ECOLOGY OF WEEDS AND INVASIVE PLANTS RELATIONSHIP TO AGRICULTURE AND NATURAL RESOURCE MANAGEMENT pdf

ECOLOGY OF WEEDS
AND INVASIVE PLANTS
RELATIONSHIP TO
AGRICULTURE AND NATURAL
RESOURCE MANAGEMENT
Third Edition

STEVEN R. RADOSEVICH
Oregon State University
Corvallis, Oregon

JODIE S. HOLT
University of California
Riverside, California

CLAUDIO M. GHERSA
University of Buenos Aires
Buenos Aires, Argentina



ECOLOGY OF WEEDS
AND INVASIVE PLANTS



ECOLOGY OF WEEDS
AND INVASIVE PLANTS
RELATIONSHIP TO
AGRICULTURE AND NATURAL

RESOURCE MANAGEMENT
Third Edition

STEVEN R. RADOSEVICH
Oregon State University
Corvallis, Oregon

JODIE S. HOLT
University of California
Riverside, California

CLAUDIO M. GHERSA
University of Buenos Aires
Buenos Aires, Argentina


Copyright # 2007 by John Wiley & Sons, Inc. All rights reserved.
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Library of Congress Cataloging-in-Publication Data:
Radosevich, Steven R.
Ecology of weeds and invasive plants: relationship to agriculture and natural resource management /
Steven R. Radosevich, Jodie S. Holt, Claudio M. Ghersa.—3rd ed.
p. cm.
Rev. ed. of: Weed ecology / Steven Radosevich, Jodie Holt, Claudio Ghersa. 1997.
Includes index.
ISBN 978-0-471-76779-4 (cloth)
1. Weeds—Ecology. 2. Weeds—Control. I. Holt, Jodie S.
II. Ghersa, Claudio. III. Radosevich, Steven R. Weed ecology. IV. Title.
SB611.R33 2007
6320 .5—dc22
2007001705
Printed in the United States of America
10 9

8 7

6 5

4 3 2

1


CONTENTS

PREFACE
BURDOCK by Charles Goodrich

xv
xvii

INTRODUCTION

1

Chapter 1: Weeds and Invasive Plants

3

Weeds, 4
Definitions, 6
Agrestals, 6
Invasive Plants, 9
Terminology, 10
Classification Systems of Weeds and Invasive Plants, 11

Taxonomic Classification, 11
Classification by Life History, 13
Classification by Habitat, 14
Physiological Classification, 15
Classification According to Undesirability, 16
Ecological Classification, 16
Classification by Evolutionary Strategy, 17
Weeds and Invasive Plants in Production Systems, 20
Weeds on Agricultural Land, 20
Reasons for Weed Control, 21
Weeds in Managed Forests, 24
Forest Regeneration, 25
v


vi

CONTENTS

Weeds in Rangelands, 26
Original Vegetation and Early Land Use History of
Great Basin, 28
Introduction of Cheatgrass and Fire, 28
Invasive Plants in Less Managed Habitats and Wildlands, 30
Local versus Regional Perspectives about Weeds, 30
Weeds in Regional and Global Context, 31
Summary, 32
Chapter 2: Principles
Ecological Principles, 35
Interrelationship of Biology and Environment, 35

Environment, 36
Scale, 38
Scale in Ecological Systems, 39
Scale in Human Production Systems, 43
Community Differentiation and Boundaries, 46
Community Structure, 47
Succession, 49
Mechanisms of Succession, 50
Succession in Production Systems, 52
Niche Differentiation, 54
Invasion Process, 56
Introduction Phase, 57
Colonization Phase, 59
Naturalization Phase, 62
Genetics of Weeds and Invasive Plants, 62
Fitness and Selection, 63
Patterns of Evolutionary Development of Weeds and
Invasive Plants, 63
Plant Demography and Population Dynamics, 67
Management Principles, 69
Assessing Risk from Weeds and Invasive Plants, 69
Management Priorities Based on Risk and Value, 71
Market-Driven Management Considerations, 73
Cost – Benefit Analysis, 73
Assessing Economic Risk, 74
Management Options in Relation to Invasion Process, 76
Social Principles, 77
Societal Aims versus Individual Objectives, 78
Social Conflict and Resolution, 79
Precautionary Principle, 79

