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PRE AND POSTEMERGENCE CONTROL OF
Poa annua IN TURF WITH ETHOFUNIESATE

By

Thomas Mark Carlson

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

1994

 

 

 

ABSTRACT

PRE AND POSTEMERGENCE CONTROL OF
Poa annua IN TURF WITH ETHOFUMESATE

By

Thomas Mark Carlson

Ethofumesate is an unique herbicide in that it has both pre and
postemergence activity to selectively remove P. annua from desirable turfgrass.
This research used various field studies to evaluate postemergence application
timings on the reduction of P. annua, injury to desirable turfgrasses, and during
renovation. Additional studies compared ethofumesate with other standard
preemergence herbicides for P. annua control. Greenhouse studies were utilized
to determine the effect of temperatures on ethofumesate efficacy. All combination
of rates and timings tested were found to be effective at controlling P. annua.
Multiple applications of ethofumesate showed safety on Kentucky bluegrass and
creeping bentgrass and the more applications, the greater the reduction in P.
annua. Preemergence herbicides provided good control in the fall with
ethofumesate being the only exception. Studies indicated freezing temperatures
prior to an ethofumesate application are more effective in P. annua reduction than

when not subjected to freezing temperatures.

 

 

 

ACKNOWLEDGNIENTS

I would like to express my sincere thanks for the guidance and support Dr.
Bruce Branham gave during my graduate studies. Thanks also to my

committee members whose advice and corrections made this thesis possible.
Finally, thanks to my family and the guys in the office who made the tough

times a little more enjoyable.

iii

TABLE OF CONTENTS

LISTOFTABLES..................... vi

LISTOFFIGURES.....................viii

CHAPTER 1:

Abstract.......................1

Introduction......................2

MaterialandMethods.................4

Results........................7

Discussion......................10

LiteratureCited....................20

CHAPTER 2:

Abstract.......................22

Introduction......................24

MaterialandMethods.................27

Results........................3O

Discussion......................34

LiteratureCited....................44

iv

 

 

 

CHAPTER 3:

Abstract .

Introduction .

Material and Methods

Results .

Discussion .

Literature Cited .

CHAPTER 4:

Abstract .

Introduction .

Material and Methods

Results and Discussion .

Literature Cited .

46

.47

49

S3

56

65

66

.67

68

71

84

 

 

 

 

CHAPTER 1

Table 1. 1

Table 1.2

Table 1.3

Table 1.4

Table 1.5

CHAPTER 2

Table 2.1

Table 2 .2

Table 2.3

Table 2.4

Table 2.5

LIST OF TABLES

Ethofumesate treatments for renovation studies

Effect of ethofumesate on turf injury and Poa annua
control during fairway renovation during 1990

Effect of ethofumesate on turf injury and Poa annua
control during fairway renovation during 1991

Effect of ethofumesate on turf injury and Poa annua
control during fairway renovation during 1992

Percent Poa annua averaged across-all ethofumesate
treatments within each seeding date

1990 Fall ethofumesate application for control of
Poa annua

1990 Fall preemergence application for control of
Poa annua

1991 Spring preemergence application for control of
Poa annua

1991 Fall preemergence application for control of
Poa annua

1992 Spring preemergence application for control of
Poa annua

vi

 

 

CHAPTER 3

Table 3.1 1990 Multiple ethofumesate applications for safety and Poa
annua control

Table 3.2 1991 ethofumesate safety on Kentucky bluegrass at fairway
height

Table 3.3 Ethofumesate safety on bentgrass varieties at greens height
Table 3.4 Walnut hills multiple ethofumesate applications
CHAPTER 4

Table 4.1 Comparison of summer and fall applications of
ethofumesate

Table 4.2 Freezing temperatures prior to an application of
ethofumesate

Table 4.3 Freezing temperatures prior to an application of
ethofumesate

vii

 

 

 

LIST OF FIGURES
CHAPTER 2

Figure 2.1 1990—1991 Poa annua germination in response to soil
temperature

Figure 2.2 1991—1992 Poa annua germination in response to soil
temperature

CHAPTER 4

Figure 4.1 Study one— clipping weights from Poa annua plants treated
with ethofumesate (first mowing)

Figure 4.2 Study one— clipping weights from Poa annua plants treated
with ethofumesate (final mowing)

Figure 4.3 Study two- clipping weights from Poa annua plants treated
with ethofumesate (first mowing)

Figure 4.4 Study two- clipping weights from Poa annua plants treated
with ethofumesate (final mowing)

viii

 

 

Chapter 1

RENOVATION USING ETHOFUMESATE

ABSTRACT

Most renovations on golf course fairways are done to eliminate Poa
annua infested areas. One major objective of a renovation program is to
prevent reinvasion of P. annua. Studies were conducted over three years to
determine if the application of ethofumesate [2-ethoxy-2, 3-dihydro-3, 3—
dimethyl—S—benzofuranyl methanesulfonate] at various rates and times could
prevent the reinvasion of P. annua. All combination of rates and timings
tested were found to be effective at controlling P. annua. In general, rates of
0.8 kg a.i. ha'l or less applied either two or four weeks after emergence of the
bentgrass provided acceptable turf quality with little injury. Turf density was
good for most treatment combinations except the ethofumesate applications at
seeding and the 1.7 kg a.i. ha‘l rate in 1991. In 1992 percent coverage was
weak for most treatments over all seeding dates due to the early, cool fall
temperatures resulting in poor growing conditions. Ethofumesate appears to be
beneficial in preventing P. annua from reestablishing in a newly seeded

bentgrass fairway.

 

 

2

INTRODUCTION

On most golf courses Poa annua (annual bluegrass) is considered an
undesirable weed. Two subspecies of P. annua exist; one is an annual, P. annua
var annua (L.) Timm, and the other is a perennial, P. annua var reptans
(Hausskn.) Timm. The annual has an upright growth habit, no or few secondary
tillers per culm, prolific seedhead production, little rooting on the culm/tiller, six
nodes or less per culm/tiller and the seed has a dormancy period (Beard 1973;
Gibeault 1974). The perennial has a creeping growth habit, numerous secondary
tillers per culm, less seedhead production, several adventitious roots on a prostrate
culm/tiller, greater than six nodes per culm/tiller and no seed dormancy (Beard
1973; Gibeault 1974). Many golf course superintendents and golfers have had to
learn to live with P. annua. If a golf course has predominantly P. annua, the
cultural management of the course will be designed to benefit the P. annua.

Many drawbacks are associated with P. annua such as the need for high fertility,
disease and insect susceptibility, and high moisture requirement. These drawbacks
are causing turf managers to attempt to remove P. annua. Cultural and chemical
techniques exist to selectively remove P. annua but progress can be slow

(Kageyama and Widell 1989). Another option is to renovate the existing turf

stand.

 

 

 

 

3

The renovation process typically results in the closure of the course for
at least 3-4 weeks. The majority of renovations are primarily done to remove
P. annua from the tees, fairways and/or greens. While the purpose of
renovation is to remove existing P. annua, one would also like to prevent the
reinvasion of P. annua.

In Michigan the recommendation has been to begin renovation in mid-
August and have a well established stand of bentgrass prior to the fall
germination of P. annua. This procedure can result in interference with play
during the peak of the season, increased demands on personnel in the peak of
the maintenance season, and P. annua may germinate all season long (Chapter
2) contrary to what was previously thought (Beard 1973). It would be highly
desirable to delay renovation into the late summer, prevent some of the
inconveniences, and prevent reestablishment of P. annua in the newly
established bentgrass.

The purpose of this research was to develop a renovation procedure for
fairways that would minimize the re—encroachment of P. annua into the newly
established turf. Ethofumesate was chosen because of its selectivity for P.
annua (Ball and Roberts 1974; Demoeden and Turner 1988; Dickens 1981;
Shearman 1986) and safety on creeping bentgrass (Demoeden and Turner

1986; Johnson et al. 1989).

 

 

 

4
MATERIAL AND METHODS

Field studies were conducted for three years and evaluations were
conducted from the initiation of the study through the following spring. The
first study began in the fall of 1989 and two additional studies were begun in
the fall of 1990 and 1991. The research site was located at the Hancock
Turfgrass Research Center, East Lansing, Michigan. The site consisted of 70-
80% P. annua since 1981 ensuring a large seed bank.

