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
class="bi x2 y12 w0 h9"
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

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
632
0
.5—dc22
2007001705
Printed in the United States of America
10987654321
MA 01923, (978) 750-8400, fax (978) 750-4470, or on the web at www.copyright.com . Requests
or online at />visit our web site at www.wiley.com.
CONTENTS
PREFACE xv
BURDOCK by Charles Goodrich 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

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
vi CONTENTS
Chapter 3: Invasibility of Agricultural and Natural Ecosystems 83
Plant Invasions over Large Geographical Areas, 84
Habitat Invasibility, 86
Community Invasibility, 87

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
CONTENTS vii
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 129
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

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

Prevention, Eradication, and Control, 259
Weed Management in Agroecosystems, 260
Economics and Biology of Weed Con trol: 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
x CONTENTS
Individual Species Approach, 272
Plant Community or Habitat Ap proach, 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

Chemical Structure, 318
Water Solubility and Polarity, 319
CONTENTS xi
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

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
CONTENTS xiii

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

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 wil l 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.
S
TEVEN R. RADOSEVICH
JODIE S. HOLT
CLAUDIO M. GHERSA
Corvallis, Oregon
Riverside, California
Buenos Aires, Argentina
October 2006
xvi PREFACE
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,

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 domesti-
cation. 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 estab-
lish 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
3
Ecology of Weeds and Invasive Plants. By Steven R. Radosevich, Jodie S. Holt, and
Claudio M. Ghersa
Copyright # 2007 John Wiley & Sons, Inc.
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 environ-
ments. Not all weeds are invasive, however. In this text, the term weed will be

Persistence and resistance
to control
The predominance and pertinacity of weeds
(Gray 1879)
Useless, unwanted,
undesirable
A plant not wanted and therefore to be destroyed
(Bailey and Bailey 1941); a plant whose virtues
have not yet been discovered (Emerson 1878)
Appearing without being
sown or cultivated
Any plant other than the crop sown (Brenchley
1920); a plant that grows spontaneously in a
habitat greatly modified by human action
(Harper 1944)
Unsightly A very unsightly plant of wild growth, often found
in land that has been cultivated (Thomas 1956)
Source: Adapted from King (1966).
4 WEEDS AND INVASIVE PLANTS