literature review of teasel (dipsacus fullonum)

7/30/2019 Literature Review of Teasel (Dipsacus fullonum)

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CHAPTER 1: GENERAL INTRODUCTION

1.1 Invasive species

There are three categories of human-induced environmental disturbance: (1)

adverse or inappropriate resource use; (2) pollution; and (3) the introduction of exotic

organisms. While the first two categories pose a serious threat to the environment, they

can be corrected by changing human behavior. On the other hand, even if exotic/invasive

organisms were no longer introduced into new areas, the existing populations would

remain and expand their range. It is unlikely that the introduction of exotic organisms is

going to end. As globalization of the world has increased, the number of exotic plants

introduced into new areas has increased dramatically (Coblentz 1990). This trend will

likely continue (Cronk and Fuller 2001). Given this information, it is unlikely that the

problems associated with exotic/invasive species will disappear in the near future.

1.1.1 Definitions

There are multiple definitions for the term invasive species. The United States

government put forth a definition in Executive Order 13112, as an alien species whose

introduction does or is likely to cause economic or environmental harm or harm to human

health (Clinton 1999). In 2006, the National Invasive Species Management Plan

(NISMP) further clarified that definition by defining an invasive species as a species


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that is non-native and whose introduction causes or is likely to cause economic or

environmental harm or harm to human health (ISAC 2006, 1). While these definitions

illustrate the potential problems with invasive species, they do not cover the mechanism

behind their spread.

The scientific community has offered definitions that more fully cover the

ecosystemic processes and mechanisms behind the spread of invasive species. Cronk and

Fuller (2001) give a definition of invasive plants as an alien plant spreading naturally

(without the direct assistance of people) in natural or seminatural habitats, to produce

significant change in terms of composition, structure or ecosystem processes (1). While

this definition points to the problem of invasive plants spreading naturally, it gives no

consideration to the scale of distribution. According to Richardson et al. (2000), the main

difference between a naturalized plant and an invasive plant is the extent which the

species can spread. They define invasive plants as naturalized plants that produce

offspring, often in very large numbers, at considerable distances from parent plantsand

thus have the potential to spread over a considerable area (Richardson et al. 2000, 98).

While these definitions include the ecological problems and/or the dispersal methods of

invasive plants, they do not cover the economic and social issues surrounding invasive

plants as the government definitions do. For this paper the following definition for an

invasive plant will be used. An invasive plant is a non-native plant, capable of spreading

great distance and establishing itself naturally; that poses a serious threat to the economic,

environmental, and/or social stability of an area.


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1.1.2 Problems

There are many problems associated with the spread of invasive species. The

economic costs from the loss of agriculture productivity and the effort spent eradicating

these species are great. According to the National Invasive Species Council (NISC),

invasive species cost the United States $125 billion annually (Baker 2001). A study done

by Mack et al. (2000) found that invasive species cost the nation $138 billion dollars

every year. This is in line with a study done by Pimentel et al. (2000). They put the

losses at $137 billion dollars per year, not including the potential monetary losses due to

the degradation of ecosystem functions, possible species extinctions, and aesthetics

issues. Exotic plants add up to $34 billion of that figure (Pimetel et al. 2000). An

introduced blight species from China was responsible for the destruction of 1 billion

American chestnut (Castanea dentata (Marsh.) Borkh.) trees in the early 1900s. This

disease not only affected the aesthetics of many towns, it significantly affected the

ecosystem functions of our forests (McNeely 2000). These are examples of the multiple

problems associated with invasive species.

There are many different ways invasive species affect the functioning of

ecosystems. Competition from invasive species has been cited as the second most

common factor that cause another species to become endangered (Wilcove et al. 1998).

This intense competition can cause a diverse ecosystem to be replaced by a monoculture

of an exotic plant. It can also cause native flora or fauna to be reduced to population

levels too low to be sustainable (Cronk and Fuller 2001). Invasive species not only

compete for resources, but they can also fundamentally alter the ecosystem so that native

species cannot find the resources needed to remain alive. In a study on the effects of


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invasive species with relation to the function of ecosystems in Florida, Gordon (1998)

found that 39 to 64% of the 31 invasive species studied could potentially alter the

geomorphology, hydrology, biogeochemistry, and disturbance regimes of their

representative ecosystems. Additionally, invasive species have been found to alter the

fire regime, nutrient cycling, and energy budgets of native ecosystems (Mack et al. 2000).

While change in ecosystem functions is a normal process, the problem lies in the rate and

direction of change that stems from invasive species introduction (Cronk and Fuller

2001).

1.2 Invasive Plant Species

1.2.1 History

Invasive plant species have been both accidentally and deliberately introduced

into the locations where they have become a problem. While a majority of the plants that

have been introduced into North America have not caused problems, a small number of

plants escaped and became invasive (White 2001). Since the 1800s, the rate of

introduction has increased dramatically, causing the cumulative numbers of invasive

species present to expand rapidly (Wilcove et al., 1998). Invasive plants have reached

new areas in many different ways. They have found transport in the ballast of ships, as

was the case with purple loosestrife (Lythrum salicaria L.) (Cox 1999). Some plants

were brought to North America for erosion control. For instance, Kudzu (Pueraria

montana (Lour.) Merr.) was first showcased at the 1876 United States Centennial

Exposition. Soon thereafter it was in use for erosion control due to its ability to grow

rapidly. The widespread planting by government agencies soon brought disaster, as it


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began to grow uncontrollably, often covering trees and buildings (Meyers and Bazely

2003). Still other plants have made their way here through botanic gardens, the

horticulture industry, and individuals (White 2001). In the United States, 235 woody

plants have been introduced as ornamentals, and 82% of these are now considered

invasive (Myers and Bazely 2003). The introduction of plants began on the eastern

seaboard as people from other countries moved to the New World. The introduction of

plants spread throughout the rest of the country as people built roads and railroads to

move to new areas (Cox 2004).