Prior to seeding, plots were sprayed with glyphosate [Tsopropylamine
salt of N—(phosphonomethyl) glycine] at 1.7 kg a.i. ha“. One week after the
glyphosate application the area was verticut with a vertical mower (Ryan Ren-
o—Thinll ) in three directions to remove much of the dead plant material and
break up the soil surface. This dead plant material was removed from the plot
area before seeding.

Three seeding times were used in each study. Seeding dates for 1989
were August 18, September 1, and September 15; August 16, August 31, and
September 13 for 1990; and August 15, August 29, and September 12 for
1991. Penncross creeping bentgrass was seeded at 49 kg ha". The area was

fertilized at seeding with 49 kg N ha‘1 as 12—12—12 and then 24 kg N ha'1

 

‘ Cushman Inc., 9036 Ryan, PO. Box 82409, Lincoln, NE 68501

 

5

applied as urea every two weeks for a total of three applications. Plots were
mowed three times weekly during the growing season and as needed during
late fall and early spring, at a height of 1.3 cm. Mowing did not begin after
seeding until seedlings were well established. Each seeding date was watered
daily until seed germinated and then only as needed.

A split plot design was used with three replications. Main plots were
seeding dates with ethofumesate treatments as subplots. Each subplot was 1.2
x 1.8 In and received ethofumesate treatments at various rates and weeks after
emergence (WAE) of the bentgrass (Table 1.1). No additional pesticides were
applied to the research area for the duration of the experiment. Treatments
were applied with a four nozzle boom—C02 backpack sprayer delivering 514
L/ha at 0.28 Mpa.

Visual evaluations were used to determine the control of P. annua
achieved with the ethofumesate applications and quality of the bentgrass.
Control was determined by rating percent P. annua on a 0—100% scale.
Quality ratings were taken on a 1—9 scale with a rating higher then 6.5 being
acceptable for a golf course fairway. A rating of 1 was worst quality and 9
was best quality. Percent turf cover was evaluated on the last two studies.

This was done to see if the application of ethofumesate inhibited germination

 

6

or rate of cover of the bentgrass. Cover ratings were on 3 0—100% scale. A

rating less than 97% would be considered unacceptable in a fairway situation.

 

7
RESULTS

1989—1990 Field Study

Turf treated with ethofumesate did not show evidence of injury over
the early and late seeding dates (Table 1.2). The 0.8 kg a.i. ha‘1 4, 6, + 8
weeks after emergence (WAE) along with 0.8 kg a.i. ha‘l 4 WAE + 1.4 kg
a.i. ha‘1 6 WAE treatments did cause some unacceptable quality on the 9/1
seeding date.

Most treatments provided significant control of P. annua on all seeding
dates. The only exception was 0.8 kg a.i. ha" 4 WAE + 1.4 kg a.i. ha’1 6
WAE on the first seeding date.

Quality, even though two treatments dropped slightly below
unacceptable, recovered nicely during the spring (data not shown).
1990—1991 Field Study

Ethofumesate injury to the turf was not observed at any seeding date
(Table 1.3). Even though there were significant differences in quality between
several treatments, this quality would be judged acceptable under fairway
conditions. Again as in the previous year, all treatments having lower quality

recovered during the spring (data not shown).

 

 

 

P. annua populations were significantly reduced by most treatments
over all seeding dates, the only exception being 0.4 kg a.i. ha'1 2 WAE + 0.8
kg a.i. ha'1 5 WAE on the first seeding date.

During this field study, the effect of ethofumesate on turfgrass
establishment was evaluated. The 0.8 kg a.i. ha‘l at seeding + 30 DAT
resulted in poor turfgrass cover on the mid— and late seeding dates, and 1.7 kg
a.i. ha'1 2 + 5 WAE had unacceptable cover on all seeding dates. Treatments
10 yielded unacceptable cover only on the latest seeding date
1991—1992 Field Study

Treatments on the first seeding date generally exhibited acceptable
quality, however, treatments 5, 7, 9, 12, 13, 14, and 18 had unacceptable
quality (Table 1.4). On the mid seeding date treatments 9 - 18 gave
unacceptable quality. On the last seeding date quality was unacceptable in all
plots, including the control plot.

Most treatments significantly controlled Poa annua. Two exceptions
were treatments 16 and 17 at the early seeding date.

Turfgrass cover was generally acceptable on the early seeding date.
Only treatments 9, 10, 12, 13, 14, and 18 gave unacceptable percent cover.
On the mid-seeding date only the two treatments, with two applications of 0.8

kg a.i. ha'l at four week intervals, resulted in acceptable turf cover. The last

 

 

9

seeding date had unacceptable percent cover for all treatments including the
control.

An unexpected result from all studies was the highly significant effect of
seeding date and ethofumesate treatment on the level of P. annua establishment
(Table 1.5). The early seeding dates had a higher percentage of P. annua than

the later seeding dates.

 

 

10
DISCUSSION

Most treatments applied at or below the label rate of 0.8 kg a.i. ha" at
two or four WAE with various application intervals had acceptable quality.
The only exception was that the late seeding date in 1992 did exhibit
undesirable injury. With the combination of cold temperatures and herbicide
applications, seedlings never really developed and poor quality resulted. With
the exception of the 1991—1992 study even treatments above 0.8 kg a.i. ha"
did not cause poor quality. Treatments applied at seeding in the last two
studies had unacceptable quality only in the 1991-1992 study.

Ethofumesate in all studies provided excellent control of P. annua. The
0.8 kg a.i. ha'l at 4 WAE followed by two additional applications at either two
or four week intervals consistently resulted in excellent P. annua control. The
0.8 kg a.i. ha" at 4 and 8 WAE had more P. annua when compared to the 0.8
kg a.i. ha'l with three applications. Treatments with 0.4 and 1.4 kg a.i. ha'l
applied to the first seeding dates of all studies had a higher percentage of P.
annua.

Turfgrass cover was not evaluated until the 1991 study. In the 1991
study all of the treatments had acceptable turf cover with the exception of

treatments applied at seeding. All treatments (except those applied at seeding)

 

 

11

applied in the 1992 study had acceptable coverage for the first seeding date but
only treatments with two applications in the mid-seeding date had acceptable
percent cover and the last seeding showed poor percent cover in all treatments.
This poor percent cover in the 1992 study was a result of cold temperatures
resulting in winter kill of the bentgrass seedlings and reduced establishment but
not winter kill of P. annua. An example is the control treatment on the last
seeding date of 1992 had 75% cover of which 52% was P. annua and
therefore only 23% bentgrass.

The poor percent cover observed where treatments were applied at
seeding in 1991 and in tilled and untilled treatment in 1992 is not totally
expected. Ethofumesate has shown some preemergence activity (Adams 1989)
therefore likely preventing the germination of creeping bentgrass especially
where organic matter has been removed through tilling (Carlson and Branham
1991). There was a greater reduction in turf cover in 1992 where treatments
were tilled versus untilled.

There are several possible reasons why the percentage of P. annua was
lower for the later seeding dates: 1) maximum activity from ethofumesate
comes when the herbicide is not watered in after application; 2) ethofumesate
was not acting as a preemergence herbicide (Chapter 3); 3) applications of

ethofumesate could be temperature dependent; or 4) P. annua germination

 

 

12

levels off or decreases during late summer and fall (Figure 2.1 and 2.2). As
the later seeding dates were irrigated to initiate germination of the bentgrass
the earlier seeding dates were receiving ethofumesate applications and also
being watered due to the layout of the experimental area, leading to reduced
ethofumesate activity in the early seeding dates. After the early seeding dates
had received all their treatments P. annua germination may have continued
with little preemergence control from ethofumesate. During later seeding dates
conditions were less conducive for P. annua germination. With less
germination and some control from the ethofumesate treatments, less P. annua
was observed with the late seedings. The preemergence activity of
ethofumesate can be better observed if a comparison of tilled versus untilled
plots from the 1992 study is made. There was significantly less establishment
of both P. annua and bentgrass in the tilled plots when compared to the
untilled plots. Most renovation projects would not till but leave the dead,
existing turf stand to provide better stability and moisture for the new,
establishing seedlings. The tilled plots do not have a layer of organic matter to
bind the ethofumesate but the untilled plots still have an organic matter layer
present, binding ethofumesate and making the application less effective. On
the early seeding dates temperatures were mild, but on the later seeding dates

temperatures were colder possibly causing increased P. annua control (Chapter

 

 

l3

3 and 4) from an ethofumesate application. As an example, in 1991 the
average low/high temperature was 14/28 for the early seeding date and 7/20

on the late seeding date.

