CHARACTERIZATION AND EVALUATION OF … · 1 characterization and evaluation of aminocyclopyrachlor...

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CHARACTERIZATION AND EVALUATION OF AMINOCYCLOPYRACHLOR ON NATIVE AND INVASIVE SPECIES OF FLORIDA

By

ANNA LIN GREIS

A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2012

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© 2012 Anna Lin Greis

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To my family for all their love and support

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ACKNOWLEDGMENTS

First and foremost, I would like to thank my major professor, Dr. Greg MacDonald,

for all the support and encouragement he has given me throughout my graduate school

experience. He took a chance on a business major and for that I am truly grateful. His

confidence in my abilities as a student and speaker gave me the confidence to believe

in myself. Along with Dr. MacDonald, Dr. Jason Ferrell has taught me so much about

agriculture, weed science, and research in general. I thank Dr. Ferrell for always being

available to meet and discuss any questions I had as well as providing guidance

throughout my research. Thanks go to Dr. Brent Sellers for his presentation advice at

many meetings and his input in my research. I’d also like to thank Dr. Kimberly Bohn for

providing input in my research and for being my forestry advisor my committee.

I would not have been able to complete any of my research without the physical

labor and moral support of my fellow graduate students and summer employees. A

special thanks to Mike Durham for helping me in each step of my research, being a

great study partner, as well as getting me addicted to coffee. I would also like to thank

Sarah Berger and Neha Rana, who have become great friends and supporters both in

and out of the office.

I would not have been able to complete this degree without the endless support

and encouragement of my parents and my brother Adam. My parents are my

inspiration and I know that with their support I can accomplish all my goals. Throughout

all of the ups and downs of this journey they have provided me with moral support,

encouraging words, and great advice for which I am so thankful. I thank my dad for

providing me with professional guidance and always supporting me in my decisions in

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life. My mom has always believed in me and my abilities, even when I faltered, and for

that I am truly grateful.

Finally, I thank my fellow employees at the Marston science library, for giving me

four hour escapes each week filled with lots of laughs and great conversation. I will be

forever grateful to my supervisor Vanessa Jewett for giving me a summer job, at which I

met Dr. MacDonald who opened the door to my weed science future.

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TABLE OF CONTENTS

page

ACKNOWLEDGMENTS .................................................................................................. 4

LIST OF TABLES ............................................................................................................ 8

LIST OF FIGURES .......................................................................................................... 9

ABSTRACT ................................................................................................................... 12

CHAPTER

1 INTRODUCTION .................................................................................................... 14

Florida’s Invasive Species ...................................................................................... 14

Controlling Invasive Species ................................................................................... 16 Aminocyclopyrachlor ............................................................................................... 17 Native Ecosystems in Florida .................................................................................. 18

2 THE EFFECT OF AMINOCYCLOPYRACHLOR APPLIED POST-EMERGENCE ON SELECTED NATIVE AND INVASIVE GRASS SPECIES UNDER GREENHOUSE CONDITIONS ............................................................................... 23

Background Information .......................................................................................... 23

Materials and Methods............................................................................................ 25 Results and Discussion........................................................................................... 26

Native Plants .................................................................................................... 26

Invasive Grasses .............................................................................................. 29

3 RESPONSE OF SELECT NATIVE SPECIES TO VARIOUS SOIL CONCENTRATIONS OF AMINOCYCLOPYRACHLOR ......................................... 50

Background Information .......................................................................................... 50 Materials and Methods............................................................................................ 52

Results and Discussion........................................................................................... 54

4 HERBICIDE EVALUATIONS FOR COGONGRASS CONTROL UNDER FIELD CONDITIONS ......................................................................................................... 79

Background Information .......................................................................................... 79

Materials and Methods............................................................................................ 81 Results and Discussion........................................................................................... 83

5 CONCLUSIONS ..................................................................................................... 92

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LIST OF REFERENCES ............................................................................................... 95

BIOGRAPHICAL SKETCH .......................................................................................... 103

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LIST OF TABLES

Table page 2-1 Summary of the effect of aminocyclopyrachlor concentration on native

species- Experiment 1. ....................................................................................... 31

2-2 Summary of the effect of aminocyclopyrachlor concentration on native species- Experiment 2. ....................................................................................... 31

2-3 Summary of the effect of aminocyclopyrachlor concentration on invasive species- Experiment 1. ....................................................................................... 32

2-4 Summary of the effect of aminocyclopyrachlor concentration on invasive species- Experiment 2. ....................................................................................... 32

3-1 Species used in revegetation study in Citra, Florida. .......................................... 57

3-2 The effect of aminocyclopyrachlor concentration on percent visual injury of selected native species 14 weeks after treatment. Experiment 1 ....................... 58

3-3 The effect of aminocyclopyrachlor concentration on percent visual injury of selected native species 10 weeks after treatment. Experiment 2 ....................... 58

3-4 The effect of aminocyclopyrachlor soil concentration on percent mortality of selected revegetation species 40 weeks after planting. Experiment 1.. .............. 59

3-5 The effect of aminocyclopyrachlor soil concentration on percent mortality of selected revegetation species 10 weeks after planting. Experiment 2. ............... 60

4-1 The effect of aminocyclopyrachlor treatments on cogongrass control over time in Hillsborough County, Florida ................................................................... 79

4-2 The effect of aminocyclopyrachlor treatment on cogongrass rhizome biomass over time in Hillsborough County, Florida. .......................................................... 89

4-3 The effect of surfactants or additives on the activity of glyphosate or imazapyr treatments on cogongrass control in Hillsborough County, Florida. .... 90

4-4 The effect of selected imidazolinone herbicides on cogongrass control over time in Hillsborough County, Florida. .................................................................. 91

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LIST OF FIGURES

Figure page 2-1 Andropogon brachystachyus response to aminocyclopyrachlor concentration.

Experiment 1 ...................................................................................................... 33

2-2 Aristida stricta response to aminocyclopyrachlor concentration. Shoot growth 4 WAT for experiment 1. ..................................................................................... 34

2-3 Andropogon virginicus response to aminocyclopyrachlor concentration.. .......... 34

2-4 Eragrostis elliottii response to aminocyclopyrachlor concentration. Experiment 1 ...................................................................................................... 35

2-5 Eragrostis spectabilis response to aminocyclopyrachlor concentration. ............. 36

2-6 Panicum anceps response to aminocyclopyrachlor concentration. Experiment 1. ........................................................................................................................ 36

2-7 Sorghastrum secundum response to aminocyclopyrachlor concentration. Experiment 1 ...................................................................................................... 37

2-8 Garberia heterophylla response to aminocyclopyrachlor concentration. Experiment 1. ..................................................................................................... 38

2-9 Liatris spicata response to aminocyclopyrachlor concentration. Experiment 1. .. 38

2-10 Pityopsis graminifolia response to aminocyclopyrachlor concentration. Experiment 1. ..................................................................................................... 39

2-11 Solidago fistulosa response to aminocyclopyrachlor concentration. Experiment 1. ..................................................................................................... 39

2-12 Andropogon brachystachyus response to aminocyclopyrachlor concentration. Experiment 2 ...................................................................................................... 40

2-13 Aristida stricta response to aminocyclopyrachlor concentration. Experiment 2 .. 41

2-14 Eragrostis spectabilis response to aminocyclopyrachlor concentration. Experiment 2 ...................................................................................................... 42

2-15 Sorghastrum secundum response to aminocyclopyrachlor concentration. Experiment 2. ..................................................................................................... 43

2-16 Hymenachne amplexicaulis response to aminocyclopyrachlor concentration. Experiment 1 ...................................................................................................... 44

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2-17 Imperata cylindrica response to aminocyclopyrachlor concentration. Experiment 1. ..................................................................................................... 44

2-18 Melinis repens response to aminocyclopyrachlor concentration. Experiment 1 .. 45

2-19 Panicum repens response to aminocyclopyrachlor concentration. Experiment 1. ........................................................................................................................ 45

2-20 Urochloa mutica response to aminocyclopyrachlor concentration. Experiment 1. ........................................................................................................................ 46

2-21 Hymenachne amplexicaulis response to aminocyclopyrachlor concentration. Experiment 2 ...................................................................................................... 47

2-22 Imperata cylindrica response to aminocyclopyrachlor concentration. Experiment 2 ...................................................................................................... 47

2-23 Melinis repens response to aminocyclopyrachlor concentration. Experiment 2 .. 48

2-24 Panicum repens response to aminocyclopyrachlor concentration. Experiment 2 ......................................................................................................................... 48

2-25 Urochloa mutica response to aminocyclopyrachlor concentration. Experiment 2 ......................................................................................................................... 49

3-1 Pinus palustris (Longleaf pine) response to aminocyclopyrachlor concentration in soil 14 WAP (weeks after planting). Experiment 1 .................... 61

3-2 Quercus laevis (Turkey oak) response to aminocyclopyrachlor concentration in soil 14 WAP (weeks after planting). Experiment 1 .......................................... 62

3-3 Quercus virginiana (Live oak) response to aminocyclopyrachlor concentration in soil 14 WAP (weeks after planting). Experiment 1 .......................................... 63

3-4 Liatris spicata (Blazing star) response to aminocyclopyrachlor concentration in soil 14 WAP (weeks after planting). Experiment 1 .......................................... 64

3-5 Solidago fistulosa (Goldenrod) response to aminocyclopyrachlor concentration in soil 14 WAP (weeks after planting). Experiment 1 .................... 65

3-6 Andropogon virginicus var. glauca (Chalky bluestem) response to aminocyclopyrachlor concentration in soil 14 WAP. Experiment 1. .................... 66

3-7 Aristida stricta var. beyrichiana (Wiregrass) response to aminocyclopyrachlor concentration in soil 14 WAP. Experiment 1 ....................................................... 67

3-8 Eragrostis spectabilis (Purple lovegrass) response to aminocyclopyrachlor concentration in soil 14 WAP. Experiment 1. ...................................................... 68

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3-9 Panicum anceps (Spreading panicum) response to aminocyclopyrachlor concentration in soil 14 WAP. Experiment 1. ...................................................... 69

3-10 Pinus palustris (Longleaf pine) response to aminocyclopyrachlor concentration in soil 10 WAP (weeks after planting). Experiment 2 .................... 70

3-11 Quercus laevis (Turkey oak) response to aminocyclopyrachlor concentration in soil 10 WAP (weeks after planting). Experiment 2 .......................................... 71

3-12 Quercus virginiana (Live oak) response to aminocyclopyrachlor concentration in soil 10 WAP (weeks after planting). Experiment 2 .......................................... 72

3-13 Liatris spicata (Blazing star) response to aminocyclopyrachlor concentration in soil 10 WAP (weeks after planting). Experiment 2 .......................................... 73

3-14 Solidago fistulosa (Goldenrod) response to aminocyclopyrachlor concentration in soil 10 WAP (weeks after planting). Experiment 2 .................... 74

3-15 Andropogon virginicus var. glauca (Chalky bluestem) response to aminocyclopyrachlor concentration in soil 10 WAP. Experiment 2. .................... 75

3-16 Aristida stricta var. beyrichiana (Wiregrass) response to aminocyclopyrachlor concentration in soil 10 WAP. Experiment 2. ...................................................... 76

3-17 Eragrostis spectabilis (Purple lovegrass) response to aminocyclopyrachlor concentration in soil 10 WAP. Experiment 2. ...................................................... 77

3-18 Panicum anceps (Spreading panicum) response to aminocyclopyrachlor concentration in soil 10 WAP. Experiment 2. ...................................................... 78

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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science

CHARACTERIZATION AND EVALUATION OF AMINOCYCLOPYRACHLOR ON

NATIVE AND INVASIVE SPECIES OF FLORIDA

By

Anna Lin Greis

May 2012

Chair: Greg MacDonald Major: Agronomy

Aminocyclopyrachlor is a synthetic auxin herbicide proposed for invasive species

management and the release or restoration of native perennial grasses. As a

component to natural areas restoration, it is also beneficial to understand the impact

that herbicide residues have on native plant species. Studies were therefore initiated to

determine the efficacy of aminocyclopyrachlor on several invasive grass species as well

as the impact of establishment and growth of native species. Postemergence

applications of aminocyclopyrachlor were evaluated under greenhouse conditions to

determine the control of several invasive grasses including natalgrass (Melinis repens),

torpedograss (Panicum repens), paragrass (Urochloa mutica), West Indian marshgrass

(Hymenachne amplexicaulis) and cogongrass (Imperata cylindrica), as well as several

native grass and broadleaf species. All invasive species showed less than 50% visual

injury and no reduction in shoot growth or regrowth to aminocyclopyrachlor with the

exception of cogongrass which showed a 25% reduction in regrowth biomass.