1.2.2 Examples of Invasive Plant Species

There many examples of invasive species that have been introduced into North

America. In the 1600s Kentucky bluegrass (Poa pratensis L.), a native of Eurasia, was

introduced into North America. It spreads mostly by rhizomes, but occasionally produces

a large quantity of seed. It has since become an invader of prairies and montane

meadows. It is still a popular turfgrass of lawn and pastures due to its tolerance of

repeated mowing or grazing. This provides the plant with more pathways of introduction

into new areas. Another aggressive invader of prairies, pastures, and cropland is Canada

thistle (Cirsium arvense (L.) Scop.). It, like Kentucky bluegrass, is a native of Eurasia. It

can out-compete native plants in these areas, often forming dense mats of vegetation. It

has rapidly developed resistance to herbicides and is so prolific that eradication would be

impossible (Cox 1999). Another invasive plant that was introduced to North America is

the Melaleuca tree (Melaleuca quinquenervia (Cav.)Blake). It was planted in Florida by

a forester in 1906 in an effort to reforest the Everglades. The seeds were even broadcast

from a plane to speed up the expansion of its range. It rapidly invades swamps, dry and


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wet flatwoods, and the transition zone between pine forests and cypress swamps (Cox

1999). It is currently on the Federal Noxious Weed List, as well as nine state noxious

weed lists (USDA-NRCS 2007).

1.2.3 Ecological Processes Behind Plant Invasion

Cronk and Fuller (2001) have divided the process of invasion into six steps: (1)

introduction, the translocation of the plant to a new site; (2) naturalization, the

establishment of the plant outside of the site of introduction; (3) facilitation, a genetic

change or suitable propagule distributor that increases the likelihood of spread; (4)

spread, the process of increasing habitat range; (5) interaction with animals and other

plants, the method by which the plant incorporates into the new ecosystems; and (6)

stabilization, the time when a species finds a new niche, whether it is as a monoculture,

or as the main component of an ecosystem. The above steps are the ideal method for a

plant to become established (Cronk and Fuller 2001). There are many constraints that

can prevent a plant species from moving from one step to the next. For instance, an

introduced plant can have reproductive issues. This would prevent the plant from

naturalizing in an area. A naturalized plant could encounter a barrier in propagule

dispersal, therefore it would remain only naturalized in one local area and would not be

able to spread. A plant that is in the process of spreading could enter a habitat in which a

predator or another aggressive plant exists and this could prevent the new plant from

establishing itself in that habitat. These interactions could have the potential to stop the

invasion of the plant, thus making the plant just a naturalized species, not an invasive one

(Richardson et al. 2000).


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1.2.4 Long-distance Dispersal Events

Long-distance dispersal events and the effects of corridors can increase the

likelihood that a plant will become invasive. Nubert and Caswell (2000) found that long-

distance dispersal events, even when rare, were the major component of invasion speed.

They suggest that more attention should be paid to the factors that govern long-distance

dispersal when studying the invasiveness of plants (Nubert and Caswell 2000). Long-

distance dispersal events are aided by corridors. There are four types of corridors: (1)

line corridors; (2) strip corridors; (3) stream corridors; and (4) networks of corridors

(Godron and Forman 1983). These corridors can increase the speed and range that plants

invade by providing suitable habitat in which the plants can grow, reproduce, and spread.

Roads are a widely used corridor for invasive plants due to our management methods of

them. The frequent mowing and upkeep road right-of-ways provides open areas for

invasive to establish themselves. Additionally, salt-tolerant invasive species can thrive in

the conditions alongside roads due to winter maintenance (Myers and Bazely 2003).

Traits of known invasive species, such as a tolerance to saline conditions, can be helpful

in identifying which plant have the potential to become invasive.

1.2.5 Traits of Invasive Plants

There are general traits of plants that can help determine if a plant will become

invasive. Baker (1974) cited five traits of invasive plants. These are: (1) rapid initial

growth rate; (2) ability to interfere with the growth rate of neighboring plants; (3) high

seed output; (4) morphological similarity to native species; and (5) self-pollination and

outcrossing (Baker 1974). While these traits can be found in many invasive plants, there

are many studies that show that these characteristics do not always predict invasiveness


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(Myers and Bazely 2003). It may not be possible to use general traits to predict the

possibility of invasiveness across all habitat types. It might be more accurate to examine

the traits of invasive species associated with particular habitat types (Cronk and Fuller

2001).

Cronk and Fuller (2001) have divided the habitat types exploited by invasive

species into four general categories: (1) aquatic habitats; (2) forest and open-woodland

habitats; (3) fire-vulnerable habitats; and (4) open habitats. The average aquatic invasive

plant can tolerate a wide variety of aquatic conditions. They can grow rapidly, mostly

through an effective method of vegetative reproduction. They are free-floating or

emergent herbaceous perennials. Plants that invade woodlands and forests habitats are

often small shrubs or trees. They have a high seed production, with birds as their

dispersal mechanism. Generally they grow rapidly and reach reproductive maturity early

in their life. The typical invasive plant in fire-vulnerable habitats often promotes an

increase in fire frequency. They are herbaceous plants with either high vegetative

reproduction or high seed production rates. The seeds have mechanisms to survive fire

and are usually light and wind dispersed. Plants that invade open habitats are generally

herbaceous perennial herbs or small shrubs. They have high seed production and are

wind-dispersed. They reach reproduction maturity early and can often reproduce

vegetatively (Cronk and Fuller 2001). A study by Smith and Knapp (2001) found that

invasive plants of tallgrass prairies do not differ from native plants with respect to

resource utilization and carbon gain. This is contrary to many predictions about the

characteristics of invasive plants in open habitats (Smith and Knapp 2001). Additionally,

invasive plants of central grasslands of the United States have been found to prefer areas


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rich in native plant diversity instead of areas with little to no plant diversity or cover.

