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ALTERNATIVES TO METHYL BROMIDE FOR WEED
CONTROL IN PERENNIAL ORNAMENTAL CROPS AND
CONIFER SEEDLINGS

presented by

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ALTERNATIVES TO METHYL BROMIDE FOR WEED CONTROL IN PERENNIAL
ORNAMENTAL CROPS AND CONIFER SEEDLINGS

By

Robert Egon Uhli g

A THESIS
Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of
MASTER OF SCIENCE
Department of Horticulture

2006

ABSTRACT

ALTERNATIVES TO METHYL BROMIDE FOR WEED CONTROL IN PERENNIAL
ORNAMENTAL CROPS AND CONIFER SEEDLINGS

By

Robert Egon Uhlig

The soil fumigant methyl bromide is being phased out in accordance with the Montreal
Protocol and will not be available in the ﬁxture. Experiments were conducted to identify
fumigants and herbicides to replace methyl bromide for weed control in conifers and
ornamental crops grown in the ﬁeld and in containers under Michigan conditions. The
fumigants methyl iodide, metham sodium, 1,3-dichloropropene, dazomet, and
chloropicrin were evaluated in a ﬁeld experiment. All of these fumigants provided good
weed control, except methyl iodide 50% plus chloropicrin 50% (224 kg/ha) tarped and
metham sodium (701 L/ha, 1:4 water) not tarped. Euphorbia polychroma, Echinops
bannaticus ‘Blue Globe’, Lavandula angustifolia ‘Hidcote Blue’, Hosta fortunei
‘Twilight PP14040’, Artemisia schmidtiana ‘Silver Mound’, Chrysanthemum x superbum
‘Snow Lady’ and Coreopsis verticillata ‘Moon Beam’ growth was not affected by any of
the fumigants. Herbicides were applied to several ornamental and conifer species to
evaluate crop tolerance and weed control in the ﬁeld and containers. There was
considerable variability in crop tolerance among the species evaluated. The woody
ornamental species Picea glauca var. ‘Dwarf Alberta’, T axus x media var. ‘Brownii’, and
I72uja occidentalis var. ‘Holmstrup’ were tolerant of most herbicide treatments, while
other species were sensitive to one or more herbicides. Terbacil gave excellent weed
control, but caused injury on most species. Flumioxazin and isoxaben plus tn'ﬂuralin

were the safest treatments on the species evaluated and gave good weed control.

To the memory of

Ing. Agr. Harry Uhlig

iii

ACKNOWLEDGMENTS

I want to thank my mentor, Dr. Bernard Zandstra for his constant support,
help and understanding. I would like to thank my other committee members, Dr.
George Bird and Dr. Bert Cregg for their guidance and constructive inputs during my
professional development.

I want to express my special thanks the members past and present of the
Zandstra’s team: Mike Particka, Robert Richardson, Sylvia Morse, Daniel Little,
William Chase, and all the crew at the Horticulture Teaching and Research Center for
their constant help not only in the ﬁeld but also for their helpful thoughts and ideas.
In addition, I would also like to thank Juan Pedro Steibel for his guidance in statistics
and for showing me the practical side of statistics.

The Horticulture Department staff, as well the Horticulture Graduate Student
organization (HOGS) gave me all their support and ﬁiendship to make my master’s
time in Michigan so enjoyable.

I would like to offer thanks my parents-in-law, Roberto Ferenczi and Nilda
Gardini for their understanding, encouragement, support and love. Arturo Ferenczi,
thanks for taking care of my obligations in Uruguay.

I especially want to thanks to my family and, especially my dad, Harry Uhli g,
who always encouraged us to expand our horizons in other countries knowing how
important it was to grow both professionally and as a person. Without his advice we
would never had the courage to take off. . .. Thanks to my mother, Cristina, my
brothers and sister, Martin, Peter, and Martha for being always there when I needed

them.

iv

Finally, I want to thank my wife Alejandra Ferenczi, and my son Harry.
Alejandra’s daily encouragement, hard work, dedication and love were vital for the
completion of my master’s degree. I deeply thank them for being my daily

inspiration.

TABLE OF CONTENTS

LIST OF TABLES ........................................................................................................ viii

CHAPTER 1

INTRODUCTION ............................................................................................................ 1
References ............................................................................................................. 5

CHAPTER 2

LITERATURE REVIEW ..................................................... ' ............................................ 6
Ornamental Industry ............................................................................................. 7
Methyl Bromide .................................................................................................... 8
Alternative ﬁrmigants ......................................................................................... 12
Other weed control methods: Non-chemical ..................................................... 21
Other weed control methods: Herbicides ........................................................... 23
Hypothesis / Plan of research ............................................................................. 28
References .......................................................................................................... 30

CHAPTER 3

COMPARATIVE EVALUATION OF SOIL FUMIGANT S ....................................... 40
Introduction ........................................................................................................ 41
Materials and Methods ........................................................................................ 50
Results and Discussion ....................................................................................... 52
Conclusions ......................................................................................................... 55
References ........................................................................................................... 56

CHAPTER 4

RESPONSE OF TEN ORNAMENTAL SPECIES TO HERBICIDE TREATMENTS 70
Introduction ......................................................................................................... 71
Materials and Methods ........................................................................................ 79
Results and Discussion ....................................................................................... 82
Conclusions ......................................................................................................... 85
References ........................................................................................................... 87

CHAPTER 5

RESPONSE OF FIELD AND CONTAIN ER-GROWN CONIFERS SEEDLINGS

TO HERBICIDES ........................................................................................................... 96
Introduction ......................................................................................................... 97
Materials and Methods ...................................................................................... 100
Results and Discussion ..................................................................................... 105
Conclusions ....................................................................................................... 1 10
References ......................................................................................................... 1 12

CHAPTER 6

HERBICIDE EFFICACY ON DIFFERENT WEED SPECIES .................................. 125
Introduction ....................................................................................................... 126

vi

Materials and Methods ...................................................................................... 131
Results and Discussion ..................................................................................... 135
References ......................................................................................................... 141

vii

LIST OF TABLES

CHAPTER 2
Table 1. Common weeds of nursery crop products ........................................................ 38
Table 2. Properties of soil ﬁimigants .............................................................................. 39
CHAPTER 3
Table 1. Properties of the soil fumigants ........................................................................ 60

Table 2. Fifteen pesticide treatments evaluated at Sawyers Nursery (Hudsonville, M1)
for management of weeds and nematodes in Euphorbia polychroma, Echinops
bannaticus, Lavandula angustifolia, Hosta, Artemisia schmidtiana,

Chrysanthemum x superbum and Coreopsis verticillata .................................... 61
Table 3. Weed evaluation at 7 months after soil fumigants application ......................... 62
Table 4. Weed evaluation at 10 months after soil fumigants application ....................... 63
Table 5. Weed evaluation at 20 months after soil fumigants application ....................... 64

Table 6. Ornamental species injury rates at 11 months after soil fumigants application65
Table 7. Plant size index of 7 perennials growing in plots treated with different

fumigant combinations ........................................................................................ 66
Table 8. Total plant dry matter of the seven ornamental species evaluated ................... 67
Table 9. Roots, foliage, and total dry weight of Euphorbia and Artemisz'a .................... 68

Table 10. Effect of Dazomet on ornamental plant visual rating, size, and dry weight...69

CHAPTER 4
Table 1. Ornamental plant injury 2 weeks after preemergence herbicides application ..90
Table 2. Ornamental plant injury at 6 weeks after preemergence herbicides

application ........................................................................................................... 91
Table 3. Plant size index taken on November 2003 and 2004 ........................................ 92
Table 4. Weed control at 2 weeks after treatment .......................................................... 93
Table 5. Weed control at 6 weeks after treatment .......................................................... 94
Table 6. Grass species control for the 2004 study at 2 and 6 weeks after preemergence
application ........................................................................................................... 95
CHAPTER 5
Table 1. Tree species and tree height average used for the ﬁeld and container studies
in 2003 and 2004 ............................................................................................... 114
Table 2. Conifer seedling injury in the ﬁeld study at 2 weeks after treatment ............. 115
Table 3. Conifer seedling injury in the ﬁeld experiment at 6 weeks after treatment....116
Table 4. Size index difference in the ﬁeld study for 2004 ............................................ 117
Table 5. Weed control in the ﬁeld study at 2 weeks after treatment ............................ 118
Table 6. Weed control in the ﬁeld study at 6 weeks aﬁer treatment ............................ 119
Table 7. Weed control in the ﬁeld study in the Poaceae family in 2004 at 6 weeks
after treatment ................................................................................................... 120

Table 8. Conifer seedling injury in the container study at 2 weeks after treatment ..... 121
Table 9. Conifer seedling injury in the container study at 6 weeks aﬁer treatment ..... 122
Table 10. Size index difference in the container study for 2004 .................................. 123
Table 11. Number of weeds in the container study at 6 weeks after treatment (2004) 124

V111

CHAPTER 6
Table 1. Yellow nutsedge control, dry weight and number of plants per container at 2
weeks after treatment in greenhouse after treatment with pre and postemergence

herbicides; grown in containers with high organic soil ................................................ 144
Table 2. Yellow nutsedge control, dry weight, and number of plants per pot in
greenhouse conditions; grown in containers with mineral soil ..................................... 145
Table 3. Hosta injury and Inula control in the container study at 4 and 9 weeks after
application of clopyralid ............................................................................................... 146
Table 4. Hosta injury in the ﬁeld study at 2, 4, and 9 weeks after application of
clopyralid in 2003 ......................................................................................................... 147
Table 5. Mugwort control at 2 and 8 WAT in both trials conducted in 2004 ............... 148

ix

CHAPTER I: INTRODUCTION

Methyl Bromide (MB) is a toxic gas used to control pests and diseases since
before World War H. In recent decades MB use as a soil fumigant has increased steadily.
Between 1984 and 1992 world wide use increased 60% (Price 1996). MB is the most
widely used fumigant in the world with 68,424 metric tons used in 1996. Almost half of
this was used in the USA. Agriculture accounts for 70% of the use, 5 to 8% is used for
quarantine purposes; 8% is used for perishable product treatment; and 12% is used for
non-perishable product treatment (Ware 2000).

Oceanic sources, biomass burning, leaded gasoline combustion, structural
fumigation, and agricultural applications contribute to MB emissions into the atmosphere.
The relative contributions of anthropogenic and natural emissions to total atmospheric
MB are not well known (Butler and Rodriguez 1996); however it was estimated that man-
made sources account for 35% and natural sources account for 65% of the total MB in the
atmosphere (Hanwant 1993).

Even though MB is in low concentration in the atmosphere (10 parts per trillion)
and has a short lifetime in the atmosphere (one year), it contains bromine, a highly active
ozone depletion compound, leading to a high ozone depletion potential in the stratosphere
(Butler and Rodriguez 1996). The bromine atom released from the MB molecule in the
stratosphere reacts with an ozone molecule (03) resulting in one oxygen (02) and one
bromine oxide molecule. The last, reacts with another ozone molecule resulting in two
molecules of oxygen and one atom of bromine which reacts with another ozone molecule.
This chain reaction affects negatively ozone concentration in the stratosphere (Bird

2005).

Montreal Protocol on Substances that Deplete the Ozone under the United
Nations Development Programme (UNDP) recognized MB as a chemical that contributes
to depletion of the earth’s ozone layer, which protects the earth from incoming UV
radiation from the sun. Excessive UV radiation can denature protein and cause nucleic
acid transformation, resulting in negative human health impacts. The Montreal protocol
set a time frame to reduce manufacture and importation of MB, and phase it out in
developed countries for agricultural uses. The protocol mandated a 25% reduction in
1999, 25% reduction in 2001, 20% reduction in 2003, and complete phase out in 2005.
Developing countries have agreed to reduce most chloroﬂuorocarbon (CFC) consumption
by 50% by 1 January 2005 and to fully eliminate these by 1 January 2010 (Anonymous
2004b)

Elimination of MB will cause economic losses to US agriculture. Research has
been conducted on high value crops (tomatoes, strawberries, peppers, tobacco, and
cucumbers) in search of alternatives for MB. Less research, however, has been done in
the omamentals nursery industry. There is a distinct need for research on MB alternatives
for nurseries and greenhouse enterprises. Nursery and greenhouse production is the
fastest growing segment in agriculture. Sales increased 30% in a seven years period
(1991-1998) (Knox et a1. 2003). Even though non-chemical methods of weed control are
practiced, chemical methods are the most widely used in the ornamental nursery
(Anonymous 2004a).

The objective of this research is to ﬁnd alternative chemicals, either fumigants or
herbicides that can replace MB for weed control in the ornamental industry. The

information obtained will provide nurseries with complementary tools for weed control,

contributing to make them less dependable on MB and, reducing the negative impact of

the elimination of MB.

References:

Anonymous. 2004a. Agricultural chemical uses 2003. Nursery and ﬂoriculture summary
[Online]. Available by United States Dept. of Agr. - National Agr. Stat. Serv.
http://usdamannlibcornell.edu/reports/nassr/other/pcu-bb/agcn0904.pdf (posted
September 2004).

Anonymous. 2004b. USDA - ARS Methyl Bromide Research [Online]
http://www.ars.usda.gov/is/mb/mebrwebhtm.

Bird, G. 2005. personal communication.

Butler, J .H., and J .M. Rodriguez. 1996. Methyl bromide in the atmosphere, p. 28-83, In
C. H. Bell, et al., eds. The methyl bromide issue, Vol. 1. John Wiley & Sons.

Hanwant, BS. 1993. An investigation of the atmospheric sources and sinks of methyl
bromide. AGU. Geophysical res. letters 20: 1 33-136.

Knox, G., T. Momol, R. Mizell, and H. Dankers. 2003. Crop timeline for nursery-grown
evergreens and shade trees. Prepared for the US EPA. Ofﬁce of pesticides
programs. North Florida Res. and Educ. Ctr, Inst. of food and Agr. Sci.,
University of Florida, Quincy.

Price, N. 1996. Methyl bromide in perspective, p. 1-24, In C. H. Bell, et al., eds. The
methyl bromide issue, Vol. 1. John Wiley & Sons, New York.

Ware, G.W. 2000. The pesticide book. 5 ed. Thomson publications, Fresno.

CHAPTER II: LITERATURE REVIEW

Ornamental industry

Nursery and greenhouse production represent the sixth largest agricultural
commodity group in the United States. This is the fastest growing segment of US.
agriculture; between 1991 and 1998 sales of this segment increased 30%. Nursery grth
is due to the strong US. economy with the expansion in housing and increase of
ornamental plant use (Knox et al. 2003).

Weeds cause an estimated 12% reduction in crop yield in United States
agriculture, representing $32 billion lost annually. In addition to direct losses, $4 billion
is spent on herbicides each year. The cost of weed control in lawns, gardens, and golf
courses is estimated in $36 billion per year (Pimentel et al. 2000).

Nursery economic losses due to weed infestations have been estimated at $7,000
per acre. Weed species populations vary from nursery to nursery depending on many
factors, such as environment, climate, and weed management (Table 1). Between $500
and $4,000 is spent per acre of containers for weed removal by hand (Mathers and Case
2003). However, hand-weeding is sometimes necessary regardless of preventive
measures utilized for weed control (Knox et al. 2003).

Although growers try to implement non-chemical weed control practices,
including mulches, plant density, and mechanical methods, chemicals are widely used for
weed control in nurseries. Herbicides represent 20% (446,000 pounds) of the total
amount of pesticides used in the nursery and ﬂoriculture industries in California, Florida,
Michigan, Oregon, Pennsylvania, and Texas (Anonymous 2004a). A survey in Florida

showed that 71% and 56% of nurseries use post-emergence and pre-emergence

herbicides, respectively, and almost half used both kinds of herbicide (Tatum and

Thompson 1993).

Methyl Bromide

Methyl Bromide (MB) is a highly toxic gas that is formulated as a fumigant that is
injected into soil before planting to control ﬁmgi, weeds, and nematodes. The United
States utilizes about 60 million pounds each year. Approximately 75% of that amount is
applied to soil, 11% is used after harvest of various commodities during storage and
before export, and 6% is used in structures such as food processing plants, warehouses,
and museums, as well as transport vehicles. The remaining 8% is used for production of
other chemicals (Anonymous 2004b).

Methyl Bromide has been used since before World War II. The total amount used
has increased steadily with a 60% increase between 1984 and 1992 (Price 1996). Among
all ﬁrmigants, MB is the most popular, with 68,424 metric tons used in 1996, almost half
of which was in the USA. Globally, 70% was used for pre-plant soil treatments in
agriculture, 5 to 8% for quarantine purposes, 8% for perishable product treatment, and
12% for non-perishable products (Ware 2000).

Synthetic MB is prepared by reﬂuxing methanol with excess hydrobromic acid in
the presence of small amounts of sulfuric acid. It is a colorless gas at temperatures above
3.5 C and at low concentrations has no noticeable odor. Many different formulations of
MB are available for various pest control objectives. Chloropicrin (2% v/v) is added as a

warning gas.

Methyl bromide is a general biocide, making mode of action determination
quite difﬁcult to determine. In fact, the mode of action is not very well understood.
Methylation of sulﬂrydryl groups and the following enzyme inactivation has been
postulated to play an important role in its toxicity. MB affects a wide range of pests
indicating that there is not a single toxic effect, and the process affected by MB has to be
ﬁmdarnental for living organisms. MB is highly soluble in lipids and has a high toxicity;
it is lethal to rabbits at oral dosages (LD50) 60 mg kg'1 (Price 1996).

Atmospheric MB originates from oceanic emissions and anthropogenic sources
such as biomass burning, agricultural applications, leaded gasoline combustion, and
structural fumigations. The relative contributions of anthropogenic and natural emissions
to the total atmospheric MB are not well known (Butler and Rodriguez 1996). Hanwant
(1993) estimated that man-made sources account for 35% and natural sources account for
65%. However, air and water concentration analysis of MB and methyl chloride in the
southern ocean (latitudes 45°-67° S, longitudes 144°-l39° E), suggested that there is no
signiﬁcant production of these gases in this region (Y von-Lewis et al. 2004). Biomass
burning represents a major contribution of bromine in the stratosphere and can be
compared to the amount produced by ocean emissions and pesticides (Mano and Andreae
1994)

Methylation of soil organic matter may be the major pathway for MB degradation
(Tao and Maciel 2002). This was conﬁrmed by Xu et a1. (2003), who found that
incorporation into soil organic matter is the predominant pathway for transforming 1,3-D
and MB in soil. Fulvic acid, one of the humic components of soil organic matter, plays a

signiﬁcant role in this process. According to the USDA 2004 annual report (Anonymous

2004b) hydrolysis is the major transformation pathway for fumigants; and soil pH,
moisture, and organic content greatly affect this process. Even though fumigants are
potent biocides, bacteria can be involved in MB degradation by directly oxidizing MB
during the furrrigation process (Miller et al. 1997). Furthermore, biodegradation of
metham sodium by resistant Gram positive bacteria has been found in a ﬁeld where this
fumigant has been used for the last decade (Warton et al. 2001).

Little attention has been paid to MB due to its low concentration in the
atmosphere (10 part per trillion) until recently, when stratospheric ozone depletion by
MB was recognized. The ozone layer in the stratosphere is essential for protection of life
on the planet from incoming ultra violet radiation from the sun (Roback 1996). Although
MB has a short lifetime of one year in the atmosphere, it contains bromine, a powerful
ozone removal compound, leading to high ozone depletion potential (ODP). When UV
radiation strikes MB in the stratosphere, free bromine radicals are released. These
combine with oxygen radicals released when UV radiation strike 02 and 03 (a natural
process), making oxygen unavailable for combining with 02 to form 03. This process
disrupts the normal stratospheric balance between 02 and 03 (Bird 2005).

The Montreal Protocol on Substances that Deplete the Ozone under the United
Nations Development Program (UNDP), ratiﬁed by 166 countries, is in charge of setting
rules and regulations for safe country development. The Montreal Protocol deﬁned MB
as a chemical that contributes to depletion of the earth’s ozone layer. Thus, manufacture
and importation of MB will be phased out in developed countries for general agricultural
uses based on 1996 levels. The reduction schedule is as follows: 25% reduction in 1999,

25% reduction in 2001 , 20% reduction in 2003, and complete phase out in 2005

10

(Anonymous 2004b). Developing countries have agreed to reduce most
chloroﬂuorocarbon (CFC) consumption by 50% by January 2005 and to ﬁrlly eliminate
these by January 2010 (Anonymous 2004c).