Weed and Invasive Plant Management in Modern Society, 80
Summary, 81

35


CONTENTS

vii

Chapter 3: Invasibility of Agricultural and Natural Ecosystems

83

Plant Invasions over Large Geographical Areas, 84
Habitat Invasibility, 86
Community Invasibility, 87
Local Invasions, 87
Safe Sites, 88
Safe Site Example, 89
Factors That Influence Invasibility, 89
Evolutionary History, 89
Community Structure, 90
Role of Plant Size in Species Dominance and Richness, 92
Propagule Pressure, 93
Relationship of Propagule Pressure to Invasion Process, 93
Relationship of Dispersal to Propagule Pressure, 94
Relationship of Human and Animal Transport to Propagule Pressure, 94
Relationship of Seed Banks to Propagule Pressure, 95
Disturbance, 95

Disturbance and Land Use, 96
Relationship of Disturbance and Succession, 97
Relationship of Stress and Disturbance, 98
Invasibility and Exotic Plant Invasiveness, 99
Summary, 101
Chapter 4: Evolution of Weeds and Invasive Plants
Evolutionary Genetics of Weeds and Invasive Plants, 104
Heritable Genetic Variation, 105
Hybridization and Polyploidy, 105
Epistatic Genetic Variance, 109
Epigenetic Inheritance Systems, 110
Adaptation Following Introduction, 111
Responses to Environmental Gradients, 112
Selection in Barnyardgrass, 112
Selection in St. Johnswort, 113
Responses to Resident Plant Species, 113
Release from Pests, Predation, and Herbivores, 114
Breeding Systems of Weeds and Invasive Plants, 114
Sexual Reproduction, 115
Self-Pollination versus Outcrossing, 115
Founder Effects, 117
Exceptions to Baker’s Rule, 117
Asexual Reproduction, 117
Advantages of Asexual Reproduction in Weeds, 118

103


viii

CONTENTS

Influence of Humans on Weed and Invasive Plant Evolution, 119
Weeds and Invasive Plants as Strategists, 119
Competitive Ruderals, 119
Stress-Tolerant Competitors, 121
Adaptations of Weeds and Invasive Plants to Human Activities, 122
Weeds, Domesticates, and Wild Plants, 122
Crop Mimics, 122
Shifts in Plant Species Composition, 126
Summary, 126
Chapter 5: Weed Demography and Population Dynamics
Principles of Plant Demography, 129
Natality, Mortality, Immigration, and Emigration, 130
Life Tables, 131
Modular Growth, 133
Models of Plant Population Dynamics, 134
Models Based on Difference Equations, 134
Transition Matrices, 138
Metapopulations, 139
Risk of Extinction, 140
Metapopulation Dynamics Applied to Invasive Species, 141
Dynamics of Weed and Invasive Plant Seed, 142
Seed Dispersal through Space, 142
Estimates of Dispersal Distance, 144
Agents of Spatial Seed Dispersal, 146
Seed Banks, 149
Entry of Seed into Soil, 150
Longevity of Seed in Soil, 152
Density and Composition of Seed Banks, 157

Fate of Seed in Soil, 162
Weed Occurrence in Relation to Seed Banks, 165
Dormancy: Dispersal through Time, 166
Descriptions of Seed Dormancy, 166
Physiological Dormancy, 167
Physical Dormancy, 168
Combinations of Physiological and Physical Dormancy, 170
Seed with Underdeveloped Embryos, 171
Using Seed Dormancy to Manage Weed Populations, 171
Recruitment: Germination and Establishment, 171
Seed Germination, 171
Light Requirement for Germination, 172
Risk of Mortality, 176
Seedlings, 176
Vegetative Propagules of Perennial Plants, 177