This is due to the favorable conditions in which native plants thrive (e.g. abundant

nutrients, water, and light) are often the best conditions for invasive plants (Stohlgren et

al. 2002). These unexpected results show that more long-term studies on predicting the

relationship between invasives and their environment must be undertaken for prediction

models to become fully developed (Committee on the Scientific Basis2002).

1.2.6 Predicting Invasions

Predicting whether or not a plant will become invasive is an important aspect of

managing natural resources. The Committee on the Scientific Basis for Predicting the

Invasive Potential of Nonindigenous Plants and Plant Pests in the United States (2002)

created a report outlining the pathways and processes behind the invasion of plants. They

created four conclusions on the current state of knowledge about predicting plant

invasions. The first conclusion was that the record of a plants ability to be invasive in

other geographic areas is the most reliable predictor of invasiveness. The second

conclusion was that there is no reliable procedure for identifying invasive plants. The

third conclusion is that the inability to predict the invasive potential of plant stems from a

lack of scientific knowledge. The last conclusion was that while some data on the natural

history of invasive plants exist, these data need to be organized in a systematic way so

that proper analysis can occur. To increase our ability to predict invasions they suggest

that standardization of methods and the increasing the number of long-term studies on

invasability must happen before any further steps are taken (Committee on the Scientific

Basis2002).


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1.3 Control Methods

The problems that invasive species pose for the stability of the economical, social,

and environmental aspects of an area dictate that control measures must be undertaken.

Predicting invasions and preventing invasive species from being established is the most

effective control method (Naylor 2000), but this is not always possible (Committee on the

Scientific Basis 2002). Additionally, many invasive species are already established,

therefore the time to prevent these species from becoming entrenched has already passed.

When the control of invasive species is the only option, a plan tailored to the specific

invasion must be developed (Cronk and Fuller 2001).

1.3.1 Planning for Control

Planning before the implementation of control methods is a necessary measure in

order to not only reduce the negative effects upon the areas under control, but to also

reduce the chance that control efforts will fail (Cronk and Fuller 2001). Proper planning

should include a broad idea of the scale and scope of the problem; this will reduce the

possibility that funds or other resources will run out before the project is completed

(Myers and Bazely 2003). Planning should begin by deciding what species is to be

controlled, where it is going to be controlled, and the proper control methods for working

at controlling that species (Cronk and Fuller 2001). The next decision in proper planning

is to decide whether continual maintenance or complete eradication is the end goal.

1.3.2 Eradication vs. maintenance

There are two strategies for the control of invasive species, eradication and

maintenance (Mack et al. 2000). Eradication can be a feasible option, especially when

the species is detected early and resources can be applied quickly (Simberloff 1997,


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Hobbs and Humphries 1995). This is often possible right after an introduced species

begins to naturalize, but before it begins to spread into other areas (Sakai et al. 2001).

There are three key factors that contribute to the success of eradication. The first is that a

proper method is used to remove the species. The second is that sufficient resources are

allocated to the removal of the species. The last factor is that widespread support from

both the agencies involved in the removal and the public at large is provided. Often

though, detection of invasive species is hindered by the time and resource allocation it

takes to effectively monitor areas. This causes invasive species to be detected when they

have reached numbers too high for eradication to be feasible. At this point, maintenance

control might be the only realistic option (Mack et al. 2000).

1.3.3 Control Method Options

There are four options for the control of invasive species: physical, environmental

management, biological, and chemical. These methods are often used in combination

with each other (Cronk and Fuller 2001). For instance, cheatgrass (Bromustectorum L.)

can be controlled by using repeated herbicide treatments and intensive grazing (Whitson

and Koch 1998). There are benefits and detriments associated with each method. Some

invoke a negative public opinion, while some require large amounts of resources for

implementation. There are also proper timings for each type of use, and to use them at

the wrong time can actually hurt control efforts. In order to decide which method is the

best for the situation, the pro and cons of each method must be known and weighed

(Mack et al. 2000).


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1.3.3.1 Physical Control Methods

Physical control consists of pulling, cutting, digging, or mowing invasive plants.

It is very labor-intensive and can be more effective when large groups are working

together (Cronk and Fuller 2001). It is often employed with volunteer groups because of

the lack of specialized training needed for implementation (Meyers and Bazely 2003).

While physical methods are effective at controlling some species, they do not work on

every species. Some species will resprout after cutting; others will send out rhizomes

when mowed. Many aquatic weeds can never be completely removed and the

disturbance associated with attempting physical removal can actually encourage the

remaining plants to grow (Cronk and Fuller 2001). Physical methods can work well in

isolated areas, but if propagules of the invasive species are somehow able to be

reintroduced, this method would not be worthwhile due to the amount of resource

allocation necessary for repeated applications (Meyers and Bazely 2003). Fire is another

method of physical control that crosses into the category of environmental management,

so it will be discussed in that later section.