Many agricultural industries will be affected by the loss of MB. The ornamental
and nursery industry in California is estimated to lose $129 million and North Carolina
$14 million (Carpenter 2000). Michigan is the sixth largest nursery and ﬂoriculture
producing state, with sales of $629 million in 2002 (Anonymous 2002). Even though
current application cost is approximately $4,000 per hectare, the ornamental industry still
relies on this product to achieve maximum yield and quality. Michigan used 220 metric
tons of MB in 2000. The target objective of MB application varies between industries; for
example, the herbaceous perennial ornamental industry targets ﬁrst nematodes, then
weeds and ftmgal diseases, and treats 90% of their planted surface with MB. On the other
hand, the woody ornamental seedling industry focuses more on fungi, then weeds, and
ﬁnally nematode control, applying the product to 75% of their acreage (Bird 2004). In the
turf industry, MB fumigation is used primarily to eliminate weeds and to ensure genetic
purity of turfgrasses, which is especially important in reconstruction and regressing of
existing sites (Unruh et al. 2002). Growers obtain excellent weed, nematode, and fungi
control with MB and depend on this fumigant to obtain desired yields in intensive and
high value crop systems.

MB phase out will affect agricultural production signiﬁcantly if no effective
alternatives are found. At the moment, there are few fumigants that can substitute for
MB. According to Duniway, (2002), “None of the chemical alternatives currently

registered and available has the full spectrum of activity and versatility of MB as a pre-

11

plant soil ﬁnnigant. Methyl iodide and propargyl bromide probably have activity that
most closely parallels that of MB in soil”. Studies conﬁrm that no EPA-registered
fumigant alternative to MB, applied alone or in combination for preplant turf soil

fumigation, exists (Unruh et al. 2002).

Alternative fumigants

Fumigants that may not deplete the ozone layer have been studied thoroughly in
recent years. Some prospective chemical alternatives to MB are metham sodium (MS),
chloropicrin (CP), 1,3-dichloropropene (1,3-D), dazomet, methyl iodide also called
iodomethane (Mel), propylene oxide (PPO), propargyl bromide, and sodium azide (Table
2).

MS is a broad spectrum biocide and may be used to control soil fungi, insects,
nematodes, and weeds, although it is most effective as an herbicide. It decomposes to
methyl isothiocyanate (MITC) which is the biocidal molecule. The transformation to
MIT C is the cause of inconsistent pest control (Unruh et al. 2002). MS has not always
provided consistent control of soil-bome diseases and pests, and does not have the
penetration capacity of MB (Messenger and Braun 2000). Control failure was also
attributed to a build up of microorganisms that can degrade the chemical.
Microorganisms with resistant stages were involved in the biodegradation of MITC in a
ﬁeld where MS has been used extensively for the past decade (Warton et al. 2001).

Unruh (2002) applied MS (748 L/ha), MS plus CP (748 L/ha: 168 kg/ha), tarped
and not tarped, and MS plus 1,3-D (748 plus 140 L/ha) and found that all treatments

provided acceptable weed control; however, MS plus CP covered with a plastic tarp for

12

48 h was the best MS treatment. This treatment controlled grass and broadleaf species
equal to MB; however, unacceptable sedge species control was observed. MS applied
alone failed to control redroot pigweed (Amaranthus retroﬂexus L.); however, MS plus
combinations provided control (Unruh et a1. 2002). That was conﬁrmed by Fennimore et
al. (2003), who found that MS (42%) was less effective than MB:CP on weed seed
control. Among MB, Mel, propargyl bromide, 1,3-D and MS and the combinations of
these with CP, MS and propargyl bromide were the most effective in controlling yellow
nutsedge (Cyperus esculentus L.) (Hutchinson et al. 2003).

The tarp laid immediately after application has an important role in ﬁrmigant
efﬁcacy. The use of both MS at 468 Uha and Telone C-17 (1,3-D plus 17% CP) at 126
um provided good pest control and had high plant yield and vigor when covered with a
polyethylene ﬁlm immediately after treatment. The same treatment not covered with
polyethylene ﬁlm but sealed with a mechanical soil cultipacker provided poor control of
weeds (Csinos et al. 1997). Application of MS (748 Uha) followed by CP 99% (168
kg/ha, shank injected) without tarp provided grass control similar to MB, but it was
reduced at ﬁve weeks aﬁer treatment (Unruh et a1. 2002). In addition, MS treatments
tarped after application improved weed control compared to the same treatment non
tarped (Westerdahl et al. 2002).

Dazomet is another pesticide that transforms into MITC. It is used for pre-plant
control of weeds, nematodes, and soil diseases in nurseries, greenhouses, turf, and
omamentals. The physical characteristics of dazomet make it difﬁcult to use. It is
formulated as a light powder, which is subject to drift. Equipment must be sealed to limit

spillage (Unruh et al. 2002). Dazomet and MS are highly dependant on soil preparation

13

and moisture for activation and uniform distribution of MITC. Inconsistent results are
often obtained because of improper methodology (Annis and Waterford 1996).

Treatments with both dazomet 99% (392 kg/ha) and CP 99% (168 kg/ha) or
dazomet 99% (392 kg/ha) and l,3-D 98% (140 L/ha) provided 80% and 51% control of
purple nutsedge (Cyperus rotundus L.) respectively, but these treatments declined in
nutsedge control within 11 months after treatment (Unruh et al. 2002). All dazomet
combinations controlled bermudagrass (Cynodon dactylon (L.) Pers.) 96 to 100%.
Carpetweed (Mollugo verticillata L.) was controlled as well as in MB with dazomet plus
CP, however the other combinations were not as efﬁcient. The efﬁcacy of dazomet and
combinations against winter annual weeds was similar to that of MB (Unruh et al. 2002).

1,3-dichloropropene (1,3-D) is registered as a nematicide. It is not known to have
fungi and insects control. High rates, 1,3-D have some efﬁcacy against a few weeds. This
fumigant does not deplete the ozone layer and has a short half-life of 7 to 12 hours.
(Messenger and Braun 2000). It has restricted usage in California due to residue problems
in air samples collected in urban areas adjacent to farms. This product has been listed in
California as a carcinogen (Ristaino and Thomas 1997).

1,3-D plus oxadiazon (140 L/ha, 168 kg/ha) did not control yellow nutsedge
(Cyperus esculentus L.) , purple nutsedge, bermudagrass, or carpetweed, but provided
83% control of the winter annual weed species (Carolina geranium - Geranium
carolinianum L, cutleaf eveningprimrose - Oenothera Iaciniata Hill, wandering cudweed
— Gamochaeta pensylvanica (Willd.) Cabrera), 71% control of alexandergrass (Urochloa
plantaginea (Link) R.D. Webster) and broadleaf signalgrass (Urochloa platyphylla

(Nash) R.D. Webster), and 80% control of tall morrringglory (Ipomoea purpurea (L.)

14

Roth), sharppod momingglory (Ipomoea cordatotriloba Dennst.), and redroot pi gweed
(Unruh et al. 2002). Application of Telone C-l7 (1 ,3-D 83%, CP 17%) resulted in an
effective concentration to give 50% mortality for yellow nutsedge control, similar to that
of Mel applied alone (Hutchinson et al. 2003). In one location, application of 1,3-D (93
L/ha) followed by MS (349 L/ha) and Telone C-17 (93 Uha) followed by MS (349 L/ha)
controlled oldﬁeld toadﬂax (Nuttallanthus canadensis (L.) BA.) and purple cudweed
(Gamochaeta purpurea (L.) Cabrera) as well as MB plus CP standard. Only combination
treatments of MS and 1,3-D, CP and 1,3-D were equivalent to MB for control of cutleaf
eveningprimrose. In the second location MS, 1,3-D plus CP plus MS and 1,3-D plus MS
were not different from MB plus CP standard treatment for control of purple cudweed,
Oldﬁeld toadﬂax and corn spur'ry (Spergula arvensis L). In addition all treatments except
CP were equal to MB plus CP standard in weed control for corn spurry, cutleaf
eveningprimrose, yellow nutsedge, henbit (Lamium amplexicaule L.) and annual sedge
(Cyperus compressus L.) in the second year experiment (Csinos et al. 2000).

Gilreath et al. (2005) found that MB plus CP consistently controlled Cyperus spp.
better than the other ﬁrmigants; however, most of the MB alternatives that included 1,3-D
reduced Cyperus spp. populations compared to the non-ﬁrmigant control. Naproparnide at
4.50 kg/ha, metolachlor at 2.25 kg/ha, and pebulate at 4.5 kg/ha, applied three weeks
before planting and incorporated, did not interact with different fumigants applied the
same day and had excellent control of goosegrass (Eleusine indica L.), southern crabgrass
(Digitaria ciliaris L.) and smooth pigweed (Amaranthus hybridus L.), but only poor to
fair control of purple nutsedge (Gilreath et al. 2004). However, the same author

concluded in 2005, that 1,3-D (325 kg ai/ha) plus CP (67 kg ai/ha) combined with

15

pebulate consistently reduced purple nutsedge density more than any other fumigant-
herbicide combination during the early stages of the crop at 5 WAT. In addition,
improved efﬁcacy was achieved when pebulate was deep incorporated (Gilreath and
Santos 2005). This result is consistent with the research done by the same author the year
before where high doses and deep incorporation of naproparnide and metolachlor
provided the best weed control; Telone C-1 7 had some purple nutsedge control but still
was insufﬁcient to achieve maximum yield (Gilreath and Santos 2004). Efﬁcacy of 1,3-D
plus CP (60%, 32%) and CP BC on seed control in little mallow (Malva parviflora L.) or
prostrate knotweed (Polygonum aviculare L.) did not differ from MB:CP (67:33)

(F ennimore et al. 2003).

Chloropicrin (CP) may be used to control nematodes, bacteria, fungi, insects, and
weeds. CP has been shown to be very effective as a fungicide when compared to MB
(Messenger and Braun 2000). CP has marginal activity against some nematodes and
weeds (Ristaino and Thomas 1997); for this reason CP is combined extensively with MB,
and more recently with 1,3-D (Unruh et al. 2002). Increased concentration and time
exposure with CP reduced common chickweed (Stellaria media (L.) Vill.), common
purslane (Portulaca oleracea L.), and prostrate knotweed seed viability. This was
conﬁrmed with a ﬁeld experiment (Haar et al. 2003). CP at 224 kg/ha provided
consistently equivalent weed control to MB 67% plus CP 33% at 392 kg/ha in common
chickweed, little mallow, common purslane, and prostrate lmotweed (Kabir et al. 2004).
CP does not degrade the ozone layer, but it is a potential groundwater contaminant

(Messenger and Braun 2000).

16

Weed seed population is an important aspect to consider in weed control
management to reduce weed population in succeeding years. Laboratory studies showed
that CP concentration and time of exposure have a direct relationship with seed viability.
Higher concentration and longer exposure resulted in reduced percentages of viable seeds
of common chickweed, common purslane and prostrate knotweed. Field studies with CP
applied at 83, 110, 138, 165 and 220 kg/ha supported this conclusion, but seeds of little
mallow and redstem ﬁlaree (Erodium cicutarium (L.) L'Hér. ex Ait.) were not affected
(Haar et al. 2003).

Iodomethane (MeI) is chemically analogous to MB and it is not currently
registered. MeI is destroyed rapidly in the troposphere with about one week of
atmospheric life (Ristaino and Thomas 1997). Research done with Mel conﬁrmed that it
is a strong candidate to replace MB. MeI is a better methylating agent than MB; it is
rapidly destroyed by UV light and therefore unlikely to be involved in stratospheric
ozone depletion. In laboratory and ﬁeld studies MeI was equal to or better than MB in
controlling soilbome pathogens and weeds (0hr et al. 1996). It is thought that he price of
Mel will be signiﬁcantly more expensive than MB. However, the current Mel price could
decrease in response to higher production and increased demand from agricultural uses
(Hueth et al. 2000).

Mel controlled grasses, sedges, and broadleaf weeds present at two locations
under different environmental conditions, but did not control redroot pi gweed (Unruh et
al. 2002). Zhang et al.(l997), however, found that redroot pigweed was the most sensitive
and yellow nutsedge was the least sensitive to Mel. Furthermore, Mel was as potent as

MB for redroot pi gweed but more potent than MB for annual ryegrass (L. multiﬂorum

17

Lam), velvetleaf (Abutilon theophrasti Medik.), common lambsquarters (Chenopodium
album L.), common purslane, wild mustard (Brassica kaber (DC.) L.C. Wheeler), yellow
nutsedge and purple nutsedge. Under ﬁeld conditions, Mel at 280 kg/ha killed all species
tested except eastern black nightshade, Solanum ptychanthum Dunal (Zhang et al. 1997).
Mel controlled velvetleaf and annual ryegrass in different soil moisture, temperature, and
soil texture. The optimal soil moisture to control those weeds was 14% water content
(WM) and the results were obtained with temperatures above 20 C. Time to 100%
mortality of weeds was 24 h for Mel fumigation and 36 h for MB when 200 mole of
fumigant was used (Zhang et al. 1998).

Propargyl bromide (PB) half-life in soil ranged from 1.2 to 5 days, depending on
the soil type. Under typical agricultural soil conditions, it diffuse readily, a desirable
characteristic for fumigants. Due to its short degradation time in soil, PB should not pose
a serious environmental risk (Yates and J ianying 1998). The concentration of PB required
to control 50% of bamyardgrass (Echinochloa crus-galli) seeds was 18 fold higher for
muck soil compared to sandy loam and loamy sand soils. The low efﬁcacy in muck soil
was a result of rapid degradation and high adsorption of the compound in the soil.
Propargyl brorrride’s half-life was 7 hours in muck soil, compared to 60 and 67 hours in
sandy loam and loamy sand, respectively (Ma et al. 2001). Degradation rate of propargyl
bromide increased with increasing soil organic matter content and the degradation
coefﬁcient (k) value was correlated to the organic carbon content (Papiernik et al. 2002).
Propargyl bromide and MS were the most efﬁcacious ﬁrmigants tested in controlling

yellow nutsedge tubers. MB, Mel, PB, 1,3-D and MS applied with 17% CP resulted in a

18

synergistic interaction; MB had more beneﬁt and PB had the least beneﬁt with this
combination (Hutchinson et a1. 2003).

Propylene oxide (PPO) is currently registered for post harvest application and
industrial uses. The Environmental Protection Agency (EPA) has classiﬁed propylene
oxide as a Group B2, probable human carcinogen (Anonymous 2005). Combination
treatments of PPO plus MS resulted in superior weed control compared with PPO or MS
alone, indicating a synergy between these compounds (Rodriguez-Kabana and Simmons
2004). PPO controlled germination of momingglory (Ipomoea spp.) seed at rates higher
than 406 kg ai/ha and yellow nutsedge germination was inhibited at all rates evaluated
(227 to 912 kg ai/ha) (Belcher et al. 2004).

Sodium azide is a highly-effective, broad-spectrum ﬁrrrrigant that controls soil-
bome weeds, nematodes, fungi, and bacteria (Richards 2004). Effective weed control was
obtained with rates higher than 85 kg ai/ha. Sodium azide at 57 and 84 kg ai/ha controlled
root diseases and weeds similarly to MB (Rodriguez-Kabana et a1. 2004). Weed control
by sodium azide at 112 kg ai/ha was as effective as MB at one experiment location
(Oxnard) but not in the other (Watsonville), but when combined with CP was equivalent
to MB in both locations (Kabir et al. 2004).

InLine (1,3-D 61% plus CP 33%) at 236 and 393 L/ha, CP (95%) at 130 and 200
L/ha, and Vapam (MS 42%) at 420 and 700 L/ha applied by drip irrigation systems
provided equal or better weed control than equivalent rates applied by shank injection
(F ennimore et al. 2003). There was no nutsedge control where Telone C-35 (1 ,3-D 65%
plus CP 35%) was applied broadcast, but when applied in-bed or broadcast followed by

in-bed application of CP, nutsedge control was comparable to MB (Gilreath et a1. 2002).

19

Alternative fumigants, Mel plus CP, Telone II, Telone C35 with high density
polyethylene, and Telone C35 with a virtually impermeable ﬁlm were as effective as MB
in reducing seed viability of ﬁeld bindweed (Convolvulus arvensis L.), annual
momingglory, johnsongrass (Sorghum halepense L.), and common purslane. However,
none of the treatments reduced seed viability of little mallow. In addition, alternative
treatments required similar amounts of hand weeding as MB treatment (Shrestha et al.
2004)

Economic impact of the MB phaseout was evaluated by other authors. Hueth et al.
(2000) analyzed the economic aspect of MB being replaced by Mel, which is a strong
candidate to replace MB from a technical point of view. Sources of raw material, product
cost, and supply-demand analysis is presented. Even though the economic aspect and the
cost analysis play an important role in deﬁning which product or production management
will be adopted, this point is beyond our scope, and it is not covered in this research.

Alternative methods can be utilized to reduce agricultural fumigant emissions into
the atmosphere. Papierrrik et al., (2004) applied 1,3-dichloropropene (1,3-D), MS, and
propargyl bromide to soil beds via drip irrigation at 15 cm depth and found that
cumulative emissions of MITC and 1,3-D were decreased approximately 80% from the
soil by tarping the bed with virtually impermeable ﬁlm (VIF) rather than high-density
polyethylene (HDPE). In addition, tarping the bed with l-mil (HDPE) or (VIP) resulted
in a more effective fumigant vapor containment (Haar et al. 2003). Another way to
reduce fumigant emissions is by chemical reaction; Mel not only is weakly sorbed, but

also is highly mobile in Salinas clay loam and Arlington sandy loam soils (Park et al.

20

2004). Emissions of this gas, however, can be controlled by spraying thiourea on the soil,

thus reducing the half-life of Mel from 300 hours to a few hours (Zheng et al. 2004).

Other weed control methods: Non-chemical

There are non-chemical alternatives to MB. For instance, soil may be treated with
steam, which controls most soil-bome pathogens and weeds. There are several systems
for applying steam to soil. However, the use of steam as a soil sterilant is limited by the
expense of application, and by the difﬁculty of use. It can be utilized successfully in
some situations such as high value crops or in a special disease control program
(Messenger and Braun 2000).

Soil solarization is the process of raising soil temperature by tarping the soil
during the warm season. The heat created by visible light converted to infrared energy
that can not pass through the tarp raises the temperature and kills organisms in the soil.
Yields of strawberry in solarized soil were similar to those of MB treated soil (Rieger et
al. 2001). This method is compatible with other physical, chemical, and biological
methods (Messenger and Braun 2000). Common purslane, tumble pigweed (Amaranthus
albus L.), and black nightshade seeds were susceptible to temperatures above the
threshold temperature of 60 C using double-tent solarization. Soils in small containers
reached higher temperatures and were maintained at high temperature (above 60 C) for a
longer period of time, than soil in larger containers. This technique can be used by
commercial growers to effectively and inexpensively produce weed-free soil and potting
mixes in warmer climate areas (Stapleton et al. 2002). Arbuscular mycorrhiza fungi were

not reduced immediately after solarization but were reduced eight months after

21

application. Solarization apparently reduces arbuscular mycorrhiza fungi by reducing the
weed pepulation that maintained infective propagules over the winter (Schreiner et al.
2001).

Crop rotation can decrease pathogen inoculurn in soil by alternating resistant crop
and susceptible crops. The drawback is the time needed to be effective and the crop is
often rotated with non-cash crops contributing little to farm income (Messenger and
Braun 2000). Biological control can be used as a part of an integrated pest management
program to target speciﬁc pathogens and pests (Ristaino and Thomas 1997). Relatively
little research on cover crops has been conducted on ornamental crops compared to corn,
soybean, and horticultural produce. Cover crops can suppress weeds through competition
for light and nutrients or allelopathy (Messenger and Braun 2000).

Cover crop and management system combinations are capable of decreasing weed
pressure. Brassicaceae cover crops also can exert a weed-suppresive effect through the
release of isothiocyanates from glucosinolates aﬁer decomposition of plant tissues
(Angelini et al. 1998). This effect, which also can reduce soil borne pathogens and
nematodes, is often referred to as bio-fumigation (Kirkegaard and Matthiessen 2004;
Melander et al. 2005)

Although integrated pest management is a valid option in controlling pests,
chemical pesticides represent the most common currently used tool for pest control.
Large numbers of pests can attack a large number of species making it difﬁcult for
growers to reduce the amount of pesticides applied. Since crop appearance is important in
the ornamental industry, preventative pesticide applications are heavily used (Tatum and

Thompson 1993). Biological weed control has not been used due to the diversity of

22

weeds present in nurseries and the speciﬁcity of biological control in weeds (Knox et al.