129


CONTENTS

ix

Epidemics of Weeds and Invasive Plants, 178
Predictive Models of Weed Reproduction, Dispersal, and Survival, 179
Example: Predictions of Changes in Weed Abundance in
Agricultural Fields, 180
Summary, 181
Chapter 6: Plant – Plant Associations
Neighbors, 184

Interference, 184
Effect and Response, 185
Is it Competition?, 187
Modifiers of Interference, 188
Space, 189
Density, 191
Species Proportion, 199
Spatial Arrangement, 200
Methods to Study Interference (Competition), 201
Additive Designs, 201
Substitutive Designs, 202
Replacement Series, 203
Nelder Designs, 205
Diallel Designs, 206
Systematic Designs, 207
Addition Series and Additive Series Designs, 207
Neighborhood Designs, 209
Approaches Used to Study Plant Interference (Competition) in
Natural and Managed Ecosystems, 212
Descriptive Studies, 213
Retrospective Studies, 214
Case Studies, 214
Gradient Studies, 216
Intensity and Importance of Competition, 216
Intensity of Competition, 217
Competition Intensity Indices, 218
Relative Yield, 218
Relative Yield Total, 219
Intra- versus Interspecific Competition, 221
Importance of Competition, 222

Competition in Mixed Cropping Systems, 223
Weed Suppression in Mixed Planting Systems, 223
Competition Thresholds, 224
Thresholds in Agriculture, 224
Damage (Density/Biomass) Thresholds, 225
Critical-Period Thresholds, 227

183


x

CONTENTS

Thresholds in Natural Ecosystems, 228
Mechanisms of Competition, 230
Theories, 230
Theories of Grime and Tilman, 230
Role of Plant Traits, 231
Plant Growth Rates and Components of Growth, 233
Other Types of Interference than Competition, 237
Negative Interference in Addition to Competition, 237
Allelopathy, 237
Responses of Plants to Allelochemicals, 241
Methods to Study Allelopathy, 242
Microbially Produced Phytotoxins, 243
Parasitism, Predation, and Herbivory, 243
Parasitism, 244
Predation, 246
Herbivory, 248

Positive Interference, 250
Facilitation, 250
Commensalism, 251
Protocooperation, 252
Mutualism, 253
Summary, 255
Chapter 7: Weed and Invasive Plant Management Approaches,
Methods, and Tools
Prevention, Eradication, and Control, 259
Weed Management in Agroecosystems, 260
Economics and Biology of Weed Control: Whether to
Control Weeds, 260
Weed Response to Control, 261
Opportunity to Improve Productivity: Crop Response
to Weeds, 261
Profitability: Value of Weed Control, 262
Influence of Weed Control on Agricultural Crops and Weed
Associations, 265
Reduction in Weed Density, 265
Alteration in Species Composition, 265
Influence of Weed Control on Other Organisms, 267
Management of Invasive Plants in Natural Ecosystems, 269
Approaches to Prioritize Management, 269
Documenting Invasions, 271
Terms Used by Land Managers, 271
Incorporating Risk Assessment into Invasive Plant Management, 272

259

CONTENTS

xi

Individual Species Approach, 272
Plant Community or Habitat Approach, 273
Risks Associated with Action and Inaction, 275
Framework to Combine Research and Management of Invasive Plants, 277
Methods and Tools to Control Weeds and Invasive Plants, 279
Physical Methods of Weed Control, 279
Hand Pulling and Hoeing, 279
Fire, 280
Flame, 281
Tillage (Cultivation)/Disturbance, 281
Mowing and Shredding, 286
Chaining and Dredging, 289
Flooding, 289
Mulching and Solarization, 289
Cultural Methods of Weed Control, 290
Weed Prevention, 290
Crop Rotation, 291
Competition, 292
Smother Crops, 293
Living Mulches and Cover Crops, 294
Harvesting, 294
Biological Control: Using Natural Enemies to Suppress Weeds, 295
Procedures for Developing Biological Control, 296
Grazing, 301
Mycoherbicides, 301
Allelopathy, 301