 

 

13

3 and 4) from an ethofumesate application. As an example, in 1991 the
average low/high temperature was 14/28 for the early seeding date and 7/20

on the late seeding date.

 

 

14

Table 1.1. ETHOFUMESATE TREATMENTS FOR RENOVATION STUDIES
RATES (kg ai ha") AND TIMINGS

19894990 Study

1) Control
2) 0.8- 4 WAE+ + 0.8- 8 WAE
3) 0.8- 6 WAE + 0.8- 10 WAE

4) 0.8— 4 WAE + 0.8— 8 WAE + 0.8— 12 WAE
5) 0.8- 4 WAE + 0.8- 6 WAE + 0.8- 8 WAE
6) 0.6 4 WAE + 0.6 6 WAE + 0.6 8 WAE
7) 0.8- 4 WAE + 1.4 6 WAE
8) 0.4 2 WAE + 0.8— 5 WAE

1990—1991 Study

1—8) Same treatments as used in the previous study plus
9) 1.7— 2 WAE + 1.7- 5 WAE

10) 0.8- 2 WAE + 0.8- 5 WAE + 0.8— 8 WAE
11) 0.6 at Seeding + 30 DAT:

12) 0.8- at Seeding + 30 DAT

1991—1992 Study

1—12) Same treatments as used in the previous study plus
13) 0.6 at Seeding + 30 DAT (plots tilled)

14) 0.8— at Seeding + 30 DAT (plots tilled)

15) 0.6 at Seeding

16) 0.8— at Seeding

17) 1.1- at Seeding

18) 1.7— at Seeding

 

 

-1.

- WAE — weeks after emergence of bentgrass
- DAT - days after treatment

 

 

 

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19

Table 1.5. PERCENT Poa annua AVERAGED ACROSS-ALL ETHOFUMESATE
TREATMENTS WITHIN EACH SEEDING DATE

 

YEAR OF STU DY

SEEDING DATE 1989-90 1990—91 1991-92
Early 9.1 14.2 10.7
Mid 3.4 3.9 0.7
Late 0.4 2.2 0.1

LSD (P = 0.05) 0.3 4.4 2.7

 

 

20

LITERATURE CITED

Adams, J.C. 1989. Control of Poa annua in cool—season turf with
ethofumesate. Proceedings Canadian T urfgrass Conference and Show. 1920.

Ball, A.P., and AR. Roberts. 1974. The use of ethofumesate for weed control

in ryegrass seed crops. Proceedings of the 12th British Weed Control
Conference. 727—732.

Beard, J .B. 1973. Turfgrass: Science and Culture. 67—70. Prentice-Hall,
Englewood Cliffs. NJ.

Carlson, TC, and BE. Branham. 1991. Pre and post emergence control of
annual bluegrass. 6lst Annual Michigan Turfgrass Conference Proceedings.

20: 108—113.

Demoeden, P.H., and TR. Turner. 1988. Annual bluegrass control and
tolerance of Kentucky bluegrass and perennial ryegrass to ethofumesate.
HortScience. 23: 565-567.

Demoeden, P.H., and TR. Turner. 1986. Selective control of Poa annua in
perennial ryegrass and creeping bentgrass with ethofumesate. Proceedings

Northeast Weed Science Society. 40: 276—277.

Dickens, R. 1981. Rates and timing of ethofumesate applications for annual
bluegrass control. Agronomy Abstracts. 124-125.

Gibeault, VA. 1974. Poa annua. California Turfgrass Culture. 24: 13-16.

Johnson, B.J., G.W. Landry Jr., and K. Kamok. 1989. Tolerance of bentgrass
to amount, frequency, and timing of ethofumesate applications. HortScience.

24: 102—104.

Kageyama, M.E., and LR. Widell. 1989. Annual bluegrass to bentgrass
conversion with turf growth retardants (TGRs). 307—311. In A.R. Leslie and
R.L. Metcalf (ed.). Integrated Pest Management for T urfgrass and
Ornamentals. United States Environmental Protection Agency. Washington,

DC.

 

 

21

Shearman, RC. 1986. Kentucky bluegrass and annual bluegrass response to
ethofumesate. HortScience. 21: 1157-1159.

 

Chapter 2

PREEMERGENCE CONTROL OF Poa annua

ABSTRACT

One chemical method for P. annua control would be the use of a
preemergence herbicide. A two year study was initiated to evaluate the
potential of preemergence herbicides for control of P. annua. P. annua
control was determined by counting the number of seedlings within observation
circles. The observation circles provided a means to evaluate the effectiveness
of the preemergence herbicides for P. annua control. P. annua seedlings were
counted every two to three weeks in the observation circles as a way to
determine the control achieved. Most preemergence herbicides provided
consistent control over both years. Products provided good control in the fall
with ethofumesate being the only exception. Products giving good control in
the fall had good control the following spring. All spring applications
provided fair control for almost 8-10 weeks. Oxadiazon [2-tert—butyl-4—(2,4
dichloro—5—isopropoxyphenyl)-A2 1,3,4—oxadiazolin—5—one], dithiopyr [3,5-
pyridinedicarbothioic acid, 2-(difluoromethyl)—4—(2—methylpropyl)-6-
(trifluoromethyl)-S, S—dimethyl ester], and prodiamine [N3, N3-Di—n-propyl—2,

4-dinitro—6-(trifluoromethyl)—m-phenylenediamine] provided the highest level of

22

 

23

control throughout the study with values ranging from 100 to 75% control.
Preemergence herbicides appear to be successful in preventing P. annua from
germination. This could be beneficial in preventing P. annua from entering a

newly established or renovated fairway.

 

 

 

24

INTRODUCTION

Controlling P. annua is a difficult task. If acceptable control cannot be
achieved with postemergence strategies, complete renovation of P. annua
infested tees, fairways, and greens is an option (Chapter 1). However even
with complete renovation, the problem is not solved. During the years an area
has been infested with P. annua, prolific production of viable P. annua seed
occurs (Lush 1988b; Grime 1981).

With postemergence control of P. annua possible and even in the case
of complete renovation, there is still a large seed bank remaining in the soil
(Grime 1981). Each P. annua inflorescence can produce between 2 to 3
viable seeds (Lush 1988a). On a golf course green this could lead to
production of 150,000 - 675,000 seeds m‘2 y'1 (Lush 19883) with 30,000 seeds
rn‘2 persisting till next season or for later years (Lush 1988b). Of the total
seeds produced there is a potential of 100,000 — 265,000 seeds germinating
(Lush 19883) with little or no dormancy needed for the seed (Warwick and
Briggs 1978). Koshy(1969) has stated the versatility of seed formation for P.
annua contributes to its conspicuous success as a weed. In addition to a

postemergence control program or following renovation, a preemergence

 

25

strategy should play an important role in preventing P. annua from
reestablishing.

The variability that exists within P. annua (Koshy 1969; Wu, Till-
Bottraud and Torres 1987; McNeilly 1984; Naylor and Abdalla 1982) could
pose a challenge in the use of a preemergence control plan for P. annua.
Germination of P. annua will vary from one golf course to the next (Wu, Till-
Bottraud and Torres 1987) and even from one part of a course to another
(Lush 1989). In addition to the variability due to location, germination will
vary depending on the requirements needed to initiate germination. P. annua
germination is most successful at temperatures between 10 and 15°C (Beard
1980; Standifer 1988; Eggens and Ormrod 1982; Naylor and Abdalla 1982),
but will germinate over a large temperature range. Most germination will
occur between 2 to 40°C and decline above and below this range (Koch 1968).
Success in germination is also dependent upon sufficient light (Naylor and
Abdalla 1982) and promoted by adequate nitrate (Williams 1983).