2003).

Other weed control methods: Herbicides

Technology such as combinatorial chemistry developed in the last decade, allows
the production of thousands of chemicals, creating libraries of information about new
molecules; these molecules can not only be tested for pharmaceutical purposes but also
for herbicide activity with “high throughput screens”, which test for herbicide activity.
However, in the last decade fewer new herbicidal molecules have been released in the
market. Companies are reluctant to release a new compound into the market because they
have to compete with glyphosate, a product that is widely known and accepted and it is a
very cost effective herbicide (Penner 2005).

Herbicide selectivity on crops depends on a wide range of factors and the
complex interactions between them. Herbicide characteristics such as absorption,
formulation, mode of action, translocation, herbicide placement, and plant factors like
stage of growth, growing point location, leaf properties, and metabolism are important
factors that determine herbicide selectivity. Weed control by cultivation can potentially
damage herbaceous perennial species because storage organs are located just below
ground and shallow roots are common. Herbicides can reduce weed control costs;
however, little information about herbaceous perennial tolerances to herbicides is
available and few herbicides are labeled for use in this production system (Calkins et al.

1996).

23

Tolerance of herbaceous perennials to pre and post emergent herbicides is highly
dependent on species (Calkins et al. 1996; Derr and Salihu 1996). Response to isoxaben
was different when applied to dwarf burning bush (Euonymus alatus (Thunb) Sieb.
‘Compacta’) foliage and in wintercreeper (Euonymusfortunei (Turcz.) Hand. Mazz.
‘Colorata’) even though they share the same genus (Salihu et al. 1999). Reductions in
quality were often associated with reduction in size. Furthermore, herbicide injury was
greater in younger plants compared to established plants, and also injury was greater in
those plants actively growing compared to the dormant plants (Calkins et al. 1996; Salihu
et al. 1998).

Herbicide crop selectivity is inﬂuenced by crop growth stage. More terbacil was
absorbed and translocated to the leaves of ﬁeld violet with 3 leaves, than ﬁeld violet with
12 leaves. In addition, most 14C in roots (77%) and foliage (57%) in the 12 leaf plants
was in polar metabolites. These characteristics make the plants with 3 leaves susceptible
to terbacil, while plants with 12 leaves are tolerant to the herbicide (Rogers et al. 2001).

Regardless of herbicide toxicity, timing of application was important in injury
occurrence. Preemergence applications were sometimes more toxic than postemergence
because some buds were initiated prior to the preemergent herbicide application, thus
causing injury. For this reason it may be better to apply preemergent herbicides in the fall
when plants are dormant (Calkins et al. 1996).

A safener is a substance that reduces toxicity of herbicides to crop plants by
physiological mechanisms (Weed Science Society of America 2002). One of seven corn
hybrids exhibited an increase in tolerance when the safener, isoxadifen-ethyl, was applied

with foramsulfuron (Bunting et al. 2004). Rogers et al. (2001) investigating terbacil

24

metabolism in strawberry plants, concluded that ﬂuazifop-P inhibited detoxiﬁcation of
terbacil by strawberry.

Injury potential can be affected by herbicide formulation. The wettable powder
and emulsiﬁable concentrate formulations of oxadiazon caused greater injury than the
granular formulation to 'Compacta' Japanese holly and 'Hershey Red' azalea 30 days after
treatment (Derr and Salihu 1996). Briggs and Whitwell (2002) found that prodiarnine
granular formulation caused greater injury to sensitive taxa compared to wettable granule
and suspension concentrates. Even herbicides with the same active ingredient but
different formulations can differ in crop injury. Different injury rates were observed in
white spruce (Picea glauca (Moench) Voss.) trees treated over the top with three
different formulations of glyphosate (Mihajlovich et al. 2004).

Mulches treated with different pre-emergent herbicides can prolong herbicide
activity. Oxyﬂuorfen, oryzalin, and isoxaben applied to different mulches provided
excellent weed control. Bark treated with oryzalin had signiﬁcantly greater efﬁcacy than
bark treated with oxyﬂuorfen or isoxaben. Furthermore, Douglas ﬁr bark treated with
oryzalin provided increased efﬁcacy and extended efﬁcacy versus untreated Douglas ﬁr
bark or oryzalin alone (Mathers and Case 2002).

Terbacil belongs to the uracil chemical family. This herbicide inhibits
photosynthesis by binding to the Qb-binding niche on the D1 protein of the
photosynthesis II complex. Terbacil controls many annual broadleaf and grass weeds
including common chickweed, henbit, common lambsquarter, tansymustard, prickly
lettuce, crabgrass spp., downy brome, foxtail spp., ryegrass, and bamyardgrass, with

partial control of nutsedge (Weed Science Society of America 2002).

25

Irnazapic, imazaquin, and halosulfuron are herbicides that block acetolactate
synthase (ALS). The ﬁrst two belong to the imidazolinone family, while halosulfuron
belongs to the sulfonylurea chemical group. These herbicides inhibit acetolactate
synthase (ALS), a key enzyme in the biosynthesis of the branched-chain amino acids
isoleucine, leucine, and valine. Irnazapic and imazaquin control many annual broadleaf
weeds such as pigweed spp., common ragweed (Ambrosia artemisiifolia L.), common
lambsquarters and many annual and perennial grasses including panicum (Panicum spp.),
johnsonsgrass, goosegrass, foxtail spp. (Setaria spp.), crabgrass (Digitaria spp.), and
purple and yellow nutsedge. Injury symptoms in plants include grth inhibition,
chlorosis of meristematic areas, and general chlorosis and necrosis (Weed Science
Society of America 2002). Irnidazolinone herbicides are anionic at higher pH, thus more
herbicide was found in soil solution at higher pH. The increase in adsorption at lower pH
could be the cause of the slower degradation observed at pH 5. Average imazaquin half
life is 8 weeks (Weed Science Society of America 2002). However, Aichele et al. (2005)
estimated imazaquin half-life at 191 weeks.

Halosulfuron controls velvetleaf, cocklebur (Xanthium spp.), and numerous other
broadleaves, as well as Cyperus species (nutsedge). Rapid grth inhibition and
chlorosis are the main symptoms. Halosulfuron applied preemergence does not inhibit
seed germination, but as soon weeds emerge chlorosis and necrosis is observed.
Halosulfuron has a short to moderate persistence in the soil of about one to two weeks
(Weed Science Society of America 2002).

Flumioxazin belongs to the N-phenyphtalimide chemical family, is used pre-

emergent, and controls broadleaf weeds such as common ragweed, common

26

lambsquarters, velvetleaf, pigweed, and black nightshade (Solanum nigrum L.). The
mode of action is believed to be inhibition of protoporphyrinogen oxidase, an enzyme
important in the synthesis of chlorophyll; porphyrins accumulate in suscepltible plants
causing photosensibilization, which leads to membrane peroxidation. Plants emerging
from treated soil become necrotic and die shortly after sunlight exposure (Weed Science
Society of America 2002). Flumioxazin affected photosynthesis, as indicated by a
reduction in foliar chlorophyll and carotenoid contents, gas exchanges and alteration in
plastid structure. As a result plant growth was strongly inhibited (Saladin et al. 2003).
Among the selective herbicides applied immediate postemergence to strawberry
transplants, ﬂumioxazin and napropamide provided the most consistent control of bur
clover (Medicago polymorpha) and shepherd's purse (Capsella bursa-pastoris) (Manning
and Fennimore 2001). Hydrolysis and photolytic degradation rate increased with the pH
increase, and the degradation products formed by photolysis were the same as those
formed by hydrolysis (Kwon et a1. 2004).

Isoxaben belongs to the benzamide chemical family. Isoxaben can be applied in
established turf, omamentals, nursery stock, non-bearing ﬁ'uit trees, and Christmas tree
plantations. Isoxaben controls common chickweed, clover spp., dandelion (T araxacum
oﬂicinale G.H. Weber ex Wiggers), henbit, prostrate knotweed, plantain spp (Plantago
spp), and many other annual broadleaf weeds. If applied preemergence, susceptible
weeds fail to emerge. Isoxaben inhibits cell wall biosynthesis. Broadleaf weeds show
stunting, reduced root growth, root hair distortion, and root clubbing (swelling of
meristematic and elongation zones), symptoms similar to those caused by dinitroaniline

herbicides. Isoxaben persistence in soil is moderate to long, with a half life of 2 to 4

27

months in ﬁeld conditions; weed control extends to 6 months (Weed Science Society of
America 2002).

Triﬂuralin belongs to the dinitroaniline chemical family. It is labeled for more
than 80 crops. It is used on nursery stock, ornamental shrubs, groundcovers and
established ﬂowers. Triﬂuralin controls annual grasses and some small-seeded broadleaf
weeds. This herbicide binds to tubulin, the major microtubule protein, resulting in
absence of the spindle apparatus, thus preventing alignment and separation of
chromosomes. Susceptible weeds fail to emerge, due to inhibition of coleoptile growth or
hypocotyls unhooking. Roots appear stubby with thickened tips. The average life time in
soil is 45 days for most soils, but depends on the temperature. Residues can persist to the
following year with the possibility of crop injury, especially on small grains and corn
(Weed Science Society of America 2002). Triﬂuralin was one of the highest volatile ﬂux

losses with 14.1% compared to metolachlor, and atrazine (Rice et al. 2002).

Hypothesis / Plan of research

Research on MB alternatives has been conducted with strawberries, tomatoes,
peppers, tobacco, and cucumber in California where MB is heavily used, but relatively
little amount has been done in omamentals and conifers. Furthermore, this information is
not applicable to Michigan because of different environmental conditions and these
results cannot be directly extrapolated to ornamental plants. Thus, MB research is needed
in Michigan to improve our knowledge about alternative products that can replace MB in

the ornamental industry in order to reduce the impact of MB phase out.

28

One of the primary reasons growers apply soil fumigants in nurseries and
greenhouses is weed control. In addition, as Calkins (1996) and Derr (1996) stated,
herbaceous perennial tolerance to herbicides is highly dependent on species. Thus,
knowledge about herbicide efﬁciency and ornamental crop tolerances will inﬂuence weed
management decisions, thus increasing the range of herbicide uses for weed control and
reducing the amount of fumigant applied to the ﬁeld.

Two approaches have been proposed to ﬁnd alternatives to MB. The ﬁrst is to
ﬁnd similar broad spectrum fumigants as MB that have potential to replace it and do not
have a negative effect on the ozone layer. Second, ﬁnd products that speciﬁcally control
certain pests and by adding these effects we achieve a broad spectrum as with MB. In our
case we evaluate herbicides that can replace MB for weed control.

The objectives are, 1) evaluate the effects of broad spectrum and ozone-harmless
fumigants on weed control and crop response, 2) evaluate herbicides for weed control,
and herbaceous perennials and conifers response to those herbicides, and 3) evaluate the

efﬁcacy of selected herbicides on selected noxious weeds.

29

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31

Gilreath, J .P., and BM. Santos. 2005. Efﬁcacy of 1,3-Dichloropropene plus chloropicrin
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32

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Mamring, GR, and SA. Fennimore. 2001. Evaluation of low-rate herbicides to
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33

Miller, L.G., T.L. Connell, J.R. Guidetti, and RS. Oremland. 1997. Bacterial oxidation of
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264.

34

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35

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(Oxford - United Kingdom) 37(3):l81-189.

36

Zhang, W.M., M.E. McGiffen, J .0. Becker, H.D. Ohr, J .J . Sims, and SD. Campbell.
1998. Effect of soil physical factors on methyl iodide and methyl bromide.
Pesticide Sci. 53 :71-7 9.

Zheng, W., S.K. Papiemik, M.X. Guo, and SR. Yates. 2004. Remediation of methyl
iodide in aqueous solution and soils amended with thiourea. Environ. Sci. &
Technol. 38:1188-1194.

37

Table 1. Common weeds of nursery crop products.

 

 

Perennial weeds Summer weeds Winter weeds
Cynodon dactylon Pilea microphylla Cardamine spp.
Stachysﬂoridana Molluga verticillata Daucus carota
Convolvulus arvensis Digitaria sp. Phyllanthus urinaria
Cerastium vulgatum Fatoua villosa Stellaria media
Eupatorium capillifolium Commelina diﬁirsa Trifolium repens
Smilax spp. Hydrocotyle spp. Gnaphalium spp.
Senecio vulgaris Eclipta sp. Geranium carolinianum
Sorghum halepense Oenothera spp. Anthem cotula
Pueraria Montana var. lobata Elusine indica Medicago trunculata
Marchantia polymorpha Chenopodium spp. Medicago lapolina
Ipomoea spp. Ipomoea spp. Brassica spp.
Cyperus rotundus F atoua villosa Lepidium spp.

Cyperus esculentus
Toxicodendron aradicans
Rosa multrﬂora

Panicum repens

Campsis radicans

Phyllanthus urinaria
Phyllanthus tenellus
Amaranthus spp.
Portulaca oleracea
Richardia scabra
Ambrosia artemisiifolia
Cyperus compressus
Cyperus globulosus
Bidens bipinnata

Chamaesyce hirta, syn. Euphorbia

hirta

Chamaesyce hirta, syn. Euphorbia

vermiculata

Chamaesyce hirta, syn. Euphorbia

humistrata

C. maculate, syn. E. maculate, E.

supine
Oxalis stricta

Lotium multiﬂorum
Capsella bursa-pastoris
Sonchus spp.

Vicia sativa

North Florida Research and Education Center, Institute of Food and Agricultural Sciences, University of

Florida.

38

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39

CHAPTER III: COMPARATIVE EVALUATION OF SOIL FUMIGANTS

40

INTRODUCTION

Fumigants are used to control soil-bome pests, which allows high yields
production of superior quality products, which are important in order to be competitive in
a high value crop market (Messenger and Braun 2000). Methyl bromide (MB) is the most
widely used fumigant, with 68,424 metric tons used in 1996, almost half of which was in
the USA (Ware 2000). MB diffuses quickly and penetrates deeply into the soil due to its
low boiling point and high vapor pressure. It has a short waiting period before planting,
and low residual phototoxicity (Messenger and Braun 2000).

MB research has been conducted extensively in high value crops such as
strawberries, tomatoes, peppers, tobacco, and cucumbers. On the other hand, there has
been limited research for MB alternatives in the ornamental and conifer industries in
Michigan, even though this state is one of the six largest nursery and ﬂoriculture
producers, with sales of $629 million in 2002 (Anonymous 2002). Nursery and
greenhouse production represent the sixth largest agricultural commodity group in the
United States. This is the fastest growing segment of the US. agriculture; between 1991
and 1998 sales of this segment increased 30%. Nursery growth is driven by the strong
US. economy with the expansion in housing and increase of ornamental plant
consumption (Knox et al. 2003).

In addition to MB, nursery operators use other weed control practices, such as
mulches, plant density, and mechanical removal, but chemical methods remain the most
used weed control method in nurseries (Anonymous 2004a).

MB has been used since before World War II. The total amount used has

increased steadily with a 60% increase between 1984 and 1992 (Price 1996). MB is a

41

fumigant that is injected into soil before planting to control fungi, weeds, pathogens, and
nematodes. The United States utilizes about 27 million kilograms each year:
approximately 75% on soil before planting crops, 11% in harvested commodities during
storage and export, and 6% in structures such as food processing plants, warehouses, and
museums, as well as transport vehicles. The remaining 8% goes to the production of other
chemicals (Anonymous 2004b). Globally, the usage percentage follows the same patterns
(Ware 2000).

Manufactured MB is a colorless gas at temperatures above 3.5 C and at low
concentrations has no noticeable odor. ChlorOpicrin at 2% is added as a warning gas.
Reactions with organic and living materials are not highly speciﬁc, making mode of
action determination quite difﬁcult. In fact, the mode of action is not very well
understood. Methylation of sulﬂrydryl groups and the following enzyme inactivation has
been postulated to play an important role in its toxicity. MB is highly soluble in lipids
and has a high toxicity; it is lethal to rabbits at oral dosages above 60 mg kg“1 (Price
1996).

Atmospheric MB originates from oceanic emissions and anthropogenic sources
such as biomass burning, agricultural applications, leaded gasoline combustion, and
structural fumigations. The relative contributions of anthropogenic and natural emissions
to the total atmospheric MB are not well known (Butler and Rodriguez 1996). However,
it was estimated that man-made sources account for 35% and natural sources account for
65% (Hanwant 1993). According to Mano et al.(l994), biomass burning represents a
major contribution of bromine in the stratosphere and can be compared to the amount

produced by ocean emissions and pesticides.

42

Methylation of soil organic matter may be the major pathway for degradation of
MB (Tao and Maciel 2002). According to the USDA 2004 Annual Report (2004b)
hydrolysis is the major transformation pathway for fumigants and soil pH, soil moisture,
and organic content can accelerate degradation. Even though fumigants are potent
biocides, bacteria can be involved in MB degradation by directly oxidizing it during ﬁeld
ﬁrmigation (Miller et al. 1997).

The Montreal Protocol deﬁned MB as a chemical that contributes to depletion of
the Earth’s ozone layer. Thus, manufacture and importation of MB will be limited until
completely phased out in developed countries for general agricultural uses in 2005, and
developing countries have agreed to eliminate most chloroﬂuorocarbon (CFC) by January
2010 (Anonymous 2004c).

Many industries will be affected by the loss of MB. The ornamental and nursery
industry in California is estimated to lose $129 million and $14 million in North Carolina
(Carpenter 2000). Even though current application cost is approximately $ 4,000 per
hectare, the ornamental industry still relies on this product to achieve maximum yield and
quality. Michigan used 220 metric tons of MB in 2000. The target objective of MB
application nematodes, weeds, and fungi (Bird 2004). In the turf industry, MB fumigation
is primarily used to eliminate weeds and to ensure genetic purity of turf grasses (Unruh et
al. 2002).

The MB phase out will adversely affect agricultural production, especially where
alternative fumigants have not been thoroughly evaluated. At the moment there are few
fumigants that can readily substitute for MB. According to Duniway (2002), “None of the

Chemical alternatives currently registered and available have the full spectrum of activity

43

and versatility of MB as a pre-plant soil ﬁrmigant. Methyl iodide and propargyl bromide
probably have activity that most closely parallels that of MB in soil”. Studies conﬁrm
that no EPA-registered fumigant alternative to MB, applied alone or in combination for
pre plant turf soil fumigation, exists (Unruh et al. 2002).

Some of the fumigants proposed to replace MB are: metham sodium (MS),
chloropicrin (CP), 1,3—dichloropropene (1,3-D), dazomet, and methyl iodide (MeI).
Fumigants that may not deplete the ozone layer and have potential to replace MB are
listed in table 1.

MS and dazomet are used to control soil fungi, insects, nematodes and weeds.
They decompose in soil to methyl isothiocyanate (MITC) which is the biocidal molecule.
Dazomet and MS are highly dependant on soil preparation and moisture for activation
and uniform distribution of MITC, thus inconsistent results are often obtained (Annis and
Waterford 1996).

MS was one of the most efﬁcacious fumigants tested in controlling yellow
nutsedge (Cyperus esculentus L) tubers. MS applied with 17% CP resulted in a
synergistic interaction (Hutchinson et al. 2003).

MS (748 L/ha) alone and MS (748 L/ha) followed by CP (168 kg/ha), tarped and
not tarped, and MS (748 L/ha) followed by 1,3-D (140 L/ha) provided acceptable weed
control; however, MS plus CP covered with a plastic tarp after treatment for 48 h was the
best MS treatment controlling grass and broadleaf species equal to MB, but unacceptable
sedge species control. MS applied alone failed to control redroot pigweed (Amaranthus
retroﬂaxus L.); however, MS plus combinations provided control (Unruh et al. 2002).

That was conﬁrmed by Fennimore et al.(2003), who found that MS was less effective

44

than MB:CP for weed seed control. Among MB, MeI, propargyl bromide, 1,3-D and MS
and the combinations of these with CP, MS and propargyl bromide were the most
effective in controlling yellow nutsedge (Hutchinson et al. 2003).

