportunity to enhance
absorption.

Though volatility increased, and absorption decreased,
for each individual treatment as the temperature was raised,
it was not necessarily true that the adjuvant giving the least
volatility was most effective in increasing absorption. This
is evidenced by the fact that Dow Corning X2-5309 had the
highest volatility at the 5° C temperature, but also had the
highest absorption. Comparing orthogonal contrasts reveals
that the X-77 treatment had significantly (p=0.001) less
volatility than dithiopyr alone (Table 7), but did not give
significantly more absorption (Table 6). Thus, comparing
volatility at different temperatures for an individual
adjuvant provides a good indication of its relative
effectiveness at each temperature, but the same is not true of
volatility comparisons made among different adjuvants at the
same temperature.

Based on the results of this experiment, turfgrass
managers would be wise to apply dithiopyr, with or without
adjuvants, at times when volatilization will be at a minimum.

Applications during the early'morning hours, when soil and air

 

 

 

 

78

temperatures are at a minimum, are recommended. Applications

during the heat of the day should be strictly avoided.

 

 

79

Table 1. Effect of adjuvants on absorption and
translocation of 1"C-dithiopyr (MON-15104) -
Experiment 1.

 

 

Adjuvant X Absorbeda X Translocateda X Not recovereda
Dow Corning X2-5309 23.1 a 0.7 a 70 bc
Activator 90 21.5 ab 0.5 ab 65 c
X-77 20.1 abc 0.4 b 70 be
Agsco Sunit 18.8 bcd 0.5 ab 70 be
Dow Corning 6955-145 18.3 bcd 0.7 a 77 a
none 18.1 bcde 0.5 ab 73 ab
Pfizer M 16.9 cde 0.4 b 74 ab
Herbimax 16.4 cde 0.5 ab 74 ab
Pfizer 14636-181-7 16.0 de 0.3 be 69 be
=2332 14.5 e 0.2 c 77 a

 

aMeans followed by the same letter are not significantly different by LSD at p=0.05.

 

 

80

Table 2. Effect of adjuvants on absorption and

translocation
Experiment 2.

of "C-dithiopyr (MON-15104) —

 

 

Adjuvant X Absorbeda X Translocateda X Not recovereda
X-77 20.3 a 0.3 ab 69 cd
Activator 90 20.2 ab 0.2 b 65 d
Dash 16.2 abc 0.3 ab 70 bcd
Pfizer M 16.1 abc 0.2 b 75 abc
Dow Corning 6955-145 16.0 abc 0.3 ab 76 ab
Dow Corning X2-5309 15.5 abc 0.2 b 78 a
none 14.9 bc 0.4 a 76 ab
Herbimax 13.1 c 0.2 b 77 a
Agsco Sunit 13.0 c 0.3 ab 75 abc
Pfizer 14636-181-7 11.5 c 0.2 b 64 d

 

aMeans followed by the same letter are not significantly different by LSD at p=0.05.

 

81

Table 3. Effect of adjuvants on absorption and
translocation of 1"C-dithiopyr (MON-15151) -
Experiment 3.

 

 

Adjuvant X Absorbeda X Translocateda X Not recovereda
X-77 22.4 a 0.3 a 60 cde
Activator 90 21.7 a 0.2 a 64 cd
Dow Corning 6955-145 19.1 ab 0.3 a 76 ab
Pfizer M 18.6 abc 0.2 a 69 bc
Herbimax 17.4 abc 0.1 b 77 ab
Dow Corning X2-S309 15.8 bc 0.3 a 78 a
MON-15104 only 15.7 be 0.2 a 76 ab
Pfizer 14636-181-7 13.4 cd 0.1 b 52 e
Agsco Sunit 10.4 de 0.2 a 64 cd
Dash 9.8 de 0.2 a 59 de
MON-15151 only 7.2 e 0.2 a 77 ab

 

aMeans followed by the same letter are not significantly different by LSD at p=0.05.

 

82

Table 4. Treatment of an isolated crabgrass leaf with
dithiopyr (MON-15151) and adjuvants -
Experiment 1.