With the success of P. annua and the variability within the species, the
use of a preemergence herbicide to control P. annua germination could be
challenging. Development of a control strategy using a preemergence
herbicide could be beneficial in preventing P. annua from establishing. The

objective of this research was to attempt to determine which herbicides provide

 

 

26

good preemergence P. annua control at fairway height. Some research has
been done on preemergence control of P. annua (Juska and Hanson 1962;
Engel 1976) but is limited and has not looked at preemergence control on
fairway height cut and the potential to develop a P. annua management
strategy. Other objectives were to determine the longevity of the
preemergence applications and the need for multiple applications. Evaluation
of preemergence control of P. annua becomes difficult in a densely populated
turf stand. Counting the number of seedlings within observation circles was a

way to overcome this problem.

 

27

MATERIAL AND METHODS

Two field studies were conducted during the fall of 1990 through the
spring of 1991 and one study in the fall of 1991 through the spring of 1992 to
evaluate ethofumesate and other preemergence herbicides for preemergence P.
annua control. The research site consisted of a predominately P. annua turf at
the Hancock Turfgrass Research Center, East Lansing, Michigan. The area
was fertilized with 46-0—0 totaling 146 kg N ha" in 1990, 98 kg N ha'I in 1991
and 76 kg N ha"1 in 1992. Pesticides applied were fenarimol [01-(2-
chlorophenyl)—or—(4—chlorophenyl)—5—pyrimidinemethanol] at 5 kg ha“ and a
combination product of 2,4-D [dimethylamine salt of 2,4—
dichlorophenoxyacetic acid]; mecoprop [dimethylamine salt of 2-(2—methyl—4-
chlorophenoxy) propionic acid]; and dicamba [dimethylamine salt of dicamba
(3,6-dichloro—o—anisic acid)] at 21 L ha'1 in 1990, two applications of
triadimefon [1—(4-chlorophenoxy)-3, 3—dimethyl-1—(1H—1, 2, 4-triazol—1—yl)—2—
butanone] at 6 kg ha‘1 and an application of chlorothalonil
[tetrachloroisophthalonitrile] at 18 kg ha'l in 1991, and sethoxydim [2-[1—
(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one] at

25 kg ha‘l were made in 1992. The plots were mowed three times weekly

 

 

28

during the growing season and as needed during late fall and early spring, at a
height of 1.3 cm. The area was irrigated as needed.

The 1990 and 1991 general preemergence studies used a randomized
complete block design with three replications. Individual plots measured 1.2
m x 3.0 m. The ethofumesate [2—ethoxy—2, 3—dihydro-3, 3—dimethyl—5-
benzofuranyl methanesulfonate] study in 1990 used a factorial design to
evaluate ethofumesate control in the fall and spring. Factor one was a fall
application and factor two was a spring application. Each factor had five rates
of ethofumesate 0.0, 0.6, 1.1, 1.7, and 2.2 kg a.i. ha“. Plot size was 1.2 m x
1.8 m. The plots in the 1990 and 1991 studies were split in half with one half
receiving both fall and spring applications. This allowed evaluation of
preemergence control of the spring and fall application.

For both studies liquid treatments were applied with a four nozzle
boom—C02 backpack sprayer delivering 514 L ha'l at 0.28 MPa for the fall
applications and 538 L ha'l at 0.28 MPa for the spring applications. Granular
treatments were weighed and applied with a shaker bottle. All treatments were
applied on 9/6/90 for the ethofumesate study. The general preemergence
studies were initiated on 9/ 11/90 and 9/11/91. Spring applications were
applied on 4/12/91 and 3/31/92. All treatments were watered in with

approximately 0.6 cm of water.

 

 

29

Observation circles measuring 11.4 cm2 were sprayed with glyphosate
[N—(phosphonomethyl) glycine] in each plot area. The observation circles
provided a means to maintain a microclirnate (temperature, moisture, organic
matter, cover, etc.) similar to an established fairway turf. Counting the
seedlings within the circles provided an estimate of P. annua control.

Seedlings were counted every two to three weeks in three of the six
observation circles in 1990-91 and four of eight circles in 1991-92. The
circles were then sprayed again with glyphosate. On the next evaluation the
remaining circles were used for evaluation and then sprayed with glyphosate.
This procedure of alternating between half of the observation circles continued
throughout the study. The average seedlings per treatment were determined
and data are reported as percent control. Experimental design was a
randomized complete block with three replications; all data were subjected to

an analysis of variance.

 

 

30

RESULTS

1990—1991 Field Studies
Ethofumesate treatments applied in the fall gave little to no control of P.

annua (Table 2.1), and the study was discontinued after the fall data was

collected.

The general preemergence study gave excellent control of P. annua
(Table 2.2). The two evaluations taken in October showed more than 90%
control with a preemergence herbicide. The last evaluation taken on 11/5
(data not shown) indicated that germination of P. annua had ceased.

Control from the fall application was still evident in the evaluation taken
at the time of the spring application. Both rates of pendimethalin [N—(l-
ethylpropyl)—3,4-dimethyl-2,6-dinitrobenzamine], dithiopyr (EC), benefm [N—
butyl-N—ethyl-(x,01,01-trifluoro-2,6—dinitro—p—toluidine], and DCPA [dimethyl
tetrachloroterephthalate]; and the low rate of dithiopyr (G) had less than 75%
control. All other treatments provided greater than 75% control of P. annua.

By the 6/17 evaluation all fall applied treatments provided 0% control.

Spring treatments were applied on 4/12/91 when germination of P.

annua had already occurred. Treatments gave excellent control (Table 2.3) on

the 5/30 evaluation with the low rates of dithiopyr (G) and benefm, and

 

31

bensulide [S—(0,0-diisopropy1 phosphorodithioate) ester of N-(2-mercaptoethyl)
benzenesulfonaminde] having less than 75% control (Table 2.3). On the 6/ 17
evaluation, almost ten weeks after application only bensulide, the low rates of
oxadiazon and prodiamine; and the high rate of dithiopyr (G) had better than
75% control. The 7/1 evaluation showed all treatments provided less than
75% control.

The spring treatments were applied on 4/12 and controlled P. annua
germination for approximately 12 weeks. The first evaluation after the spring
application taken on 5/10 showed no germination in any of the treatments
including the control plots. Research has shown that when soil is dry and
temperatures are high, emergence of P. annua may be delayed and when
temperatures are low, emergence is delayed or reduced (Wells 1974). This
may explain the rating on 5/ 10 with no germination, since prior to the
evaluation the environmental conditions were cool and dry and not conducive
to P. annua germination.

1991-1992 Field Studies

Fall treatments provided greater than 75% control of P. annua

germination on the 10/22 evaluation date with the exception of both rates of

ethofumesate and the low rate of benefm(Table 2.4). All treatments on the

 

32

11/8 evaluation had better than 75% control except the low rate of
ethofumesate.

The first spring evaluation on 4/23 showed that the low rates of
oxadiazon and pendimethalin; both rates of benefin, bensulide and
ethofumesate; the high rate of dithiopyr (EC); and benefm + trifluralin [N-
butyl-N-ethyl-(x,0t,(x—triflu0ro—2,6-dinitro—p—toluidine + a,(x,01—trifluoro-2,6-
dinitro-N,N-dipropyl~p—toluidine] had less than 75% control. The 5/ 13
evaluation showed that benefin + trifluralin; the low rates of oxadiazon [2—
tert-butyl-4—(2,4 dichloro—5—isopropoxyphenyl)—A2 1,3,4—oxadiazolin-5—one],
dithiopyr(EC), prodiamine, bensulide; the high rate of DCPA [Dimethyl
tetrachloroterephthalate]; and both rates of benefin and ethofumesate gave less
than 75% control. On 6/1 the low rate of prodiamine; the high rates of
dithiopyr (G) and bensulide; and both rates of pendimethalin and DCPA gave
better than 75% control. The final evaluation taken on 6/22 showed no
treatments giving better than 75% control.