Treatments with both dazomet 99% (392 kg/ha) and CP 99% (168 kg/ha) or
dazomet 99% (392 kg/ha) and 1,3-D 98% (140 L/ha) provided 80% and 51% control of
purple nutsedge respectively, but these combinations declined in nutsedge control 44
weeks after treatment. All dazomet combinations controlled 96 to 100% of bermudagrass.
Carpetweed was controlled as well as in MB with dazomet (392 kg/ha) followed by CP
(168 kg/ha), however the other combinations were not as effective. The efﬁcacy of
dazomet and combinations against winter annual weeds was similar to that of MB (Unruh
et al. 2002).

1,3-D is registered as a nematicide. 1,3-D has restricted usage in California due to
residue problems in air samples collected in urban areas adjacent to farms. It is listed in
California as a carcinogen (Ristaino and Thomas 1997).

1,3-D shank injected at 140 L/ha followed by oxadiazon 2% granular at 168 kg/ha
broadcast applied did not control yellow nutsedge, purple nutsedge (Cyperus rotundus
L.), or coastal bermudagrass (Cynodon dactylon (L.) Pers.) and carpetweed (Mollugo
verticillata L), but provided 83% control of the winter annual weed species (Unruh et al.
2002). Combining 1,3-D (Telone H) with 17% CP resulted in an ECso value for yellow
nutsedge control similar to that of Mel applied alone (Hutchinson et al. 2003).
Application of 1,3-D (93 L/ha) followed by MS (349 L/ha) and Telone _C-17 (93 L/ha)
followed by MS (349 Uha) controlled oldﬁeld toadﬂax (Nuttallanthus canadensis (L.)

D.A.), corn spurry (Spergula arvensis L.), evening primrose (Oenthera laciniata Hill),

45

yellow nutsedge, henbit (Lamium amplaxicaule L.), annual sedge (Cyperus compressus
L. ), and purple cudweed (Gamochaeta purpurea (L.) Cabrera) as well as MB plus CP
standard. On the other hand, CP was the least effective (Csinos et al. 2000).

1,3-D plus CP (83:17) at 330 Ma combined with napropamide at 4.50 kg/ha,
metolachlor at 2.25 kg/ha, pebulate at 4.50 kg/ha did not interact with the fumigants and
had excellent control of goosegrass (Eleusine indica L.), southern crabgrass (Digitaria
ciliaris L.) and smooth pigweed (Amaranthus hybridus L.), but only poor to fair control
of purple nutsedge (Cyperus rotundus L.) (Gilreath et al. 2004). However, the same
author concluded in 2005, that 1,3-D (325 kg ai/ha) plus CP (67 kg ai/ha) combined with
pebulate consistently reduced purpule nutsedge density more than any other fumigant-
herbicide combination during the early stages of tomato at 5 WAT. In addition, improved
efﬁcacy was achieved when pebulate was deeply incorporated (Gilreath and Santos
2005). This result is consistent with the research done in tomato and pepper by the same
author the year before where high doses and deep incorporation of napropamide and
metolachlor provided the best weed control; Telone C-17 (1 ,3-D 83%) reduced purple
nutsedge density but still was not enough to achieve maximum yield (Gilreath and Santos
2004). Efﬁcacy of InLine (1,3-D 60% plus CP 32%) and CP EC 95% applied through
drip irrigation system on seed control in little mallow (Malva parviflora L.) or prostrate
knotweed (Polygonum aviculare L.) did not differ from MB:CP (67:33) (Fennimore et al.
2003).

CP may be used to control nematodes, bacteria, fungi, insects, and weeds. CP has
marginal activity against nematodes and weeds (Ristaino and Thomas 1997),

furthermore, CP alone provided poor weed control (Csinos et al. 2000); for this reason

46

'MM A... 'v~

CP is combined extensively with MB, and more recently with 1,3-D (Unruh et al. 2002).
Laboratory studies found that increased concentration and exposure time with CP
reduced common chickweed (Stellaria media (L.) Vill.), common purslane (Portulaca
oleracea L.), and prostrate knotweed (Polygonum aviculare L.) seed viability. This was
conﬁrmed with a ﬁeld experiment (Haar et al. 2003). CP at 224 kg/ha provided
equivalent weed control to MB 67% plus CP 33% at 392 kg/ha in common chickweed,
little malow, common purslane, and prostate knotweed (Kabir et al. 2004). Even though
CP does not degrade the ozone layer, it is a potential groundwater contaminant
(Messenger and Braun 2000).

Mel is chemically analogous to MB and it is not currently registered. Research
with Mel combined with CP conﬁrmed that it is a strong candidate to replace MB. Mel is
a better methylating agent than MB; it is rapidly destroyed by UV light and therefore
unlikely to be involved in stratospheric ozone depletion. In laboratory and ﬁeld studies
Mel was equal to or better than MB in controlling soil borne pathogens and weeds (0hr
et al. 1996). Mel is an expensive chemical, however Mel current price could change
dramatically in response to increased demand from agriculture uses (Hueth et al. 2000).

Mel controlled grass species, sedge species, and broadleaf weeds present at the
two locations under different environmental conditions, but did not control redroot
pigweed (Unruh et al. 2002). Zhang et al. (1997) found that redroot pigweed was the
most sensitive and purple nutsedge was the least sensitive to Mel. Furthermore, Mel was
as potent as MB for redroot pigweed but more potent than MB for annual ryegrass (L.
multiﬂorum Lam.), velvetleaf (Abutz'lon theophrasti Medik.), common lambsquarters

(Chenopodium album L.), common purslane, wild mustard (Brassica kaber (DC .) LC.

47

Wheeler), yellow nutsedge and purple nutsedge. Under ﬁeld conditions, Mel at 280 kg/ha
killed all species tested except black nightshade (Solanum nigrum L.) (Zhang et al. 1997).
Mel controlled velvetleaf and annual ryegrass in different soil moisture, temperature, and
soil texture. The optimal soil moisture to control those weeds was 14% water content
(W/W) and the results were obtained with temperatures above 20 C. Time to 100%
mortality of weeds was 24 h for Mel fumigation and 36 h for MB, indicating Mel is more
effective on a molar basis (Zhang et al. 1998).

Propargyl bromide half-life in soil ranged from 1.2 to 5 days, depending on the
soil type, and it should not pose a serious environmental risk (Yates and J ianying 1998).
Propargyl bromide weed control efﬁcacy is reduced greatly in muck soil due to its rapid
degradation and high adsorption of the compound in the soil. Propargyl bromide half-life
was only 7 hours in the muck soil compared to 60 and 67 hours in the sandy loam and
loamy sand, respectively (Ma et al. 2001).

Propylene oxide (PPO) is currently registered for post harvest uses. PPO is used
in the production of polyethers (the primary component of polyurethane foams) and
propylene glycol and in the fumigation of foodstuffs and plastic medical instruments and
in the manufacture of dipropylene glycol and glycol ethers, as herbicides, as solvents, and
in the preparation of lubricants, surfactants, and oil emulsiﬁers. Environmental Protection
Agency (EPA) has classiﬁed propylene oxide as a Group B2, probable human carcinogen
(Anonymous 2005). PPO combined with MS resulted in superior weed control compared
with PPO or MS alone, this indicates a high synergy between these compounds

(Rodriguez-Kabana and Simmons 2004). PPO controlled germination of morning glory

48

(Ipomoea spp.) seed at rates higher than 406 kg ai/ha and yellow nutsedge germination
was inhibited in all rates (227 to 912 kg ai/ha) (Belcher et al. 2004).

Sodium azide formulated as SEP 100, has proven to be a hi ghly-effective, broad-
spectrum pesticide that controls soil-bome weeds, nematodes, fungus and bacteria
(Richards 2004). Effective weed control was obtained with rates higher than 85 kg ai/ha.
Sodium azide at 57 and 84 kg ai/ha controlled root diseases and weeds similarly to MB
(Rodriguez-Kabana et al. 2004). In addition, sodium azide at 112 kg ai/ha combined with
CP was equivalent to MB in weed control (Kabir et al. 2004).

The tarp applied immediately after application is important in ﬁimigant
efﬁciency. The combination of MS (468 L/ha) plus 1,3-D plus 17% CP (126 Ma)
provided good pest control and had high plant yield and vigor when covered with a
polyethylene ﬁhn immediately aﬁer treatment. The similar treatment not covered with
polyethylene ﬁlm but sealed with a mechanical soil cultipacker provided poor weed
control (Csinos et a1. 1997). MS plus CP without tarp provided grass control similar to
MB, but it was reduced at ﬁve weeks after treatment (Unruh et al. 2002).

MB plus CP, Mel plus CP, Telone H (1,3-D 97.5%), Telone C-35 (1,3-D 63%)
with high density polyethylene, and Telone 035 with a virtually impermeable ﬁlm were
as effective as MB in reducing the viability of the seeds of ﬁeld bindweed (Convolvulus
arvensis L.), annual morningglory, johnsongrass (Sorghum halepense L.), and common
purslane. However, none of the treatments reduced seed viability of little mallow. In
addition, alternative treatment required similar amount of time to hand weed as MB

treatment (Shrestha et al. 2004).

49

Application of emulsiﬁed formulations of 1,3-D, CP, and MS through drip
irrigation system provided equal or better weed control than equivalent rates applied by
shank injection (Fennimore et a1. 2003). There was no nutsedge control where Telone C-
35 was applied broadcast, but when applied in bed or broadcast followed by in bed
application of CP, nutsedge control was comparable to MB (Gilreath et al. 2002).

Economic impact of MB phaseout was evaluated by other authors. Hueth et al.
(2000), analyzed the economic aspect of MB replacement by Mel, a strong candidate
from technical point of view. Sources of raw material, product cost, and supply-demand
analysis is presented. Even though the economic aspect and the cost analysis play an
important role in deﬁning which product or production management will be adopted, this
point goes beyond the scope of our work.

Even though there are numerous ways to control diseases and pests as mentioned
previously, this research studied the potential of ﬁve soil fumigants: metham sodium,
chloropicrin, 1,3-Dichloropropene, methyl iodide, dazomet and their combinations to
replace MB in weed control and their inﬂuence in growth of six ornamental plants:
Euphorbia polychroma, Echinops bannaticus ‘Blue Globe’, Lavandula angustzfolia
‘Hidcote Blue’, Hosta ‘Twlight PP14040’, Artemisia schmidtiana ‘Silver Mound’,

Chrysanthemum x superbum ‘Snow Lady’ and Coreopsis verticillata ‘Moon Bearn’

MATERIALS AND METHODS
The experiment was conducted in cooperation with an operational nursery,
Hudsonville, Michigan. The soil in the site is a sandy loam soil with 81% sand, 8% silt

and 11% clay. The soil pH was 6.2, phosphorus and magnesium concentrations in the soil

50

were the optimum and potassium was slightly below the optimum for ornamental crop
production.

Fiﬁeen treatments were applied on September 12, 2002 (Table 2). Each treatment
was tarped immediately aﬁer application, except for one of the non-treated controls, one
of the MS plots, and the dazomet plot, which remained uncovered. Weather conditions at
application were: 24 C air temperature, soil moistures 0.1 to 0.2 (cm3/cm3), relative
humidity 36%, soil temperature at 5 cm and 12 cm depth, 25.5 C and 22.2 C respectively,
and wind speed was 8 km/h from the W. Plots were 1.22 m wide and 30.5 m long.

The ﬁrmigants were injected about 15 to 20 cm below the surface with a nitrogen
pressurized fumigation rig at a pressure of 550 to 827 kPa (80-120 psi), mounted on a
tractor with eleven Chisels per bed spaced 30 cm apart. Dazomet is a granular fumigant
which was applied evenly over the plot surface and incorporated immediately after
application with a rototiller.

Seven ornamental species were planted mechanically in June 2003 (nine months
after treatment): Euphorbia polychroma, Echinops bannaticus ‘Blue Globe’, Lavandula
angustifolia ‘Hidcote Blue’, Hosta ‘Twlight PP14040’, Artemisia schmidtiana ‘Silver
Mound’, Chrysanthemum x superbum ‘Snow Lady’ and Coreopsis verticillata ‘Moon
Beam’. The number of plants planted in each plot varied among species: 15 to 20
Lavandula plants , 6 to 8 plants of Euphorbia polychrome, Echinops bannaticus, and
Hosta, and a complete row (25 to 30 plants) of Chrysanthemum x superbum and
Coreopsis verticillata.

Plant injury was rated on July 23, 2003 and August 20, 2003. Rating was done

visually in a range of l to 10, meaning 1 no injury and 10 dead plant. Weed evaluation

51

was done on April 24, July 9, 2003, and May 7, 2004. Plant size was measured on
November 14, 2003 and May 19, 2004. Plant size index was determined by adding the
highest point and the widest point of the plant and dividing by two (Briggs and Whitwell
2002)

Plant samples were taken from each plot and from each cultivar during September
to October 2004. The number of plants per sample was between four and six depending
on the number of plants present in the ﬁeld. The plants were kept in a reﬁigeration room
at 5 C until each plant was cut in the transition zone between roots and foliage. Foliage
and roots from each plant were weighed fresh and after drying at 40 C for 7 to 10 days
until a constant dry weight was achieved.

A randomized complete block design was used for weed control statistical
analysis and split plot design was used for all measurements taken on the crop (injury,
size index, fresh weight, and dry weight). A split plot design is justiﬁed by assigning
fumigant treatments randomly to the main plots as a ﬁrst step and cultivars (subplot) were
allocated within each treatment as a second step. The site had six replications.
Replications 1, 3, and 5 contained 15 treatments; and replications 2, 4, and 6 contained 14
treatments; the difference is because dazomet treatment was applied only in the odd

numbered replications.

RESULTS AND DISCUSSION
All treatments controlled 80% to 100% of annual weeds, except Mel 50% plus CP
50% (224 kg/ha, tarped) and MS (1 :4 water, 701 um, not tarped), which resulted in

lower control of common chickweed, mouseear cress (Arabidopsis thaliana (L.) Heynh.)

52

on April 2003 and May 2004 (Table 3 and 5), and common lambsquarters and common
purslane on July 2004 (Table 4). However, Mel 50% plus CP 50% at higher rate (336
kg/ha, tarped) had good control of these weeds, suggesting that the rate of 224 kg/ha was
below the threshold for weed control and the most efﬁcient rate should be between 224
and 336 kg/ha. MS (1 :4 water, 701 L/ha, not tarped) did not control weeds well as in the
same treatment tarped, indicating that tarping the plot after fumigation was an important
factor in controlling weeds. This result agrees with Csinos et al, 1997, who found that
pest control, yield and plant vigor were greater in MS (468 L/ha) plus 1,3-D plus 17% CP
(126 L ha—l) covered with polyethylene; and Unruh et al, 2002 who found that MS plus
CP without tarp provided good weed control but for a short period (5 weeks).

Crop injury was not noticeable in any of the treatments on July 23, 2003 (data not
shown). However on August 20, 2003 a slight injury (1.7 from 10) was observed in
Euphorbia with Telone C-35 (1,3-D, 65%) 327 um tarped, MeBr (98%) plus 2% CP
392 kg/ha tarped, Mel (98%) plus 2% CP 168 kg/ha tarped, and MeBr (67%) plus 33%
CP 392 kg/ha tarped when compared with the control (Table 6). F umigant modes of
action are not well known, so speciﬁc or particular fumigant lesions can not be expected,
which makes it difﬁcult to separate fumigant injury from other causes like diseases that
could affect plants in the same manner.

There were no differences in plant size between treatments on November 2003
(data not shown) and on May 2004 (Table 7), except for Euphorbia in 2004, in which
plants were smaller in the same treatments where injury was observed.

Considering fresh weight, treatments Telone C-35 (1,3-D, 65%) 327 L/ha tarped

and Mel (98%) plus 2% CP 168 kg/ha tarped reduced Euphorbia weight. All treatments,

53

except MS 701 L/ha (1 :4 water, not tarped), reduced Lavandula weight, compared to the
control. The other species had either no difference in weight or treatments resulted in
heavier plants compared to the control. However, considering total dry weight analysis
there were no signiﬁcant differences between treatments except for Euphorbia and
Artemisia (Table 8). Telone C-35 (1,3—D 65% plus CP 35%) 327 L/ha tarped reduced
(P<0.05) total plant weight in Euphorbia compared to the control. F urtherrnore, this
reduction in weight was caused by a reduction in root and foliage biomass (Table 9). Mel
plus CP (50:50) 336 kg/ha tarped caused the lowest plant weight in Artemisia, but was
not signiﬁcantly different from the control. In addition root and foliage biomass were not
different from the control.

Dazomet was not included for the statistical analysis because it was not applied in
all blocks and results obtained from this application would greatly inﬂuence the overall
results. As a general comment, dazomet gave good weed control in the three evaluation
dates except for prickly lettuce (Lactuca serriola L.) in May 2004. This ﬁrmigant injured
slightly Euphorbia (2.6 out of 10) and produced the smallest plants in this species.
Dazomet treatment provided the lowest fresh weight in all species except for Hosta,
which was not signiﬁcantly different, and for Artemisia, which resulted in heavier plants
compared to the control. Considering dry weight, dazomet treatment resulted in the
lowest biomass in Euphorbia, Lavandula and Coreopsis (Table 10). However, the
reduced number of replications may not allow us to compare these results directly with

other treatments.

54

CONCLUSIONS

Most fumigants tested had good weed control up to 20 months after application.
Mel 50% plus 50% CP (tarped, 224 kg/ha) and MS not tarped (701 L/ha, 1 :4 water) had
the poorest control of most summer annual weeds. In the ﬁrst case, lower rate and in the
second case, tarp could be the factors that contributed to the poor weed control.

In general, most fumigants did not injure the ornamental crops evaluated in this
experiment. Minor injury to Euphorbia caused by some treatments was reﬂected in the
size when measured in November 2003 and May 2004 and in plant biomass weight at end
of experiment. However, as mentioned previously, fumigants mode of action is not
known in detail and plant response to them could be variable, thus, making it difﬁcult to
separate fumigant injuries from other causes. In addition, further investigation needs to be
done to determine if any other variable could have been the cause of this injury and
smaller Euphorbia plants.

All of the fumigants tested have a potential to replace MB. They had good weed
control and did not interfere with crop development and yield. Further studies in fumigant
decomposition, interaction with the environment, effects in other omamentals and human
effects are required in order to use them safety. Furthermore, ﬁrmigants combined with
herbicides are promising options for weed control in the ornamental industry, thus further

research in this area is needed in order to evaluate the real potential.

References:

55

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59

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60

Table 2. Fifteen pesticide treatments evaluated at Sawyers Nursery (Hudsonville, M1) for
management of weeds and nematodes in Euphorbia polychroma, Echinops bannaticus,
Lavandula angustifolia, Hosta, Artemisia schmidtiana, Chrysanthemum x superbum and

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N° Treatment Tarp Rate

1 Non-treated No ---

2 Non-treated (tarped) Yes ---

3 Methyl iodide (50%) + 50% chloropicrin Yes 336 kg/ha

4 Methyl iodide (50%) + 50% chloropicrin Yes 224 kg/ha

5 Telone C-35 "' Yes 327 L/ha

6 Methyl Bromide (98%) + 2% chloropicrin Yes 392 kg/ha

7 Methyl iodide (98%) + 2% chloropicrin Yes 168 kg/ha

8 Metham sodium No 701 L/ha (1:4 water)
9 Metham sodium Yes 701 L/ha (1:2 water)
10 Metham sodium Yes 701 L/ha (1 :4 water)
11 Telone II " Yes 327 L/ha

12 Telone II “and Metham Yes 327 L/ha + 701 L/ha (l :4 water)

13 Methyl Bromide (67%)+ 33% chloropicrin Yes 392 kg/ha
14 Telone C-35 *and Metham Yes 327 W + 701 Lt/ha (l :4 water)

15 Dazomet No 393 kg/ha

 

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69

CHAPTER IV: RESPONSE OF TEN ORNAMENTAL SPECIES T0 HERBICIDE

TREATMENTS

7O

INTRODUCTION

Nursery and greenhouse production of ornamental plants represents the sixth
largest agricultural commodity group in the United States. This is the fastest growing
segment of the US. agriculture; between 1991 and 1998 sales of omamentals increased
30%. Growth in ornamental sales is caused by the strong US. economy with the
expansion in housing and increase of ornamental plant consumption (Knox et al. 2003).