Eragrostis elliottii was the most tolerant native grass evaluated. Aristida stricta and

Eragrostis spectabilis were the most sensitive grasses with I50 values of 0.11 and 0.09

kg-ai ha-1, respectively. All other grasses were tolerant to rates below 0.19 kg-ai ha-1. All

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broadleaf natives were highly sensitive (<0.13 kg-ai ha-1) to rates of

aminocyclopyrachlor except Garberia heterophylla which showed less than 50% injury

at 0.24 kg-ai ha-1.

To assess the impact of aminocyclopyrachlor soil residues on native species,

seedlings of several common forbs, grasses, and tree species were transplanted into

field plots treated with varying rates of aminocyclopyrachlor. Solidago fistulosa and

Liatris spicata showed greater than 50% injury at all rates of aminocyclopyrachlor. Pinus

palustris was tolerant to rates below 0.16 kg-ai ha-1, and Andropogon virginicus var.

glauca showed no injury to aminocyclopyrachlor. Aminocyclopyrachlor caused

significant injury to all other species at rates above 0.1 kg-ai ha-1. Utilizing plant

species injury, optimal planting dates were determined for these species based on a 90

day half-life of aminocyclopyrachlor with grasses having the shortest plant back interval.

To further investigate the potential of aminocyclopyrachlor for cogongrass control,

a field study was conducted in Hillsborough County, Florida. Aminocyclopyrachlor was

evaluated alone or in combination with imazapyr or glyphosate and compared to

standard rates of imazapyr and glyphosate. Aminocyclopyrachlor alone showed initial

control 31 WAT but no long term control 92 WAT of cogongrass. The addition of

aminocyclopyrachlor to glyphosate or imazapyr did not improve control relative to

glyphosate and imazapyr applied alone. Two additional experiments were established

and found that imazapic and imazamox were ineffective for cogongrass control.

Surfactant type and ‘Cogon-X’ did not influence the activity of glyphosate or imazapyr

for cogongrass efficacy.

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CHAPTER 1 INTRODUCTION

Florida’s Invasive Species

The state of Florida has over 13 million ha of diverse natural areas ranging over 81

natural community types. More than 4,000 native species of trees, shrubs, and other

flowering plants in Florida are being displaced by over 900 escaped exotic species

(Frank et al. 1997; Simberloff et al. 1997; Westbrooks 1998; Whitney et al. 2010).

Florida is a prime area for invasive species due to its mild climate, many international

ports, cultural diversity, and previous lenient importation laws (Anonymous 1999).

Collectively this led to Florida becoming the epicenter for more exotic species than

almost any other region in the US (Anonymous 1999). In 1994, over 684,000 ha were

impacted by the top seven exotic species: Australian pine (Casuarina equisetifolia L.),

water hyacinth (Eichhornia crassipes), hydrilla (Hydrilla verticillata), old world climbing

fern (Lygodium microphyllum), melaleuca (Melaleuca quinquenervia), torpedograss

(Panicum repens), and Brazilian peppertree (Schinus terebinthifolius) (Anonymous

1999). Currently the top 10 most abundant invasive plants in Florida according to

EDDSMaps are Brazilian peppertree, melaleuca, old world climbing fern, cogongrass

(Imperata cylindrica), Japanese climbing fern (Lygodium japonicum), Chinese tallowtree

(Triadica sebifera), Caesarweed (Urena lobata), Australian pine (Casuarina equisetifolia

L.), air potato (Dioscorea bulbifera), and mimosa tree (Albizia julibrissin).

Invasive species are a leading cause of native species becoming protected under

the Endangered Species Act, with 54 endangered species existing in Florida (Pimentel

et al. 2000; US FWS 2012). Important impacts of invasive plants are ecosystem

modification through altering fire frequency and intensity, flooding, erosion and land

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stabilization, nutrient cycling, and competition with native species. Worst case scenarios

result in species decline to the point of extinction (Henderson et al. 2006; Mauchamp et

al. 1998; Westbrooks 1998). These impacts and several others have prompted the

control and elimination of invasive species as a top priority.

One of the major invasive plant species in the Southern US and throughout the

world is cogongrass. Cogongrass, Imperata cylindrica, has invaded over 500 million

hectares worldwide and over 500,000 ha in the US (Holm et al 1977; MacDonald 2007;

Holzmueller and Jose 2010). It is a prolific seed producer with over 3,000 seeds per

plant (MacDonald 2009) and also propagates through rhizomes. Cogongrass was

brought to the US as possible forage, but experimental trials eliminated this use due to

silica accumulation in the cogongrass leaf tissue and poor nutritive quality (Hubbard

1944; Dickens and Moore 1974; Coile and Shilling 1993; Dozier et al. 1998; MacDonald

2009). Cogongrass tolerates a wide range of soil and light conditions and can be found

in varying environments from shorelines to upland forests, reclaimed mined land, and

abandoned agriculture fields (Hubbard 1944; MacDonald 2009). Cogongrass is also a

pyrogenic species, maintaining a thick layer of dry leaf thatch for fuel (Holm et al. 1977).

Cogongrass fires are very intense and hot, which eliminates the native species in the

immediate area and provides openings for cogongrass spread (Eussen and Wirjahardja

1973; Seavoy 1975; Eussen 1980). It has been reported that cogongrass rhizomes may

exude allelopathic substances that inhibit the growth of other plants (Eussen 1979;

Boonitte and Ritdhit 1984; Casini et al. 1998). As cogongrass invades an area, the

rhizomes form a dense mat preventing the growth of native species and eventually

forming a monoculture. This in turn reduces native plant productivity, reduces nutrient

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availability, and decreases native species biodiversity (Collins et al. 2007; Daneshgar et

al. 2008; Daneshgar and Jose 2008). This is why cogongrass is considered one of the

world’s worst weeds and is listed on both state and federal noxious weed lists (Lowe et

al. 2004; Plant Protection and Quarantine 2010).

Controlling Invasive Species

Integrated management plans utilize a variety of control options for invasive

species control. These include prevention, mechanical, biological, cultural, and

chemical control options. Ideally these should be used in tandem to not only prevent

the spread of invasion but also to control and eliminate the invasive species once it has

spread to natural areas. A complete eradication of a species once it has become

established is extremely difficult; therefore these control options are used to reduce their

impact (Weber 2003). For many invasive species, the most and often only cost effective

option is to use chemical control. The primary herbicides used in natural areas are

glyphosate (Roundup ®1, others), imazapyr (Arsenal ®2, Chopper ®2, Stalker ®2, Habitat

®2, others), and triclopyr (Garlon ®3, others) due to their broad spectrum control on many

invasive plants. Triclopyr is only effective on broadleaf species and has little to no soil

activity. Glyphosate, the most common herbicide used for invasive species control,

possesses no soil residual activity and therefore provides no residual control.

Conversely, imazapyr possesses considerable residual activity, which is desirable

for long term control, however this may result in non-target injury to native species or

1 Monsanto Company, St. Louis, MO

2 BASF Specialty Products, Raleigh, NC

3 Dow AgroSciences LLC, Indianapolis, IN

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prevent native species establishment (MacDonald et al. 2008). Herbicides that provide

selective control plus soil residual activity could change how land managers address

invasive species management.

Aminocyclopyrachlor

Aminocyclopyrachlor is a synthetic auxin herbicide belonging to the pyrimidine

carboxylic acids class of chemistry. Aminocyclopyrachlor is formulated in the acid and

methyl-ester form-- DPX-MAT28 and DPX-KJM44, respectively (Bukun et al. 2010). The

methyl-ester was the formulation initially tested, however, the acid is now the current

product under evaluation (DuPont Crop Protection 2010). Aminocyclopyrachlor is

absorbed through foliage and roots, translocates extensively throughout the plant, and

accumulates in meristematic tissues (DuPont Crop Protection 2010; Bell et al. 2011).

Research has indicated it is both xylem and phloem mobile (Bell et al. 2011). Once

reaching the meristematic region, it acts similarly to other auxin mimic herbicides,

causing stem and leaf epinasty and wilting (Senseman 2007). Aminocyclopyrachlor

shows good herbicidal activity on broadleaf weeds and brush species. It shows some

activity on grasses, but is highly species specific. Research indicates activity on several

species in the Asteraceae, Chenopodiaceae, Convolvulaceae, Euphorbiaceae,

Fabaceae, and Solanaceae families as well as woody plant species such as Acer

rubrum, Acer negundo, Celtis occidentalis, Salix alba, Nyssa sylvatica, Prosopis juliflora

and Ulmus Americana. (Bukun et al. 2008; Claus et al. 2008; Armel et al. 2009; Blair

and Lowe 2009; Evans et al. 2009; Gannon et al. 2009; Montgomery et al. 2009; Roten

et al. 2009; Turner et al. 2009; Westra et al. 2009; Wilson et al. 2009; Rupp et al. 2011).

It also controls many ALS (acetolactate synthase), PPO (protoporphyrinogen oxidase),

triazine, and glyphosate herbicide resistant weeds (Blair and Lowe 2009; Turner et al.

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2009). As mentioned, aminocyclopyrachlor shows selectivity for many perennial grasses

and some broadleaf species which is important for the restoration of desirable native

species (DuPont Crop Protection 2010; Wallace and Prather 2011). One of the

proposed uses of aminocyclopyrachlor is for the release or restoration of native

perennial grasses (DuPont Crop Protection 2010). Other desirable characteristics of

this new herbicide include low use rates (≤ 0.28 kg-ai ha-1), low toxicity profile, and

favorable environmental profile (DuPont Crop Protection 2010). In order to utilize a

chemical in natural areas, it is important to understand the vulnerabilities of native

species and unique ecosystems.

Native Ecosystems in Florida

Florida is home to a variety of ecosystems. There are 81 natural communities in

Florida consisting of 13 million hectares of diverse natural areas encompassing forests,

flatwoods, prairies, swamps, marshes, and waterways (Myers and Ewel 1990; FNAI

2010; Whitney et al. 2010). Within these ecosystems there are more than 4,000 native

species of trees, shrubs, and other flowering plants; 300 of which are endemic to Florida

(Whitney et al. 2010). Florida’s temperate to subtropical climate and 300 soil types,

which comprise 7 of the 11 soil orders in the US, provide for a diverse range of native

habitats (Brown et al. 1990). South Florida has a subtropical climate while north Florida

receives cold fronts in winter and has more varied temperatures and rain than winters

farther south (Whitney et al. 2010). With the Gulf of Mexico on Florida’s west coast and

the Atlantic Ocean on its east coast, the moving warm water produces high humidity

and abundant rain with 137 centimeters per year on average, though this varies

throughout the state (Carriker and Borisova 2008). The four major native plant

communities that exist in the interior uplands of Florida are the high pine grasslands,

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flatwoods and prairies, interior scrub, and temperate hardwood hammocks (Whitney et

al. 2010).

High pine grasslands, also known as upland pines, sandhills, and pine rocklands,

have existed on the southern coastal plain for more than 20 million years. Many species

are unchanged for at least 2 million years including many endemic species to Florida

(Whitney et al. 2010). At one time this ecosystem covered over 8 million hectares in

Florida, but is now almost completely gone (Whitney et al. 2010). This ecosystem

consists of a widely spaced canopy, typically longleaf pine (Pinus palustris), sparse

midstory of turkey oak (Quercus laevis) and scrub oak (Quercus sp.), and diverse

understory dominated by wiregrass (Aristida stricta) (FNAI 2010; Whitney et al. 2010).

This is a fire dependent community, relying on frequent, low intensity fires to suppress

hardwoods, stimulate seed release, provide sunlight for seedlings, and to keep dry litter

at a minimum to prevent hot, damaging fires (Whitney et al. 2010; Myers 1990).

Flatwoods and prairies, also known as savannas, grasslands, and plains, were the

most extensive grasslands in the southeastern US and covered half of Florida

(Edmisten 1963; Davis 1967; Abrahamson and Hartnett 1990; Whitney et al. 2010).

Many of these natural systems have disappeared due to development and conversion

to agricultural fields (FNAI 2010; Whitney et al. 2010). These prairies are characterized

by a low, flat topography and relatively poorly drained sandy acidic soils. They are

dominated by a continuous layer of grasses and forbs with few scattered trees

(Abrahamson and Hartnett 1990; Whitney et al. 2010). In the past, fires were frequent

as many of the grass species, including wiregrass, are fire dependent (Abrahamson and

Hartnett 1990; Whitney et al. 2010).

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Interior scrublands are unique xeric communities on well-drained, infertile sand

formations in the coastal and interior areas of Florida (Whitney et al. 2010). The largest

interior scrub is located in and around the Ocala National Forest and is thought to be

over a million years old (Myers 1990; Whitney et al. 2010). Much of the interior

scrubland has been lost to development and citrus cultivation (Myers 1990). This is a

pyrogenic natural community that depends on infrequent (every 10 to 50 years) high-

intensity fires (Myers 1990; Whitney et al. 2010). Many scrub plants produce allelopathic

chemicals or are home to toxic fungi that inhibit the reproduction of other plants and

even their own seeds until the parent plant dies, making scrubland one of the most

botanically unique and important ecosystems in the United States (Whitney et al. 2010).