Chemical Control, 302
Herbicides, 303
Summary, 305
Chapter 8: Herbicides
Herbicides as Commercial Products, 307
Laws for Herbicide Registration and Use in United States, 308
Information on Herbicide Label, 309
Voluntary and Legislative Restrictions on Herbicide Use, 309
Properties of Herbicides that Affect Human, Animal, and
Environmental Safety, 311
Toxicity, 312
Biological Magnification, 314
Persistence, 315
Voluntary Selection Criteria for Herbicide Use, 315
Chemical Properties of Herbicides that Affect Use, 318
Chemical Structure, 318
Water Solubility and Polarity, 319

307


xii

CONTENTS

Volatility, 321
Formulations, 321
Carriers and Adjuvants for Herbicide Applications, 322
Herbicide Classification, 322
Classification Based on Chemical Structure, 322

Classification Based on Use, 323
Soil-Applied Herbicides, 323
Foliage-Applied Herbicides, 324
Soil Residual Herbicides, 324
Soil Fumigants, 326
Aquatic Herbicides, 326
Classification Based on Biological Effect in Plants, 326
Herbicide Symptoms and Selectivity, 327
Symptoms, 327
Abnormal Tissues and Twisted Plants, 327
Disruption of Cell Division, 327
Chlorosis, Necrosis, and Albinism, 327
Altered Geotropic and Phototropic Responses, 328
Reduced Leaf Waxes, 328
Selectivity, 328
Plant Factors of Herbicide Selectivity, 329
Chemical Factors of Herbicide Selectivity, 332
Environmental Factors of Herbicide Selectivity, 332
Herbicide Application, 333
Proper Rate (Dose), 334
Proper Distribution, 334
Application Equipment, 334
Fate of Herbicides in Environment, 335
Herbicide Displacement in Environment, 336
Herbicide Movement in Air, 337
Herbicides in Soil, 338
Herbicide Movement with Water, 341
Herbicide Decomposition in Environment, 342
Photochemical Decomposition, 343
Chemical Decomposition, 344

Microbial Decomposition, 344
Reduction of Herbicides in Agriculture and Natural Resource
Production Systems, 345
Summary, 345
Chapter 9: Systems Approaches for Weed and Invasive
Plant Management
Cycles of Land Use, Expansion, and Intensification for Production, 350
Evolution of Modern Integrated Pest Management, 351

349


CONTENTS

xiii

Evolution of Weed Science, 352
Approaches for Pest and Weed Management, 353
Integrated Weed Management, 354
Levels of Integrated Weed Management, 354
Ecological Principles to Design Weed Management Systems, 355
Future Directions in Integrated Weed Management, 357
Novel Ecosystems, 366
Novel Weed/Invasive Plant Management Systems, 368
Agriculture, 369
Managed Forests and Forest Plantations, 369
When Limited Herbicide Use Is Acceptable, 371
Rangeland, 372
Value Systems in Agricultural and Natural Ecosystem Management, 374
Role of Human Institutions in Weed Management, 375

The 2,4,5-T Controversy, 375
Atrazine and Water Quality, 376
Herbicide-Resistant Crops, 377
Consequences of Human Values on Weed and Invasive Plant
Management, 378
Simplification, Deterioration, and Loss of Biological Regulation
in Agriculture, 379
Weeds and Invasive Plants as Symptoms of Ecosystem Dysfunction, 380
Weed Occurrence on Deteriorating Soil Base, 380
Other Examples of Ecosystem Deterioration, 380
Socioeconomic Influences on Weed and Invasive
Plant Management, 381
Future Challenges for Scientists, Farmers, and Land Managers, 381
Summary, 382
References