Ornamental and ﬂoriculture nurseries in California, Florida, Michigan, Oregon,
Pennsylvania, and Texas used 335 pesticide active ingredients and a total of 2.2 million
kg of chemicals in 2003; herbicides accounted for 20% (446,000 kg) of the total amount
used. Among herbicides, glyphosate is the most popular, being used in 26% of the
operations, followed by oxyﬂuorfen with 8%, and oryzalin with 6% of the operations
(Anonymous 2004).

Economic losses of nurseries due to weed infestations have been estimated to be
about $7,000 per acre. Nurseries may spend $500 to $4000 per acre of containers for
manual removal of weeds (Mathers and Case 2003). However, hand-weeding sometimes
is necessary regardless of preventative measures utilized for weed control (Knox et al.
2003). Cultivation may damage herbaceous perennial species because storage organs
(bulbs, rhizomes, roots) are located just below the soil surface. Herbicides usually reduce
weed control costs; however, little information about tolerance of herbaceous perennials
to herbicides is available and very few herbicides are labeled for use on omamentals
(Calkins et a1. 1996).

Methyl bromide (MB) fumigation has been used widely to control soil borne

diseases and nematodes, and a wide spectrum of weeds. However, due to the Montreal

71

Protocol decision to phase out MB because of its harmful effect on the ozone layer, it
may not be available to growers after 2005. As a consequence, herbicides will become
more important in weed control programs for omamentals.

A number of herbicides are registered for some ornamental crops. Terbacil
belongs to the uracil chemical family. This herbicide inhibits photosynthesis by binding
to the Qb-binding niche on the D1 protein of the photosynthesis II complex. Terbacil
controls many annual broadleaf and grass weeds, including common chickweed (Stellaria
media (L.) Vill.), henbit (Lamium amplaxicaule L.), common lambsquarters
(Chenopodium album L.), prickly lettuce (Lactuca serriola L.), crabgrass (Digitaria
spp.), downy brome (Bromus tectorum L.), foxtail (Setaria spp.), ryegrass (Lolium spp.),
and bamyardgrass (Echinochloa crus-galli (L.) Beauv.), with partial control of nutsedge
(Cyperus spp.). Its half life is four months (Vencill 2002).

Imazapic, imazaquin, and halosulfuron are herbicides that inhibit acetolactate
synthase (ALS), a key enzyme in the biosynthesis of the branched-chain amino acids
isoleucine, leucine, and valine. Imazapic and imazaquin belong to the imidazolinone
chemical family while halosulfuron belongs to the sulfonylurea chemical group. Their
main symptoms are growth inhibition, chlorosis, and necrosis. Halosulfuron applied pre
emergence does not inhibit seed germination, but as soon they emerge symptoms are
observed. In addition halosulfuron persistence varies with the soil type from 7 to 34 days
(V encill 2002).

Halosulfuron applied foliarly at 0.009 and 0.018 kg/ha provided 87 to 91% purple
nutsedge control and 79 to 84% yellow nutsedge control. Regrth measurements taken

5 WAT showed 88 to 90% reduction in purple nutsedge resprouting and 75 to 83%

72

reduction in yellow nutsedge resprouting (Hurt and Vencill 1994a). Halosulfuron applied
with 0.25 and 0.5% (v/v) adjuvants such as X-77, Scoil, Sun-It II, Agridex, and Action
“99”, injured Japanese holly, forsythia, green liriope, and weigela but not ‘Blue Girl’
holly (Ilex x meserveae S.Y. Hu ‘Blue girl’) (McDaniel et a1. 1999). Azalea, redtip
photinia, green liriope, white petunias, red petunias, lavender petunias, celosia, vinca,
African marigold, bronce-leaved begonias, and purple salvia tolerated 0.009 and 0.018
kg/ha of halosulfuron (Hurt and Vencill 1994a). In addition Ilex x meserveae S.Y. Hu
‘China girl’ showed no visual injury or growth reduction from applications of
halosulfuron at 0.017, 0.035, 0.070 kg ai/ha, imazaquin at 0.035, 0.070, 0.14 kg ai/ha or
isoxaben at 0.56, 1.12, 2.24 kg ai/ha (Altland et a1. 2000).

Imazaquin provided excellent control of large crabgrass (Digitaria sanquinalis
(L.) Scop.), redroot pigweed, Pennsylvania bittercress (Cardamine pennsylvanica Muhl.
ex. Willd.), common chickweed, yellow woodsorrel (Oxalis stricta L.), and creeping
woodsorrel (Oxalis comiculata L.) at 0.56 kg ai/ha for 14 weeks, but was phytotoxic to
vegetative azaleas (Moore et a1. 1989). Imazaquin was one of the most effective PRE
treatments for reducing yellow nutsedge shoot weight. Furthermore, imazaquin applied
POST reduced yellow nutsedge shoot weight by 72 to 87% at 2 WAT, comparable to
chlorimuron , pyridate, bentazon, and g1yphosate(Derr and Wilcut 1993). Hurt et al.
(1994a) obtained 70 to 77% yellow nutsedge control and 56 to 59% purple nutsedge
control with imazaquin applied at 0.430 kg/ha and 0.560 kg/ha, respectively.

Foliar applications of imazapic at 0.07 g/ha controlled 95% of purple nutsedge
and 61% of yellow nutsedge; however Azalea 'Macrantha Orange' was not tolerant to any

of the imidazolinone herbicides tested. Green liriope was tolerant of all herbicide

73

treatments 4 WAT (Hurt and Vencill 1994b). The application method of imazapic can
injure the following crop. Imazapic was more injurious to cotton when applied preplant
incorporated to the preceding peanut crop, compared with postemergence application.
Imazapic applied preplant incorporated at 0.07 and 0.14 kg/ha visibly injured cotton 19 to
58%. The same rate applied postemergence caused minor injury to cotton but did not
affect yield (York et al. 2000).

The incorporation of adjuvants in the tank mix can affect the herbicide efﬁcacy.
The beneﬁt of adjuvants appears greater for imazethapyr than imazapic. No advantage in
purple nutsedge control was observed when adjuvants were added to imazapic (Grichar
and Sestak 2000).

Imazaquin visibly injured barberry (10 to 18%), liriope (0 to 21%), daylily (0 to
25%), compacta “holly” (0 to 8%), azalea (35 to 39%), photinia (0 to 19%), and did not
injure Burford holly and juniper. Imazaquin at 0.25 and 0.5 kg/ha reduced growth of
azalea, liriope and day1i1y(Derr and Wilcut 1993).

Visual ratings may not detect injury from imidazolinone herbicides to certain
nursery species. Although no observable injury Was evident 5 WAT, imazethapyr
reduced juniper size indices. There are different responses between woody nursery crops
and herbaceous species; the woody nursery crops outgrew the visible damage from
chlorimuron observed 5 WAT as no reduction in size was noted 10 WAT. However,
growth of the herbaceous species liriope and daylily was reduced by this herbicide,
indicating that chlorimuron has a greater potential for use in woody species (Derr and

Wilcut 1993).

74

F lumioxazin belongs to the N-phenyphtalimide chemical family. It gives good
preemergence control of many broadleaf weeds, including common ragweed, common
lambsquarters, velvetleaf, pigweed, and black nightshade (Solanum nigrum L.). The
mode of action is believed to be inhibition of protoporphyrinogen oxidase, an enzyme
important in the synthesis of chlorophyll; after absorption, porphyrins accumulate in
susceptible plants causing photosensibilization, which leads to membrane peroxidation.
Plants emerging from treated soil become necrotic and die shortly after sunlight exposure
(V encill 2002). Flumioxazin affects photosynthesis by reducing foliar chlorophyll and
carotenoid contents, gas exchanges and alteration in plastid structure. As a result, plantlet
growth was greatly inhibited (Saladin et al. 2003). Hydrolysis and photolytic degradation
rate increased with the pH increase, and the degradation products formed by photolysis
were the same as those formed by hydrolysis (Kwon et al. 2004).

Flumioxazin alone controlled giant foxtail (Setariafaberi Herrrn.) 18-81%,
velvetleaf 83-88%, common ragweed 79-83%, ivyleafmomingglory(1pomoea hederacea
(L.)) 92-93%, and common waterhemp (Amaranthus rudis Sauer) 48-100%. Velvetleaf
and ivyleaf momingglory control with ﬂumioxazin was improved with the addition of
clomazone plus chlorimuron or pendimethalin plus chlorimuron (N iekamp and Johnson
2001). The water dispersible granular formulation of ﬂumioxazin at 0.19 kg ai/ha was the
only treatment that caused injury on Spirea bumalda. The injury declined 4 weeks after
application. In addition, this treatment resulted in the best large crabgrass and tall
momingglory control. On the other hand, the poorest weed control was observed with the
lowest rate (0.19 kg ai/ha) of the granular ﬂumioxazin. Combinations with other

herbicides such as isoxaben, dithiopyr, or dinitroaniline herbicide may increase and

75

broaden the weed control spectrum (Czamota et al. 2001). Flumioxazin at 0.28, 0.42, and
0.56 kg ai/ha was safe on 'Nellie R. Stevens' holly (Ilex x 'Nellie R. Stevens'), arbivitae
(Thuja occidentalis 'Emerald'), and 'Green Luster' holly (Ilex crenata 'Green Luster'), but
injured ‘Goldmound' spirea (Spirea x 'Goldmound') and daylily (Hemerocallis x 'Stela de
oro') (Wooten and Neal 2001).

Isoxaben belongs to the benzamide chemical family. Isoxaben can be applied in
established turf, omamentals, nursery stock, non-bearing fruit trees, and Christmas tree
plantations. Isoxaben controls common chickweed, clover spp., dandelion (T araxacum
oﬂicinale G.H. Weber ex Wiggers), henbit, prostrate knotweed (Polygonum aviculare L.),
plantain spp (Plantago spp), and many other animal broadleaf weeds. If applied pre-
emergent, susceptible weeds fail to emerge. Isoxaben inhibits cell wall biosynthesis and
broadleaf weeds show stunting, reduced root growth, root hair distortion, and root
clubbing (swelling of meristematic and elongation zones) symptoms, similar to those
caused by dinitroaniline herbicides. Isoxaben persistence in soil is moderate to long, with
a half life of 50 to 120 days in ﬁeld conditions; weed control extends to 6 months
(V encill 2002).

Isoxaben at 0.84 and 1.1 kg ai/ha did not provide acceptable control of large
crabgrass, but prostate spurge (Euphorbia humistrata Engelm. Ex Gray) was controlled
62 and 80%, respectively (Skroch et al. 1994). When the active ingredients isoxaben and
oryzalin were appplied in combination, weed control was better than that provided by
either compound alone. Isoxaben plus oryzalin at 4.48 kg ai/ha and a tank mix of
isoxaben (1.12 kg ai/ha) plus oryzalin (3.36 kg ai/ha) provided the best weed control,

reducing the weed numbers by 93 to 99% respectively compared to control (Calkins et al.

76

1996). Isoxaben applied to dwarf burning bush (Euonymus alatus (Thunb) Sieb.
‘Compacta’) foliage caused 20 to 30% injury, but only slight reductions in root and shoot
weight were observed. On the other hand, isoxaben at 0.84 and 1.69 kg/ha did not reduce
shoot and root weight in wintercreeper (Euonymusfortunei (Turcz.) Hand. Mazz.
‘Colorata’ (Salihu et al. 1999).

Triﬂuralin belongs to the dinitroaniline chemical family. It is labeled for more
than 80 crops. It is used on nursery stock, ornamental shrubs, groundcovers and
established ﬂowers. Triﬂuralin controls annual grasses and some small-seeded broadleaf
weeds. This herbicide binds to tubulin, the major microtubule protein, resulting in
absence of the spindle apparatus, thus preventing alignment and separation of
chromosomes. Susceptible weeds fail to emerge, due to inhibition of coleoptile growth or
hypocotyls unhooking. Roots appear stubby with thickened tips. The average life time in
soil is 45 days for most soils, but depends on the temperature. Residues can persist to the
following year with the possibility of crop injury (Vencill 2002).

Granular Rout (Oxyﬂuorfen 2% plus oryzalin 1%, 3.36 kg ai/ha), Snapshot TG
(triﬂuralin 2% plus isoxaben 0.5%, 4.2 kg ai/ha), Regal O-O (oxyﬂuorfen 2% plus
oxadiazon 1%, 3.36 kg ai/ha), 0H2 (oxyﬂuorfen 2% plus pendimethalin 1%, 3.36 kg
ai/ha), Corral (pendimethalin 2.68%, 2.24 kg ai/ha), and Pendulum 2G (pendimethalin
2%, 2.24 kg ai/ha) did not injure Hydrangea macrophylla and all treatments had greater
than 94% weed control. Injury was induced by increasing the rate two and three times.
However, no signiﬁcant differences were observed after 14 days after application and
hydrangea growth was not affected (Conwell et al. 2002). In addition, pendimethalin at

3.4 kg ai/ha or pendimethalin plus oxyfluorfen at 3.4 kg ai/ha or 6.7 kg ai/ha applied prior

77

to simulated shipping in an enclosed environment did not injure Japanese Barberry
(Berberis thunbergii DC var. atropurpurea ‘Crimson Pygmy’) (Hubbard et al. 1992).

'Mary Nell' holly [(Ilex cornuta "Burfordii' x I. pemyi 'Red Delight') x I latifolia]
was not injured by pendimethalin, oryzalin, oxyﬂuorfen, isoxaben and simazine more
than 10%. Norﬂurazon produced temporary discoloration of the older foliage. Growth
indices were not inﬂuenced by any herbicide treatment (Reeder et al. 1994). Similar
results were obtained by Derr et al. (1996), when he found that plant size of holly (Ilex
aquifolium L. x Ilex cornuta Lindl.) treated twice annually with oryzalin plus isoxaben
over a two year period was not different from those treated with oryzalin plus simazine or
oryzalin plus oxyfluorfen; however oryzalin, suppressed shoot grth of Chinese holly
(Ilex comuta Lindl.). In addition, Ruter et a1. (1992) found that dinitroaniline herbicides
such as oryzalin and pendimethalin reduced the root growth of ‘Helleri’ holy (ﬂex
crenata Thunb. ‘Helleri’). Ilex cornuta Lindl. and Praxt. ‘Needle point’ holly was injured
by the three formulations but injury was greater with the granular formulation of
prodiamine at 1.68 kg ai/ha (Briggs and Whitwell 2002).

Isoxaben at 1.1 kg/ha did not reduce shoot fresh weight of Rhododendron spp, but
reduced shoot fresh weight of English ivy (Hedera helix L.) and common lilac (Syringa
vulgaris L.) (Derr and Salihu 1996).

Azalea (Rhododendron indicum x ‘Macrantha Orange’) was susceptible to
imazaquin, imazapic, and imazethaphyr, which caused cholrosis, leaf tip necrosis, and
loss of apical dominance. Even though azaleas treated with these herbicides produced

more ﬂowers, those were slightly discolored and smaller. In addition, the imidazolinones

78

reduced juniper growth 17 to 35%, but they did not reduce liriope grth 4 WAT. The
only taxa tolerant of imazethapyr was French marigold (Hurt and Vencill 1994b).
Ornamental plant tolerance to herbicides depends on many factors, but one of the
most important factors is plant genetics. In the experiment we evaluated crop injury and
grth distortion in response to selected herbicides. This information will provide
growers new managerial practices for weed control in ornamental production, therefore

less MB dependency to achieve their weed control objective.

MATERIALS AND METHODS

Ten ornamental species: Japanese Barberry (Berberis thunbergii ‘Burgundy
Carousel’); Redosier Dogwood (Camus stolonifera ‘Alleman’s Compact’); Winged
Euonymus (Euonymous alatus ‘Chicago Fire’); Panicle Hydrangea (Hydrangea
paniculata ‘Kyushu’); Holly ‘Blue Prince’(Ilex x ‘Blue Prince’); White Spruce (Picea
glauca ‘Dwarf Alberta’); Japanese Spirea (Spiraeajaponica ‘Fire Light’); Preston Lilac
(Syringa x prestoniae ‘Donald Wyman’); Anlojap Yew (T axus media ‘Browni’); and
White Cedar (Ihuja occidentalis ‘Holmstrup’) were planted at the Horticulture Research
and Teaching Center located near East Lansing, MI.

All these plants belong to the class Magnoliopsida except for Thuja occidentalis,
T axus media, and Picea glauca which belong to Pinopsida class.

The soil type was a clay loam with a range of 28 to 42% sand, 28 to 36% silt and
30 to 36% clay, and pH ranging from 6.5 to 7.1. P, Mg and K were not limiting factors.

The plant materials were obtained ﬁ'om a local nursery.

79

The plants were planted on June 30 and July 1, 2003 using a mechanical
transplanter. Each replication had 10 rows and each row was planted with one species.
The species order in each replication was randomly assigned. Distance between plants
was 30 cm with 120 cm between rows and the row length was 40 m. The ﬁrst quarter (10
m) of the row was used to set up the plots; the last quarter of each row was reserved for
the next year (2004) experiment. Herbicide plots were arrange perpendicular to the plant
rows and they were 1.5 m wide and 11 m long and each plot crossed the ten ornamental
species.

For the crop evaluation (injury and size index) a split block design with 4
replications was used, being treatments the main plot and species the subplot. Weed
control evaluation was analyzed as a randomized complete block design.

Terbacil (1.12 kg ai/ha), imazapic (0.07 kg ai/ha), imazaquin (0.42 kg ai/ha),
halosulfuron (0.035 kg ai/ha), ﬂumioxazin granular (0.28 kg ai/ha), isoxaben (1.12 kg
ai/ha) plus triﬂuralin (0.84 kg ai/ha) were applied over the top of the plants on July 14,
2003. An untreated plot was left as a control. Herbicides were applied using a C02
backpack sprayer with a two nozzle boom (FF 11002, Teejet® nozzle, Spraying Systems
Co, Wheaton, Illinois) at 207 kPa with 187 L/ha output. Flumioxazin granular was
applied manually with a shaker. After planting, plots were irrigated to incorporate the
herbicides into the soil. At the application time air temperature was 26 C, relative
humidity 43%, 15% cloudy; soil was dry and soil temperature was 26 C.

At application, a few common lambsquarters, 1 to 3 cm, and redroot pigweed, 1 to

4 cm height were present.

80

Ornamental injury and weed control were evaluated on July 22, July 29, August 4
and August 28, 2003. Plant injury was rated from 1 to 10; with 1 indicating no injury and
10 indicating a dead plant. Chlorosis, necrosis, and malformation or distorted growth and
the degree of those symptoms were the parameters used to evaluate injury.

Weed control was rated visually from 1 to 10, with 1 indicating no control and 10
indicating 100% control. Weed control was evaluated for each weed species present in
the control plot.

Plant size index was measured on November 14, 2003 and J une 3, 2004 and was
calculated by using the following formula: (height + width)/2. Three plants from each
species were measured, and the average of those three was used for the statistical
analysis.

In 2004, plants at the opposite end of the row were used for the experiment. All
procedures were the same as 2003. Weeds were pulled within the row on June 3 and
weeds between rows were mechanically removed. Plots were sprayed with the
corresponding treatments on June 25. Air temperature was 19 C, wind speed 11 km/h,
soil temperature 23 C and 10% cloudy at time of application.

Weeds within the rows were hand-weeded frequently in order to prevent
competition with plants. Plant injury was evaluated on July 9, July 23, August 5, 2004,
and weed control was evaluated on August 5, and August 20, 2004. Size index was

measured on November 12, 2004.

81

RESULTS AND DISCUSSION

If the herbicide by year interaction was signiﬁcant, mean separation was done for
each year; if not signiﬁcant, means were pooled across years. For statistical analysis, the
2 and 6 week after treatment (WAT) evaluations for each year are presented.

Herbicides did not cause injury on Ilex ‘Blue Prince’, Picea glauca, T axus media,
and Thuja occidentalis at 2 WAT except for terbacil and ﬂumioxazin which produced 2.3
injury on Ilex ‘Blue Prince’ in 2004 and for imazapic and halosulﬁiron which injured 2.0
and 2.8 T axus in 2004; however these treatments were safe in 2003 (Table 1).
Furthermore, Ilex ‘Blue Prince’, Picea glauca, T axus media, and Thuja occidentalis were
not injured by any treatment at 6 WAT in either year (Table 2). That agrees with
McDaniel et al. (1999), who found that ‘Blue Girl’ holly (Ilex x meserveae S.Y. Hu ‘Blue
girl’) was tolerant of halosulﬁiron. Altland et a1. (2003) also found that China girl holly
(Ilex x meserveae S.Y. Hu ‘China girl’) was tolerant to halosulfuron, imazaquin or
isoxaben; however, imazaquin visibly injured Japanese holly (Ilex crenata ‘Compacta’)
but not Burford holly (Ilex cornuta 'Burfordii').