Temperate hardwood hammocks occur along the southeastern coastal plain of the

US (Platt and Schwartz 1990). Hardwood hammocks are categorized by three types:

xeric, mesic, and hydric (FNAI 2010; Whitney et al. 2010). Xeric hardwood hammocks

are an evergreen forest on well drained soils consisting of a closed canopy of oaks,

often live oak (Quercus virginiana) and laurel oak (Quercus laurifolia) (FNAI 2010;

Whitney et al. 2010). Mesic hammocks are a mixture of many tree species, ranging from

dry upland forests to wet bottomland forests (Whitney et al. 2010). Hydric forests consist

of oaks and palms, generally live oak, laurel oak, cabbage palm (Sabal palmetto), and

red cedar (Juniperus virginiana) (FNAI 2010; Whitney et al. 2010). These hammocks

are not fire dependent and where fire has been excluded due to burning restrictions and

development, new areas of hammocks have emerged (Whitney et al. 2010).

Maintaining these natural communities are important, and many areas are being

restored to their natural state after being disturbed (Myers and Ewel 1990). Exotic

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species hinder these restoration efforts because habitat occupied by invasives is

unavailable for native species recruitment (Myers and Ewel 1990). Exotic species

compete for nutrients, water, and light that would otherwise be available to native

species (Myers and Ewel 1990). Phosphate mining creates anthrosols (human-created

soils), that appear to provide favorable environment for invasive species while hindering

restoration efforts (Myers and Ewel 1990). In such areas where an ecosystem has been

greatly altered, the control of the invading exotic species and restoration of its native

properties are necessary to return the land to its natural state (Gordon 1998). Therefore,

the establishment of a self-sustaining native plant community is critical to return a land

to its natural state and prevent new invasions (Shilling 2003; Ewel 1986).

Invasive species control must be accomplished before native plant restoration

techniques can be successful and understanding the impact of herbicide residue

potential is paramount for the success of a restoration effort. If aminocyclopyrachlor is

found to be effective on invasive species, this herbicide could change how land

managers address invasive species management for many areas. However before this

can be accomplished, several questions rise with respect to this herbicide and its

activity under Florida conditions: How does aminocyclopyrachlor effect invasive and

native plants post emergence; Does the soil residual of aminocyclopyrachlor impact

native species transplant success; and can this chemical be used to control cogongrass

infestations in Florida conditions. Therefore, the objectives of this research were to: 1)

determine the efficacy of aminocyclopyrachlor on select native and invasive plants

grown under greenhouse conditions; 2) evaluate native plant tolerance to various soil

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concentrations of aminocyclopyrachlor; and 3) evaluate the use of aminocyclopyrachlor

for cogongrass control under field conditions.

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CHAPTER 2 THE EFFECT OF AMINOCYCLOPYRACHLOR APPLIED POST-EMERGENCE ON SELECTED NATIVE AND INVASIVE GRASS SPECIES UNDER GREENHOUSE

CONDITIONS

Background Information

In Florida, more than 4,000 native species are being displaced by over 900

invasive exotic species (Frank et al. 1997; Simberloff et al. 1997; Westbrooks 1998;

Whitney et al. 2010). Florida has become an epicenter for invasive species due to its

mild climate, international ports, and historically lenient importation laws (Anonymous

1999). Torpedograss, Panicum repens, and cogongrass, Imperata cylindrica, are two

species that have historically been the most problematic exotic species in the state

(Anonymous 1999; EDDSMaps 2012). Cogongrass causes ecosystem destruction by

outcompeting native species, as well as eliminating species during prescribed or natural

burns due to its pyrogenic characteristics (Eussen and Wirjahardja 1973; Seavoy 1975;

Eussen 1980). Two other invasive grasses impacting Florida are West Indian

marshgrass (Hymenachne amplexicaulis) and paragrass (Urochloa mutica). West

Indian marshgrass and paragrass are category 1 exotic species on the Florida Exotic

Pest Plant Council Invasive Plant List for central and south Florida (FLEPPC 2011).

Category 1 invasives alter native plant ecosystems by displacing natives, changing

community structure and functions, or hybridizing with native species (FLEPPC 2011).

Finding new herbicides to control these invasive species as they invade a natural area

is imperative for maintaining Florida’s natural communities.

When controlling invasive plants in natural areas, the response of native plants to

the chemical treatment must be considered. Selectivity is key to finding a useful

herbicide for invasive species management in natural areas. Two common herbicides

24

used for grass control in natural settings are glyphosate and imazapyr, though

limitations exist with both. Glyphosate is broad spectrum and therefore does not show

selectivity to many native species, as well as possessing no soil residual activity,

meaning long-term control of invasive grasses is limited with this product (Cornish and

Burgin 2005). Imazapyr, another broad spectrum, non-selective herbicide, possesses

considerable residual activity. This is desirable for long-term control of invasive species,

but residual activity also impacts native plant recruitment over the long term

(MacDonald et al. 2008). Therefore practitioners are always looking for new chemicals

that will provide control of invasive species while minimizing non-target injury/damage

and encouraging the recruitment of desirable natives.

Aminocyclopyrachlor is a synthetic auxin herbicide proposed for restoration of

native perennial grasses (DuPont Crop Protection 2010). The low use rates and

selectivity of this herbicide may allow for its use as a post-emergence herbicide for

invasive species control where native plants are present (DuPont Crop Protection

2010). It is active on many broadleaf and brush species as well as some grass species,

but appears to be highly species specific (Bukun et al. 2008; Claus et al. 2008; Armel et

al. 2009; Blair and Lowe 2009; Evans et al. 2009; Gannon et al. 2009; Montgomery et

al. 2009; Roten et al. 2009; Turner et al. 2009; Westra et al. 2009; Wilson et al. 2009;

Rupp et al. 2011). Post-emergence experiments on native species have been utilized

for other natural area chemicals such as hexazinone, glyphosate, imazapyr, imazapic,

2, 4-D, and sulfometuron methyl (Lym and Kirby 1991; Kluson et al. 2000; Richardson

et al. 2003; Jose et al. 2010). However, little research has been conducted with

aminocyclopyrachlor in this regard. Therefore, post-emergence activity on a variety of

25

native species and invasive grasses were conducted under greenhouse conditions to

determine potential invasive grass control and native plant selectivity.

Materials and Methods

Native plant species were established from seed obtained from a native plant

nursery1 in Florida. Plants were grown under greenhouse conditions (30°C day; 20°C

night temperatures, natural sunlight) until they had vigorous growth and multiple leaves

on the broadleaf species or multiple leaf blades on the grass species to adequate

transplant size. The number of native plant species evaluated was limited in the second

experiment due to poor seed germination. Cogongrass plants were established from

rhizomes obtained from naturally growing populations in Gainesville, Florida. Paragrass,

West Indian marshgrass, and torpedograss were established from propagule cuttings of

plants obtained from south Florida. Natalgrass was grown from seeds collected from an

established natalgrass population in central Florida. All grasses were grown for 8 to 10

weeks to ensure a healthy root and/or rhizome mass and shoot growth accumulation.

Due to the natural aquatic environment of paragrass, West Indian marshgrass, and

torpedograss, the pots were submerged in 1” water pans to maintain desirable moisture

conditions. Experiment 1 occurred in spring 2010 and experiment 2 occurred in summer

2011. All species were grown in 0.5 L pots with commercial potting soil. Plant height

(cm) was taken before treatment and due to the variability in native plant growth, native

plants were grouped by height and distributed evenly among the six treatments.

1 The Natives, Inc., Davenport, FL, USA.

2 Induce, Helena Chemical Company, Collierville, TN

26

Herbicides were applied with a nonionic surfactant2 (0.25% v/v) at a spray volume of

187 L ha-1. Treatments included aminocyclopyrachlor applied at rates of 0, 0.0175,

0.035, 0.07, 0.14, and 0.28 kg- ai ha-1. Visual estimation of injury (100 = complete

death, 0 = no visual injury rating scale) was evaluated at 1, 2, 3, and 4 weeks after

treatment (WAT). At 4 WAT aboveground biomass was harvested and dry weights

obtained. The native grasses were cut to1 cm and the invasives to 2.5 cm height and

allowed to re-grow for 4 weeks. After 4 weeks, shoot regrowth was harvested, dried,

and weighed.

The experimental design was a 2-way factorial with aminocyclopyrachlor rate and

plant species as main effects. Treatments were arranged in a randomized complete

block design with 4 replications. Analysis of variance (ANOVA) was used to test for

treatment by experiment interactions. For both greenhouse experiments there was a

significant treatment by experiment interaction, so data are presented separately. A

log-logistic model for predicting dose response curves, as adopted from Seefeldt et al.

(1995), was utilized for regression analysis to show species response to

aminocyclopyrachlor rate and generate predictive I50 values.

Results and Discussion

Native Plants

Eight of the native species used in experiment one showed a response of

increased injury corresponding to increasing levels of aminocyclopyrachlor based on

visual evaluation. For shoot weight, nine of the eleven species were evaluated using

regression analysis while Sorghastrum secundum and Garberia heterophylla did not

have a consistent trend of shoot weight verses aminocyclopyrachlor application rate

(Figure 2-7 and 2-8).

27

Grasses. For visual evaluation, Andropogon brachystachyus had an I50 value of

0.22 kg ai ha-1 in experiment one (Table 2-1, Figure 2-1) and showed less than 50%

injury in experiment two (Table 2-2). For shoot growth it had an I50 value of 0.20 kg- ai

ha-1 in experiment one and greater than the maximum labeled rate of 0.28 kg- ai ha-1 in

experiment two. A 50% reduction of regrowth has been predicted at 0.19 kg- ai ha-1for

Andropogon brachystachyus in experiment one.

Andropogon virginicus was tolerant to aminocyclopyrachlor with a visual I50 value of 0.23

kg- ai ha-1 and a shoot growth I50 value of 0.24 kg- ai ha-1 (Table 2-1, Figure 2-3). Re-

growth data are not shown due to damage across all rates caused by the cutting

procedure and plant death seen across all rates and the untreated control. Visual data

are not shown for Aristida stricta due to the lack of observable visual symptoms for both

experiments. Aristida stricta had a shoot growth I50 value of 0.11 kg- ai ha-1 in

experiment one (Table 2-1, Figure 2-2) and no injury in experiment two (Table 2-2).

However, Aristida stricta had an I50 value greater than 0.28 kg- ai ha-1 for experiment

two. Greenhouse environmental issues such as uneven watering may have also caused

the reduced shoot growth in experiment one when compared to experiment two.

Eragrostis elliottii showed less than 50% injury at all rates of aminocyclopyrachlor,

an I50 value greater than the maximum labeled rate of 0.28 kg- ai ha-1 for shoot growth

and a high predicted I50 of 0.25 kg- ai ha-1 for shoot regrowth (Table 2-1, Figure 2-4).

Overall, Eragrostis elliottii was the most tolerant grass species evaluated. Conversely,

Eragrostis spectabilis showed greater than 50% injury at all rates of

aminocyclopyrachlor and had a shoot growth I50 value of 0.12 kg- ai ha-1 (Table 2-1,

Figure 2-5). Regrowth was highly inconsistent and therefore was not regressed for this

28

species. Significant plant injury was observed at even the lowest application rates,

indicating that injury may have been exacerbated by stress factors such as irrigation

problems coupled with aminocyclopyrachlor damage.

Panicum anceps had no visual injury at all rates of aminocyclopyrachlor but

showed a shoot growth I50 value of 0.17 kg ai ha-1 and a regrowth I50 value greater than

0.28 kg- ai ha-1 (Table 2-1, Figure 2-6). Sorghastrum secundum injury had an I50 value

of 0.13 kg ai ha-1 in experiment one (Table 2-1, Figure 2-7) which is slightly lower than a

half rate of aminocyclopyrachlor and showed less than 50% injury to all rates of

aminocyclopyrachlor in experiment two (Table 2-2, Figure 2-15). For shoot growth and

regrowth data, Sorghastrum secundum was not significantly affected by

aminocyclopyrachlor with all I50 values greater than 0.28 kg ai ha-1.

The greater overall injury seen in experiment one may be due to a watering issue

in the greenhouse because greater damage is seen across all species. Many of these

species, such as Eragrostis species, Sorghastrum secundum, Andropogon virginicus,

and Aristida stricta are common to xeric upland ecosystems in Florida (Grelen and

Hughes 1984). These natural xeric sites are characterized by excessively drained soils

(Florida Native Plant Society 2004). Overwatering in the greenhouse may have caused

mold and disease, which was seen in some pots, thus stressing these species and

leading to the increased damage observed.