Spring applications were applied on 3/31/92 and unlike the previous
year P. annua had not yet germinated. Spring applied treatments gave
excellent control until 6/22 with most treatments giving greater than 75%
control of P. annua compared to the check plot (Table 2.5). On the 6/22

evaluation treatments began to show reduced control. The only treatments

 

 

33

giving better than 75% control were the high rates of oxadiazon,

pendimethalin, and prodiamine.

 

 

 

34

DISCUSSION

As cited in the literature, P. annua produces prolific amounts of seed
and the viability of that seed is high; the need to prevent germination is very
important. These results show the potential preemergence herbicides could
play in the overall control strategy of P. annua. Preemergence herbicides can
prevent P. annua seed from reestablishing.

Preemergence herbicides gave significant control except ethofumesate.
Ethofumesate has been shown to have both post and preemergence properties
for P. annua control (Adams 1989). In a preemergence study done at
Michigan State University in 1987 (Carlson and Branham 1991), ethofumesate
gave excellent preemergence control of P. annua. The 1987 study was
conducted on bare soil with all rates of ethofumesate providing good control of
P. annua. Why was ethofumesate effective in the bare soil study but gave
little to no control in these preemergence studies? In the bare soil study, there
was little organic matter on the soil surface. Thus, the organic matter
inherently present with turf, approximately 0.6—1.3 cm of thatch in these
studies, may bind ethofumesate making it ineffective as a preemergence
control.

Most herbicides provided consistent control over both years.

Preemergence herbicides provided good control in the fall with ethofumesate

 

 

35

being the only exception. In the evaluations, oxadiazon, pendimethalin,
dithiopyr (G), prodiamine, and DCPA provided good control. Benefin,
dithiopyr (EC), and bensulide had fair control with ethofumesate and benefin
+ trifluralin having poor control. In 1992 control was observed
approximately one month longer than 1991 and was probably the result of the
unseasonably cool fall in 1991 giving little reduction of the herbicide activity.

Spring herbicide applications provided control for about 8-10 weeks
before they began to have reduction in preemergence control. Benefm,
dithiopyr (EC) bensulide, DCPA, and ethofumesate provide the weakest
control.

These conclusions drawn from both years may not be totally
representative of what is occurring. The observation circles were small in size
and few in number making variability high. In addition the circles were
lacking plant cover so were not totally representative of a turf stand. This may
account for some of the variability with a product over both years.

The next logical step in controlling P. annua is to determine the
optimum timing to apply the preemergence herbicide for the most effective
results. Germination of P. annua occurs much earlier in the spring than
expected. The average number of seedlings in the control plots was plotted

against time for both 1991 and 1992. The results show that P. annua

 

 

36

germinates early and all season long (Figure 2.1 and 2.2). There are several
times at which no germination occurred and this is probably related to
conditions not conducive to germination. Previous investigators (Beard et
al.1978) thought that P. annua germinated in the spring and fall and stopped
during the summer. These results suggest that two or more preemergence
applications may be needed to achieve season long control. A fall application
is beneficial for fall germination and gives some control the following spring.
With the early germination of P. annua it is important to get a spring
application out as early in the spring as possible. With these studies giving
approximately eight good weeks of control before germination started, an
additional one or two applications would be needed to prevent germination and

give season long control.

 

 

 

37

Table 2.1. 1990 FALL ETHOFUlVIESATE APPLICATION FOR
CONTROL OF Poa annua

ETHOFUMESATE‘F PERCENT CONTROL:
kg a.i. ha'I 9/29/90 10/22/90 11/5/90

2.2 l3 l7 3

1.7 7 13 0

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0.6 9 30 5

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LITERATURE CITED

Adams, J .C. 1989. Control of Poa annua in cool-season turf with
ethofumesate. Proceedings Canadian Turfgrass Conference and Show. 19-20.

Beard, J.B. 1980. Minimum temperatures for turfgrass seed germination.
Grounds Maintenance. February. 32—36.

Beard, J.B., P.E. Rieke, A.J. Turgeon, and J.M. Jr. Vargas. 1978. Annual
bluegrass (Poa annua L.): description, adaptation, culture and control.
Michigan State Agricultural Experiment Station Research Report. 352: 1—31.

Carlson, TC, and BE. Branham. 1991. Pre and post emergence control of
annual bluegrass. 61st Annual Michigan T urfgrass Conference Proceedings.

20: 108—113.

Eggens, J.L., and DP. Ormrod. 1982. Creeping bentgrass, Kentucky
bluegrass, and annual bluegrass seed germination response to elevated
temperature. HortScience. 17: 624-625.

Engel, RE. 1976. New approaches to annual bluegrass control. Proceedings
of the 17th Illinois T urfgrass Conference. 17: 30-31.

Grime, J .P. 1981. The role of seed dormancy in vegetation dynamics. Annals
of Applied Biology. 98: 555—558.

Juska, F .V., and AA. Hanson. 1967. Factors affecting Poa annua L. control.
Weeds. 15: 98-101.

Koch, W. 1968. Environmental factors affecting the germination of some
annual grasses. Proceedings 9th British Weed Control Conference. Vol. 1. 14-
19.

Koshy, T.K. 1969. Breeding systems in annual bluegrass, Poa annua L. Crop
Science. 9: 40—43.

Lush, W.M. 1989. Adaptation and differentiation of golf course populations of
annual bluegrass (Poa annua). Weed Science. 37: 54-59.

 

45

Lush, W.M. 1988a. Biology of Poa annua in a temperate zone golf putting
green (Agrostis stolonifera / Poa annua) I. The above-ground population.
Journal of Applied Ecology. 25: 977—988.

Lush, W.M. 1988b. Biology of Poa annua in a temperate zone golf putting
green (Agrostis stolonifera / Poa annua) II. The seed bank. Journal of Applied

Ecology. 25: 989-997.

McNeilly, T. 1984. Ectotypic differentiation in Poa annua: Within population
variation in response to competition and cutting. New Phytologist. 96: 307-
316.

Naylor, R.E.L., and AF. Abdalla. 1982. Variation in germination behavior.
Seed Science and Technology. 10: 67-76.

Standifer, LC. 1988. Dormancy studies in three populations of Poa annua L.
seeds. Weed Research. 28: 359—363.

Warwick, 5.1., and D. Briggs. 1978. The genecology of lawns weeds. New
Phytologist. 81: 725-737.

Wells, G]. 1974. The Germination and Growth of Poa annua Sown Monthly
in the Field. Proceeding 12th British Weed Control Conference. 525—532.

Williams, ED. 1983. Effects of temperature, light, nitrate and pre-chilling on
seed germination of grassland plants. Annuals Applied Biology. 103: 161—172.

Wu, L., Irene Till—Bottraud, and Armando Torres. 1987. Genetic
differentiation in temperature-enforced seed dormancy among golf course
populations of Poa annua L. New Phytologist. 107: 623-631.

 

 

 

Chapter 3

SAFETY AND EFFICACY OF MULTIPLE
APPLICATIONS OF ETHOFUMESATE ON TURFGRASSES

ABSTRACT

Ethofumesate [2-ethoxy-2, 3-dihydr0—3, 3-dimethyl—5-benzofuranyl
methanesulfonate] is a unique herbicide which requires multiple applications to
achieve acceptable control. Various multiple application studies were done
evaluating safety on Kentucky bluegrass and creeping bentgrass. Two studies
were also conducted to determine the control of P. annua achieved with
multiple applications. Ethofumesate showed safety on Kentucky bluegrass at
rough height but some injury at fairway height. Ethofumesate showed
exceptional safety on creeping bentgrass varieties. The greater the number of

applications of ethofumesate made the greater the reduction in P. annua.

46

 

 

47

INTRODUCTION

Control of P. annua has long been a highly sought goal by golf course
superintendents. Many old and new golf courses not following proper
management practices have had a problem with the invasion of P. annua. The
concerns over P. annua are fivefold: 1) interferes with the rolling golf ball,
2) affects course appearance, 3) requires increased amounts of water, 4)
requires more nitrogen than bentgrass, and 5) increased susceptibility to
disease and insect injury. The desire for control is probably related both to
environmental and economical factors, i.e., over-watering and fertilizer and
pesticide applications.