In our research, the woody omamentals Ilex ‘Blue Prince’, Picea glauca, T axus
media, and Thuja occidentalis were the most tolerant plants. Derr et a1. (1993) suggested
that chlorimuron had greater potential in woody omamentals. In addition, Wooten at al.
(2001) found that ﬂumioxazin was safer on woody omamentals, Ilex x ‘Nellie R.
Stevens’, Ilex crenata ‘Green Luster’, and Thuja occidentalis ‘Emerald’, rather than in
herbaceous plant Spiraea x ‘Goldmound’.

Terbacil at 1.12 kg ai/ha caused the most injury to all species evaluated at 2 and 6

WAT for both years, except for Syringa x prestoniae which was not injured in 2003, but

82

had 5.8 injury in 2004 at 6 WAT, and for Euonymous alatus which was not injured at 2
WAT, but had 4.5 injury at 6 WAT.

Imazaquin, imazapic, and halosulfuron had similar injury effect. At 2 WAT these
treatments caused injuries on Berberis thunbergii, and Cornus stolonifera in both years,
and Hydrangea paniculata in 2004. At 6 WAT, injury rates were higher in these species
except for halosulfuron which was not different from the control in Berberis thunbergii in
2004 and Hydrangea paniculata in both years. Imazquin and halosulfuron injured slightly
Syringa x prestoniae, with ratings of 2.5 and 2.8, respectively in 2004, but not in 2003. In
addition imazaquin and imazapic injured Spiraea japonica 3.1 and 3.5, respectively.

F lumioxazin was one of the safest herbicides in all the crop species. Even though
some injuries were observed in Hydrangea in 2004 and Spiraea in both years at 2WAT,
when evaluated at 6 WAT none of the treatments were different form the control.

Isoxaben plus triﬂuralin was the safest treatment. It did not cause injury in any of
the species evaluated at 2 and 6 WAT.

Euonymous alatus did not show injury in our study; however, Derr et a1. (1996)
reported 20 to 30 % injury with isoxaben to Euonymous alatus (Thunb) Sieb.
‘Compacta’, but only slight reductions in root and shoot weight. This treatment was safe
on Hydrangea paniculata. Similar results were reported by Conwell et al. (2002) with
Hydrangea macrophylla.

Plant size index analysis is shown in Table 3. Measurements taken in November,
2003 and 2004 were used for the statistical analysis. Since interaction of species by year
was signiﬁcant in Camus stolonifera, data for this species is presented by year.

Treatments applied to all species did not have any differences compared to the control

83

except for Cornus stolonifera and Spiraea japonica. None of the treatments were
different (PS0.05) from the control in Spiraeajaponica. Treatments applied to Cornus
stolonifera were not different from the control in 2003; but in 2004, imazaquin and
imazapic treatments resulted in the smallest plants, and plants treated with ﬂumioxazin
resulted in the largest plants. As mentioned previously, injury produced to Cornus
stolonifera by imazaquin and imazapic reduced grth and resulted in the smallest
plants.

Weed control ratings are presented in Tables 4 for 2 WAT and 5 for 6 WAT.
Terbacil had the best broadleaf weed control at 2 and 6 WAT. Imazaquin and
ﬂumioxazin effectiveness was comparable to terbacil at 6 WAT, with some exceptions.
Imazaquin did not control common lambsquarters in 2003 and ﬂumioxazin was less
effective in controlling common lambsquarters in 2003, and common groundsel and
common chickweed in 2004.

Imazapic gave poor redroot pi gweed and common lambsquarters control in 2003,
but gave good control in 2004. Imazapic controlled all weeds evaluated within a range of
8.3 to 9.8, and had acceptable control of common purslane (7.5) and common groundsel
(6.3) at 6 WAT.

Halosulfuron provided variable weed control among weed species. It had the best
control of common groundsel, curly dock, and redroot pigweed in 2004 at 6 WAT;
however, it gave fair control (3.0 to 8.3) of the rest of the species evaluated.

Isoxaben plus triﬂuralin gave good weed control at 2 WAT, except for common
mallow (4.0). Redroot pigweed and common lambsquarters control was fair (7.0) at 2

WAT in 2003, but weed control was one of the highest at 6 WAT in 2004. Isoxaben plus

84

triﬂuralin had poor control of dandelion (4.0), but controlled eastern black nightshade,
common purslane, common groundsel, common chickweed, and curly dock within a
range of7.2 to 8.8.

Terbacil, imazaquin, and imazapic had the best grass control in all species
evaluated except for imazapic, which gave only fair control of annual bluegrass at 2 and 6
WAT (Table 6). In general, halosulfuron, ﬂumioxazin, and isoxaben plus triﬂuralin
provided poor grass control. However, ﬂumioxazin and isoxaben plus triﬂuralin provided

10 and 7.8 control of witchgrass at 6 WAT, respectively.

CONCLUSIONS

Herbicide tolerance was clearly different among species. Herbicides applied were
safe to woody omamentals belonging to the Pinopsida class: Ilex, Picea glauca, Thuja
occidentalis, and Taxus media. Size index (plant growth) was not affected by any of the
treatments in these species.

Terbacil was one of the best treatments for weed control but injured most of the
crop species evaluated. Even though those injuries were not reﬂected in the size index,
injuries were severe and would affect plant marketability.

In general, the higher weed control the higher injury observed on crops; however,
ﬂumioxazin and isoxaben plus triﬂuralin were the safest herbicides and they had a
relatively high weed control.

Crop injury and weed control was variable among years. More speciﬁc, injuries
were different between years in Berberis thunbergii, Cornus stolonifera, and Syringa x

prestoniae, and weed control was different in common lambsquarters and redroot

85

pigweed. More knowledge about herbicide variability between years is required in order
to improve safety of herbicide application in omamentals.

Herbicides tested have the potential to effectively control weeds in the ornamental
plants evaluated, and they have the potential to replace MB application when used for
weed control purposes. Herbicide combinations, application methods, formulations, and
rate of application are areas where research is required in order to achieve a higher crop

safety and a wider weed control spectrum.

86

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Hubbard, J ., T. Whitwell, and J. Kelly. 1992. Inﬂuence of herbicides on shipping quality
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87

Hurt, R.T., and WK. Vencill. 1994a. Phytotoxicity and nutsedge control in woody and
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Hurt, R.T., and WK. Vencill. 1994b. Evaluation of three imidazolinone herbicides for
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Knox, G., T. Momol, R. Mizell, and H. Dankers. 2003. Crop timeline for nursery-grown
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Kwon, J .W., K.L. Arrnbrust, and TL Grey. 2004. Hydrolysis and photolysis of
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89

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95

CHAPTER V: RESPONSE OF FIELD AND CONTAINER-GROWN CONIFERS
SEEDLIN GS TO HERBICIDES

96

INTRODUCTION

The Christmas tree and short rotation woody crop industries in the United States
include almost 15,000 farmers. This industry sold $400 million of products in 2002. In
Michigan there were 1,076 growers in 2002, which represents 7% of the total United
States growers, and their sales reached $31 million in 2002 (Anonymous 2002).
California, Florida, Michigan, Oregon, Pennsylvania, and Texas are the major producing
states of nursery and ﬂoriculture crops (Anonymous 2004).

Methyl bromide (MB) is a fumigant extensively used to control a broad spectrum
of soil diseases. The woody ornamental seedling industry uses MB for fungi, weed, and
nematode control, applying it to 75% of their acreage (Bird 2004).

MB is an efﬁcient fumigant to help achieve high yields and good quality;
however, its use in ﬁeld applications will be banned at the end of 2005. Bromine, which
is one of the atoms present in the MB molecule, degrades ozone molecules in the
stratosphere. The ozone layer protects the earth from incoming UV light. As a
consequence of the ozone degradation, more UV radiation hits the earth, which causes
human skin cancer or cataracts, and also may contribute to global warming (Miller 1996).

The MB phase out will limit weed control tools available for the conifer industry.
As a consequence herbicides will become more important for weed control.

Growers in the major producing states of nursery and ﬂoriculture crops applied
2.16 million kg of pesticide active ingredients in 2003. Herbicides accounted for 20%
(0.44 million kg) of the total pesticide use. Coniferous evergreens, Christmas trees, and

deciduous shrubs account for 39% of the 0.44 million kg. The most commonly used

97

herbicides in this industry are glyphosate (26%), oxyﬂuorfen (8%), and oryzalin (6%)
(Anonymous 2004).

Shape, density, and height are the main factors in tree choice when consumers are
selecting a Christmas tree (F lorkowski et al. 1992). Chemical weed control plays an
important role in achieving those desired characteristics. Christmas tree qualities, such as
foliage density and tree weight generally improved with more ﬁequent herbicide
application. Furthermore, Colorado spruce (Picea pungens), Douglas ﬁr (Pseudotsuga
menziesii), and Fraser ﬁr (Abiesfraseri) beneﬁted more by the higher frequency of
herbicide application than Scots or white pine (Pinus sylvestris, Pinus strobus) (Brown et
al. 1989). In addition, herbicides reduced weed competition and improved ﬁrst—year
growth, and most of the species evaluated, including eastern white pine, showed a
signiﬁcant growth beneﬁt from weed control (Seifert and Woeste 2002). Furthermore,
Norway spruce growth during the late part of the growing season was increased by
glyphosate application and fertilization treatment; however, allocation of growth to roots
was highest in the herbicide treatment with glyphosate and lowest for the fertilization
treatment (Nilsson and Orlander 2003).

Weed control practices can greatly inﬂuence feeding damage to roots by grubs
(e. g. Phyllophaga spp and Polyphylla spp), thus inﬂuencing wood volume and tree
health. Tree plots treated entirely and in strips with herbicide contained the healthiest,
least damaged trees with the highest wood volume, while supporting the lowest mean
grub densities, l4 and 22 grubs per m2, respectively. On the other hand, mowed sod plots
supported the densest grub populations and contained trees with the most severe root

damage, lowest wood volume and poorest health (Kard and Hain 1987).

98

The application of molecular biology techniques such as genetic engineering has
resulted in signiﬁcant gains in many agricultural crops. Traits such as herbicide resistance
have the potential to reduce weed control cost, particularly in high density plantations.
Furthermore, Bishop-Hurley et al. reported transgenic conifers, Pinus radiata (D. Don)
and Picea abies (Karst) to be resistant to glufosinate.

Timing of application during the crop growing season, herbicide rate and part of
the plant sprayed can greatly affect crop injury and severity. Metn'buzin at 1.12 kg/ha and
hexazinone at 2.0 kg/ha applied in early spring and directed to hit the lower part of
dormant trees caused unacceptable injury to white pine (Pinus strobus) but the herbicides
were tolerated at half rate. Late season applications of glyphosate at 1.1 or 2.2 kg/ha,
triclopyr ester at 1.1 or 2.2 kg/ha and dichlorprop at 2.2 kg/ha caused only minor injury to
fraser ﬁr (Abiesfraseri), balsam ﬁr (A. balsamea) and white spruce (Picea glauca). In
addition, glyphosate controlled a broad spectrum of perennial weeds and brush, including
Rubus sp. On the other hand, white pine and Douglas ﬁr (Pseudotsuga menziesii) were
more sensitive to triclopyr and glyphosate in autumn (Ahrens and Dwyer 1982).

Herbicide selectivity not only depends on herbicide active ingredient uptake,
translocation and metabolism, but also depends on plant morphology and physiology.
McNeil et al. (1984) found that foliar accumulation of 14C-hexazinone varied between
tree species, being higher in loblolly pine, then in bur oak, then in black walnut and
eastern red cedar, whereas tebuthiuron foliar concentration was higher in bur oak, then
loblolly pine, then eastern red cedar and black walnut. Furthermore, the presence of
hexazinone metabolites in loblolly pine suggest that it may be resistant to this herbicide

as a result of its ability to degrade hexazinone (McNeil et al. 1984). However, Jensen et

99

al. (1990) found that hexazinone metabolism was similar in bristly dewberry (Rubus-
hispidus L) and black chokeberry (Pyms melanocarpa) and the difference in
concentration was because of a higher root:foliage (weight) ratio in black chokeberry.
Green et al. (1992) found that Loblolly pine (Pinus taeda L.) and yaupon (Ilex vomitoria
(L.) Ait.) absorbed signiﬁcantly less glyphosate than red maple (Acer rubrum L.) or white
oak (Quercus alba L.) and white oak accumulated more glyphosate in the roots compared
to red maple.

Preemergence application was more effective than postemergence application to
control weeds grown from seeds. Isoxaben applied preemergence provided very good
control of all weed species evaluated. However, applied postemergence, it was ineffective
against many weed species tested. The activity of preemergence herbicides in containers
was greater than in ﬁeld situations, and the earliest application dates had the best weed
control (Dixon and Clay 2004).

Our objective was to compare and evaluate herbicide tolerance and weed control
efﬁciency in seven species of conifers grown in ﬁeld and containers. This research will
provide Christmas tree growers with information that will improve weed control practices

and allow growers to be less dependent on MB.

MATERIALS AND METHODS

Herbicide evaluation in seedlings grown in field

2003 experiment
Douglas Fir (DF) — (Pseudotsuga menziesii), Black Hills Spruce (BHS) — (Picea

glauca ‘densata '), White Spruce (WS) — (Picea glauca), Colorado Blue Spruce (CBS) —

100

(Picea pungens glauca), Eastern White Pine (EWP) — (Pinus strobus) were planted at the
Horticulture Teaching and Research Center located near East Lansing, M1 on June 24,
2003. Tree species and height for the ﬁeld and container experiment are shown in Table
1. The plant material was provided by Van’s Pine nursery, West Olive, MI. Tree roots
were trimmed and moistened with wet paper and trees were stored at 3 C for l to 3 days
until planted.

Replications 1 and 2 of the experimental site were on a Marlette ﬁne sandy loam,
2 to 6% slope that has moderately slow permeability. The third replication was on
Colwood-Brookston loams that is poorly drained.

A randomized complete block design was used as a model for the statistical
analysis with 3 replications. Trees were machine planted on June 24, 2003. Each
replication had one row of each seedling species. The species order among replications
and treatments within replication were assigned randomly. The rows for one replication
were 25 m long and trees were planted 60 cm apart and rows were 3 m apart. Plots were
set across the species row and they were 12 m long and 3 m wide, corresponding to 5
trees of each species. A 1.5 m aisle between plots and a 3 m aisle between replications
were left to separate treatments.

Terbacil (1.12 kg ai/ha), imazaquin (0.42 kg ai/ha), ﬂumioxazin granular (0.28 kg
ai/ha), isoxaben (1.12 kg ai/ha) plus tn'fluralin (0.84 kg ai/ha), mesotrione (0.28 kg ai/ha),
triﬂoxysulﬁiron (0.01 kg ai/ha) were applied on July 16, 2003. An untreated plot was left
for comparison. A rototiller was passed through to eliminate weeds between rows the day
of herbicide application. However, a few weeds were present within rows, where the

rototiller could not reach. These included common lambsquarters 2-8 cm, eastern black

101

night shade 2-4 cm, common purslane 2-8 cm diameter and redroot pigweed 2-8 cm
height.

Herbicides were applied using a C02 backpack sprayer with a four nozzle boom
(8002 EVS nozzle) at 207 kPa with 187 L/ha output. Herbicides were sprayed over the
top of the trees at an elevation of 50-60 cm and the spray orientation was along with the
tree row. The theoretical coverage strip was 2.2 m leaving a small strip between rows that
was not covered by the application. Flumioxazin granular was spread with a shaker. After
application, the ﬁeld was irrigated to incorporate the herbicides into the soil. At
application time air temperature was 27 C, relative humidity 36%, 10% cloudy; soil was
dry and soil temperature was 27 C.

Weed control and tree injury were graded on July 28, August 4, August 11, and
August 28, 2003. Weed control was visually evaluated on a scale from 1 to 10, meaning 1
no weed control and 10 complete weed control. Tree injury was visually graded from 1 to
10, meaning 1 no injury and 10 dead tree.

Tree size index (growth index) was measured on October 30, 2003 and June 8,
2004. Size index of each tree was calculated by adding the highest and widest point and
dividing by two (Briggs and Whitwell 2002). Five trees of each species were measured
and the mean was used for statistical analysis. On the ﬁrst date, dead trees were not
considered to calculate the average; however, since dead trees could be caused by the

herbicide effect, they were considered for the second measurement.

2004 experiment

102

For the second year experiment six conifer species were evaluated. Since white
spruce and black hills spruce belong to the same genus and species, white spruce was
deleted and replaced with Canaan ﬁr (CA) - (Abies balsamea var. phanerolepis). Due to
the importance of Fraser Fir (FF) - (Abiesfraseri) for the Christmas tree industry, this
species was added. Tree species and their height are shown in table 1.

The ﬁrst row, which contained BHS in the replications 1 and 2 and EWP in the
replication 3, was planted on May 13, 2004 and the rest of the rows were planted on June
9, 2004 due to weather conditions.

The experimental site was located adjacent to the 2003 experiment, sharing the
same soil characteristics.

The same treatments as in 2003 were applied on June 18, 2004, including an
untreated control. A rototiller was passed through 4 days before spraying to eliminate
weeds between rows. In addition, no weeds were present at the application time, except
for the ﬁrst row, which was planted earlier and the rototiller could not be passed through.
In that row, weeds were larger and grasses were the most predominant weeds.

Herbicide application was done as in 2003, except for pressure, which was 248
kPa. The higher pressure increased our output to 205 L/ha (9.6% more compared to
2003). At application time air temperature was 25 C, relative humidity 55%, cloud cover
was 30% and wind speed was 4 km/h from the west; the soil was dry and 27 C.

Weed control and tree injury were rated on July 2, July 16, and July 28, 2004.
Tree size was measured at planting and on November 11, 2004. Size index was calculated

for both dates and the difference between dates was used for statistical analysis.

Herbicide evaulation in seedlings grown in containers

103

2003 experiment

Tree species and their height (cm) for both years are shown in the table 1.
Seedlings were planted in 12 L containers and placed on a gravel pad on June 17, 2003.
Soil used to ﬁll pots was sandy loam. Long roots were trimmed off the seedlings before
planting.

A randomized complete block design was used for the statistical analysis with 4
replications and 10 treatments. Each plot had 5 trees of each species and they were one
meter apart. The order of species in each replication was randomized as well as the
treatments.

Terbacil (1.12 kg ai/ha), imazaquin (0.42 kg ai/ha), ﬂumioxazin (0.28 kg ai/ha),
isoxaben (1.12 kg ai/ha) plus triﬂuralin (0.84 kg ai/ha), mesotrione (0.28 kg ai/ha),
triﬂoxysulfuron (0.01 kg ai/ha), rimsulfuron (0.025 kg ai/ha), imazapic (0.070 kg ai/ha),
and lactofen (0.28 kg ai/ha) were applied on July 18, 2003, and an untreated control plot
was leﬁ for comparison. Herbicides were applied using a C02 backpack with a two
nozzle boom (9502 EVS nozzle) at 207 kPa with 187 L/ha output. Treatments were
sprayed over the top of the seedlings. Flumioxazin granular was applied using a manual
shaker. Containers were watered after application. At application time air temperature
was 24 C, relative humidity 59%, 15% cloudy and wind was 9 km/h from the NE. Soil in
containers was moist.

Tree injury was graded as in the ﬁeld experiment on July 25, August 6, August
12, and September 6, 2003. Weeds in containers were counted on August 12, and
September 6, 2003. Tree size index was measured in October 30, 2003 and June 14, 2004

(Briggs and Whitwell 2002).

104

2004 experiment

For the second container experiment, sandy clay soil was used to ﬁll containers.
To prevent soil erosion, containers were ﬁlled ﬁrst with 4 to 7 cm wood chips, and then
soil was added to 3 cm below container top edge. Seedlings were planted on June 15,
2004.

Treatments and equipment were the same as in 2003. Herbicides were applied on
June 24, 2004. At application time air temperature was 17 C, relative humidity 52% and
wind speed 10 km/h ﬁom west.

Tree injury was graded on July 7, July 22, and August 5, 2004. Weeds species
grown in the containers were counted on July 7, July 22, and August 5, 2004.