Broadleaves. Garberia heterophylla was the least sensitive broadleaf evaluated

with an I50 value for injury of 0.24 kg ai ha-1, however shoot growth was inconsistent

across all treatments and no data were collected for this parameter. Liatris spicata had

a visual injury predicted value of 0.08 kg ai ha-1 and a shoot growth predicted value of

29

0.12 kg ai ha-1. Solidago fistulosa was the most sensitive species evaluated with visual

I50 value of 0.02 kg- ai ha-1 and shoot growth I50

value of 0.09 kg- ai ha-1. Due to the

broad spectrum broadleaf weed control observed with aminocyclopyrachlor, the

significant damage seen on these native broadleaf plants in the greenhouse was not

surprising (DuPont Crop Protection 2010).

Invasive Grasses

All species had less than 50% injury at all rates of aminocyclopyrachlor at 4 WAT,

therefore, I50 values are not listed. For Hymenachne amplexicaulis, regrowth I50 values

for all experiments were above 0.28 kg- ai ha-1 (Table 2-3 and 2-4). Imperata cylindrica

was not regressed for regrowth due to data inconsistencies in experiment one however

it had a regrowth I50 value of 0.09 kg- ai ha-1 in experiment two (Table 2-4). Melinis

repens averages of four means at three treatments are graphed for experiment one but

significant injury due to cutting was seen at all rates above 0.035 kg- ai ha-1. Therefore

data cannot be analyzed for experiment one, but Melinis repens had an I50 value above

0.28 kg- ai ha-1 for shoot regrowth in experiment two (Table 2-4). Panicum repens was

not regressed for shoot weight in experiment one, however it had an I50 value at the

highest rate (0.28 kg- ai ha-1) in experiment two (Table 2-4). Urochloa mutica did not

show significant shoot growth reductions at all rates of aminocyclopyrachlor in either

experiment. Shoot regrowth of Urochloa mutica in experiment one was also not

affected by aminocyclopyrachlor, however in experiment two a predicted 50% reduction

in regrowth was seen at 0.15 kg- ai ha-1.

Discussion. For native species, grasses showed less injury and therefore a

higher I50 value than all broadleaf species excluding Garberia heterophylla. Though

native plants rarely exhibit uniform growth, the I50 values show a trend that grasses are

30

more tolerant to aminocyclopyrachlor than native forbs. These results are to be

expected, as grasses have been found to be tolerant to other growth regulating

herbicides (Crafts 1946; Shinn and Thill 2002; Rinella et al. 2010). An experiment by

DiTomaso et al. (2006) found an increase in annual grass composition and decrease in

legumes in a grassland treated for two years with the growth regulator clopyralid. For

the grass regrowth evaluation, most species had I50 values ≥ 0.19 kg- ai ha-1. In

experiment 1, Eragrostis spectabilis was an exception to this high I50 value trend while

other species in both experiments showed damage from the actual cutting procedure.

The invasive grasses had more consistent growth patterns than the native grasses. The

I50 values for all invasive grasses tested were > 0.28 kg- ai ha-1 for initial growth

evaluations. Imperata cylindrica and Urochloa mutica showed reduction in regrowth in

experiment two. All other grasses evaluated had regrowth I50 values ≥ 0.28 kg- ai ha-1.

Overall, these five invasive grasses are not highly sensitive to aminocyclopyrachlor.

Brecke et al. (2010) also found similar results that indicated torpedograss cannot be

controlled by a post application of aminocyclopyrachlor. Differences in plant response in

replicated greenhouse experiments have been noted in other greenhouse trials which

emphasize the need for additional greenhouse and field trials to get a complete

understanding of herbicide efficacy (Viswanath et al. 2011).

31

Table 2-1. Summary of the effect of aminocyclopyrachlor concentration on native species- Experiment 1. I50 values reflect the predicted aminocyclopyrachlor concentration that would result in 50% visual injury 4 WAT, 50% reduction in shoot growth 4 WAT, and 50% reduction in shoot regrowth 8 WAT

Species

I501

aminocyclopyrachlor values (kg- ai ha-1)

I502


I503


Andropogon brachystachyus

0.22 0.19 0.17

Aristida stricta -4 - 0.11

Andropogon virginicus 0.23 - 0.24

Eragrostis elliottii > 0.28 0.25 > 0.28

Eragrostis spectabilis - 0.09 0.12

Garberia heterophylla 0.24 - -

Liatris spicata 0.08 - 0.12

Panicum anceps - > 0.28 0.20

Pityopsis graminifolia 0.04 - 0.18

Solidago fistulosa 0.02 - 0.09

Sorghastrum secundum

0.13 - -

1 I50 aminocyclopyrachlor value for less than 50% visual injury 4 WAT

2 I50 aminocyclopyrachlor value for reduction in growth 4 WAT

3 I50 aminocyclopyrachlor value for reduction in regrowth 8 WAT

4 Species did not show a response

Table 2-2. Summary of the effect of aminocyclopyrachlor concentration on native

species- Experiment 2. I50 values reflect the predicted aminocyclopyrachlor concentration that would result in 50% visual injury 4 WAT, 50% reduction in shoot growth 4 WAT, and 50% reduction in shoot regrowth 8 WAT

Species

I501


I502


I503


Andropogon brachystachyus

> 0.28 > 0.28 -

Aristida stricta - > 0.28 > 0.28

Eragrostis spectabilis > 0.0 > 0.28 -

Sorghastrum secundum

> 0.28 > 0.28 > 0.28

1 I50 aminocyclopyrachlor value for less than 50% visual injury 4 WAT


3 I50 aminocyclopyrachlor value for reduction in growth 4 WAT

32

Table 2-3. Summary of the effect of aminocyclopyrachlor concentration on invasive species- Experiment 1. I50 values reflect the predicted aminocyclopyrachlor concentration that would result in 50% reduction in shoot growth 4 WAT and 50% reduction in shoot regrowth 8 WAT

Species

I501


I502


Hymenachne amplexicaulis

> 0.28 > 0.28

Imperata cylindrica > 0.28 -

Melinis repens > 0.28 -

Panicum repens - > 0.28

Urochloa mutica > 0.28 > 0.28 1 I50 aminocyclopyrachlor value for reduction in growth 4 WAT


Table 2-4. Summary of the effect of aminocyclopyrachlor concentration on invasive

species- Experiment 2. I50 values reflect the predicted aminocyclopyrachlor concentration that would result in 50% reduction in shoot growth 4 WAT and 50% reduction in shoot regrowth 8 WAT

Species

I501


I502


Hymenachne amplexicaulis

> 0.28 > 0.28

Imperata cylindrica > 0.28 0.09

Melinis repens > 0.28 > 0.28

Panicum repens > 0.28 0.28

Urochloa mutica > 0.28 0.15 1 I50 aminocyclopyrachlor value for reduction in growth 4 WAT


33

Figure 2-1. Andropogon brachystachyus response to aminocyclopyrachlor concentration. A) visual injury 4 WAT; B) shoot growth 4 WAT; C) shoot regrowth 8 WAT for experiment 1. Means of 4 replications present with standard error. Regression curves shown when applicable. Experiment 1

y=0.05626*(1-exp(-42.61*x))

R2= 0.83

aminocyclopyrachlor concentration (kg- ai ha-1

)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% inju

ry

0

20

40

60

80

100


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.0

0.5

1.0

1.5

2.0

2.5

y= 1.258*exp(-4.053*x)

R2= 0.67


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

y = 0.3397*exp(-3.664*x)

R2= 0.47

A B

C

34

Figure 2-2. Aristida stricta response to aminocyclopyrachlor concentration. Shoot growth 4 WAT for experiment 1. Means of 4 replications present with standard error.

Figure 2-3. Andropogon virginicus response to aminocyclopyrachlor concentration. A) visual injury 4 WAT; B) shoot growth 4 WAT for experiment 1. Means of 4 replications present with standard error. Regression curves shown when applicable.


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.0

0.1

0.2

0.3

0.4

0.5

y= 0.3449*exp(-6.272*x)

R2= 0.85

y=0.609*(1-exp(-7.51*x))


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% inju

ry

0

20

40

60

80

100

R2= 0.80


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

y= 0.7922*exp(-2.952*x)

R2= 0.30

A B

35

Figure 2-4. Eragrostis elliottii response to aminocyclopyrachlor concentration. A) shoot growth 4 WAT; B) shoot regrowth 8 WAT for experiment 1. Means of 4 replications present with standard error. Regression curves shown when applicable.


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

weig

ht (g

)

0.0

0.5

1.0

1.5

2.0

2.5

y= 1.293*exp(-1.646*x)

R2= 0.24


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

y = 17.23*exp(-41.03*x)

R2= 0.32

A B

36

Figure 2-5. Eragrostis spectabilis response to aminocyclopyrachlor concentration. A) shoot growth 4 WAT; B) shoot regrowth 8 WAT for experiment 1. Means of 4 replications present with standard error. Regression curves shown when applicable.

Figure 2-6. Panicum anceps response to aminocyclopyrachlor concentration. A) shoot growth 4 WAT; B) shoot regrowth 8 WAT for experiment 1. Means of 4 replications present with standard error. Regression curves shown when applicable.


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

y= 2.281*exp(-5.857*x)

R2= 0.65


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

y= 1.025+0.3835*exp(-7.546*x)

R2= 0.82


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

weig

ht (g

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

y = 0.5991*exp(-1.958*x)

R2= 0.14


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

weig

ht (g

)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

y= 1.946*exp(-5.997*x)

R2= 0.57

A

A

B

B

37

Figure 2-7. Sorghastrum secundum response to aminocyclopyrachlor concentration. A) visual injury 4 WAT; B) shoot growth 4 WAT; C) shoot regrowth 8 WAT for experiment 1. Means of 4 replications present with standard error. Regression curves shown when applicable.

y=0.001047*(1-exp(-36.43*x))


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% in

jury

0

20

40

60

80

100

R2= 0.98


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7


)

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

weig

ht (g

)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

A B

C

38

Figure 2-8. Garberia heterophylla response to aminocyclopyrachlor concentration. A)

visual injury 4 WAT; B) shoot growth 4 WAT for experiment 1. Means of 4 replications present with standard error. Regression curves shown when applicable.

Figure 2-9. Liatris spicata response to aminocyclopyrachlor concentration. A) visual

injury 4 WAT; B) shoot growth 4 WAT for experiment 1. Means of 4 replications present with standard error. Regression curves shown when applicable.

y=59.69*(1-exp(-7.711*x))


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% inju

ry

0

20

40

60

80

100

R2= 0.84


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.0

0.1

0.2

0.3

0.4

0.5

y=0.7665*(1-exp(-0.1366*x))


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% in

jury

0

20

40

60

80

100

R2= 0.84


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

weig

ht (g

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

y= 01.541*exp(-3.531*x)

R2= 0.59

A

A

B

B

39

Figure 2-10. Pityopsis graminifolia response to aminocyclopyrachlor concentration. A) visual injury 4 WAT; B) shoot growth 4 WAT for experiment 1. Means of 4 replications present with standard error. Regression curves shown when applicable.

Figure 2-11. Solidago fistulosa response to aminocyclopyrachlor concentration. A) visual injury 4 WAT; B) shoot growth 4 WAT for experiment 1. Means of 4 replications present with standard error. Regression curves shown when applicable.

y=0.9823*(1-exp(-0.1614*x))


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% in

jury

0

20

40

60

80

100

R2= 0.99


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

y= 0.8574*exp(-3.843*x)

R2= 0.81

y=0.8259*(1-exp(-0.3812*x))


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% in

jury

0

20

40

60

80

100

R2= 0.93

y= 1.273*exp(-7.959*x)

R2= 0.51


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

A

A

B

B

40

Figure 2-12. Andropogon brachystachyus response to aminocyclopyrachlor concentration. A) visual injury 4 WAT; B) shoot growth 4 WAT; C) shoot regrowth 8 WAT for experiment 2. Means of 4 replications present with standard error. Regression curves shown when applicable.


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% in

jury

0

20

40

60

80

100

y= 17.23*(1-exp(-41.03*x))

R2= 0.59


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.0

0.1

0.2

0.3

0.4

0.5

y= 0.2473+0.03015*exp(-48.64*x)

R2= 0.05


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.0

0.1

0.2

0.3

0.4

A B

C

41

Figure 2-13. Aristida stricta response to aminocyclopyrachlor concentration. A) visual injury 4 WAT; B) shoot growth 4 WAT; C) shoot regrowth 8 WAT for experiment 2. Means of 4 replications present with standard error. Regression curves shown when applicable.