 

 

Adjuvant X Controla
Pfizer M 77 a
Agsco Sunit 72 ab
Pfizer 14636-181-7 70 ab
Herbimax 66 abc
x-77 63 abc
Activator 90 59 bed
Dash 51 cd
none 44 de
Dow Corning X2-5309 41 de
Dow Corning 6955-145 28 e

 

aMeans followed by the same letter are not significantly different by LSD at p=0.05.

83

Table 5. Treatment of an isolated crabgrass leaf with
dithiopyr (MON-15151) and adjuvants -
Experiment 2.

 

 

Adjuvant X Controla
Pfizer 14636-181-7 61 a
Pfizer M 55 ab
Agsco Sunit 52 abc
none 40 abcd
Dash 38 abcd
Activator 90 30 abcd
Herbimax 29 abcd
X-77 27 bed
Dow Corning 6955-145 28 cd
Dow Corning X2-5309 4 d

 

aMeans followed by the same letter are not significantly different by LSD at p=0.05.

 

 

84

 

 

 

 

 

Table 6. Effect of temperature on dithiopyr uptake with
adjuvants.
X Uptake
------------------------------------ Adjuvant------------------------------------
Dow Corning Agsco No
Temp. (0C) Dash x2-5309 Sunit x-77 adjuvant
5 3L6 310 326 3L9 3L1
15 17.0 28.6 17.3 20.1 17.5
25 10.5 16.1 10.9 10.8 9.9
35 45 6A 42 53 43
Mean: 15.9 22.5 16.3 17.2 15.7
Contrast
x2-5309 vs. ***
rest
X-77 vs. NS

no adjuvant

* *i‘

, , *** Denote significance at p=0.05, 0.01 and 0.001, respectively.

 

 

85

Table 7. Effect of temperature on non-recoverability of
dithiopyr with adjuvants.

 

Not recovered

 

 

n.1- -
HHJUVDIIL

 

 

 

Temp. (0C) Dow Corning Agsco no
Dash X2-5309 Sunit X-77 adjuvant
5 49 55 49 46 52
15 76 67 70 67 73
25 88 82 87 86 89
35 95 92 95 93 95
Mean: 77 74 75 73 77
Contrast
X2-5309 vs. *
rest
X-77 vs. ***

no adjuvant

*, *** Denote significance at the p=0.05 and 0.001

levels, respectively.

 

86

Figure 1. Effect of site of application of dithiopyr on
large crabgrass control-- Experiment 1.

 

 

 

 

87

 

A936 9; NEE
3.0 no.6 mono 5.0
520 «<30... «I
f/ 520 ._.om arm
1 ill 83%: .2302 616

 

 

OOAV

o

lop

ION

I

new

j

10...

Ion
s
row

 

Ioow

'IOéJlNOO _-lO %

88

Figure 2. Effect of site of application of dithiopyr on
large crabgrass control-- Experiment 2.

 

 

89

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Ra Rs 8.8. m3 3.6

 

ow_r_n_n_< 4<2moz 010
>._ZO m<_._or._ «10

>420 .__Om mim—

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WON
mom
woo
wow
wow
won
wow
mom
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‘lOELLNOO :lO %

90

Figure 3. Effect of temperature on absorption of 1"C-
dithiopyr alone and in combination with
adjuvants.

IIIIIII 1

0. mm Esme 2m:
0.0+ 0.0m 0.0m. 0.0m 0.0m 0.0— 0.0 F 0.0 0.0
_ b _ _ .

0 0
l0.m
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I06 F
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91

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lodn

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t... .xwodtan.78.0.41A . no.6...
. 10.9.

 

. r. 0.00

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92

Figure 4. Effect of temperature on non-recoverability of
1‘C—dithiopyr alone and in combination with
adjuvants.

93

o. mmaszzE

0.0+ 0.0m. 0.0m 0.0m 0.0N 0.0 — 0.0p
_ _ _ _ _ h _

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4...... .xnodrimwinanus

 

 

100—

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LITERATURE CITED

Buhler, D. D. and O. C. Burnside. 1984. Effect of
application factors on postemergence phytotoxicity of
fluazifop-butyl, haloxyfop-methyl, and sethoxydim. Weed
Sci. 32:574-583.