Tree size was measured at planting date and on November 11, 2004, the size
index (growth index) was calculated for both dates and the difference between those was

used for statistical analysis.

RESULTS AND DISCUSSION

Results analysis and interpretation were based on data collected at 2 and 6 weeks
after treatment (WAT) for injury and weed control in both years and in both experiments.
If herbicide by year interaction was not signiﬁcant, the average for both years was

considered for mean separation; if signiﬁcant, data was presented for each year.

Field experiments

Tree injury of all species in all treatments was not different from the control at 2

WAT for both years, except for ﬂumioxazin which slightly injured CBS (Table 2). In

105

addition, treatments applied to white spruce in 2003, and Canaan and Fraser ﬁr in 2004
did not differ ﬁom the control.

There was no injury to CBS and EWP from any of the treatments at 6 WAT in
both years and to WS in 2003. Terbacil application resulted in severe injury to BHS in
both years, and to CA and FF in 2004 (4.8, 6.3, and 7.0 respectively). Injuries consisted
of a generalized needle chlorosis and necrosis but more evident on the branch tips. The
other treatments were not different from the control in BHS and CA. FF was injured 2.7
only by ﬂumioxazin.

Douglas ﬁr analysis resulted in herbicide by year interaction, thus results were
separated by year (Table 3). In 2003 at 6 WAT, no treatment caused signiﬁcant injury on
DF. However, in 2004, terbacil and mesotrione caused signiﬁcant injury. Mesotrione
injuries consisted of needle discoloration (white needles), which is a particular
characteristic of this pi grnent inhibitor herbicide. The higher rate (9.6% more) used in
2004 could be the reason for this increased injury in 2004.

Plant size index was not signiﬁcant among treatments for all species on October
30, 2003 and on June 8, 2004 for the 2003 study.

In the 2004 experiment, size index taken in November 2004, was not signiﬁcant
for all species. However, when considering the size index difference between planting
date and November 2004 (Table 4), FF and BHS had signiﬁcant differences in injury
among treatments. In both species terbacil resulted in the smallest difference, but only in
BHS was the herbicide treatment signiﬁcantly smaller than the control.

Terbacil, ﬂumioxazin, mesotrione, imazaquin, and triﬂoxysulfuron had good

control at 2 WAT on redroot pigweed (Amaranthus retroﬂexus L.) in both years and

106

common lambsquarters (Chenopodium album L.) in 2004 (Table 5). Common
lambsquarters control in 2003 was poor with ﬂumioxazin and triﬂoxysulfuron. All
herbicides, except triﬂoxysulfuron, provided good eastern black nightshade (Solanum
ptychanthum Dunal) control; also isoxaben plus triﬂuralin provided good control of this
weed. The best common purslane (Portulaca oleracea L.) control was achieved with
terbacil and ﬂumioxazin, the rest provided control within a range 4.6 to 7.3. In addition,
isoxaben plus triﬂuralin provided 4.3 and 4.0 control of redroot pi gweed and common
larnsquarter in 2003 respectively. None of the applications gave 100% grass control; the
best treatments for grass control were triﬂoxysulfuron, imazaquin, terbacil, and
mesotrione, which controlled grasses in a range of 7.1 to 8.5. In addition, all treatments
provided good control of common mallow (Malva neglecta Wallr.) at 2 WAT.

Overall weed control at 6 WAT (Table 6) was similar to the control at 2 WAT.
Terbacil, ﬂumioxazin, mesotrione, and imazaquin gave good weed control on all weeds
evaluated. However, ﬂumioxazin had poor control of redroot pigweed and common
lambsquarters in 2003, but these weeds were controlled almost 100% in 2004.
Mesotrione had unacceptable common purslane control (4.0) and imazaquin had poor
common lambsquarters control in 2003. Triﬂoxysulfuron and isoxaben plus triﬂuralin
provided fair to poor control of common purslane in both years, and redroot pigweed,
common lambsquarters, and common mallow in 2003. However triﬂoxysulfuron had
excellent control of redroot pigweed and common lambsquarters in 2004, and isoxaben
plus triﬂuralin provided good control over eastern black nightshade in both years and

buckhom plantain in 2004.

107

F lumioxazin, imazaquin, triﬂoxysulfuron and isoxaben plus triﬂuralin provided a
higher control of redroot pigweed and common lambsquarters in 2004 than in 2003.
These weeds were already emerged when the preemergence herbicides were applied in
2003. Dixon and Clay (2004) reported that the earlier the preemergence herbicide
application, the better the weed control. Probably in our 2003 study, the presence of small
weeds already emerged was enough to reduce their control for the next weeks.

At 6 WAT grass control was slightly reduced in all treatments. Terbacil,
ﬂumioxazin, imazaquin and triﬂoxysulfuron had the highest control (Table 6). Grass
control by species was recorded in 2004 (Table 7). Species present in the plots were
green foxtail (Setaria viridis (L.) Beauv.), witchgrass (Panicum capillare L.), large
crabgrass (Digitaria sanguinalis (L.) Scop.), fall panicum (Panicum dichotomiﬂorum
Michx.), yellow foxtail (Setaria glauca (L.) Beauv.), and bamyardgrass (Echinochloa
crus-galli (L.) Beauv). Even though all treatments, except isoxaben plus triﬂuralin, had
some grass control compared to the untreated control, none of them provided 100%

control at 6 WAT.

Container experiment

Treatments applied to all species in both years did not result in any injury at 2
WAT (Table 8).

At 6 WAT (Table 9), terbacil had the highest injury rate in all species except for
DF and WS in 2003. Furthermore, the other herbicides were not different ﬁ'om the

control in DF, EWP, CA, FF and WS with some exceptions. Mesotrione injured DF, WS,

108

and FF 2.2, 3.0 and 1.7 respectively in 2004. Imazaquin slightly injured (1.7) FF in 2004,
and lactofen injured EWP 3.8 both years.

Contrary to the ﬁeld experiment, the container study resulted in severe injuries to
BHS for all treatments at 6 WAT, except for triﬂoxysulfuron. In addition, ﬂumioxazin,
imazaquin, triﬂoxysulfuron, imazapic, and lactofen resulted in injuries on CBS compared
to the control.

DF and WS analysis showed herbicide by year interaction, thus results were
separated by year. These species were injured by terbacil and slightly less by mesotrione
in 2004, but not in 2003.

In the 2003 container experiment, the size index taken in October 30, 2003 was
not signiﬁcantly different among treatments; however the measurement taken in June 14,
2004 showed differences in EWP and WS (data not shown). Seedlings treated with
rimsulfuron resulted in the biggest EWP and the rest of the treatments were not different
from control. In addition, none of the treatments were different from the control in WS.
The container experiment in 2004 showed only signiﬁcant differences among treatments
in WS. However, when the difference in size index between July and November was
analyzed, FF and CA became signiﬁcant (Table 10). Terbacil had the lowest growth rate
in those species. These growth reductions were in accordance with the plant injury
observed in the terbacil plots.

Conclusions about weed control in the container (Table 11) are difﬁcult to state
due to the poor weed growth for some weed species in the control. However, terbacil,
ﬂumioxazin, mesotrione, and triﬂoxysulfuron provided good common lambsquarters

control at 2 and 6 WAT in 2003 (data not shown). In 2004, all treatments provided good

109

control of redroot pigweed, carpetweed (Mollugo verticillata L.), and annual sowthistle
(Sonchus oleraceus L.). Fall panicum was also controlled by all treatments, except for
imazaquin and imazapic. Finally, black medic (Medicago lupulina L.) was controlled in

all treatments except for imazaquin, isoxaben plus triﬂuralin, and imazapic.

CONCLUSIONS

Terbacil caused the most injury and gave the best weed control. In the ﬁeld study,
terbacil did not injure EWP and CBS in both years and WS in 2003 compared to the
control, but produced severe injuries to BHS, DF in both years and CA and FF in 2004.
The higher injury in 2004 may be explained by a higher rate (9% more) in that year. If
this is the case, the optimum rate for weed control is very close to the rate that can be
harmful to seedlings. Field research is required to determine if a lower rate of terbacil
could still have good weed control and reduce plant injury.

All herbicides except terbacil may be safe to be used in all species evaluated,
however environmental conditions year by year can inﬂuence the likelihood of injury.

Even though WS and BHS share the same genus and species; they differ in
herbicide response. WS was more tolerant to herbicides than BHS. More ﬁeld research is
required to extend our knowledge in these species.

Plant size index was not. in accordance with seedling injury observed in 2003. The
grth in this period may have not been enough to detect statistical differences; however,
for the ﬁeld and container studies in 2004, when the size index difference was

considered, thus analyzing only grth and taking out the individual tree size variability,

110

differences in growth were statistically detectable in the ﬁeld and container study. Injury
persistence was long enough to interfere with the normal growth.

Terbacil, ﬂumioxazin, mesotrione, and imazaquin had an overall good weed
control, controlling most weeds present in the ﬁeld. In addition, triﬂoxysulfuron and
isoxaben plus triﬂuralin had variable control among weed species being some times

unacceptable.

 

Bare soil at application time improves weed control. Flumioxazin,

triﬂoxysulfuron, imazaquin, and isoxaben plus triﬂuralin had better weed control when

 

weeds were not present at the application time.

111

References

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plantings. Proc. Northeastern Weed Sc. Soc. 36:215-216.

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112

 

 

 

Kard, B.M.R., and F .P. Hain. 1987. White grub (Coleoptera: Scarabaeidae) densities,
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www

113

Table 1. Tree species and tree height average used for the ﬁeld and container studies in
2003 and 2004.

 

 

 

 

Tree species 2003 2004
cfrifrilnfrs Field Containers
cm

Black Hills Spruce (BHS) 33 20 —-1
Eastern White Pine (EWP) 45 27 27
Colorado Blue Spruce (CBS) 40 20 20
Douglas Fir (DF) 22 3O 30
White Spruce (WS) 50 " 20
Fraser Fir (FF) -- 17 17
Canaan (CA) -- 17 17

 

I Box without number indicates that this particular species was not evaluated for the study in this year.

 

114

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124

CHAPTER VI: HERBICIDE EFFICACY ON DIFFERENT WEED SPECIES

125

INTRODUCTION

Nursery and greenhouse production represents the sixth largest agricultural
commodity group in the United States. This is the fastest growing segment of the US.
agriculture; between 1991 and 1998 sales of this segment increased 30%. Nursery growth
is caused by the strong US. economy with the expansion in housing and increase of
ornamental plant consumption (Knox et al. 2003).

Nurseries and ﬂoriculture operations in the states of California, Florida,
Michigan, Oregon, Pennsylvania, and Texas use 335 active ingredients and a total of 4.77
million pounds of chemicals; herbicides account for 20% (984,000 pounds) of the total
amount. Glyphosate is the most popular herbicide, being used in 26% of the operations,
followed by oxyﬂuorfen used in 8%, and oryzalin used in 6% of the operations
(Anonymous 2004).

Economic losses in the nursery industry due to weed infestations have been
estimated at $7,000 per acre. Nurseries may spend $500 to $4000 per acre of containers
for manual removal of weeds (Mathers and Case 2003). However, hand-weeding
sometimes is necessary regardless of chemical weed control (Knox et al. 2003).

Although growers try to implement non-chemical weed control practices,
chemicals are widely used for weed control in nurseries. Herbicides represent 20% of the
total amount of pesticides used in the nursery and ﬂoriculture industries in California,
Florida, Michigan, Oregon, Pennsylvania, and Texas (Anonymous 2004). A survey in
Florida showed that 71% and 56% of nurseries use postemergence and preemergence
herbicides, respectively, and almost half used both kinds of herbicides (Tatum and

Thompson 1993).

126

 

 

 

Yellow nutsedge (Cyperus esculentus L.) is a perennial weed of most agricultural,
horticultural, and nursery crops as well as turfgrass and landscape (Uva et al. 1997). It is
listed as one of the most troublesome weeds for the omamean industry. Yellow
nutsedge grows in many soil types and propagates primarily by tubers and rhizomes.
These characteristics make this weed very hard to control once established in the ﬁeld. In
addition, there are not many effective herbicides to control yellow nutsedge.

Metolachlor is the only preemergence herbicide currently labeled for nursery

crops that is effective against nutsedge (Altland et al. 2003). Metolachlor at 3.3 kg and

 

6.6 kg ai/ha provided excellent yellow nutsege control at both rates and the combination I
of metolachlor plus simazine also provided excellent yellow nutsedge and annual grass
control at 12 WAT (Setyowati et al. 1995). Metolachlor and other acetanilides herbicides
adsorption to the soil is controlled mainly by the content of organic matter in the soil
(Weber et al. 2003).

Halosulfuron applied foliarly at 0.009 and 0.018 kg/ha provided 87 to 91% purple
nutsedge and 79 to 84% yellow nutsedge control. Re-growth measurements taken 5 WAT
showed 88 to 90% and 75 to 83% reduction in purple nutsedge and yellow nutsedge
resprouting respectively (Hurt and Vencill 1994a). In addition, yellow nutsedge re-
growth for halosulfuron, imazapic, glyphosate, and MSMA was below 5% of the
untreated control (Ferrell et al. 2004).

Imazapic and imazaquin control many annual broadleaf weeds as well as the
perennial yellow nutsedge. Both have similar symptoms in plants, including grth
inhibition, chlorosis of meristematic areas and general chlorosis and necrosis (V encill

2002). Imazaquin was one of the most effective preemergence treatments for reducing

127

yellow nutsedge shoot weight (89%). Imazaquin at 0.25 and 0.5 kg ai/ha applied
postemergence reduced yellow nutsedge shoot weight by 72 to 77% at 2 WAT,
comparable to chlorimuron (83%) , pyridate (82%), bentazon (82%), and glyphosate
(87%) (Derr and Wilcut 1993). Hurt et al. (1994b) obtained 70 to 77% of yellow
nutsedge control and 56 to 59% of purple nutsedge control with imazaquin applied at

0.43 kg/ha and 0.56 kg/ha, respectively. Foliar application of imazapic at 0.070 kg/ha

 

controlled 95% purple nutsedge and 61% yellow nutsedge (Hurt and Vencill 1994b).

Imazapic applied postemergence at 0.05 and 0.07 kg ai/ha, imazethapyr applied
preplant incorporated or postemergence at 0.07 kg ai/ha, and metolachlor applied
preplant incorporated at 1.7 kg ai/ha controlled yellow nutsedge at least 75%, but
imazapic controlled yellow nutsedge more consistently than the others. Yellow nutsedge
tuber densities in herbicide-treated plots were 51 to 75% less than in untreated control
plots (Grichar 2002).

Imazaquin and imazethapyr were the most effective preemergence treatments for
reducing yellow nutsedge shoot weight. Applied postemergence, they reduced yellow
nutsedge shoot weight by 72 to 87% at 2 WAT (Derr and Wilcut 1993).

Bentazon, halosulfuron, and imazaquin are effective postemergence nutsedge

 

herbicides (Altland et al. 2003). Imazaquin, bentazon and glyphosate applied
postemergence reduced yellow nutsedge shoot weight by 72 to 87% at 2 WAT (Derr and
Wilcut 1993). In addition, regrowth from bentazon was 44% of the control and was the
least effective herbicide tested, whereas halosulfuron and imazapic were most effective

for yellow nutsedge control (Ferrell et al. 2004).

128

Yellow nutsedge control with mesotrione was inconsistent. Increasing the rate of
mesotrione from 0.070 to 0.140 kg/ha, and adding atrazine, improved control of yellow
nutsedge at 56 DAT (Summerlin et al. 2000). Mesotrione was less effective reducing
nutsedge regrowth compared to halosulﬁrron and MSMA. Mesotrione-treated yellow
nutsedge regrth was 58% of the control regrowth, while regrth from halosulfuron
and MSMA treatments was between 0 and 5% (Earl et al. 2004).

Triﬂoxysulfuron applied to yellow nutsedge or purple nutsedge leaves is absorbed
and translocated acropetaly and basipetaly, and no more than 4% is translocated to tubers
and roots. Half-life of triﬂoxysulfuron on the plant was estimated at 4 h in both purple
and yellow nutsedge (Troxler et al. 2003). The effect of triﬂoxysulfuron plus 0.25% NIS
(non-ionic surfactant) was similar when applied at four or six-leaf stages of yellow
nutsedge (Singh and Singh 2004). Soil-applied triﬂoxysulfuron reduced shoot number,
shoot weight, and root weight more than foliar-applied triﬂoxysulfuron (McElroy et al.
2003)

Bispyribac will be used to control grasses, sedges, and broad leaf weeds in rice
production. Another potential use is in non-cropland weed control (V encill 2002).

F lumioxazin gives good preemergence control of many broadleaf weeds. The
mode of action is believed to be inhibition of protoporphyrinogen oxidase, an enzyme
important in the synthesis of chlorophyll; after absorption, porphyrins accumulate in
susceptible plants causing photosensibilization, which leads to membrane peroxidation.
Plants emerging from treated soil become necrotic and die shortly after sunlight exposure

(V encill 2002). F lumioxazin affects photosynthesis by reducing foliar chlorophyll and

129

carotenoid contents, gas exchanges and alteration in plastid structure. As a result, plantlet
growth was greatly inhibited (Saladin et al. 2003).

Rimsulfuron controlled yellow nutsedge 40 to 70% and nutsedge control was not
increased with the addition of glyphosate in the tank mixure (Nelson and Renner 2002).

Mugwort (Artemisia vulgaris L.) is a rhizomatous perennial with erect ﬂowering
stems. Reproduction is usually by rhizomes and rarely by seeds. Its persistent rhizomes
make mugwort difﬁcult to control in perennial crops (Uva et al. 1997). Little to no long-
terrn control of mugwort is achieved with applications of glufosinate, metsulfuron,
triclopyr, or the dimethylamine salt and the isooctyl ester of 2,4-D, even at exceptionally
high use rates. Long-term mugwort control may be achieved with relatively low use rates
of picloram (0.28 kg/ha) and clopyralid (0.28 kg/ha), but higher rates are needed for
glyphosate (8.9 kg/ha) and dicamba (8.9 kg/ha) to obtain same control (Bradley and
Hagood 2002a). In addition, sequential herbicide treatment and sequential mowing are
strategies that enhance mugwort control (Bradley and Hagood 2002b).

British yellowhead (Inula britannica L.) is a perennial plant that reproduces from
seed or roots. It is a relatively new weed to Michigan. It was ﬁrst reported in Michigan in
1990, but has the potential to become a wide spread weed.

Yellow nutsedge, mugwort, and British yellowhead were selected to study their
susceptibility to herbicides. Information obtained from this research will be valuable for

the omamean industry to improve control of these weeds.

130

MATERIALS AND METHODS
Three experiments were conducted to evaluate herbicide efﬁciency in yellow
nutsedge (Cyperus esculentus L.), mugwort (Artemisia vulgaris L.), and British

yellowhead (Inula britannica).

Yellow Nutsedge

Two sets of experiments were conducted in the greenhouse at Michigan State
University.

Four tubers were planted in each pot ﬁlled with high organic media (sphagnum
peat 70 — 80%) in August 5, 2004. The tubers were obtained from Azlin Seed Service,
Leland MS. Four days after planting, the following preemergence herbicides were
applied: ﬂumioxazin (0.28 kg ai/ha), metolachlor plus ﬂumioxazin (2.1 lb ai/a, 0.28 kg
ai/ha), and metolachlor (2.1 kg ai/ha) were sprayed. Postemergence herbicides were
applied on August 20, 2004 when nutsedge had ﬁve to six leaves (15 cm heigh).
Postemergence treatments were bentazon (1.12 kg ai/ha), bispyribac (0.07 kg ai/kg),
glyphosate (0.56 and 1.12 kg ai/ha), halosulfuron (0.07 kg ai/a), imazapic (0.07 kg ai/ha),
imazaquin (0.56 kg ai/ha), mesotrione (0.1 kg ai/ha), triﬂoxysulfuron (0.007 kg ai/ha),
rimsulfuron (0.025 kg ai/ha), and an untreated control. Soil media was moist at
application time.

All treatments were applied with a bench sprayer utilizing a teejet nozzle 8001B,
172 kPa pressure, 187 L/ha output and 1.6 km/h speed.

Yellow nutsedge control was evaluated 2 weeks after postemergence applications.

The rating was done visually on a scale of 1 to 10, 1= no control and 10= 100% control.