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% in

jury

0

20

40

60

80

100


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

weig

ht (g

)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

y = 0.2003*exp(-1.027*x)

R2= 0.12


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

weig

ht (g

)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

y= 0.07165*exp(-1.073*x)

R2= 0.03

A B

C

42

Figure 2-14. Eragrostis spectabilis response to aminocyclopyrachlor concentration. A) visual injury 4 WAT; B) shoot growth 4 WAT; C) shoot regrowth 8 WAT for experiment 2. Means of 4 replications present with standard error. Regression curves shown when applicable.


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% in

jury

0

20

40

60

80

100

y= 56*(1-exp(-1799*x))

R2= 0.96

y= 0.922+1127*exp(-0.0014*x)

R2= 0.21


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.0

0.5

1.0

1.5

2.0


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.0

0.1

0.2

0.3

0.4

0.5

A B

C

43

Figure 2-15. Sorghastrum secundum response to aminocyclopyrachlor concentration. A) visual injury 4 WAT; B) shoot growth 4 WAT; C) shoot regrowth 8 WAT for experiment 2. Means of 4 replications present with standard error. Regression curves shown when applicable.

y= 32.31*(1-exp(-22.13*x))

R2= 0.45


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% in

jury

0

20

40

60

80

100

y = 0.3719*exp(-9.94*x)

R2= 0.13


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

weig

ht (g

)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

y= 0.1872*exp(-0.1842*x)

R2= 0.006

A B

C

44

Figure 2-16. Hymenachne amplexicaulis response to aminocyclopyrachlor concentration. A) shoot growth 4 WAT; B) shoot regrowth 8 WAT for experiment 1. Means of 4 replications present with standard error. Regression curves shown when applicable.

Figure 2-17. Imperata cylindrica response to aminocyclopyrachlor concentration. A) shoot growth 4 WAT; B) shoot regrowth 8 WAT for experiment 1. Means of 4 replications present with standard error. Regression curves shown when applicable.


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.0

0.5

1.0

1.5

2.0

2.5

y= 0.1.202*exp(-0.4408*x)

R2= 0.01


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

weig

ht (g

)

0.3

0.4

0.5

0.6

0.7

0.8

0.9

y= 0.6188*exp(-1.365*x)

R2= 0.49


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

weig

ht (g

)

2

4

6

8

10

12

14

16

18

y= 8.013*exp(-1.267*x)

R2= 0.09


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

weig

ht (g

)

1

2

3

4

5

6

7

8

A

A

B

B

45

Figure 2-18. Melinis repens response to aminocyclopyrachlor concentration. A) shoot growth 4 WAT; B) shoot regrowth 8 WAT for experiment 1. Means of 4 replications present with standard error. Regression curves shown when applicable.

Figure 2-19. Panicum repens response to aminocyclopyrachlor concentration. A) shoot growth 4 WAT; B) shoot regrowth 8 WAT for experiment 1. Means of 4 replications present with standard error. Regression curves shown when applicable.

y= 0.7953*exp(-0.9622*x)

R2= 0.74


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.5

0.6

0.7

0.8

0.9

1.0


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

weig

ht (g

)

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

y= 0.6186*exp(-2.133*x)

R2= 0.44


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.10

0.15

0.20

0.25

0.30

0.35

0.40

A

A

B

B

46

Figure 2-20. Urochloa mutica response to aminocyclopyrachlor concentration. A) shoot growth 4 WAT; B) shoot regrowth 8 WAT for experiment 1. Means of 4 replications present with standard error. Regression curves shown when applicable.


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.5

1.0

1.5

2.0

2.5

3.0

y= 0.2.024*exp(-0.3276*x)

R2= 0.03


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.2

0.4

0.6

0.8

1.0

1.2

y= 0.8694-0.2865*exp(-4.974*x)

R2= 0.63

A B

47

Figure 2-21. Hymenachne amplexicaulis response to aminocyclopyrachlor concentration. A) shoot growth 4 WAT; B) shoot regrowth 8 WAT for experiment 2. Means of 4 replications present with standard error. Regression curves shown when applicable.

aminocyclopyrachlor concentration (kg-ai ha-1

)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

weig

ht (g

)

0

1

2

3

4

5

6

7

y= 3.553*exp(-7.063*x)R

2= 0.57

Figure 2-22. Imperata cylindrica response to aminocyclopyrachlor concentration. A)

shoot growth 4 WAT; B) shoot regrowth 8 WAT for experiment 2. Means of 4 replications present with standard error. Regression curves shown when applicable.


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

y= 1.393*exp(-0.7545*x)

R2= 0.10


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

weig

ht (g

)

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

y= 0.8901*exp(-0.2398*x)

R2= 0.03


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

2

4

6

8

10

12

14

16

18

y= 9.877*exp(-2.015*x)

R2= 0.32

A

A

B

B

48

Figure 2-23. Melinis repens response to aminocyclopyrachlor concentration. A) shoot

growth 4 WAT; B) shoot regrowth 8 WAT for experiment 2. Means of 4 replications present with standard error. Regression curves shown when applicable.

Figure 2-24. Panicum repens response to aminocyclopyrachlor concentration. A) shoot

growth 4 WAT; B) shoot regrowth 8 WAT for experiment 2. Means of 4 replications present with standard error. Regression curves shown when applicable.


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

y= 0.617*exp(-2.239*x)

R2= 0.69


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

y= 0.7336*exp(-0.2413*x)

R2= 0.02


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

weig

ht (g

)

0.0

0.2

0.4

0.6

0.8

1.0

y= 0.6562*exp(-2.469*x)

R2= 0.45


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.10

0.15

0.20

0.25

0.30

0.35

0.40

A

A

B

B

49

Figure 2-25. Urochloa mutica response to aminocyclopyrachlor concentration. A) shoot growth 4 WAT; B) shoot regrowth 8 WAT for experiment 2. Means of 4 replications present with standard error. Regression curves shown when applicable


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.6

0.8

1.0

1.2

1.4

1.6

1.8

y= 1.366*exp(-1.369*x)

R2= 0.61


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

we

igh

t (g

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

y= 1.224*exp(-4.546*x)

R2= 0.85

A B

50

CHAPTER 3 RESPONSE OF SELECT NATIVE SPECIES TO VARIOUS SOIL CONCENTRATIONS

OF AMINOCYCLOPYRACHLOR


Florida consists of 13 million hectares of diverse natural areas encompassing a

wide variety of ecosystems (Myers and Ewel 1990; FNAI 2010; Whitney et al. 2010).

These natural ecosystems support a high diversity of 4,000 native plant species

throughout the state (Whitney et al. 2010). The four major native plant communities in

the state are the high pine grasslands, flatwoods and prairies, interior scrub, and

temperate hardwood hammocks (Whitney et al. 2010). Native grasses and broadleaves

are important in maintaining a diverse ecosystem. There are several key species that

dominate the understory of these ecosystems. Wiregrass, Aristida stricta, is a dominant

species in longleaf pine ecosystems of Florida (Brockway et al. 1998; Clewell 2003).

According to Norcini et al. (2003), wiregrass is the most desirable species to include

when restoring pineland habitats. In the northwestern panhandle of Florida, longleaf

pine forest understories may also be dominated by bluestem (Andropogon) species

(Brockway et al. 1998). These two grasses, along with longleaf pine (Pinus palustris)

are keystone species in these fire dominated ecosystems (Platt et al. 1988; Brockway et

al. 1998). Their ability to carry a fire makes them ideal for these frequently burned

habitats.

Several other forbs and grasses are used for restoring degraded sites. Blazing

star, Liatris spicata, is a perennial wildflower found throughout the state of Florida. It is

browsed by deer and its flowers are attractive to many species of butterflies and insects

(Norcini et al. 2003). It has been shown to be adaptable to sand tailings in reclaimed

mined sites (Norcini et al. 2003). Chalky bluestem (Andropogon virginicus var. glauca),

51

and lopsided indiangrass (Sorghastrum secundum) are used for erosion control,

livestock forage, and wildlife cover (Norcini et al. 2003). Silkgrass, Pityopsis

graminifolia, has been studied for use in restoring reclaimed phosphate mine sites in

Florida (Pfaff et al. 2002). Lovegrasses such as Eragrostis elliottii and Eragrostis

spectabilis are native pioneer grass species that can compete with invasive grasses

while allowing smaller native plants to become established (Segal et al. 2001).

Direct seeding and transplanting are the two main options for reestablishing native

species on a site. Direct seeding is the least expensive, however there are several

complications with using this method. Native seeds are often light, with awns or hairs

that make planting with conventional equipment difficult (Pfaff et al. 2002). Many native

species lack seed vigor and cannot outcompete established invasive species (Pfaff et

al. 2002; Norcini et al. 2003). In addition, seed dormancy is a common occurrence with

native seeds with germination occurring only during certain seasons (Pfaff et al. 2002).

Though planting containerized seedlings is more costly, it is a popular method for

quickly re-establishing native species (Glitzenstein and Streng 2003).

When transplanting natives, it is important to understand the residual effects of an

herbicide that has been previously employed on the site for weed control. Previous plant

back studies have been conducted on native species in response to imazapyr,

glyphosate, and hexazinone (Miller et al. 2002; Barron et al. 2005; Cornish and Burgin

2005; Jose et al. 2010). When herbicide residues persist in the environment, there is a

risk that damage to the replanted species will result (Cornish et al. 1996; Cornish and

Burgin 2005). An experiment conducted by Barron et al. (2005) evaluated imazapyr

52

residuals on native species and found all species were highly injured at rates above

0.56 kg ai ha-1.

Aminocyclopyrachlor is a synthetic auxin herbicide proposed for natural areas

management and the restoration of native perennial grasses (DuPont Crop Protection

2010). This herbicide is active on many broadleaf and brush weeds and has shown

some activity on grasses, though it is highly species specific. Some grasses that are

intolerant of aminocyclopyrachlor are Bromus marginatus Nees ex Steudel, Leymus

cinereus (Scribn. & Merr.) A., and Stenotaphrum secundatum Walt. Kuntze. (Bukun et

al. 2008; Brecke et al. 2010; Claus et al. 2008; Armel et al. 2009; Blair and Lowe 2009;

Evans et al. 2009; Gannon et al. 2009; Montgomery et al. 2009; Roten et al. 2009;

Turner et al. 2009; Wallace and Prather 2010; Westra et al. 2009; Wilson et al. 2009;

Rupp et al. 2011). Aminocyclopyrachlor does possess soil residual activity with a half-

life ranging between 22 and 164 days in bareground studies (DuPont Crop Protection

2010). If this chemical is to be used for restoration purposes, it is important to

understand how native species respond to this product after re-introduction into a

treated landscape. Therefore the response of native species to various soil

concentrations of aminocyclopyrachlor was evaluated.


Field experiments were conducted in the summer of 2011 at the Plant Science

Research and Education Unit in Citra, Florida. The soil type is a Sparr sand (Loamy,

siliceous, subactive, hyperthermic Grossarenic Paleudults taxonomic class) consisting

of deep, somewhat poorly drained, slowly permeable soil (Soil Survey Staff 2004). The

field was prepared using conventional tillage practices and had no previous treatments

53

of aminocyclopyrachlor. Aminocyclopyrachlor was applied at 0, 0.009,0.018, 0.035,

0.07, 0.14, and 0.28 kg-ai ha-1 with a CO2 backpack sprayer calibrated to deliver 187 L

ha-1. Applications occurred on June 1st 2011 and July 6th 2011 for the first and second

experiments, respectively. Immediately after application, the herbicide was

incorporated into the top 8 cm of soil. Within 24 hours after application, the native

seedlings were hand planted into each plot.

A native plant nursery1 supplied the native species used in both experiments.

These included three tree species, four grasses, and two forb species (Table 3-1). The

plants were evaluated 10 and 14 weeks (Experiment 1 and 2) after treatment for

percent mortality and plant injury 10 and 14 weeks (Experiment 1 and 2) after treatment

where 0 = no injury and 100 = plant death. The experimental design was a 2-way

factorial with aminocyclopyrachlor rate and plant species as main effects. Plots were 3

by 6 m2 and arranged in a completely randomized block design with 4 replications.

Data was subjected to analysis of variance to test for treatment by experiment

interactions. There was a significant treatment by experiment interaction (p<0.05),

therefore data is presented separately. Regression analysis was used to predict I30 and

I50 values for all species (Table 3-2 and 3-3). Due to initial transplant shock and activity

of aminocyclopyrachlor, only 14 weeks after treatment for experiment 1 and 10 weeks

after treatment for experiment two are shown to allow for greatest plant response and

possible recovery. Plant back days were determined for each species based on a 90

day half life of aminocyclopyrachlor (estimated for Florida sandy soils) applied at 0.28

kg ai ha-1 maximum labeled rate.