385

Index

439



PREFACE

This book, now in its third edition, began almost 25 years ago when Weed
Ecology: Implications for Vegetation Management was published in 1984. That
text concentrated on the need for farmers, foresters, rangeland managers, and the
researchers who advised them to understand better the biology of weeds and

the role people play in creating and maintaining weeds in agriculture and other
production systems. We were assisted in that first effort by the writings of many
early scientists, such as J. L. Harper, H. G. Baker, and E. J. Salisbury, who
studied the biology of weeds as a class of vegetation. We continue to be grateful
for their pioneering work and theoretical perspectives that they provided.
Our focus on the biology of weeds continued though the second edition, which
was published in 1997. We described the many empirical findings that had
emerged since our first edition about the biology of weeds and discussed these
findings within an ecological framework to explain how weed invasions occur,
how weed communities continue to exist, and even how agroecosystems and
other natural ecosystems work. We also added three chapters about the technology of weed control which had developed over the previous four decades and had
become part of the general knowledge about weeds in farms, forests, or rangelands. Our emphasis, however, continued to be the ecological underpinnings of
the discipline of weed science. We believed then and continue to believe that
better management results from the understanding of how plants interact with
each other and their environment and management to create and maintain weed
populations.
We find with this latest edition, Ecology of Weeds and Invasive Plants:
Relationship to Agriculture and Natural Resource Management, that weeds are
now at the forefront of many ecologists’ minds. Their recent interest in weed and
xv


xvi

PREFACE

invasive plant ecology has generated new understanding about the concepts of
invasibility and in the disciplines of genetics and plant population dynamics. In
addition, considerable research has incorporated the principles of integrated pest
management (IPM) and ecological thresholds into weed and invasive plant management. While many new and enlightening papers have been written about

weeds, invasive plants, and their management over the last decade, we found as
we updated our text that in some instances little had changed or that seminal
papers on a subject had already been published, often decades earlier. Thus, we
cite both new and vintage papers in our third edition.
Ecologists have a history of working predominantly in natural ecosystems and
only recently have incorporated disturbance and human impacts into their research
on a large scale. Weed scientists, on the other hand, have traditionally worked in
agricultural and managed ecosystems and focused on the applied disciplines, with
less emphasis on basic science. With the recognition of the impacts of invasive
plants and their weedy attributes, the two disciplines, ecology and weed science,
have begun to converge on the study of weeds and invasive plants. Thus, we hope
that ecologists will examine carefully and apply the approaches and tools of weed
science while weed scientists continue to embrace the principles of ecology. In
this way, we believe both disciplines can move forward together toward better
understanding and land management.
We suggest humbly, while also reminding ourselves, that there is never
epiphany in the unprepared mind.
STEVEN R. RADOSEVICH
JODIE S. HOLT
CLAUDIO M. GHERSA
Corvallis, Oregon
Riverside, California
Buenos Aires, Argentina
October 2006


Charles Goodrich
Burdock
Few seeds as tenacious as burdock,
clutching the dog’s fur

tight as ticks. The leaves aren’t as plush as mullein,
but will pass for Kleenex in a pinch.
We haven’t tried digging it up,
roasting the roots in an open pit, then
grinding the mess together with berries and fat
for pemmican.
but I own a sharp spade.
I’m not afraid to eat
bitter, woody plants,
or creatures that wiggle and squeal.
When I pull the burrs out of her fur,
I toss them to the dog
and she eats them.
Good dog.

xvii



INTRODUCTION

In one of his early texts on weed control, A. S. Crafts begins by saying, “in the
beginning there were no weeds.” What Dr. Crafts meant was that even though
plants have existed for a long time, weeds did not exist before humankind. Now,
with the ever-increasing movement of people across the globe and the occurrence
of worldwide trade, weeds are no longer locally restricted to agricultural and
managed lands and the problem of exotic invasive plants has become widespread.
Still, however, weeds and invasive plants exist because of our human ability to
judge and select among the various species of the plant kingdom. This anthropomorphic perspective of weeds and invasive plants provides little insight into
their evolution, biological characteristics, or interactions that occur so markedly

in managed and natural ecosystems. In this text, our focus is on these biological
features of weeds and invasive plants, especially as they exist in agriculture,
forests, rangelands, and natural ecosystems. By considering weeds foremost as
plants and by relying heavily on the concepts of plant ecology, we hope to
provide a better understanding about this vegetation and therefore better management of the ecosystems so often invaded by them.