Hess, F. D. 1985. Herbicide absorption and translocation
and their relationship to plant tolerances and
susceptibility. p. 191-214 in S.O. Duke, ed. Weed
Physiology, vol. 2: Herbicide Physiology. CRC Press Inc.,
Boca Raton, FL.

Holly, K. 1964. Herbicide selectivity in relation to
formulation and application methods. p. 423-464 in L.J.
Audus, ed. The Physiology and Biochemistry of Herbicides.
Academic Press, New York.

Kirkwood, R. C., I. McKay, and R. Livingstone. 1982. The
use of model systems to study the cuticular penetration of
“C-MCPA and 1C-MCPB. p.237-252 in D. F. Cutler, K. L.
Alvin and C. E. Price, eds. The Plant Cuticle. Academic
Press, New York.

McWhorter, C. G. 1985. The physiological effects of
adjuvants on plants. p. 141-158 in S. 0. Duke, ed. Weed
Physiology, vol. 2: Herbicide Physiology. CRC Press Inc.,
Boca Raton, FL.

Nash, R. G. 1988. Dissipation from soil. p.131-l69 in R.
Grover, ed. Environmental Chemistry of Herbicides, vol. 1.
CRC Press, Inc., Boca Raton, FL.

Sands, R. and E. P. Bachelard. 1973. Uptake of picloram by
eucalypt leaf discs: I. Effect of surfactants and nature
of the leaf surfaces. New Phytol. 72:69-86.

Swietlik, D. 1989. Adjuvants affect the efficacy of
glyphosate on selected perennial weeds. HortScience
24:470-472.

Taylor, A. W. and D. E. Glotfelty. 1988. Evaporation from
soils and crops. p. 89-129 in R. Grover, ed. Environmental

94

 

10.

11.

95

Chemistry of Herbicides, vol. 1. CRC Press, Inc., Boca
Raton, FL.

Thompson, 0. A. 1986. Use of frigate with glyphosate. Can.
J. Plant Sci. 66:203.

Wanamarta, G., D. Penner and J. J. Kells. 1989.
Identification of efficacious adjuvants for sethoxydim and
bentazon. Weed Tech. 3:60-66.

 

 

APPENDIX

 

96
APPENDIX

INFORMATION ON THE CHEMICAL COMPOSITION

OF SELECTED ADJUVANTS

Table A1. Chemical composition of the ten adjuvants used in
field, laboratory, and greenhouse experiments.

 

Adjuvant

Composition

Manufacturer

 

Activator 90

a mixture of alkyl polyoxyethylene
ether, free fatty acids, 8

isopropanol

 

Agsco Sunit

Loveland Industries, Inc.,
Greeley, CO

 

methylated vegetable oil and
surfactant

 

CSY-77715512

Agsco, Inc., Grand Forks,
ND

 

experimental vegetable oil-based
adjuvant

 

Dash

 

connercial, proprietary adjuvant

 

Dow Corning X2-5309
(Dow Corning product
Sylgard 309)

(composition unknown)

BASF Corp., Research
Triangle, NC

 

organo-silicone based adjuvant

Dow Corning Corp., Midland,
MI

 

Dow Corning 6955-145

organo-silicone based adjuvant

Dow Corning Corp., Midland,
MI

 

Herbimax

a mixture of paraffin base petroleun
oil, and mono and diesters of

hydroxypgly oxyethylene

 

Pfizer M

Loveland Industries, Inc.,
Greeley, CO

 

experimental adjuvant (composition
unknown)

 

Pfizer 14636-181-7

unknown)

Pfizer Inc., Groton, CT

 

experimental adjuvant (composition

 

X-77

 

 

Pfizer Inc., Groton, CT

 

a mixture of alkylaryl polyoxyethylene
glycols, free fatty acids, and
isopropanol

 

Chevron Chem. Co., San
Francisco, CA

 

 

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