1 The Natives, Inc., Davenport, FL, USA.

54

The equation used to predict plant back intervals is:

Days =((LN(I50/0.28))/LN(0.5))*90.


Overall, experiment two showed less visual injury for all species as compared to

experiment one. This could be due to transplant shock differences between the two

experiments.

To hinder reestablishment of invasive plants such as cogongrass, it is often

important to establish tree species during the later control phase of restoration (Faircloth

et al. 2005). Quercus virginiana had an I50 value of 0.024 kg ai ha-1 in experiment 1

(Table 3-2, Figure 3-3) and 0.08 kg ai ha-1 in experiment 2 (Table 3-3, Figure 3-12).

Based on these values, plant back days ranged from 163 to 319 days after a 0.28 kg ai

ha-1 application of aminocyclopyrachlor. Pinus palustris had I50 values of 0.071 and 0.16

kg ai ha-1 (Table 3-2 and 3-3). The plant back time ranged from 73 to 178 days after

treatment. Quercus laevis was regressed for experiment two only due to high injury

rates for all treatments including the untreated in experiment one. Experiment two

shows that Quercus laevis is a sensitive species with an I50 value of 0.06 kg ai ha-1 and

a plant back time of 200 days post treatment (Table 3-3). In experiment two, Quercus

laevis was the most sensitive tree species evaluated. Mortality rates for all tree species

were below 60% in experiments one and two (Table 3-4 and 3-5).

One of the uses of aminocyclopyrachlor is for the release or restoration of native

perennial grasses and so it is important to determine which native grasses can be

planted back into an area that has been previously treated with aminocyclopyrachlor for

weed control (DuPont Crop Protection 2010). Mortality was less than 60% for most

grass species in experiment one (Table 3-4) and all grasses in experiment two

55

(Table 3-5). Andropogon virginicus var. glauca was the least sensitive species, showing

no injury at all rates of aminocyclopyrachlor and therefore had a plant back time of 0

days. Aristida stricta was regressed in experiment one and showed high sensitivity with

an I50 value of 0.01 kg ai ha-1 and greater than 30% injury at all rates (Table 3-2, Figure

3-7). Based on the I50 value, the plant back time was 433 days. Aristida stricta showed

greater than 60% mortality at rates above 0.09 kg ai ha-1 (Table 3-4). This grass is very

important for restoring longleaf pine ecosystems so knowing the plant back interval is

very important to reduce mortality and injury and increase the chance for survival and

seeding (Whitney et al. 2010). Eragrostis spectabilis had higher injury in experiment one

than experiment two which may be due to a combination of transplant shock and

aminocyclopyrachlor damage because 60% injury is seen at the two lowest rates of

aminocyclopyrachlor (Figure 3-8). In experiment two, injury was too low to enable

prediction of an I50 value. Panicum anceps also displayed a greater level of injury in

experiment one and no injury in experiment two. In experiment one, Panicum anceps

had an I50 value of 0.096 kg ai ha-1 with a plant back time of 139 days (Table 3-2) and a

mortality P60 value of 0.21 kg ai ha-1 (Table 3-4). In experiment two, no injury over 50%

was seen. Panicum anceps can be planted immediately after application (0 days) and

show less than 50% injury.

Aminocyclopyrachlor is known to control many broadleaf weeds (Armel et al. 2009;

Blair and Lowe 2009; Bukun et al. 2008; Claus et al. 2008; Evans et al. 2009; Gannon

et al. 2009; Montgomery et al. 2009; Roten et al. 2009; Rupp et al. 2011; Turner et al.

2009; Westra et al. 2009; Wilson et al. 2009) and this injury is replicated on the two

broadleaf native species evaluated. Injury of both Liatris spicata and Solidago fistulosa

56

was significant at all rates of aminocyclopyrachlor and plant back dates for both species

were greater than a year (Table 3-2 and 3-3). Mortality of Liatris spicata was greater

than 60% at all rates in experiment one and Solidago fistulosa was sensitive with P60

value of 0.024 kg ai ha-1 (Table 3-4). In experiment two, both species showed less than

60% mortality (Table 3-5). Solidago fistulosa showed 50% injury at all rates. If

restoration to broadleaf natives is the goal, aminocyclopyrachlor may complicate the

revegetation process.

57

Table 3-1. Species used in revegetation study in Citra, Florida.

Common Name Scientific Name Plant Volume

Longleaf pine Pinus palustris 3.8 L pots

Live oak Quercus virginiana 3.8 L pots

Turkey oak Quercus laevis 3.8 L pots

Chalky bluestem Andropogon virginicus var. glauca 10.2 cm tublings

Wiregrass Aristida stricta var. beyrichiana 10.2 cm tublings

Purple lovegrass Eragrostis spectabilis 10.2 cm tublings

Spreading panicum Panicum anceps 10.2 cm tublings

Blazing star Liatris spicata 10.2 cm pots

Goldenrod Solidago fistulosa 10.2 cm pots

58

Table 3-2. The effect of aminocyclopyrachlor concentration on percent visual injury of selected native species 14 weeks after treatment. I30 and I50 values reflect the predicted aminocyclopyrachlor concentration that would result in visual 30% and 50% injury. Plant back days for 50% or less injury- Experiment 1

Plant Species R2

aminocyclopyrachlor values (kg ai ha-1) I30 I50

Plant Back Time (days) 1

Pinus palustris 0.52 0.03 0.07 180

Quercus virginiana 0.68 0.02 0.06 200

Andropogon virginicus var. glauca

0.10 -2 - 0

Aristida stricta 0.79 >0.0 0.01 433

Eragrostis spectabilis 0.19 - - -

Panicum anceps 0.42 0.07 0.10 139

Liatris spicata - - - -

Solidago fistulosa 0.51 >0.0 >0.0 - 1Based on 90 day half life of aminocyclopyrachlor applied at 0.28 kg ai ha

-1

2 Data not regressed

Table 3-3. The effect of aminocyclopyrachlor concentration on percent visual injury of

selected native species 10 weeks after treatment. I30 and I50 values reflect the predicted aminocyclopyrachlor concentration that would result in visual 30% and 50% injury. Plant back days for 50% or less injury - Experiment 2

Plant Species R2

aminocyclopyrachlor values

(kg ai ha-1) I30 I50

Plant Back Time (days)1

Pinus palustris 0.50 0.12 0.16 73

Quercus laevis 0.25 0.02 0.05 224

Quercus virginiana 0.39 0.03 0.08 163


-2 - 0

Eragrostis spectabilis 0.19 0.15 - 0

Panicum anceps 0.16 0.28 - 0

Liatris spicata - - -

Solidago fistulosa - - - 1Based on 90 day half life of aminocyclopyrachlor applied at 0.28 kg ai ha

-1


59

Table 3-4. The effect of aminocyclopyrachlor soil concentration on percent mortality of selected revegetation species 40 weeks after planting. Experiment 1. P60 values reflect the predicted aminocyclopyrachlor concentration that would result in less than 60% mortality.

Plant Species Regression equation

R2 P60 values (kg ai ha-1)

Pinus palustris y= -1.279+33.78*(1-exp(-8.284*x)) 0.41 1

Quercus laevis -3 - -

Quercus virginiana y= -2.07+31.17*(1-exp(-9.053*x)) 0.48 1


y= 0.6263+21410*(1-exp(-0.002*x)) 0.15 1

Aristida stricta y= 40.74+72.63*(1-exp(-3.605*x)) 0.34 0.086

Eragrostis spectabilis

y= 16.67+31.67*(1-exp(-94370000*x)) 0.10 1

Panicum anceps y= -4.208+103*(1-exp(-4.603*x)) 0.71 0.21

Liatris spicata y= 66.67+25*(1-exp(-2292*x)) 0.19 2

Solidago fistulosa y= 15.65+84.82*(1-exp(-31.48*x)) 0.68 0.024 1Species exhibits less than 60% mortality at all rates of aminocyclopyrachlor in soil.

2Species exhibits greater than 60% mortality at all rates of aminocyclopyrachlor in soil.


60

Table 3-5. The effect of aminocyclopyrachlor soil concentration on percent mortality of selected revegetation species 10 weeks after planting. Experiment 2. P60 values reflect the predicted aminocyclopyrachlor concentration that would result in less than 60% mortality.

Plant Species Regression equation

R2 P60 values (kg ai ha-1)

Pinus palustris y= -34000+10860*(1-exp(-0.004*x)) 0.45 1

Quercus laevis y= 0.2503+36.81*(1-exp(-4.609*x)) 0.04 1

Quercus virginiana

y= 36.81*(1-exp(-4.609*x)) 0.28 1


-2 - 1

Aristida stricta y= 35.26*(1-exp(-5.981*x)) 0.33 1

Eragrostis spectabilis

y= -1.931+418.2*(1-exp(-0.2448*x)) 0.24 1

Panicum anceps y= 16.67+-13.89*(1-exp(-6620*x)) 0.15 1

Liatris spicata y= 4.949+243700*(1-exp(-0.0007*x)) 0.47 1

Solidago fistulosa - - 1 1Species exhibits less than 60% mortality at all rates of aminocyclopyrachlor in soil.


61

Figure 3-1. Pinus palustris (Longleaf pine) response to aminocyclopyrachlor concentration in soil 14 WAP (weeks after planting) immediately after aminocyclopyrachlor application for experiment 1. Means of 4 replications present with standard error.


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% inju

ry

0

20

40

60

80

100

y= 132.6+((-133.17)/(1+((x/0.1340) 0.7713))) R2= 0.52

62

Figure 3-2. Quercus laevis (Turkey oak) response to aminocyclopyrachlor

concentration in soil 14 WAP (weeks after planting) immediately after aminocyclopyrachlor application for experiment 1. Means of 4 replications present with standard error.


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% i

nju

ry

0

20

40

60

80

100

63

Figure 3-3. Quercus virginiana (Live oak) response to aminocyclopyrachlor



)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% inju

ry

0

20

40

60

80

100

y= -2.626+((94)/(1+((x/0.0363) 1.6217))) R2= 0.68

64

Figure 3-4. Liatris spicata (Blazing star) response to aminocyclopyrachlor concentration

in soil 14 WAP (weeks after planting) immediately after aminocyclopyrachlor application for experiment 1. Means of 4 replications present with standard error.


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% inju

ry

0

20

40

60

80

100

y= 77.5+14.18*(1-exp(-320*x))

R2= 0.29

65

Figure 3-5. Solidago fistulosa (Goldenrod) response to aminocyclopyrachlor



)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% inju

ry

0

20

40

60

80

100

y= 9.3893+((111.41)/(1+((x/0.0224) 0.7203))) R2= 0.51

66

Figure 3-6. Andropogon virginicus var. glauca (Chalky bluestem) response to

aminocyclopyrachlor concentration in soil 14 WAP (weeks after planting) immediately after aminocyclopyrachlor application for experiment 1. Means of 4 replications present with standard error.


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

%in

jury

0

20

40

60

80

100

y= 3.2214+((39.42)/(1+((x/0.285) 2.61))) R2= 0.10

67

Figure 3-7. Aristida stricta var. beyrichiana (Wiregrass) response to



)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% inju

ry

0

20

40

60

80

100

y= 45.56+65.07*(1-exp(-0.7713*x))

R2= 0.79

68

Figure 3-8. Eragrostis spectabilis (Purple lovegrass) response to aminocyclopyrachlor



)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% i

nju

ry

0

20

40

60

80

100

69

Figure 3-9. Panicum anceps (Spreading panicum) response to aminocyclopyrachlor



)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% inju

ry

0

20

40

60

80

100

y= 5.2432+((66.21)/(1+((x/0.0792) 3.9694))) R2= 0.42

70

aminocyclopyrachlor (kg ai ha-1

)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% in

jury

0

20

40

60

80

100

Figure 3-10. Pinus palustris (Longleaf pine) response to aminocyclopyrachlor


y= 65.4696+((-54.6711)/(1+((x/0.1356)5.1174))) R2= 0.50

71

Figure 3-11. Quercus laevis (Turkey oak) response to aminocyclopyrachlor



)

0.0 0.1 0.2 0.3

% inju

ry

0

20

40

60

80

100

y= 78.3222+((-47.3068)/(1+((x/0.0732)2.6756))) R2= 0.25

72

Figure 3-12. Quercus virginiana (Live oak) response to aminocyclopyrachlor concentration in soil 10 WAP (weeks after planting) immediately after aminocyclopyrachlor application for experiment 2. Means of 4 replications present with standard error.


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% inju

ry

0

20

40

60

80

100

y= 116.4+((-103.3399)/(1+((x/0.1357)1.1045))) R2= 0.39

73

Figure 3-13. Liatris spicata (Blazing star) response to aminocyclopyrachlor



)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% inju

ry

0

20

40

60

80

100

74

Figure 3-14. Solidago fistulosa (Goldenrod) response to aminocyclopyrachlor concentration in soil 10 WAP (weeks after planting) immediately after aminocyclopyrachlor application for experiment 2. Means of 4 replications present with standard error.


