Purpose and Philosophy

The purpose of this book is to provide you with information about the biology of agricultural weeds, including identification, management strategies and ecological facts that will help you understand and manage them. The book is focused on the weeds of arable cropping systems. It does not discuss the management of weeds in forests, turf, permanent pastures or perennial bioenergy crops. Weed management issues in forage production are discussed to some extent since forages are often rotated with other crops. 

The basic philosophy behind the book is that understanding the biology of weeds is critical to ecological weed management. Ecological management of weeds is information intensive rather than input intensive. This book is intended to provide the information you need to grow crops without synthetic herbicides, great expense or backbreaking work. By understanding how weeds work as organisms in the context of your farm ecosystem, the task of weed management becomes easier. By learning about the biology of weeds that cause you problems and then exploiting their weaknesses you can make weed management an integral part of your overall management effort. That does not mean that learning about particular weed control practices is useless. On the contrary, ecological weed management depends on a large bag of tricks. The key to success, however, lies in knowing when to apply a particular tactic, and that requires an understanding of how weeds operate, both in general and as particular species.

The premise of this book is that although weeds can be useful as food and as protection for the soil, most farmers will prefer to strictly limit their abundance. Weeds are neither always bad nor always good, but usually they tend to reduce yield, hinder harvest and cause a variety of other problems.

Some readers may wonder why we refer to the system of weed management described in this book as “ecological” rather than as “organic.” There are two reasons. First, the principles described here apply equally well whether you are fully committed to organic management or whether you still use some chemical fertilizers and pesticides. They are adequate to provide successful weed management on an organic farm, but they can be useful on any farm. Second, we wish to emphasize that the principles and methods are based on careful scientific investigation. Ecology provides the theoretical basis for the applied science of weed management, much as physics provides the theoretical basis for the applied science of engineering. To build a sewer system one does not need to be a physicist, but some knowledge of loads, stresses and fluid mechanics will reduce the cost of materials and prevent the drains from backing up. Similarly, a minimal knowledge of some specific ecological ideas will help you minimize your weed management effort and improve your success.

Finally, thinking about your farm from an ecological perspective has an additional bonus. Ecology is the science of how organisms interact with their environment. Its subject encompasses the workings of the everyday biological world that you see and touch. We expect that understanding something about the small corner of this science that deals with agricultural weeds will enrich your life. The great ecologist Richard Root once commented that the best preparation one could have for the serious study of ecology is to grow a vegetable garden and become fascinated by a particular group of organisms, e.g., plants or insects, that are encountered and how their behavior can change from season to season. We hope that this book will help you better understand weeds and how to manage them.

How to Use This Book

The book is divided into two main sections. The initial chapters contain general information on the ecology of weeds and methods of ecological management. Some of the information in Chapter 2 (“How to Think About Weeds”) may not seem immediately relevant to weed management. As you learn more about the application of ecological management methods and about individual weed species, however, you will see that understanding how weeds work as organisms is the key to effective management. Chapter 3 (“Cultural Management of Weeds”) and Chapter 4 ("Mechanical Weed Management") describe the many and varied methods of ecological weed management. Often a method will work well to help control one species but not another. Thus, your management will be most effective if you combine the general information in chapters 3 and 4 with specific information about the particular weed species present in your fields. Additional documentation of most statements made in chapters 2, 3 and 4 can be found in the book Ecological Management of Agricultural Weeds by Liebman, M., C.L. Mohler and C.P. Staver. 2001. Cambridge University Press: New York. Additional references have been added where needed. Chapter 5 gives case studies of how ecological management methods have been applied on farms around the United States.

Because we believe that effective ecological weed management requires a multi-year approach that involves a varied sequence of crop types, this book takes a weed-centered rather than a crop-centered approach. Thus, although the book contains much information you will find useful for the management of weeds in wheat, corn, carrots or other specific crops, the book does not contain sections addressing management of individual crops.

The second section of the book contains species-by-species information on most of the common agricultural weeds of the United States and Canada. Each species entry is divided into three sections. The first, Identification, gives a description of the weed, photographs of various stages in the weed’s life cycle and tips on distinguishing the species from similar looking species. The second, Management, gives a deliberately brief summary of major control strategies. Use chapters 3 and 4 to get more information on particular procedures mentioned in the management section. The third, Ecology, provides a series of short but specific statements about various aspects of the species’ ecology. This information provides much of the basis for the recommendations in the management section. Farms differ greatly in soils, climate, economic resources and the management style of the farmer. Understanding the ecological behavior of your weeds will help you manage them in cases where the general recommendations in the management section do not apply. The relevance of the information will only be apparent, however, through study of the management section and chapters 2, 3 and 4. 

We have attempted to keep technical terminology to a minimum throughout the book. Descriptions of plants and their ecological behavior become longwinded or even inaccurate, however, without the introduction of a few technical terms. These are defined in the Glossary. Also, some specialized tools have been developed to facilitate weed management, and many readers will be unfamiliar with some of these. Rather than describe the tool each time it is mentioned, we refer to it by its usual name and describe it in the Glossary. Pictures of implements are provided in appropriate places in the text, and the page reference for these is given in the Glossary.

Few people ever read a book of this sort in its entirety. We believe that you will find study of chapters 2, 3 and 4 highly useful, and Chapter 5 may give you some ideas about how to combine various tactics into an overall control plan. Then read about the weeds that are actually giving you problems. Finally, combine the specific information on those weeds with the general principles and methods from chapters 2, 3 and 4 to derive a weed management strategy that works with your particular mix of soils, crops and resources. We, the authors, would greatly appreciate you contacting us with your stories of success and failure using this approach to weed management.