1.3.3.2 Environmental Management Control Methods

Environmental management control is a broad term that encompasses any changes

to ecosystem properties that reduce the dominance of invasive species. This can include

restoration of the hydrologic cycle, changes in nutrient availability, or alteration of the

fire cycle (Cronk and Fuller 2001, Perry et al. 2004). The restoration of the hydrologic

cycle in a salt-affected wetland in Kansas was shown to significantly increase the cover

of some native species, as well as exotic species. Additionally, it significantly reduced

the amount of bare ground and increased the amount of a nativeEleocharis species in


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playa lake communities (Kindscher et al. 2004). In a greenhouse experiment, changes in

the availability of inorganic nitrogen in carbon-enriched wetland soils have been shown

to reduce the competitive effect ofPhalaris arundinacea L. (Perry et al. 2004). The

alteration of the fire cycle can have differing effects on both native and invasive plant

communities. Fire disturbance can both inhibit and promote growth of native and

invasive plants (Grace et al. 2001). Burning has been shown to significantly reduce the

number of garlic mustard (Alliariapetiolata (Bieb.) Cavara and Grande) plants in a

woodland in Illinois (Nuzzo 1991). Additionally, invasive plants can suppress the ability

of fire to burn, reducing its effects as a control method (Grace et al. 2001). All

environmental management techniques require that managers have intimate knowledge of

the interplay between invasive species, the native species, and their representative habitat,

so that native plant communities are not harmed by the process (Cronk and Fuller 2001,

Zavaleta et al. 2001).

1.3.3.3 Biological Control Methods

Biological control (biocontrol) is essentially an aspect of ecological control, but

because it specifically uses predator/prey relationships, it will be dealt with separately.

Biocontrol consists of using the natural enemies of a species to reduce their number. For

plants, the vector of control is typically insects, but mites, nematodes, fungi, bacteria, or

viruses can be used as well (Coombs et al. 2004). A biocontrol project often takes many

years to come to fruition due to permitting, screening for detrimental effects, and the

amount of time it takes an introduced species to grow into a large enough population in

order to have an effect on the target species (Myers and Bazely 2003, Coombs et al.

2004). The most critical aspect of the biological control of plants is the host-specificity


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of the control vector. There have been instances where organisms were introduced with

little regard to host-specificity. This had disastrous effects on some non-target species,

but now there is extensive legislation to reduce the possibility that this will not happen

again (Cronk and Fuller 2001). The classic approach to biological control is to introduce

an organism into an area where it does not naturally occur and let the populations grow

on their own, all the while attacking the target plant. One example of traditional

biological control is the introduction of a weevil (Rhinocyllus conicus) [Coleoptera:

Curculionidae] to control musk thistle (Carduus nutans L.). The weevil was introduced

in Virginia between 1969 and 1972. A study on the effectiveness of this agent found that

by 1975 it was attacking 90% of the thistle plants in the area, causing over 10% of the

terminal flower heads to be aborted (Kok and Surles 1975). Another biocontrol approach

that is not as widely used is the bioherbicidal method. In this method, biological agents

are grown and applied to target species like an herbicide treatment. This method is not as

cost-effective as the classical approach due to the cost of specialized equipment, but it

takes less time to see results. In general, biocontrol is being used more often due to the

relatively low costs to control species over a large area as compared to physical,

chemical, and ecological methods, but is often overlooked due to the extensive planning

associated with it (Coombs et al. 2004).

1.3.3.4 Chemical Control Methods

Chemical control of invasive plants consists of using an herbicide to alter or

inhibit the growth of the plant, causing the plant to die or become incapable of

reproduction (Peterson et al. 2001). There are multiple ways to employ chemical control

methods. Individual invasive species can be isolated and targeted for removal. Large


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areas of mixed plant composition can be targeted to either kill every species present, or to

favor some species over others (Cronk and Fuller 2001). Herbicides can also be used to

cause a disturbance that shifts plant composition to a more desired state (Krueger-

Mangold et al. 2006, Radosevich and Holt 1984). There are many potential issues

associated with the use of herbicides. Targeting individual plants can be costly and time

consuming; often multiple applications are necessary. Applying herbicides to large areas

can cause non-target organisms to be affected, often hurting the species that are supposed

to be helped (Cronk and Fuller 2001). Large-scale use of herbicides can lead to an

increase in herbicidal-resistant plants that will then need to be controlled using another

technique (Radosevich and Holt 1984). Additionally, if treatments do not completely

eliminate the target invasive, the plant will often re-establish itself in the area (Cox 1999).

If herbicides are used for plant control, an understanding of how they work is needed so

that the proper herbicide is selected for use (Peterson et al. 2001).

1.3.3.4.1 Modes and Sites of Action of Herbicides

Herbicides vary widely in their modes of action and their sites of action. The

mode of action for herbicides is defined as all interactions between the herbicide and the

target plant. This encompasses everything from application and absorption, to the

physiological response of the plant to the herbicide. Herbicides can affect different

processes of the target plant, but often they affect a process necessary for normal growth

and development. The site of action is the specific area of a plant affected by the

herbicide. Some will affect shoot growth, while others cause changes to normal hormone

production. Herbicides can vary in selectivity, some affect only broadleaf plants or

grasses, while others will kill any plant. Some herbicides are used before seedling


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emergence, some after. Some herbicides are translocated within the plant to cause

changes, while others cause effects by contact. Contact herbicides, as their name

suggests, must come in contact with the site of action (Peterson et al. 2001). For

instance, Scythe disrupts the normal plant processes in the leaves it comes in contact

with, causing burndown, leaving the below ground plant parts intact (Mycogen

Corporation 2004). Systemic herbicides can be applied to different plant surfaces and

then are translocated to the site of action. Knowledge of where and how an herbicide

works is necessary in order to select the proper herbicide and select the correct method of

use (Peterson et al. 2001).

1.3.3.4.2 Herbicidal Methods of Application

Herbicides can be applied to target plants in a multitude of ways. The application

method chosen is dictated by the size and growth type of the species, as well as

equipment availability. For low-growing herbaceous species, a foliar application is often

used. This can range from a single person using a backpack sprayer in small land areas,

to aerial spraying of larger areas to remove large swaths of pest plants. Foliar application

can often result in non-target species being affected, due to herbicidal drift. This can be

avoided by using a weed wand, a hollow pipe with a wick on the end. Woody species,

especially larger specimens, require different approaches in order for control methods to

be effective. Often foliar spraying will not kill woody species after a single application,

making this method less efficient due to repetition of control measures. Cutting down the

plants and applying herbicide to the cut stumps is one method of woody plant control.