)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% inju

ry

0

20

40

60

80

100

75

Figure 3-15. Andropogon virginicus var. glauca (Chalky bluestem) response to



)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% in

jury

0

20

40

60

80

100

76

Figure 3-16. Aristida stricta var. beyrichiana (Wiregrass) response to



)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% in

jury

0

20

40

60

80

100

77

Figure 3-17. Eragrostis spectabilis (Purple lovegrass) response to aminocyclopyrachlor



)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% inju

ry

0

20

40

60

80

100

y= 32.9165+((-30.9165)/(1+((x/0.1398)53.8695))) R2= 0.19

78

Figure 3-18. Panicum anceps (Spreading panicum) response to aminocyclopyrachlor



)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

% in

jury

0

20

40

60

80

100

y= 55.6525+((-48.0156)/(1+((x/0.2937)3.2998))) R2= 0.16

79

CHAPTER 4 HERBICIDE EVALUATIONS FOR COGONGRASS CONTROL UNDER FIELD

CONDITIONS


Cogongrass (Imperata cylindrica) is considered one of the top ten worst weeds in

the world (Lowe et al. 2004). This aggressive, rhizomatous perennial grass is listed as

a noxious weed federally, as well as by 7 southern states including Florida (Plant

Protection and Quarantine 2010). It has invaded many areas in Florida ranging from

pine plantations to reclaimed phosphate mining sites and other disturbed natural areas

(Hubbard 1944; MacDonald 2009). Cogongrass originated in the US as an escape from

a Satsuma orange crate around Grand Bay, Alabama in 1912 (Hubbard 1944). It was

also intentionally introduced into Mississippi in 1921 as potential forage (Dickens and

Moore 1974), and was brought into Florida in the 1930s and 1940s as potential forage

and for soil stabilization (Hubbard 1944). Initial research indicated potential as a pest

and unfortunately, it continued to spread from illegal plantings and by accidental means.

Cogongrass is now estimated to cover over 500,000 ha in the US and over 500 million

ha worldwide (Holm et al 1977; MacDonald 2007; Holzmueller and Jose 2010).

Cogongrass can spread by wind-blown seeds and rhizomes (MacDonald 2009).

Established stands can produce over 40 tons of rhizomes per acre (Terry et al 1997). It

has been reported that cogongrass rhizomes may exude allelopathic substances that

inhibit the growth of other plants (Eussen 1979; Bryson and Carter 1993; Casini et al.

1998). As cogongrass invades an area, all other vegetation is generally excluded,

forming a dense monoculture. The difficulty in managing cogongrass is that all

rhizomes must be completely killed to eliminate cogongrass from an area.

80

Cogongrass is also a detriment to the fire dependent ecosystems of the

southeastern US. Cogongrass is a fire adapted species and retains dead leaf blades

throughout the year, providing a large amount of fuel (Holm et al. 1977). Cogongrass

fires are extremely hot and fast moving, often destroying surrounding trees and native

vegetation (Eussen and Wirjahardja 1973; Seavoy 1975; Eussen 1980). In addition,

these fires are a safety hazard for firefighters and prescribed burn managers. In the past

ten years there has been a greater effort to educate the public about this grass, find

adequate control measures, and prevent the spread of cogongrass to other states in the

US.

Currently the recommended herbicide treatments for cogongrass are 1.64 kg ai ha-

1 imazapyr or 3.28 kg ai ha-1 glyphosate (Shilling et al. 1997; Willard et al. 1997). Both

of these chemicals are non-selective products used to control a wide range of species.

Imazapyr generally provides control for a longer period of time due to its soil

persistence, however off-target damage limits its use to certain areas. Herbicides that

are selective and are least harmful to the environment are important for natural area

managers. Aminocyclopyrachlor is a synthetic auxin herbicide that has been shown to

be highly effective on a wide range of plants and has a much lower use rate than typical

natural area herbicides. In Mississippi, cogongrass control with aminocyclopyrachlor

treatments have been reported, but little work has been conducted under conditions in

Florida (Wright and Byrd 2009). This new herbicide also promises greater selectivity

potential for native plants compared to non-selective herbicides such as glyphosate and

imazapyr.

81

In addition to aminocyclopyrachlor, several herbicide combinations (either

glyphosate or imazapyr mixtures) have been anecdotally tested for cogongrass control

(Willard et al. 1997; Faircloth et al. 2005). Other trials suggest specific additives will

enhance activity of glyphosate or imazapyr (Bennett 2007; Demers et al. 2008; Williams

and Minogue 2008). The additive ‘Cogon-X’ is a combination of seaweed extract and

nutrients that claim to promote deeper, denser roots and temporarily increase

photosynthesis (Ramsey et al. 2006). Previous studies on this additive have had mixed

results when combined with standard rates of glyphosate and imazapyr (Ramsey et al.

2006; Wright and Byrd 2009). However, there has not been a study on ‘Cogon-X’ in

combination with a lower rate of imazapyr, which might also serve as a potential

treatment to gain cogongrass control and native plant tolerance. Therefore, the

objectives of this research were to: 1) evaluate aminocyclopyrachlor alone and in

combination for cogongrass control; 2) evaluate surfactants in combination with

glyphosate or imazapyr for cogongrass control; and 3) evaluate alternative herbicides

for cogongrass control.


Field studies were conducted at Chito Branch Reserve in Hillsborough County,

Florida. Chito Branch is a 2,232 ha reserve purchased in 2001 by the Southwest Florida

Water Management District in cooperation with Tampa Bay Water. The goal of this

purchase was to provide a reservoir for collecting and storing drinking water for the

Hillsborough County area. This unique property consists of a variety of habitats with a

diversity of wildlife and native plant species. An 81 ha tract of Chito Branch, consisting

of abandoned agricultural land, has now become a heavily infested monoculture of

82

cogongrass. The entire area was burned in August of 2009 and all three studies

described here were initiated in October 2009.

All herbicides were applied using an ATV fitted with a CO2 pressurized sprayer

calibrated to deliver 187 L ha-1. Unless otherwise stated, a non-ionic surfactant (0.25%

v/v) was added to each herbicide treatment. Herbicides were evaluated in three

separate studies. The first study evaluated aminocyclopyrachlor alone and in

combination with glyphosate and imazapyr. Treatments included aminocyclopyrachlor at

0.28 kg-ai ha-1, aminocyclopyrachlor at 0.28 kg-ai ha-1 plus imazapyr at 0.32 kg-ai ha-1

or 0.64 kg-ai ha-1, and aminocyclopyrachlor at 0.28 kg-ai ha-1 plus glyphosate at 1.64

kg-ai ha-1 or 3.28 kg-ai ha-1. Treatments also included imazapyr at 0.64 kg-ai ha-1 and

glyphosate at 3.28 kg-ai ha-1 to represent standard application rates.

The second study evaluated imazapic, imazamox, and combinations of glyphosate

with imazapic and imazapyr. Treatments included imazapic at 0.1 kg-ai ha-1 and 0.2 kg-

ai ha-1, imazamox at 0.27 kg-ai ha-1 and 0.54 kg-ai ha-1, glyphosate at 0.25 kg-ai ha-1

plus imazapic at 0.09 kg-ai ha-1, glyphosate at 1.29 kg-ai ha-1 plus imazapic at 0.1 kg-ai

ha-1, and glyphosate at 1.29 kg-ai ha-1 plus imazapyr at 0.64 kg-ai ha-1. Treatments also

included imazapyr at 0.64 kg-ai ha-1 and glyphosate at 3.28 kg-ai ha-1 as standards.

The third study evaluated Cogon-X1, combinations of Cogon-X with glyphosate

and imazapyr, and imazapyr with three types of adjuvants. Treatments included Cogon-

X at 0.64 kg-ai ha-1 alone, Cogon-X at 0.64 kg-ai ha-1 plus glyphosate at 0.64 kg-ai ha-1

1 Stimupro, LLC, Robertsdale, AL

2 Induce, Helena Chemical Company, Collierville, TN

3 Helena Chemical Company, Collierville, TN

83

and 3.28 kg-ai ha-1, Cogon-X at 0.64 kg-ai ha-1 plus imazapyr at 0.32 kg-ai ha-1,

imazapyr at 0.64 kg-ai ha-1 plus a non-ionic surfactant2 and 1% or 2% methylated seed

oil3. Treatments also included glyphosate alone at 3.28 kg-ai ha-1 and 0.64 kg-ai ha-1.

Treatments for all three experiments were arranged in a randomized complete

block design with four replications for each treatment. Plot size was 7.25 x 15 meters.

Visual evaluations were taken every three months based on the following scale: 0 = no

control; 100 = complete control. Rhizomes were collected every six months and used

for a growth study and dry weight data for the aminocyclopyrachlor experiment (Study

1). Three soil cores (10cm2 diameter x 15 cm deep) per plot were collected for rhizome

biomass data. The rhizomes were sorted, dried, and weighed. For the growth study,

three 15 cm rhizomes from each plot were planted in pots in the greenhouse. Shoot

emergence data was collected over a period of 6 weeks.

The data was analyzed using proc GLM program in SAS 9.2. Analysis of variance

(ANOVA) was used to test for treatment by experiment interactions. Means of 4

replications for studies 1 and 2 and 3 replications for study 3 (because of space

constraints) were separated using Fishers Protected Least Significant Difference

Procedure at p < 0.05.


Aminocyclopyrachlor provided 10%-92% less cogongrass control when compared

to glyphosate and imazapyr treatments (Table 4.1). At 24 WAT there was little

difference between all treated plots with injury ranging from 88% to 98%. At 31 WAT,

control of cogongrass was significantly less for the aminocyclopyrachlor alone treatment

(69%) compared to those treatments containing imazapyr. By 58 WAT

aminocyclopyrachlor provided no control and only the imazapyr alone treatment

84

provided greater than 90% control. Glyphosate alone and aminocyclopyrachlor plus the

high rate of imazapyr still showed acceptable (> 75%) control, but all other combinations

with aminocyclopyrachlor were ≤ 54%. However, control from all treatments declined to

unacceptable levels 92 WAT, emphasizing the need for follow-up control measures to

eradicate cogongrass from an area (Holzmueller and Jose 2010; Willard et al. 1996).

The addition of aminocyclopyrachlor to both imazapyr and glyphosate did not

provide increased cogongrass control compared to imazapyr or glyphosate applied

alone. Interestingly, at 58 WAT there was a significant decrease in cogongrass control

in the aminocyclopyrachlor plus 3.28 kg-ai ha-1 glyphosate compared to 3.28 kg-ai ha-1

glyphosate alone (51% and 79%, respectively). This phenomenon of reduced

cogongrass control with the addition of auxin-type herbicides to glyphosate and

imazapyr has been previously documented (Shaw and Arnold 2002; Koger et al. 2007;

Kammler et al. 2010).

Rhizome biomass was also measured over time in this study (Table 4.2). At 36

WAT, all treated plots showed reduced rhizome biomass compared to the control plots.

By 66 WAT all imazapyr and glyphosate treatments, regardless of combinations,

showed a decrease in rhizome biomass by at least 50%. All treated areas showed a

reduction in rhizome biomass over time from 36 to 82 WAT. Imazapyr alone, glyphosate

alone, and aminocyclopyrachlor plus imazapyr at 0.64 kg-ai ha-1 had significantly less

rhizome biomass at 82 WAT (2.9 g, 2.75 g, and 0.90 g, respectively) compared to the

untreated control (13.2 g). The aminocyclopyrachlor alone treatment displayed no

significant decrease in rhizome biomass compared to the untreated areas (9.75 g and

13.2 g).

85

Overall, 0.64 kg-ai ha-1 imazapyr provided the greatest control of cogongrass over

time while also providing a significant reduction in rhizome biomass.

Aminocyclopyrachlor plus 0.64 kg-ai ha-1 imazapyr also provided extended cogongrass

control and reduced rhizome biomass. Conversely, the aminocyclopyrachlor alone

treatment did not provide extended cogongrass control and did not significantly reduce

rhizome biomass. Though aminocyclopyrachlor was shown to suppress cogongrass

(Wright and Byrd 2009) and reduced shoot regrowth in the greenhouse study, it failed to

provide acceptable control in Florida field trials. Differences between the Mississippi and

Florida field studies may be due to genetic variability within the cogongrass populations,

or environmental and edaphic factors (Bryson et al. 2010).

The effect of tank-mix additives with imazapyr or glyphosate herbicide for

cogongrass control was also evaluated. On all evaluation dates, Cogon-X did not

provide significant control of cogongrass when applied alone, and did not significantly

increase cogongrass control when combined with either rate of glyphosate (Table 4.3).