Several methods have been used to reduce P. annua but are labor
intensive and/or slow in response. One approach has combined two cultural
practices; collecting clippings and managing to encourage the desired turfgrass.

The other has been the use of plant growth regulators to control the P. annua
growth giving the desired turf an advantage or suppressing seedhead
production (Kageyama and Widell 1989), hence less seed produced.

Another approach to controlling P. annua is through the use of the
selective herbicide ethofumesate (Ball and Roberts 1974, Demoeden and

Turner 1988, Dickens 1981, Shearman 1986). Ethofumesate selectively

 

 

48

controls P. annua and is safe over a wide range of turf species (Demoeden
and Turner 1986, Johnson et al. 1989). Multiple applications of ethofumesate
are needed to obtain an acceptable level of efficacy (Coats and Krans 1986,
Shearman 1986). The number of applications may be reduced by waiting until
later in the growing season (Chapter 4).

There were two objectives of this research. One was to determine the
safety of multiple applications of ethofumesate on desirable turfgrasses. The
other was to evaluate the effects of multiple ethofumesate applications on P.

annua control.

 

 

49

MATERIAL AND METHODS

1990—1991 Field Studies

Two field studies were conducted in the fall of 1990 and through the
spring of 1991. One study examined safety on Kentucky bluegrass. The
second study evaluated P. annua reduction and safety on creeping bentgrass.

The Kentucky bluegrass study was located at the Hancock Turfgrass
Research Center, East Lansing, Michigan. This site received 146 kg N ha" as
46—0-0 during the study. Pesticides other than ethofumesate were not applied
during this study. The plot area was mowed weekly at a height of 7.6 cm.

The creeping bentgrass study was located at the Detroit Golf Club,
Detroit, Michigan. The study was located on a fairway and maintained at
typical high maintenance level. The fairway consisted of approximately 40%
P. annua and 60% creeping bentgrass.

A randomized complete block design with three replications was used
for both studies. The Kentucky bluegrass study had two or three applications
of ethofumesate at 0.8 or 1.7 kg a.i. ha". The creeping bentgrass study had

rates of 0.8 or 1.7 kg a.i. ha" with various treatment combinations. Individual

plots in both studies measured 1.2 m x 1.8 m.

 

 

50

For both studies treatments were applied with a four nozzle boom—C02
backpack sprayer delivering 514 L ha‘l at 0.28 MPa. All evaluations were
visual. Injury to desirable turf was rated on a 1—9 injury scale with 9 showing
no injury and 1 being completely dead. P. annua control was rated from 0—
100% with 0% being no P. annua present and 100% having P. annua present
in the entire plot. Percent cover was evaluated on the bentgrass study from 0-
100% with 0% having no turf present and 100% having complete turf cover,
with anything less than 97% considered unacceptable in a fairway situation.
1991-1992 Field Studies

Three field studies were conducted during the fall of 1991 and through
the spring of 1992. Two studies examined safety, on bentgrass varieties
mowed at greens height and Kentucky bluegrass mowed at fairway height. An
additional study was done to evaluate multiple ethofumesate applications on P.
annua reduction.

The study on Kentucky bluegrass was located at Forest Akers Golf
Course, East Lansing, Michigan. This study was maintained under high
maintenance practices typical of a golf course.

The bentgrass variety study was at the Hancock Turfgrass Research
Center, East Lansing, Michigan. This safety study on bentgrass was fertilized

with 20—0—10 at 98 kg N ha'1 and 25-0-25 at 73 kg N ha‘1 in 1991; and 25-0-25

 

 

51

at 24 kg N ha", 46-0-0 at 49 kg N ha", and 8-4-24 at 24 kg N ha'1 in 1992.
In 1991 pesticides applied were metalaxyl [N-(2,6-dimethylphenyl)-N-
(methoxyacetyl) alanine methyl ester] at 1.0 kg ha"; fenarimol [Oi-(2-
chlorophenyl)—d-(4—chlorophenyl)-5—pyrimidinemethanol] at 0.5 kg ha“;
chlorpyrifos [0,0-diethyl O—(3,5,6-trichloro-2—pyridinyl) phosphorothioate] at
1.1 kg ha“; chlorothalonil [tetrachloroisophthalonitrile] at 9.5 kg ha"; and a
combination product of 2,4—D [dimethylamine salt of 2,4-
dichlorophenoxyacetic acid]; mecoprop [dimethylamine salt of 2-(2-methyl—4—
chlorophenoxy) propionic acid]; and dicamba [dimethylamine salt of dicamba
(3,6-dichloro-o-anisic acid)] at 1.6 L ha". In 1992 pesticides applied were
mancozeb [zinc ion and manganese ethylene bisdithiocarbamate] at 25 L ha“
and propiconazole [1-[[2-(2-, 4-dichlorophenyl)-4-propyl-1, 3-dioxolan—2y]
methyl]— 1 H-1, 2, 4-triazole] at 3.2 L ha". The plots were mowed at a height
of 0.4 cm five days a week during the growing season and as needed during
late fall and early spring. The area was irrigated daily.

The multiple application study was located at Walnut Hills Country
Club, East Lansing, Michigan. This study was maintained under high fairway
maintenance conditions typical of a golf course.

A randomized complete block with three replications was used for the

Kentucky bluegrass and multiple application studies. The Kentucky bluegrass

 

 

study had two or three applications receiving 0.8 or 1.7 kg a.i. ha". The
multiple application study used 0.8 kg a.i. ha" with various treatment
combinations. Individual plots measured 1.2 m x 1.8 m. The safety study on
bentgrass varieties was a split plot design with three replications. With variety
as the main plot and ethofumesate rate as the subplots. Rates of ethofumesate
were 0.0, 0.6, or 0.8 kg a.i. ha". Individual plots measured 1.2 m x 1.2 m.
The three studies had treatments applied with a four nozzle boom C02
backpack sprayer delivering 538 L ha‘1 at 0.28 MPa. Ratings for injury, P.

annua control, and percent cover were all evaluated the same way as the 1990—

1991 studies.

 

 

 

53

RESULTS

1990-1991 Field Studies

The safety study on Kentucky bluegrass gave no observable injury
during fall or spring evaluations (data not shown).

Ethofumesate applied at 0.8 kg a.i. ha'1 and 1.7 kg a.i. ha'l gave
significant control of P. annua on the creeping bentgrass study (Table 3.1).
All treatments with multiple 0.8 kg a.i. ha" applications; treatments 2, 3, 4,
and 5; gave acceptable ground cover on all rating dates. Acceptable ground
cover was achieved with one application of ethofumesate at 1.7 kg a.i. ha'l
plus various multiple 0.8 kg a.i. ha“ applications consisting of treatments 6, 9,
10, and 13 with only two exceptions.

Treatments 8, 12, 14, 15, 16, 17, 18, 19, 20, and 21 gave significant
control of P. annua, the percent ground cover ratings indicated unacceptable
fairway turf. On the final coverage rating, unacceptable coverage was still
observed with treatments 12, 16, 17, 18, 20, and 21.

The April applications in this study gave unexpected results. The percent
of P. annua in the April treatments was less when compared to the equivalent

Sept, Oct, and/or Nov combination treatments.

 

 

54

Injury was severe on treatments 8, 12, 14, 15, 16, 17, 18, 19,20, and 21,
which were applied at twice the label rate of 0.8 kg a.i. ha" (Table 3.1). The
early spring injury rating taken on 3/21 was evaluated before greenup and
some injury was visible on all treatments. By mid-April injury was not visible
on any plots receiving two or more applications at 0.8 kg a.i. ha".

1991-1992 Field Studies

The study on Kentucky bluegrass at fairway height gave some injury
(Table 3.2). Injury was only unacceptable at the 1.7 kg a.i. ha" rate. All
injured turf recovered by mid-May.

Percent cover in this study for most treatments on all rating dates
dropped below an acceptable level, with the exception of the 0.8 + 0.8 kg a.i.
ha'l treatment. This poor coverage was a result of reduction to the P. annua
population.