This is only effective if the herbicide is applied quickly to the living sapwood of the

plant, otherwise the plant will not absorb the herbicide into the sapwood. Herbicide can


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also be applied to living trees by ringing or notching the tree and applying the herbicide,

or injecting the chemical straight into the sapwood. These methods ensure that the plant

takes up the herbicide, unlike the cut-stump method (Cronk and Fuller 2001).

1.3.3.5 Integrated Control Methods

Often it is necessary to use multiple methods of control in tandem to achieve the

desired results. This is one aspect of Integrated Pest Management (IPM), a specific

integrated control method. IPM uses a variety of cultural, biological, and chemical

techniques to reduce pest problems (Krischik and Davidson 2004). This method of

controlling pest species began as a way to protect plants from insects and pathogens

(Kogan 1998), but it has been adopted as a method for controlling invasive plants

(Britton 2004). A study done on the control of yellow starthistle (Centaureasolstitialis

L.) found that burning the plant in the first year and then applying the herbicide

clopyralid in the second year provided the best control (DiTomaso et al. 2006). Another

study done in Wyoming found that cheatgrass (Bromustectorum L.) can be controlled by

using repeated herbicide treatments along with intensive grazing, while native grass is

actually encouraged to grow (Whitson and Koch 1998). These examples illustrate the

potential for integrated pest management to control invasive plants.

1.4 Description ofDipsacus fullonum L.

1.4.1 Nomenclature

Dipsacus fullonum L.Fuller's teasel, common teasel, teasel. Kingdom: Plantae;

Subkingdon: Tracheobionta; Superdivision: Spermatophyta; Division:Magnoliophyta;


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Class:Magnoliopsida; Subclass:Asteridae; Order:Dipsacales; Family:Dipsacaceae

(USDA-NRCS 2007).

The nameDipsacus fullonum L. is the current binomial used by United States

Department of Agriculture, Natural Resources Conservation Service. They also

recognize three synonyms: (1) D. fullonum L. ssp.fullonum L.; (2)D. fullonum L. ssp.

sylvestris (Huds.) Clapham; and (3)D. sylvestris Huds. (USDA-NRCS 2007). D.

sylvestris Huds. is the most common binomial found in the literature, especially in North

American publications (Werner 1975d). In order to remain consistent with the USDA-

NRCS, the binomialD. fullonum L. will be used here.

1.4.2 Species Description

Common teasel (Dipsacus fullonum L.) is a monocarpic perennial, meaning that

upon reaching a certain size, it flowers once and then dies (Czarapata 2005). It is often

mistaken for a biennial due to its ability to flower and die in two years. Actually, it can

remain as a vegetative rosette for up to five years before flowering (Werner 1975b). It

produces a low, almost prostrate vegetative rosette up to 60 cm in diameter. The rosette

persists throughout winter. The leaves of the rosette are lanceolate to oblanceolate, entire

or undulate, with rigid spines on the underside of the midrib and smaller spines on the

surface of the leaf. It has a thick taproot that can exceed 75 cm in depth. Once a rosette

diameter of 30 cm is reached and a subsequent over-wintering has occurred, the plant will

form a flowering stem 0.5 to 2.5 m in height. The flowering stem is pithy or hollow with

opposite branching, often forming multiple branches. The stems can persist for up to two

years, long after the rosette has died. The leaves on the flowering stem are opposite,

basally connate, and form a cup that catches rainwater (Dipsacus originates from a Greek


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word meaning thirst). Each branch ends in a cylindrical flowering head (capitulum).

Each capitulum is 2.5 - 10 cm long, surrounded by multiple bracts, arranged in groups of

five. The bracts are spiny, upwardly curving, with the outermost set reaching above the

capitulum. The receptacle bracts of the flowers are ovate to lanceolate, ending in a awn

that extends beyond the flowers (Werner 1975d). The flowers resemble a white tube with

four purple lobes at the end of the tube. There are four stamens that alternate with the

lobes. A reduced calyx encircles the flower at the base and adheres to the inferior ovary

(epigyny). The flowers are arranged in a low spiral on the capitulum, so that they appear

to be arranged in diagonal rows. The flowers begin blooming in the middle of the

capitulum and continue both upward and downward along the flower head, a unique trait

of this genus (Jurica 1921).

Figure 1.1. Picture of common teasel rosettes (Dewey 2006).


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Figure 1.2. Line drawing of vegetative growth, inflorescence, flowers, and achene of

common teasel (Britton and Brown 1913).


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1.4.2.1 Reproduction

D. fullonum produces flowers from July to September. Each teasel capitulum can

produce hundreds of flowers, each of which produces a single seed (achene). The

achenes are 4 to 5 mm in length, slightly four-angled, and grayish brown in color. Since

teasel plants have multiple flower heads, a single plant can produce up to 3,000 seeds

(Werner 1975d). The seeds have no adaptations for wind or animal dispersal. Most fall

passively from the plant, with over 99% of the seed falling within 1.5 m of the parent

plant (Werner 1975a). This adaptation is especially useful because the new seedlings can

take advantage of the bare ground left by the dead parents rosette (Solecki 1993, Werner

1977). Additionally, seeds have been shown to float on water, providing a method for

long distance dispersal. Germination studies have shown that seeds floating in water

after 16 days still had the ability to germinate. This accounts for the plants spread along

waterways (Werner 1975d). Humans can also provide another mechanism for long-

distance dispersal. The mowing of mature seedheads has been shown to throw the seed

farther than they would have fallen naturally (Cheesman 1998).