However, Cogon-X combined with a lower rate of imazapyr (0.32 kg-ai ha-1) maintained

greater than 90% control of cogongrass at 92 weeks after treatment. In previous

studies, imazapyr alone at rates lower than 0.5 kg-ai ha-1 showed cogongrass control at

approximately 82% (Faircloth 2007; Johnson et al. 1999; Shilling and Gaffney 1995).

The ability to reduce the application rate of a broad-spectrum herbicide like imazapyr

with the addition of Cogon-X may increase selectivity and allow for faster recolonization

with native species. At 24 and 31 WAT, significant cogongrass control (>80%) was seen

with all treatments of glyphosate and imazapyr regardless of rate or adjuvant used. By

86

58 WAT, only the treatments with the highest rates of glyphosate and imazapyr

treatments provided greater than 70% control of cogongrass.

Though previous research has indicated methylated seed oils can decrease

surface tension and increase herbicidal activity (Miller and Westra 1996), there was no

difference between the non-ionic surfactant and 1% and 2% methylated seed oil for

cogongrass control 92 WAT (98%, 95%, and 94% control, respectively). Overall, the

greatest cogongrass control was seen with imazapyr treatments (≥ 93%). All glyphosate

treatments failed to provide acceptable control 92 WAT, regardless of rate or the

addition of Cogon-X.

The effect of selected imidazolinone herbicides for cogongrass control is shown in

Table 4.4. Significant control (> 75%) of cogongrass was seen at 24 and 31 WAT for

imazapyr plus glyphosate, imazapic plus the high rate of glyphosate, imazamox at the

high rate, and glyphosate and imazapyr alone treatments. By 58 WAT control of

cogongrass for the imazamox at the high rate had dropped below the 75% acceptable

level to 49%. At 92 WAT, the 0.1 kg-ai ha-1 imazapic plus 1.3 kg-ai ha-1 glyphosate

treatment showed significantly greater cogongrass control (80%) compared to all other

imazapic or imazamox treatments (3%- 48%). Imazapyr plus glyphosate (84%),

glyphosate alone (71%), and imazapyr alone (97%) treatments also provided significant

control of cogongrass though not significantly different from the 0.1 kg-ai ha-1 imazapic

plus 1.3 kg-ai ha-1 glyphosate treatment. The use of imazapic plus a lower rate of

glyphosate (1.286 kg-ai ha-1 compared to 3.28 kg-ai ha-1) may provide land managers

with an opportunity to increase selectivity with less damage on certain native grasses

87

which in turn could increase native species recruitment and competition for future

cogongrass regrowth (Faircloth et al. 2005).

The goal of these three separate studies was to evaluate herbicide treatments to

increase selectivity for cogongrass control. Selectivity can be achieved through the use

of new herbicides such as aminocyclopyrachlor (experiment one), herbicide

combinations with reduced rates of imazapyr and glyphosate (experiment two), and the

addition of adjuvants to tank mixes (experiment three). Combining the results from all

three studies, it was found that imazapyr still provided the only long-term acceptable

control of cogongrass. However, study of the use of Cogon-X combined with a low rate

of imazapyr for cogongrass control should be repeated, as this product combination

may allow for reduced rates of imazapyr and increase the selectivity for native species.

88

Table 4.1. The effect of aminocyclopyrachlor treatments on cogongrass control over time in Hillsborough county, Florida

Weeks After Treatment

24 31 58 92

Herbicide Treatment kg ai ha-1 -------% cogongrass control1-------

Aminocyclopyrachlor 0.28 88 69 0 0

Imazapyr 0.64 98 98 92 61

Glyphosate 3.28 98 89 77 35

Aminocyclopyrachlor + Imazapyr

0.28 + 0.64 98 96 79 58

Aminocyclopyrachlor + Imazapyr

0.28 + 0.32 97 95 54 34

Aminocyclopyrachlor + Glyphosate

0.28 + 3.28 97 86 51 28

Aminocyclopyrachlor + Glyphosate

0.28 + 1.64 95 79 18 10

LSD 0.052

8 24 33 36

1Percent visual data based on the following scale: 0= no control; 100= complete death

2Means of 4 replications separated using Fishers Protected Least Significant Difference Procedure at

p < 0.05

89

Table 4.2. The effect of aminocyclopyrachlor treatment on cogongrass rhizome biomass over time in Hillsborough County, Florida.


36 66 82

Herbicide Treatment kg ai ha-1 Average rhizome biomass (g)

Untreated

27.8 30.8 13.2

Aminocyclopyrachlor 0.28 27.1 25.3 9.7

Imazapyr 0.64 18.3 6.5 2.9

Glyphosate 3.28 12.6 6.4 2.7

Aminocyclopyrachlor + Imazapyr 0.28 + 0.64 16.4 6.5 0.9

Aminocyclopyrachlor + Imazapyr 0.28 + 0.32 15.8 10.0 4.1

Aminocyclopyrachlor + Glyphosate 0.28 + 3.28 15.8 9.0 5.2

Aminocyclopyrachlor + Glyphosate 0.28 + 1.64 14.5 14.2 6.0

LSD 0.051

7.9 6.6 7.7

1Means of 4 replications separated using Fishers Protected Least Significant Difference Procedure at p <

0.05.

90

Table 4.3. The effect of surfactants or additives on the activity of glyphosate or imazapyr treatments on cogongrass control over time in Hillsborough County, Florida.


24 31 58 92


Cogon-X 0.64 0 0 3 0

Glyphosate 0.64 87 75 38 7

Glyphosate 3.28 98 99 92 78

Glyphosate + Cogon-X1 0.64 + 0.64 83 82 52 23

Glyphosate + Cogon-X 3.28 + 0.64 98 96 93 67

Imazapyr + Cogon-X 0.32 + 0.64 97 99 98 93

Imazapyr + NIS2 1.64 98 99 100 98

Imazapyr + MSO 1%3 1.64 98 99 70 95

Imazapyr + MSO 2%3 1.64 98 99 100 94 LSD 0.05

5

15 18 18 20

1Stimupro, LLC, Robertsdale, AL

2Induce, Helena Chemical Company, Collierville, TN

3Helena Chemical Company, Collierville, TN



0.05

91

Table 4.4. The effect of selected imidazolinone herbicides on cogongrass control over time in Hillsborough County, Florida.


24 31 58 92


Imazapic + glyphosate 0.09 + 0.25 40 40 8 26

Imazapic 0.1 15 0 3 3

Imazapic 0.2 45 45 21 48

Imazapic + glyphosate 0.1 + 1.29 89 91 81 80

Imazapyr + glyphosate 0.64 + 1.29 98 99 96 84

Imazamox 0.27 61 36 16 5

Imazamox 0.54 93 90 49 30

Glyphosate 3.28 97 86 85 71

Imazapyr 1.64 98 99 99 97

LSD 0.052

31 22 28 32



0.05

92

CHAPTER 5 CONCLUSIONS

Aminocyclopyrachlor is a synthetic auxin herbicide proposed for invasive species

management and native species restoration (DuPont Crop Protection 2010). It is both

foliar and soil active and is effective on a range of broadleaf and brush weedy species

as well as possible selectivity for invasive grass control (Bukun et al. 2008; Claus et al.

2008; Armel et al. 2009; Blair and Lowe 2009; Evans et al. 2009; Gannon et al. 2009;

Montgomery et al. 2009; Roten et al. 2009; Turner et al. 2009; Westra et al. 2009;

Wilson et al. 2009; Rupp et al. 2011). Unlike other herbicides commonly used in natural

areas such as glyphosate and imazapyr, the selectivity of aminocyclopyrachlor provides

the potential for invasive plant control with less damage to desired native species. The

natural ecosystems in Florida are home to over 4000 native plants with 300 endemic to

Florida (Whitney et al. 2010). The mild climate and range of soil types throughout the

state provide for this diverse range of habitats, however these factors are also

conducive to invasive plants (Brown et al. 1990; Anonymous 1999). Over 900 escaped

exotic species exist in the state currently, displacing native plant ecosystems, disrupting

ecosystem functions, and hybridizing with native species (Whitney et al. 2010; FLEPPC

2011). When developing a new herbicide for invasive plant control, it is important to

consider its effects on native species and soil residual effects for restoration scenarios.

Three studies were established to evaluate the effectiveness of

aminocyclopyrachlor for invasive grass control and native plant tolerance. Greenhouse

studies evaluated the post-emergence effects of aminocyclopyrachlor on a variety of

native grasses and broadleaf species as well as five invasive grasses; West Indian

marshgrass (Hymenachne amplexicaulis), cogongrass (Imperata cylindrica), natalgrass

93

(Melinis repens), torpedograss (Panicum repens), and paragrass (Urochloa mutica). All

five invasive grasses initial growth was not reduced at any rate of aminocyclopyrachlor,

however Imperata cylindrica and Urochloa mutica shoot regrowth was reduced by 50%

at 0.09 and 0.15 kg- ai ha-1, respectively. Of the native species evaluated, Eragrostis

elliottii was the most tolerant, and Aristida stricta and Eragrostis spectabilis were the

most sensitive grasses. All broadleaves evaluated except Garberia heterophylla were

highly sensitive to all rates of aminocyclopyrachlor. These results indicate that

aminocyclopyrachlor is selective to both invasive and native grasses evaluated.

Therefore if it is applied to an area that is a mixture of invasives and native species, the

native grasses will tolerate the application while the broadleaves will be highly injured.

In order to determine optimal plant back times for native plant species restoration,

tolerance of several of these native species to soil residual levels of

aminocyclopyrachlor was evaluated. Utilizing plant species injury, optimal plant back

times were determined for these species based on the half life of aminocyclopyrachlor

in a given soil type. Seedlings of several native forbs, grasses, and trees were

transplanted into field plots treated with varying rates of aminocyclopyrachlor. The two

broadleaf species, Liatris spicata and Solidago fistulosa showed greater than 50% injury

at all rates. Pinus palustris was tolerant to rates below 0.16 kg- ai ha-1 and Andropogon

virginicus var. glauca showed no injury to aminocyclopyrachlor. Aminocyclopyrachlor

caused significant injury (>80%) to all other species.

Based on these findings, Andropogon virginicus var. glauca could be planted

immediately after herbicide application. Broadleaf species, Liatris spicata and Solidago

fistulosa, showed injury at all rates regardless of plant back interval. With the exception

94

of Aristida stricta, grasses had the shortest plant back interval ranging from 0 to 194

days. The plant back interval for trees ranged from 73 to 200 days and over a year for

both broadleaf species.

Because cogongrass severely impacts many ecosystems in Florida, a field study

was conducted to investigate the potential for cogongrass control with

aminocyclopyrachlor (Hubbard 1944; Lowe et al. 2004; MacDonald 2009).

Aminocyclopyrachlor was evaluated alone and in combination with imazapyr or

glyphosate and compared to standard treatments. Aminocyclopyrachlor alone provided

good initial control (31 weeks after treatment) but no long term control (92 WAT) of

cogongrass. There was also no advantage of combining aminocyclopyrachlor with

imazapyr or glyphosate. Two additional experiments indicated that neither imazapic nor

imazamox were effective for cogongrass control.

The additive ‘Cogon-X’ and different surfactant types did not influence the efficacy

of glyphosate for cogongrass control, however when Cogon-X was combined with a low

rate of imazapyr, greater than 90% control was observed. Additional studies of the use

of Cogon-X with lower rates of imazapyr are warranted.

Aminocyclopyrachlor can be useful in natural area restoration, as it provides

effective control of numerous invasive plant species (Bukun et al. 2008; Claus et al.

2008; Armel et al. 2009; Blair and Lowe 2009; Evans et al. 2009; Gannon et al. 2009;

Montgomery et al. 2009; Roten et al. 2009; Turner et al. 2009; Westra et al. 2009;

Wilson et al. 2009; Rupp et al. 2011). However it does not appear to offer a unique role

of selectivity and long term cogongrass control in Florida’s natural areas.

95

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BIOGRAPHICAL SKETCH

Anna Lin Greis was born to Linda and John Greis of Tallahassee, Florida. She

grew up in Snellville, Georgia and moved back to Tallahassee her sophomore year of

high school. She graduated from Leon High School in 2005 and began her

undergraduate studies at the University of Florida, Gainesville. In 2009 she graduated

with a Bachelor of Science degree in business with a major in marketing and minors in

landscape architecture and environmental horticulture. Her love for plants and the

outdoors along with guidance from Dr. Greg MacDonald led her to pursue a master’s

degree in weed science. During her studies she has worked for the UF libraries, as a

graduate assistant in weed science, and as a SCEP student for the USDA Forest

Service Southern Regional Office. After completing her Master of Science degree in

agronomy with a minor in forestry, she plans to work for the US Forest Service and

pursue a career in weed science.

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