Bentgrass varieties at greens height treated with ethofumesate showed
exceptional safety over all creeping bentgrass varieties (Table 3.3). The only
exceptions were BR 1518, Tracenta, Bardot, Egmont, and Allure which are not
creeping bentgrass varieties and showed serious injury at the 0.8 kg a.i. ha'l
rate.

The multiple application study gave some interesting and expected

results. For simplicity, treatments are displayed in groups of one, two, three,

 

 

55

or four applications. The single application showed the most promising
results. Injury was acceptable with single applications except October 15 but
injury recovered during early spring. P. annua reduction was significant for
the November 1 and 15 applications. A single application did not adversely
affect percent ground cover. Treatments applied later in the season usually
gave a greater reduction in P. annua compared to the control plot or earlier
applied treatments.

Multiple applications showed expected results with two or three
applications providing good P. annua reduction. The injury observed with the
Oct 15 plus Nov 1 or Nov 15 treatments was not acceptable but recovered by
late April. All treatments with three applications gave unacceptable injury in
early April but by the end of April only the Sept 15 + Oct 1 + Nov 1 and
Oct 1 + Oct 15 + Nov 15 had not recovered to an acceptable level. Two and
three applications did affect ground cover when evaluations were taken in early
April but by mid-May coverage was acceptable with the exception of the Sept
15 + Oct 1 + Nov 1 and Sept 15 + Oct 15 + Nov 1 treatments. Four and
five applications provided excellent P. annua reduction but the injured turf

never recovered to an acceptable level for a golf course fairway situation.

 

 

56

DISCUSSION

Ethofumesate on Kentucky bluegrass at the label rate of 0.8 kg a.i. ha'l
was safe at both 7.6 and 1.3 cm mowing heights. Even though there was
some injury at the 1.3 cm height this turf did recover. Some of the injury
effect could possibly be explained by the relationship of Kentucky bluegrass
and P. annua. Both Kentucky bluegrass and P. annua are in the same genus
Poa. With such a close botanical relationship susceptibility to injury from an
ethofumesate application between these two species is possible.

Ethofumesate also showed exceptional safety on creeping bentgrasses at
green heights. At the present time ethofumesate is not labeled for use on golf
greens. This gives some indication for the potential use of ethofumesate on
golf course greens.

Three conclusions can be drawn from the multiple application studies.
First, the later ethofumesate is applied after freezing temperatures have
occurred the better P. annua reduction achieved. The Walnut Hills study
showed the benefit of waiting later in the fall to make an application to achieve
better P. annua reduction. The second conclusion was the benefit of an April
application. The April application resulted in greater P. annua reduction from

just having prior fall applications. The applications may be acting as a

 

57

postemergence and/or preemergence. The postemergence activity is acting on
the P. annua plants present but the preemergence activity may be a result of
the prior fall applications having removed P. annua leaving bare soil giving
control of germinating P. annua. The third conclusion was related to the
effect multiple applications have on P. annua reduction. More applications
usually result in a greater reduction of P. annua. Even though greater
reduction in P. annua is possible by waiting until after freezing temperatures,
this can be overcome with multiple applications. This could be beneficial if a
little P. annua reduction was desired, instead of making two applications the
more beneficial technique may be to only make a single application late in the
season. If there is a large amount of P. annua present, instead of three
applications, waiting and make two applications late in the season may give the
same amount of control that three applications would. The end result would

give both economical and environmental benefits.

 

 

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LITERATURE CITED

Ball, A.P., and AR. Roberts. 1974. The use of ethofumesate for weed control
in ryegrass seed crops. Proceedings of the 12th British Weed Control
Conference. 727-732.

Coats, GE, and J .V. Krans. 1986. Evaluation of ethofumesate for annual
bluegrass (Poa annua) and turfgrass tolerance. Weed Science. 34: 930-935.

Demoeden, P.H., and TR. Turner. 1988. Annual bluegrass control and
tolerance of kentucky bluegrass and perennial ryegrass to ethofumesate.

HortScience. 23: 565—567.

Demoeden, P.H., and TR. Turner. 1986. Selective control of poa annua in
perennial ryegrass and creeping bentgrass with ethofumesate. Proceedings

Northeast Weed Science Society. 40: 276-277.

Dickens, R. 1981. Rates and timing of ethofumesate applications for annual
bluegrass control. Agronomy Abstracts. 124-125.

Johnson, B.J., G.W. Landry Jr., and K. Kamok. 1989. Tolerance of bentgrass
to amount, frequency, and timing of ethofumesate applications. HortScience.

24: 102—104.

Kageyama, M..,E and LR. Widell. 1989. Annual bluegrass to bentgrass
conversion with turf growth retardants (TGRs). 307—311. In A.R. Leslie and
R.L. Metcalf (ed.). Integrated Pest Management for T utfgrass and
Ornamentals. United States Environmental Protection Agency. Washington,

DC.

Shearman, RC. 1986. Kentucky bluegrass and annual bluegrass response to
ethofumesate. HortScience. 21: 1157-1159.

 

 

Chapter 4

GREENHOUSE STUDIES ON THE EFFECT OF COLD TEMPERATURE
ON ETHOFUMESATE EFFICACY.

ABSTRACT

Ethofumesate [2-ethoxy—2, 3—dihydro—3, 3-dimethyl—5—benzofuranyl
methanesulfonate] provides little reduction of P. annua populations when
applied in the summer but fall applications give a greater reduction.
Temperature appears to have an effect on ethofumesate efficacy. Greenhouse
studies indicated freezing temperatures prior to an ethofumesate application is
more effective in P. annua reduction than when not subjected to freezing
temperatures. Two different studies were used to evaluate this hypothesis.
Studies involved the use of visual and regrowth measurements to evaluate the
relationship of freezing temperatures and ethofumesate applications. Plants
exposed to freezing temperatures prior to an application of ethofumesate
consistently were injured more and had less growth than those plants not
exposed to freezing temperatures. Field application of ethofumesate could be

more effective is applied after freezing temperatures.

66

 

 

 

67

INTRODUCTION

Selective control of P. annua has become a possibility only in the last
eight years. Ethofumesate is a unique herbicide which provides selective P.
annua control (Ball and Roberts 1974, Demoeden and Turner 1988, Dickens
1981, Shearman 1986). One unique characteristic of ethofumesate is the
application timing. According to the label the first application of ethofumesate
is not to be applied until after the first of September. Another characteristic of
ethofumesate is the need for multiple applications to achieve acceptable control
of P. annua (Coats and Krans 1986, Shearman 1986).

Some inconsistent results have been seen with this application schedule.

Some years turf managers may see acceptable results and in other years they
may see little if any control of P. annua.

The hypothesis developed was that the temperature around the time of
application influences the efficacy of ethofumesate on P. annua. Growth
chamber studies were designed with the objective of determining the
relationship between temperature and ethofumesate. The objective of this
study was to determine the effect of freezing temperatures prior to an

application of ethofumesate on P. annua growth and dry matter production.

 

 

68

MATERIAL AND METHODS

P. annua was taken from the Hancock Turfgrass Research Center, East
Lansing, Michigan and transplanted into 355 ml Styrofoam cups containing
Baccto (Michigan Peat Company) potting media. Plant material was
approximately 7.6 cm thick (soil and thatch) when placed into the cups. The
cups were placed in the greenhouse and watered as needed to prevent
desiccation of plant material. Supplemental lighting from fluorescent lights
provided a 16 hour day length. Greenhouse temperatures were maintained at
20/18°C day/night cycle and relative humidity at 40—75%. Plants were
fertilized with Peters Professional Water Soluble Fertilizer Source 20—0-20 at
237 ppm N 9.3 m ’2 every two weeks. Plant material remained in the
greenhouse for approximately two weeks to allow for recovery from
transplanting.

Plant material was then placed in a growth chamber at 21/ 10°C with a
9/15 hours day/night cycle to begin acclimation. This continued for five days
with an additional five days at 4/4°C under the same day/night cycle before
plants were subjected to freezing temperatures.

Plant material was subjected to freezing temperatures in a freezer prior

to ethofumesate application. Temperatures were —6°C during the night cycle

 

 

 

 

69

and 3°C during the day. Duration of the freeze cycles before chemical
application were 0, 1, 2, 4, and 8 days for the first two experiments; 0, 5, and
10 days for the third experiment; 0 and 5 days for the fourth. After
ethofumesate was applied, plants were again placed in a growth chamber at
21/10°C with a 9/15 hours day/night cycle.