D. fullonum germinates from April to June. Teasel germination rates vary greatly

between greenhouse studies and natural conditions. In one greenhouse study, fresh seed

germination rates were 99.7% 0.6. Additionally, the time to 50% germination was four

days for fresh seed and seven days for two-year old seed (Werner 1975d). The rates of

germination in successional fields have been shown to be variable, based on the amount

and type of surrounding plant matter. One field study showed that common teasel had a

28 to 86% germination rate within two years of seedling introduction. The field with

28% germination rate had a thick cover of quackgrass (Agropyron repens L.), while the


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field with the 86% germination rate had sparseA. repens cover and large patches of bare

ground (Werner 1972). This illustrates the fact that leaf litter presence affects

germination. As shown from the above germination rates,A. repens plant litter can

suppress germination of teasel seed greatly (Werner 1975c). Litter from other plants,

such as Kentucky bluegrass (Poa pratensis L.), as well as many other forbs, has been

shown to reduce germination up to 41% (Bosy and Reader 1995). Despite these modes

of suppression, the high rate of germination and the high number of seeds per plant

provide a recipe for invasiveness.

Figure 1.3. Picture of common teasel flowering (Alexander 2007).


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1.4.2.2 Invasiveness and Competition

D. fullonum is native to Eurasia and Northern Africa, having been brought to

North America for use as a tool used in yarn production and as a dried ornamental plant

in flower arrangements (Rodale 1984, Werner 1975d). It is distributed throughout much

of the contiguous United States (Solecki 1993). Currently it is present in every

contiguous state except Georgia, Florida, Louisiana, Maine, Minnesota, North Dakota,

and South Carolina. It is listed as a noxious weed in Colorado, Missouri, Iowa, and New

Mexico (USDA-NRCS 2007). Teasel is found on many different soil types, from sandy

soil with abundant moisture, to heavy clay soils. It has a moderate-salinity tolerance, and

can therefore thrive in roadside conditions. Both roadsides and cemeteries, where its

presence is contributed to flower arrangements, act as depositories for teasel populations.

From these refuges, it can invade natural areas (Solecki 1993). It has the capacity to

cover prairies, sedge meadows, seeps, and savannas in the Midwestern United States, as

well as waterways in the more arid climates of the Southwest United States (Solecki

1993, Glass 1991, Huenneke and Thomson 1995).

As with all plants, teasel has effects on the growth and development of other

plants living in close proximity; and these plants affect the growth and development of

teasel. The number of established plants after germination will dictate the effects on

surrounding community members. In one field experiment, Patricia Werner (1977)

introducedD. fullonum into habitat types with varying amounts of grass cover,

herbaceous dicot cover, and shade levels. She found that the growth rates of teasel plants

in areas with moderate levels of both grasses and dicots and no shade cover were

relatively quick, with plants reaching flowering stage in the 2nd and 3rd years. In areas


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with low levels of grass, high levels of dicots, and no shade cover, teasel established

quickly, but had slower growth rates, often taking up to four years to flower. In areas

with dense grasses and no dicots or shade cover, and areas with low grasses, high dicot

cover amounts, and high shade cover, teasel could not establish itself, with plants dying

shortly after germination (Werner 1977). These levels of establishment point to a model

that suggests that the growth rates of teasel populations can be reduced by shade and the

success of the rest of the plant community (Werner and Caswell 1977). Werner (1976)

showed that teasel can reduce the net primary production (NPP) of established

herbaceous dicots, but not that of the established grasses. This can be attributed to the

fact that the grasses tested had shallow roots, while the dicots and the teasel plants had

deeper root systems. Once the roots of a teasel plant reach below those of the grasses,

they are effectively out of competition for nutrients and water. The opposite holds true

for the herbaceous dicots tested. Their roots grow to the same levels as the roots of teasel

do, thus putting them in direct competition (Werner 1976). The ability of the roots to

compete for water and nutrient resources is just one of the mechanisms of competition

that allows teasel to thrive in certain conditions.

Common teasel has many mechanisms that help it out-compete its neighbors. Its

horizontally oriented leaves produce heavy shade beneath them. Its taproot extends

deeper than many of the grasses around it, reaching deeper water sources. It produces a

large amount of seed, up to 3,000 seeds per plant. Once a seedling has established itself,

it has an increased chance of survival due to its hold on resources (Werner 1975d).

Teasel colonies can completely cover an area, so much so that the leaves of the rosettes

can be packed so tightly that they are forced to grow upwards instead of horizontally


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(Werner 1977). These dense colonies can remain present in an area for an extended

period of time. One population in Michigan has been present for over 25 years (Werner

1975d). The ability to remain established in a site stems from the fact that when the

parent plant dies it provides an open site for germinating seedlings. If no teasel seeds are

available, often short-lived winter annuals will inhabit the area, allowing the germination

space to be opened again in the spring (Werner 1977). This mechanism of population

growth allows colonies to expand, often forming large monocultures that exclude native

vegetation (Glass 1991).

1.4.2.3 Long-distance Dispersal of Dipsacus fullonum

As was illustrated in an earlier section, long-distance dispersal events can have a

major effect on the invasiveness of a species. Teasel is no exception. There have been

reports of birds eating seed, possibly being a vector for long-distance dispersal (Pohl and

Sylwester 1963). Laboratory experiments have shown that teasel seeds can float for up to

16 days and still germinate, making water dispersal ideal for longer distances (Werner

1975d). Additionally, between 1877 and 1900 common teasel had migrated from

Niagara Falls, Ontario to the east coast of North America. This corresponds to a

movement of around 27 km/year (Nuebert and Caswell 2000). This rate is much faster

than that calculated from population models done by Neubert and Caswell (2000). They

state that while the probability of such long-distance dispersal events occurring is low, it

is certainly not impossible. For instance, a seed would have to only float in a river

flowing at 0.5 m/s to cover 21 km in 12 hours. They also suggest that multiple

introductions ofD. fullonum could be responsible for the quick movement rates (Nuebert

and Caswell 2000).


