Contents

Preface ix

1 Weed management: a need for ecological approaches 1

Matt Liebman Introduction 1

Weed management objectives 2 Herbicide sales and use 5 Unintended impacts ofherbicide use 8 Weed management and farm profitability 19 Transitions to ecological weed management 24 Summary 30

2 Weed life history: identifying vulnerabilities 40

Charles L. Mohier

Weeds from an ecological perspective 40

The life history of weeds 42

Dormancy and germination 46

Survival ofweed seeds in the soil 53

Hazards of establishment 60

Vegetative growth and crop-weed competition 62

Survival after emergence 67

Life span and seed production 71

Dispersal ofseeds and ramets 75

Conclusions 84

3 Knowledge, science, and practice in ecological weed management: farmer-extensionist-scientist interactions 99

Charles P. Staver Introduction 99

Knowledge and technology for weed management: an historical perspective 100

Contrasting perspectives of farmers, extensionists, and scientists on weeds 104

Weed patchiness and uncertainty: the challenge to improving weed management 109 Three approaches to farmer management of weed patchiness and uncertainty 113

Adaptive management and farmer-extensionist-scientist interactions 117 Participatory learning for ecological weed management: a proposal 118 Farmers, extensionists, and scientists learning together: four examples 127 Aconcluding note 133

4 Mechanical management ofweeds 139

Charles L. Mohier

Introduction 139

Tillage: pros and cons 140

Mechanical management of perennial weeds 141

Effects of tillage on weed seedling density 151

Basic principles of mechanical weeding 169

Machinery for mechanical weeding 173

Comparison of chemical and mechanical weed management 190 Directions for future research 192

5 Weeds and the soil environment 210

Matt Liebman and Charles L. Mohier

Introduction 210

Temperature management 212

Water management 215

Fertility management 220

Crop residue management 229

Toward the integration of weed and soil management 250

6 Enhancing the competitive ability of crops 269

Charles L. Mohier Introduction 269 Crop density 270 Crop spatial arrangement 281 Crop genotype 287 Phenology 297 Conclusions 305

7 Crop diversification for weed management 322

Matt Liebman and Charles P. Staver Introduction 322

Crop diversity in conventional, traditional, and organic farming systems 323 Principles guiding crop diversification for weed management 325 Crop rotation 326 Intercropping 336

Agroforestry 351

Obstacles and opportunities in the use of crop diversification for weed management 363

8 Managing weeds with insects and pathogens 375

Matt Liebman Introduction 375

Conservation of resident herbivores and pathogens 377 Inoculative releases of control agents 380 Inundative releases of control agents 391 The integration of multiple stress factors 398 Moving ahead with weed biocontrol 400

9 Livestock grazing for weed management 409

Charles P. Staver Introduction 409

Matching grazing strategies with weed problems 410 Weed control through herbivory in short-cycle crops 420 Aftermath and fallow grazing for weed control 421 Grazing for weed control in tree crops 423 Grazing for weed control in pastures and rangelands 427 Research directions 435

10 Weed evolution and community structure 444

Charles L. Mohler Introduction 444

Formation and management of weed communities 445 Human-dominated ecosystems as an evolutionary context 454 Origins ofweeds 455 Weed genecology 463

Managing the adaptation of weed populations 474 Controlling the spread of new weeds 481 Conclusions 484

11 Weed management: the broader context 494

Charles L. Mohler, Matt Liebman, and Charles P. Staver Introduction 494

If ecological weed management is effective, why do farmers rely heavily on herbicides.? 495 Feeding a growing human population 502 Developing an environment for research on ecological weed management 506 Implementing ecological weed management 510

Taxonomic index 519 Subject index 525

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