Ecology of Weeds and Invasive Plants. By Steven R. Radosevich, Jodie S. Holt, and
Claudio M. Ghersa
Copyright # 2007 John Wiley & Sons, Inc.

1



1
WEEDS AND INVASIVE PLANTS

Weeds exist as a category of vegetation because of the human ability to select
desirable traits from among various members of the plant kingdom. Just as some
plants are valued for their uses or beauty, others are reviled for their apparent
lack of these characteristics. Weeds are recognized worldwide as an important
type of undesirable, economic pest, especially in agriculture. However, the value
of any plant is unquestionably determined by the perceptions of its viewers.
These perceptions also influence the human activities directed at this category of
vegetation.
Harlan, in the middle of the last century, described how vegetation evolved
under the impacts of humans. He suggested that vegetation, in relation to the
degree of human involvement with it, exists as three categories: wild plants,
weeds, and crops. Crops were domesticated from wild plants while weeds
evolved from wild plants as an unintentional consequence of growing crops.

Some crops also were once weeds and some have again escaped from domestication. In Harlan’s concept neither weeds nor crops can permanently displace
wild plants from wild habitats over time (DeWet and Harland 1975).
Invasive plants, unlike agricultural weeds, are those that can successfully establish and spread to new habitats after their introduction, seemingly without further
assistance from humans. These plants can spread into new areas already occupied
by a native flora and displace those species. Such invasions from the intentional or
unintentional transport of plants to new regions now seriously threaten the
biodiversity, structure, and function of many of the world’s ecosystems. Invasive
Ecology of Weeds and Invasive Plants. By Steven R. Radosevich, Jodie S. Holt, and
Claudio M. Ghersa
Copyright # 2007 John Wiley & Sons, Inc.

3


4

WEEDS AND INVASIVE PLANTS

plants are thus weeds in the broadest sense because they evoke human dislike and
often some form of management to eradicate or contain them in their new environments. Not all weeds are invasive, however. In this text, the term weed will be
used in the broad sense and to describe undesirable plants in agricultural systems,
while invasive plant will be used for those weeds that can spread beyond their
point of introduction, often in natural ecosystems.
WEEDS
A “plant growing out of place,” that is, plants growing where they are not
wanted, at least by some people, is a common, accepted explanation for what
weeds are. This notion of undesirability imparts so much human value to the idea
of weediness that it is usually necessary to recognize who is making the determination as well as the characteristics of the plants themselves. For example, certain
plants growing in a cereal field or pasture or along a fence row may be unwanted
by a farmer or rancher, but they also may be wildflowers or a valuable wildlife

cover to other people. Vine maple, Acer circinatum, is a valued source of deer
browse in the spring and a spectacular source of coloration in the Cascade
Mountains of Oregon and Washington in the United States, during autumn, but it
also is known to hamper forest regeneration. It can be argued that many weeds in
agricultural fields, forest plantations, and rangelands are not “out of place” at all
but are simply not wanted there by some people.
In Table 1.1 we list many of the “human” characteristics that have been used
to describe weeds. Most of these characteristics are based on some judgment of
TABLE 1.1 Definitions and Descriptions of Weeds
Definition
Growing in an undesirable
location
Competitive and aggressive
behavior
Persistence and resistance
to control
Useless, unwanted,
undesirable
Appearing without being
sown or cultivated

Unsightly
Source: Adapted from King (1966).

Description
A plant growing where it is not desired (Weed
Science Society of America 1956)
A plant that grows so luxuriantly or plentifully
that it chokes all other plants that possess more
valuable properties (Brenchley 1920)

The predominance and pertinacity of weeds
(Gray 1879)
A plant not wanted and therefore to be destroyed
(Bailey and Bailey 1941); a plant whose virtues
have not yet been discovered (Emerson 1878)
Any plant other than the crop sown (Brenchley
1920); a plant that grows spontaneously in a
habitat greatly modified by human action
(Harper 1944)
A very unsightly plant of wild growth, often found
in land that has been cultivated (Thomas 1956)