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1.4.2.4 Case Study on Invasiveness

Huenneke and Thomson (1995) provide a study on the changes of teasel

distribution in central New Mexico and how this is affecting a federally threatened native

thistle (Cirsiumvinaceum Woot. and Standl.). They examined habitat requirements of

the two species by surveying existing populations in 1990 and 1993. They also looked at

the outcome of competition between the two species using both greenhouse and field

experiments. There was an increase in the majority of the existing teasel populations

surveyed. Additionally, there was not a single case of an existing teasel population

becoming extinct between the two survey times. Overall, teasel increased its

representation in the thistle habitat. In the greenhouse experiments, they planted both

species using a deWitt replacement series. They found that while teasel had a significant

negative effect on the growth ofC. vinaceum, the thistle had no effect on the growth of

teasel. In the field experiments, they randomly created 0.25 m2

plots that contained a

desired amount of thistle and a desired amount or more of teasel. Teasel numbers were

thinned to reach the desired amounts of plants, but since the thistle is a threatened

species, these plants could not be thinned. Replicate plots were established with: 100%

thistle; 75% thistle, 25% teasel; 50% thistle, 50% teasel; 25% thistle, 75% teasel; and

100% teasel. Most of the tested variables had no significant effect. Teasel did show

significantly lower growth rates when it was a minority, but the researchers cite low

replication numbers for the inconclusiveness of the data. Despite this reduction on the

growth of teasel, the authors state that there appears to be substantial potential for

interference effects of teasel on the threatened Cirsiumvinaceum (Huenneke and

Thomson 1995, 423).


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1.5 Control Methods of Common Teasel

1.5.1 Current Literature

While there is some information available about the control of common teasel,

what is available is anecdotal, with no scientific study supporting the findings. Glass

(1991) uses knowledge from Illinois natural areas managers to put forth a few

recommendations for control. The only specific recommendation for herbicide control is

to use Roundup at 1.5% concentration during the late fall or early spring. He also

states that the herbicides 2,4-D and triclopyr can be used for control, but he gives no

concentration guidelines. Solecki (1993) recommends that periodic late spring burns

could control isolated rosettes, though they could be unaffected if the fire does not reach

a high enough temperature. Even a hot fire has no effect on large clumps of teasel

because of the absence of dead plant material to burn (Glass 1991, Solecki 1993).

Digging up teasel plants can be effective in areas of small infestation, but plants can grow

back if not enough root is removed (Glass 1991). Werner (1975d) suggests that repeated

cutting of flowering stems prior to flowering can reduce population effectively, but if the

stems are not cut low enough, the plants can resprout flowering stems (Glass 1991).

Additionally, seed from the seedbank, as well as imported seed from nearby plants, can

cause new plants to germinate. For these reasons, stem cutting has to be closely

monitored and may have to be repeated for several years for this method of control to

work (Glass 1991). Mowing a teasel infested area can actually increase the amount of

teasel plants by increasing potential germination sites, as well as spreading the seed

farther than it would have normally reached (Cheeseman 1998). Additionally, mowing

must be repeated many times due to the possibility of the flowering stems resprouting


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(Glass 1991). While there are some recommendations for control in the literature, there

has not been a quantitative study on the effects of herbicidal control of teasel.

1.5.2 Biological control of common teasel

Recently researchers have been examining candidates for biological control of

teasel species. Field surveys of the native range of teasel occurred with emphasis on

insects or pathogens that attack the rosettes or seedheads of teasel plants. The surveys

yielded 102 species of insects, 27 species of fungi, three mites, two viruses, and one

nematode that are natural enemies of plants in the family Dipsacaceae (Rector et al.

2006). Preliminary experiments have shown that the leaf beetle, Galeruca pomonae

(Coleoptera: Chrysomelidae), feeds on the leaf blades and the tips of the rosette. The

amount of damage depends on the number of larvae per plant and the size of the rosette.

Given a large enough population of insects, the beetles can cause whole mats of the

rosettes to be defoliated. Additionally, choice and no-choice tests between teasel, radish,

carrot, lettuce, turnip, and cabbage, showed that the beetle prefers to eat only teasel

(Sforza 2004). There has also been a report that the powdery mildew, Sphaerotheca

dipsacearum, has begun attacking common teasel in Washington State. This is the first

reported instance of this occurring (Dugan and Glawe 2006). This could be another good

prospect for biological control of teasel.


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1.6 Herbicides and Adjuvants Tested

The herbicides and adjuvants tested are listed below under their trade names.

Lists of active ingredients can be found in Appendix B.

1.6.1 BK 800

BK 800 is a broadleaf specific herbicide. Its main ingredient is Isoctyl (2-

ethylhexyl) ester of 2,4-dichlorophenoxyacetic acid (2,4-D ester) (PBI/Gordon

Corporation 2005). It mimics natural growth hormones in plants, causing the plants

hormone balance to be upset (Peterson et al. 2001). Specifically, it mimics the hormone

auxin. This disrupts several growth processes, causing the plant to grow uncontrollably

and eventually die (Tu et al. 2001). When used on plants, they exhibit stem twisting, leaf

malformations, stem callus formation, and stunted root growth (Peterson et al. 2001). BK

800 is an ester compound which is oil-soluble. Ester formulations tend to volatize readily

and cause vapor drift. 2,4-D has a short half-life, about ten days in soil and less than ten

days in water. There is no longer a patent on the product so it is a cheap, widely-used

herbicide (Tu et al. 2001).