131

Plants were counted and cut on September 7, 2004. Plants were dried for four
days at 45 C and weighed. The statistical model was a randomized complete block with
ﬁve replications.

The same procedure was followed in the second experiment except that a different
media was used, which was a mixture of 50% sandy loam soil, 30% peat, and 20% sand.
In this experiment foliage re-growth was cut and weighed again at 3 weeks after the ﬁrst
cut. The four tubers were planted on August 24, 2004 and the preemergence herbicides
were applied on August 26. The postemergence herbicides were applied on September
10, 2004. Weed control evaluation was done on September 23. Nutsedge plants were

counted, cut, weighed and dried on September 28.

Hosta infested with British yellowhead
Container experiment

Container and ﬁeld experiments were conducted at the Horticulture Teaching &

 

Research Center, East Lansing, Michigan.

Hosta spp. and British yellowhead were grown together in 4 L containers. The
soil type was loamy sand containing sand 82%, silt 13%, and clay 5%. Pieces of 4 to 5
cm British yellowhead roots were placed in the containers containing hosta plants. Root
pieces were taken ﬁom British yellowhead plants grown in the greenhouse. At
application hostas were 10 to 30 cm high and British yellowhead size varied greatly
among containers from 5 to 35 cm. Clopyralid rate is between 0.105 to 0.28 kg ai/ha. In
our study three different rates (0.10, 0.14, or 0.21 kg ai/ha) within the recommended

range were applied with or without organosilicone surfactant (OSS) (Silwet L-77,

132

Loveland Industries Inc., Greeley, CO) at 0.5% v/v in July 18, 2003. There was also an
untreated control.

Treatments were applied with a backpack C02 sprayer and two nozzle boom (FF
9502, Teejet® nozzle, Spraying Systems Co, Wheaton, Illinois ) at 172 kPa and 187
L/ha. At application time the air temperature was 24 C, the relative humidity 38%, 15%
cloudy, wind speed 8 km/h, and soil in the container was moist.

Aﬁer spraying, all pots were placed in a lathehouse with 60% shade. Hosta injury
and British yellowhead control were visually rated on a 1 to 10 scale, with 1= no injury or
no weed control and 10= 100% dead plants or complete weed control. Ratings were done
4 and 9 weeks aﬁer herbicide application.

A randomized complete block design with four replications was used for the
experiment. The data were analyzed with SAS.

The experiment was repeated in 2004. The procedure was the same, treatments
were applied on July 1, and air temperature at application time was 26 C, relative

humidity 42%, wind 11 anh from the west.

Field experiment

A ﬁeld experiment was conducted to determine Hosta spp. susceptibility to
clopyralid in ﬁeld conditions. Clopyralid was applied at 0.10, 0.14, or 0.21 kg ai/ha with
or without OSS at 0.5% v/v. An untreated control was left for comparison. A randomized
complete block design with 3 replications was used. Each replication had one row of
hostas and treatments were assigned randomly in each replication. Plots were 3 m long

and had 6 to 8 plants. Soil was a loamy sand containing sand 83%, silt 9%, and clay 7%

133

 

and the pH was 6.0. Treatments were applied on July 18, 2003. The same scale was used
for crop injury. Injury was rated at 2, 4, and 9 WAT. At the application time air
temperature was 24 C, soil temperature 28 C, relative humidity 39%, and wind speed was

10 km/h from the east.

Mugwort

Two sets of experiments were conducted at the Horticulture Teaching & Research
Center.

Three to four pieces of mugwort rhizomes (3 to 5 cm long) were planted in 2 L
containers ﬁlled with sandy clay soil in June 2003. The rhizomes were taken ﬁ'om
original plants grown in the greenhouse. Clopyralid 0.14 or 0.28 kg ai/ha, glufosinate
1.12 kg ai/ha, ﬂumioxazin 0.28 kg ai/ha (plus NIS 0.25 % v/v), bentazon 1.12 kg ai/ha
(plus NIS 0.25 % v/v), mesotrione 0.10 kg ai/ha, bentazon plus mesotrione (1.12 and 0.10
kg ai/ha) (plus COC 1.0 % v/v), bispyribac 0.07 kg ai/ha (plus NIS 0.25 % v/v),
triﬂoxysulfuron 0.007 kg ai/ha (plus NIS 0.25 % v/v), and glyphoste 1.12 kg ai/ha were
applied on July 7, 2004. One plot was left as a control. Mugwort plants were 5 to 15 cm
high at application.

Treatments were applied with a C02 backpack sprayer with a two nozzle boom
(FF 11002 nozzles) at 172 kPa and 187 L/ha output. At application the air temperature
was 20 C, the relative humidity 69%, 100% cloudy, wind speed 3 km/h, and the soil in
containers was moist.

After application the plants were placed in a poly house. Treatments were visually

rated at 2 and 8 WAT as described above.

134

The second experiment was conducted similarly as explained above, except that
plants were placed in a shady area in a lath house after application. Herbicides were
applied on July 14, 2004. Temperature was 21 C, 80% cloudy, relative humidity was
71%.

Randomized complete block with four replications was used for statistical

analysis in both trials.

RESULTS AND DISCUSSION
Yellow Nutsedge

Results vary between the two experiments mainly due to the different type of soil
utilized in each experiment.

In the high organic soil study (Table 1), non of the treatments provided complete
nutsedge control. The best weed control was achieved by halosulfuron (7.4). Mesotrione,
glyphosate (1 . 12 kg ai/ha), imazapic, triﬂoxysulfuron, imazaquin, rimsulfuron, and
bispyribac provided fair control of 5.6 to 6.4. The rest of the treatments provided poor
control (rating < 3.8). In addition, the preemergence treatments gave the lowest weed
control.

Halosufuron, imazapic, triﬂoxysulfuron, and imazaquin reduced nutsedge
biomass.

In the second experiment, preemergence herbicides were the most effective in
controlling yellow nutsedge (Table 2). The combination of ﬂumioxazin plus metolachlor
was the best treatment, with a visual rating of 9.4 at 2 WAT. Metolachlor alone provided

good control (7.0) and flumioxazin alone fair control (5.2). Among the postemergence

135

 

 

 

herbicides, triﬂoxysulfuron and halosulfuron had the best control, with 5.8 and 5.6,
respectively. The other treatments resulted in poor control within a range of 3.0 to 4.8.

Metolachlor plus ﬂumioxazin, metolachlor, triﬂoxysulfuron, and halosulﬁrron had
the lowest nutsedge dry weight at 2 WAT. In addition, number of plants was signiﬁcantly
different between treatments. F lumioxazin plus metolachlor and metolachlor had the
lowest number of plants. The other treatments were not different from the control (Table
2).

Dry weight of nutsedge regrowth at 5 WAT was signiﬁcantly reduced by all
treatments, except for bispyribac, glyphosate (0.56 kg ai/ha), and rimsulfuron, which
were not different from the control (Table 2). Imazaquin, imazapic, mesotrione,
triﬂoxysulfuron, and halosulfuron did not provide good control, but regrowth in these
treatments was zero at 5 WAT. In addition, the number of live plants per pot was zero in
these treatments, except for triﬂoxysulfuron which was 0.2 (Table 2).

Hurt and Vencill (1994a) obtained 75 to 83% of yellow nutsedge regrowth
reduction at 5 WAT in nutsedge treated with halosulfuron at 0.009 and 0.018 kg/ha,
respectively. In our study, regrowth was zero at 5 WAT, but the rate used was 0.07 kg
ai/ha. In addition, Ferrell (2004) obtained less than 5% regrowth with imazapic and
halosulfuron, both applied at 0.07 kg/ha.

High organic matter in the soil reduced the activity of metolachlor, ﬂumioxazin
and their combination against yellow nutsedge. As suggested by Weber (2003),
metolachlor adsorption in the soil was positively related with the amount of organic
matter in the soil. The high amount of organic matter in our research could lead to a high

adsorption of metolachlor, thus reducing signiﬁcantly its activity. In addition,

136

 

 

metolachlor and ﬂumioxazin, especially in combination, provided excellent weed control
when applied to nutsedge grown in soil with low organic matter content.

Among postemergence herbicides, halosulfuron, mesotrione, and glyphostate
(1.12 kg ai/ha) had the best yellow nutsedge control in organic soil, while
triﬂoxysulfuron and halosulfuron had the best control in mineral soil (Table 1 and 2).

Imazaquin, imazapic, mesotrione, triﬂoxysulfuron, and halosulfuron had medium
nutsedge control at 2 WAT, but they prevented 100% nutsedge regrowth at 5 WAT.
Similar results were obtained by Derr et al. (1993). They obtained 95% regrth
reduction at 8 WAT with a lower imazaquin rate (0.5 kg ai/ha). In addition, Grichar et al.
(2002) found that imazapic consistently controlled nutsedge and also reduced the number
of tubers. Even though imazaquin, imazapic, mesotrione, triﬂoxysulfuron, and
halosulfuron did not have high control ratings at 2 WAT, there is evidence that these may

be used in long term nutsedge control programs.

Hosta infested with British yellowhead
Containers

Mean separation was pooled across years because crop injury by year interaction
and weed control by year interaction were not signiﬁcant.

All treatments caused injury to hosta at 4 and 9 WAT (Table 3). Due to the mode
of action of clopyralid, which is a growth regulator, injury consisted mainly of distorted
grth such as twisted and rolled leaves. Clopyralid at 0.14 kg ai/ha plus OSS and
clopyralid at 0.1 kg ai/ha produced the lowest injury at 2 WAT. At 9 WAT all treatments

had signiﬁcant injury within a range of 2.7 to 3.2.

137

 

The addition of OSS did not increase or reduce hosta injury at 4 or 9 WAT (Table
3). Clopyralid 0.21 kg ai/ha plus OSS, clopyralid 0.21 kg ai/ha, clopyralid 0.14 kg ai/ha
plus OSS, and clopyralid 0.1 kg ai/ha plus OSS resulted in the highest British yellowhead
control at 4 and 9 WAT (Table 3). Addition of OSS to the lowest rate increased weed

control comparable to the highest rates.

Field

In the ﬁeld, no treatment caused crop injury at 2 WAT (Table 4). However,
clopyralid at 0.1 and 0.14 kg ai/ha without the addition of OSS were the only treatments
without injury compared to the control at 4 and 9 WAT. The other treatments produced
injuries within a range of 2.3 to 3.3. The addition of OSS caused a slight but not
signiﬁcant increase in injury at all clopyralid rates. This result contrasts with those
obtained from the containers in which the addition of OSS did not show any inﬂuence on
hosta injury rates.

In conclusion, clopyralid injured hosta at all rates tested either in the container
and ﬁeld experiment, except for the ﬁeld experiments for the lower rates (0.1 and 0.14 kg
ai/ha) without OSS. Clopyralid at 0.1 and 0.14 kg ai/ha without OSS, not only had
reduced injury in the ﬁeld but also provided 6.2 and 6.7 British yellowhead control in the
container study. Even though not signiﬁcantly different, the addition of the surfactant
tended to increase injury in the ﬁeld but not in the container study and increased British
yellowhead control. OSS increase droplet surface tension in leaves allowing clopyralid to
be absorbed more rapidly, thus, causing an increase in British yellowhead control but also

an increase in crop injury.

138

 

 

Further studies on a larger scale are needed to obtain information about the effect
of OSS and other potential adjuvants in a clopyralid tank mix on British yellowhead
control and hosta injury. Since injury consisted in increased leaf twisting, knowing the

impact of these injuries on crop marketability will be useful for rate adjustments.

Mugwort

The interaction of weed control by treatment trial was signiﬁcant at 2 and 8 WAT,
so data is presented by trial in Table 5.
First trial

Bentazon plus mesotrione, glufosinate, and glyphosate resulted in the best
mugwort control at 2 WAT. However, at 8 WAT, bentazon plus mesotrione and
glufosinate control declined to 6.0 and 4.0 respectively, while glyphosate and clopyralid
at 0.28 kg ai/ha still had excellent control. The lower rate of clopyralid provided good
mugwort control (7.5) at 8 WAT. Flumioxazin provided mugwort control 8.3 and 7.0 at 2
and 8 WAT, respectively. Triﬂoxysulfuron, bentazon, and mesotrione controlled
mugwort 6.3, 3.0, and 2.8 at 8 WAT, respectively. Bispyribac provided very poor control

being not different form the untreated control.

Second trial
Flumioxazin and glufosinate had excellent control at 2 WAT, but it declined to
5.8 and 2.8 at 8 WAT. Same results were observed in the ﬁrst trial (Table 5). Clopyralid

at 0.28 kg ai/ha had medium control at 2 WAT but was excellent (9.3) at 8 WAT.

139

 

 

Bentazon plus mesotrione controlled mugwort 6.8 at 2 WAT and 8.8 at 8 WAT. The
other treatments provided mugwort control within a range of 3.8 to 4.8.

In conclusion, inconsistent results were observed between trials. However,
clopyralid at 0.28 kg ai/ha had the best mugwort control in both trials. This agrees with
Bradley et al. (2002), who suggested that low rates of clopyralid (0.28 kg ai/ha) may
control mugwort in the long term. Bentazon plus mesotrione and glyphosate had
excellent mugwort control in one of the two trials. Bradley et al (2002) reported complete
mugwort control after one year of applying a high rate of glyphosate (8.9 kg ai/ha).
However, in our study the 1.12 kg ai/ha rate was too low to achieve acceptable control in
our second trial. Bentazon plus mesotrione had a complementary effect on mugwort
control in both trials. In addition, glufosinate gave excellent early control but control
declined 60-7 0% at 8 WAT. This result agrees with Bradley et al. (2002) who observed
50% control aﬁer one year of treatment at a higher rate (8.9 kg ai/ha) of glufosinate.

Research in sequential applications of different herbicides, different modes of
action, with different rates and timing is necessary to implement a more efﬁcient

mugwort control program.

140

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143

Table 1. Yellow nutsedge control, dry weight and number of plants per container at 2
weeks after treatment in greenhouse after treatment with pre and postemergence

herbicides; grown in containers with high organic soil.

 

 

 

 

Herbicide Rate Timing Ratingl Dry weight Live plants
2 WAT
kg ai/ha g/pot number
Flumioxazin 0.28 Pre 1.6 4.82 3.0

Flumioxazin +

 

Metolachlor 0.28 + 2.1 Pre 2.2 3.14* 2.6
Metolachlor 2. 1 Pre ] ,8 3 ,57* 2 .8
Bentazon 1.12 Post 2,4 266* 3 ,4
Bispyribac 0.07 Post 3 .8 L63" 3 .0
Glyphosate 0.56 Post 2,0 35* 3.0
Glyphosate 1.12 Post 6,4 0,97" 3 .2
Halosulfuron 0.07 Post 7.4 0.54“ 3.4
Imazapic 0.07 Post 5.8 0.64“ 3.0
Imazaquin 0.56 Post 5.6 073* 3.2
Mesotrione 0.1 Post 6.4 1 _09* 3 .0
Rimsulfuron 0.025 Post 5.6 1.07“ 3.6
Triﬂoxysulfuron 0.007 Post 5 .8 0.8 1 * 3 .0
Untreated --- --- 1 .0 4.88 2.8
LSD (0.05) 1.1 0.86 NS

 

' Control rating was taken on a scale of l to 10, meaning 1= no weed control, and 10=complete weed

control. * Indicates signiﬁcantly different from the untreated at P3005.

144

Table 2. Yellow nutsedge control, dry weight, and number of plants per pot in

greenhouse conditions; grown in containers with mineral soil.

 

 

 

Herbicide Rate Timing RatingI Dry Weight No. of plants Dry Weight No. of plants
2 WAT 2 WAT 2 WAT S WAT S WAT
kg ai/ha g/pot number g/pot number
Flumioxazin 0.28 Pre 5.2* 079* 3.0 014* 1.6*
Flu+Met 0.28 + 2.1 Pre 9.4* 011* 1.8* 001* 04*
Metolachlor 2.1 Pre 7.0* 029* 1.8* 006* 06*
Bentazon 1.12 Post 48* 075* 2.8 015* 1.0*
Bispyribac 0.07 Post 46* 1.02* 3.0 0.55 2.4
Glyphosate 0.56 Post 3.0* 1.36* 2.6 0.49 2.6
Glyphosate 1.12 Post 48* l. 14* 3.4 021* 1.6*
Halosulfuron 0.07 Post 5.6* 069* 3.4 0* 0*
Imazapic 0.07 Post 3.6* 1.41* 3.6 0* 0*
Imazaquin 0.56 Post 48* 075* 3.0 0* 0*
Mesotrione 0.1 Post 4.4* 085* 3 .6 0* 0*
Rimsulfuron 0.025 Post 48* 076* 2.8 0.66 2.4
Triﬂoxysulfuron 0.007 Post 5.8* 058* 2.4 0* 02*
Untreated --- --- 1.0 2.21 3 .0 0.65 3 .0
LSD (0.05) 1.7 0.58 1.0 0.21 0.8

 

' Control rating was taken on a scale of l to 10, meaning l= no weed control, and 10=complete weed

control. * Indicates significantly different from the untreated at P5005.

145

Table 3. Hosta injury and Inula control in the container study at 4 and 9 weeks after

application of clopyralid.l

 

 

 

Treatnents Rate Timing Hosta injuryT Inula control 3
kg ai/ha 4 WAT 9 WAT 4 WAT 9 WAT
Clopyralid 0.1 Post 2 .6 2.7 4.4 6.2
Clopyralid + 0332 0.1 Post 2.7 2.9 5.9 7.6
Clopyralid 0.14 Post 2.8 3.2 5.1 6.7
Clopyralid + OSS 0.14 Post 2.7 3.0 6.1 8.1
Clopyralid 0.21 Post 3.0 3.0 6.6 8.6
Clopyralid + OSS 0.21 Post 3.4 3.2 7.6 9.0
Untreated m 1.0 1.0 1.0 1 .0
LSD (0.05) 0.6 0.8 1.6 2.2

 

' 2003 and 2004 data was combined for analysis.
2 oss= Silwet L-77 added at 0.5% v/v

3 Ratings: l= no weed control or no crop injury, and 10=complete weed control or dead plant.

146

 

Table 4. Hosta injury in the ﬁeld study at 2, 4 and 9 weeks aﬁer application of clopyralid

 

 

 

in 2003.
Treatments Rate 2 WAT 4 WAT 9 WAT
Kg ai/ha ------------- ratingy --------------
Clopyralid 0. 1 1.7 1.7 2.0
Clopyralid + 0332 0.1 2.0 2.7* 2.7*
Clopyralid 0.14 1.7 1.3 1.7
Clopyralid + OSS 0.14 2.3 2.7* 2.3*
Clopyralid 0.21 2.0 2.3* 33*
Clopyralid + 033 ‘ 0.21 1.7 2.7* 3.0*
Untreated --- l .0 1 .0 1.0
LSD (0.05) NS 1.2 1.0

 

2 oss= Silwet L-77, added at 0.5% v/v

’ Injury rating l= no injury, and 10= dead plant

* Indicates signiﬁcantly different from the untreated at P5005.

147

Table 5. Mugwort control at 2 and 8 WAT in both trials conducted in 2004.

 

Treatment Rate First trialI Second triall

 

2 WAT 8 WAT 2 WAT 8 WAT

 

 

 

 

 

kg ai/ha rating "

Bentazon + NIS 1.12 4.0 3.0 4.5 4.0
Bentazon +

mesotrione + COCy 1.12 + 0.1 9.0 6.0 6.8 8.8
Bispyribac + NIS 0.07 2.0 2.3 2.5 3.8
Clopyralid 0.14 5.0 7.5 2.0 4.0
Clopyralid 0.28 6.3 8.8 6.0 9.3
Flumioxazin + NISy 0.28 8.3 7.0 8.8 5.8
Glufosinate 1.12 10 4.0 10 2.8
Glyphosate 1.12 9.3 10 2.8 4.5
Mesotrione 0.1 2.5 2.8 4.0 4.8
Triﬂoxysulfuron + NIS 0.007 2.8 6.3 4.8 4.0
Untreated --- l .0 l .0 1.0 1.0
LSD (0.05) 1.2 1.6 1.4 2.6

 

' Herbicides were applied on July 7, 2004 for the ﬁrst trial and July 14, 2004 for the second trial.
’ Crop oil concentrate (COC) applied at 1% v/v and non ionic surfactant (NIS) at 0.25 % v/v.

x Weed control rating l= no control, and 10= 100% control.

148

   

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