Prior to plant material being placed in the 4/4°C acclimation
temperatures, plants were mowed weekly at a height of 2.5 cm. Plants were
again mowed weekly after the application of ethofumesate at 0.6 cm. In
studies one and two, visual evaluations were used to make observations of
differences among treatments. The results from the two studies were
inconclusive and a more quantitative measurement was needed which would
possibly show significant differences. In the third and fourth studies regrowth
was mowed off above the lip of the cup at 0.6 cm using scissors. Clippings
were collected with a vacuum cleaner, placed in a tared beaker and fresh
weights determined. Then data was converted and reported as percent control.

This continued for a total of four collection dates.

A randomized complete block design with four replications was used for
experiments one and two. For experiments one and two, plant material was
subjected to a freezing duration of 0, 1, 2, 4, and 8 days before treatment with

0.8 kg a.i. ha" of ethofumesate. Studies three and four used a factorial design

 

70

with four replications. Freezing duration of 0, 5, and 10 days in study three
or 0 and 5 days in study four were one factor and ethofumesate rates of 0.0,
0.2, 0.6 and 0.8 kg a.i. ha'l were a second factor. Freezing duration was
prior to the application of ethofumesate. Ethofumesate treatments were applied

using a track sprayer delivering 187 L ha‘1 at .22 MPa.

 

 

71

RESULTS AND DISCUSSION

Comparing summer versus fall applications (Table 4.1) shows that little
injury resulted from summer applications but the same applications in the fall
displayed a marked increase in injury. This led to the idea that temperatures at
the time ethofumesate is applied are related to P. annua reduction.

The control plants in study one showed little injury with only the plants
in freezing temperatures 8 days significantly injured (Table 4.2).

The treated plants even without freezing temperatures prior to treatment
showed some injury. This injury was not as severe as those plants having a
freezing duration prior to an ethofumesate treatment. The treated plants not
exposed to freezing temperatures began to show some recovery, but the treated
plants exposed to freezing temperatures did not. This same trend was evident
in study two (Table 4.3), but there were no significant differences among
freezing intervals.

A more quantitative measurement was used to evaluate significant
differences. Clippings collected from plant material were used to evaluate
percent control when ethofumesate was applied after freezing temperatures.
This technique was modified into a rate study with plant material subjected to

freezing temperatures for 0, 5 or 10 days before treatment.

 

 

72

One week after treatment (Table 4.4) the three rates of ethofumesate
applied to the plants in freezing temperatures 10 days were giving almost 75
percent reduction or better along with the high rate on the plants in freezing
temperatures 5 days. The plants in freezing temperatures 5 days at the low
rate and all rates on all plants receiving no freezing temperatures had less than
50 percent reduction. The only exception being the high rate on the plants in
freezing temperatures 0 days. The second and third mowing had near 100
percent reduction from the two highest rates of the plants in freezing
temperatures 5 and 10 days. The fourth mowing had 100 percent reduction
with the two high rates on plants in freezing temperatures 5 and 10 days and
the high rate on the plants receiving no freezing temperatures. This may be
better observed graphically (Figure 4.1 and 4.2) showing percent reduction at
various rates for different freezing durations.

These results were consistent with a fourth study (Table 4.5). Because
of limitations of plant material only 0 and 5 day freezing duration was
possible. Percent reduction for treated plants in freezing temperatures were
consistently higher than treated plants never exposed to freezing temperatures
(Figure 4.3 and 4.4).

This study did show good significant results on the final mowing.

Plants receiving a freezing duration prior to an application of ethofumesate

 

 

73

resulted in greater P. annua reduction than if no freezing duration was
encountered. This same trend has been observed in the field (Chapter 3).
Before data was converted to percent reduction the fresh weights
revealed that the frozen controls consistently had less clippings than the
unfrozen controls. This was not totally unexpected due to the susceptibility of
P. annua to cold temperatures (Beard 1973). Some of the injury and reduction
are possibly a result of cold temperatures. This may explain why freezing
temperatures prior to an application of ethofumesate has an effect on the P.
annua. Some of the plants may have been killed or injured because of the
cold temperatures. Making the application of ethofumesate on less P. annua
and/or injured plants makes the end result appear as greater reduction. In
comparison ethofumesate applications made to plants receiving no freezing
temperatures prior to being treated have to work on non-injured P. annua.
Ethofumesate may also be more effective in the fall because of the germination
cycle of P. annua (Chapter 2). During the warmer months of summer P.
annua is still germinating. Injured turf could recover by new seedlings filling
in bare ground. During the fall P. annua germination declines. Turf that has
been injured from ethofumesate has less of a potential for new seedlings filling

in injured turf areas when germination rates are lower.

 

 

74

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Table 4.4. PERCENT REDUCTION OF POA ANNUA CLIPPING
WEIGHTS IN FREEZING TEMPERATURES PRIOR TO
AN ETHOFUMESATE TREATMENT (Study Three)

First Mowing Final Mowing
0 Freezing Day Duration

0.0 kg a.i. ha‘1 0 0
0.3 kg a.i. ha‘l l8 0
0.6 kg a.i. ha" 42 57
0.8 kg a.i. ha"1 77 100
5 Freezing Day Duration
0.0 kg a.i. ha" 0 O
0.3 kg a.i. ha“ 39 26
0.6 kg a.i. ha‘1 68 100
0.8 kg a.i. ha'1 73 100
10 Freezing Day Duration
0.0 kg a.i. ha’1 0 0
0.3 kg a.i. ha" 73 50
0.6 kg a.i. ha" 99 100
0.8 kg a.i. ha‘1 96 100
ANOVA Table
Freezing Duration (F) ** * (21H
Ethofumesate Rate (E) *** ***
F x E NS NS

*. **. *** Significant at the 0.05, 0.01. and 0.00] level of probability. respectively; NS, not
significant at P > 0,].
7‘ Number in parenthesis is LSD value at 0.05 probability level.

 

 

78

Table 4.5. PERCENT REDUCTION OF POA ANNUA CLIPPING
WEIGHTS IN FREEZING TEMPERATURES PRIOR TO
AN ETHOFUMESATE TREATMENT (Study Four)

First Mowing Final Mowing
0 Freezing Day Duration

0.0 kg a.i. ha‘1 0 0
0.3 kg a.i. ha'1 21 37
0.6 kg a.i. ha" 50 37
0.8 kg a.i. ha’I 32 69
5 Freezing Day Duration
0.0 kg a.i. ha’I O 0
0.3 kg a.i. hal 37 49
0.6 kg a.i. hal 37 83
0.8 kg a.i. ha" 69 98
ANOVA Table
Freezing Duration (F) ** ***
Ethofumesate Rate (E) *** ***
F x E NS * (23)?

*. **. *** Significant at the 0.05, 0.01. and 0.001 level of probability. respectively; NS. not
significant at P > 0.1.
+ Number in parenthesis is LSD value at 0.05 probability level.

 

 

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83

LITERATURE CITED

Ball, A.P., and AR. Roberts. 1974. The use of ethofumesate for weed control
in ryegrass seed crops. Proceedings of the 12th British Weed Control

Conference. 727—732.

Beard, J.B. 1973. Turfgrass: Science and Culture. 67-70. Prentice-Hall,
Englewood Cliffs. NJ.

Coats, GE, and J.V. Krans. 1986. Evaluation of ethofumesate for annual
bluegrass (Poa annua) and turfgrass tolerance. Weed Science. 34: 930—935.

Demoeden, P.H., and TR. Turner. 1988. Annual bluegrass control and
tolerance of kentucky bluegrass and perennial ryegrass to ethofumesate.
HortScience. 23: 565—567.

Dickens, R. 1981. Rates and timing of ethofumesate applications for annual
bluegrass control. Agronomy Abstracts. 124—125.

Shearman, RC. 1986. Kentucky bluegrass and annual bluegrass response to
ethofumesate. HortScience. 21: 1157—1159.

 

 

 

 

 

 

 

 

 

 

 

 

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