1.6.2 Glyphomax

Glyphomax is a glyphosate-based non-selective herbicide (Dow AgroSciences

2004). It inhibits the Enolpyruvyl-shikimate-phosphate (EPSP) enzyme (Peterson et al.

2001). This enzyme is involved in the syntheses of aromatic amino acids, which are

involved in protein synthesis (Tu et al. 2001). Plants affected by glyphosate will not

show injury until three to five days after exposure. Symptoms include stunting, foliage

discoloration, and slow death (Peterson et al. 2001). Glyphosate is generally non-toxic to

mammals. It is strongly adsorbed to soil particles which can inhibit degradation, causing


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the average half-life to be two months. It is no longer under patent, so generic brands are

becoming widely available (Tu et al. 2001).

1.6.3 Transline

Transline is a clopyralid-based broadleaf selective herbicide (Dow

AgroSciences 2005). It, like 2,4-D, is an auxin mimic, causing the plant hormone

balance to be upset (Peterson et al. 2001). For more information on the site and mode of

action see section 1.6.1. It is more selective about which broadleaf species it affects. It

has little effect on the mustard family (Brassicaceae). Its half-life in soil can be up to one

year. It is almost completely degraded by microbes, but it does not degrade in sunlight.

It does not bind to soil particles readily and might pose problems to water resources due

to this mobility. It is generally non-toxic to mammals, birds, and fish (Tu et al. 2001).

1.6.4 Diesel Fuel

Diesel fuel is listed as an adjuvant in the instructions of BK 800. It is listed as an

acceptable adjuvant for foliar spraying, basal bark application, cut-stump application, and

ring-cut stump application. Diesel fuel has been shown to not increase the degradation of

2,4-D herbicides (Norris and Greiner 1967). A study done on the plant yaupon (Ilex

vomitoria Ait.), in Texas found that diesel alone killed 92% of yaupon while a 5%

solution of triclopyr had a 96% kill rate (Cathey et al. 2006).

1.6.5 Nu-Film-IR

Nu-Film-IR is a non-ionic surfactant created by Miller Chemical and Fertilizer

Corporation. Non-ionic surfactants are the most commonly recommended herbicide

adjuvant (Tu et al. 2001). It produces a sticky film that binds the herbicide to the plant

surface and reduces the washing effects of rainfall. It also reduces degradation of the


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herbicide due to ultra-violet light. It allows the herbicide to slowly invade the leaf

surface by reducing leaf burn which can negatively affect translocation (Miller Chemical

and Fertilizer Corporation 2001).

1.7 Site Description

Cooper Farm (UTM coordinates: Zone 16; 631379E; 4454074N; elevation: 288

meters above sea level) is a field station owned by Ball State University and managed by

the Field Station and Environmental Education Center staff. It consists of a 14 hectare

(35 acre) wooded area and a 23 hectare (57 acre) open area undergoing various stages of

succession. Esther L. Cooper and Dr. Robert H. Cooper donated the woodland to the

university in 1969. The area was grazed by cattle and swine before 1951. In 1959 it was

placed in United States Department of Agriculture soil reserve for five years. After

donation to the university, wildlife habitat was planted by students. In 1993 trail clearing

and pathway mowing in the natural area was greatly reduced to allow the habitat to

undergo succession (LeBlanc 2007).

The soils of Cooper Farm are Blount-Del Rey silt loams on 0 to 1 percent slopes,

eroded Glynwood silt loam on 1 to 4 percent slopes, and Pewamo silty clay loam on 0 to

1 percent slopes (NRCS 2007). There are restored prairies sections, sections undergoing

natural selection, forest areas, and wet swales. Due to micro-topography and the

presence of drain tiles, the swales remain wet until July while other sections dry earlier in

the year. Most notably, a 0.36 hectare swale runs through the southwestern corner of the

property, directly south of the study site (Taylor 2004).


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The study area is in the process of being restored to native prairie, with the wetter

swale areas being restored to a wet meadow habitat type. Plantings of native species

have occurred yearly since 2002. Different blocks are planted each year, causing the

restored prairie to be at different stages of development. The large prairie areas have

been planted with native grasses and wildflowers using a seed drill. The smaller wetter

areas have been planted with plugs and hand-broadcast seeds. Each are was repeatedly

sprayed with glyphosate and 2,4-D products prior to and during restoration (Taylor

2004).

The area of study was treated with 1% BK800 broadleaf herbicide in August 2003

and September 2004. It was also treated with 2% glyphosate in April and May 2004.

The area was then seeded with prairie grasses and a cover crop in May and June 2004.

The September 2004 treatment of BK 800 damaged the native grass plantings due to their

young age (Taylor 2004). By the time of plot delineation in the study area, teasel was

observed to be the dominant plant. The study area had an average of 25 plants/m2, with a

high density of 83 plants/m2 observed in one plot. Due to the previous years herbicidal

treatment, all the plants were one to two year-old rosettes. After the study period, some

flowering stalks were observed in areas not treated during the study.


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1.8 Project Overview

This research study was designed to provide baseline quantitative data on

herbicidal control methods of common teasel. An area that was densely covered with

first and second-year teasel rosettes were divided into 20 blocks containing 12 plots each.

Three different concentrations of three widely-used herbicides were applied to a plot in

each block. The adjuvants used with the herbicides were also applied to plots to see if

they had any isolated effect. A Kruskal-Wallis test and post hoc Mann-Whitney U tests

were used to uncover differences in herbicidal efficacy. It was expected that herbicides

would reduce the number of teasel rosettes and that there would be differences in the

efficacy of the herbicide concentrations tested. This study addresses three questions: (1)

Do herbicide treatments have an effect on the control of common teasel? (2) What is the

most efficient concentration of each herbicide tested for the control of common teasel?

(3) What is the optimum herbicide treatment for controlling common teasel?


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literature review of teasel (dipsacus fullonum)

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