Handbook of Weed Management Systems

Albert E. Smith

• Publisher: Routledge
• Year: 2017
• ISBN:
  9781351441827
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Botany
• Index: Biological Sciences

This work provides the fundamental information necessary for the development of weed management strategies for all the major US crops using concepts that can be applied worldwide. Weed management systems are provided for cotton, peanut, soybean, wheat, barley, oat, sorghum, rice, fruits, nut crops, and more. The dynamics involved in creating the best management approaches for specific types of crops are explained.

1

Introduction

Robert L. Zimdahl

Colorado State University, Fort Collins, Colorado

I. CHARACTERISTICS OF WEEDS

There it is, a plant you don’t want in your field, lawn, garden, pond, or some other site where you have decided it shouldn’t grow. Why? What’s the matter with it? It is growing quite well, probably better than what you planted and want to grow there. However, you don’t want it because you regard it as a weed and the decision is yours. A weed is a plant growing where it is not desired (Buchholtz, 1967). The definition is clear. It is also clear, on examination, that the burden and responsibility for defining what plants are weeds rest with people who decide when a plant, in a particular place and time, is not desired. Human attitudes play a fundamental role in determining what plants are weeds. Weeds share the characteristic of being unwanted by some people.

Not everyone agrees that a particular plant is a weed.The plants someone doesn’t want growing in a front lawn may be valued or ignored by a neighbor, who doesn’t regard them as undesirable or weedy. Most cattle ranchers know that leafy spurge is a weed. It is an aggressive perennial plant that reproduces by seed and vegetatively and can dominate rangeland and pastures. Cattle don’t eat it. The sheep rancher, on the other hand, may know it is a weed but doesn’t regard it with the same disdain because sheep readily eat leafy spurge.

Do these plants we label as weeds have some characteristics in common other than a human attitude toward them? There are many weedy plants. The Weed Science Society of America recognizes no fewer than 2076 plants as weeds and the list is growing (Composite List, 1989). They share some traits, but not all weeds have all the traits of weediness. Among the shared traits is the fact that weeds often grow better than what was planted or what is desired and they are difficult to control. Weeds are successful and often succeed precisely where we don’t want them. They interfere with human activities.

It is not just location—a plant growing where it is not desired—that defines what a weed is; it is something it does. It interferes with our activities, whether growing a crop, having a weed-free flower bed or lawn, or having a pond free of aquatic weeds.

To define a weed we need to understand the characteristics that allow them to be where we don’t want them and to interfere with our activities. We might be able to tolerate a plant that is present but doesn’t interfere with anything.

All weeds share some characteristics that make them plants capable of growing where they are not desired and that make controlling and managing them difficult. Not all weeds have identical characteristics but all share some weedy traits. The characteristics are usually divided into those related to 1) weed physiology, growth, and competitiveness; 2) reproduction; or 3) cultural practices (see Chapter 2 for a complete discussion).

II. HISTORY OF WEED MANAGEMENT

Weed management, a relatively new concept in weed science, has not yet achieved the status of having an official definition. Integrated pest management, developed for insect control, is older; it is

a pest control strategy based on determination of an economic threshold that indicates when a pest population is approaching the level at which control measures are necessary to prevent a decline in net returns—that is—when the predicted value of the impending crop damage exceeds the cost of controlling the pest. (Composite List, 1989)

Weed control, on the other hand, has been defined as “the process of reducing weed growth and/or infestations to an acceptable level” (Herbicide Handbook, 1989). Control rather than management is what weed science has been about almost since its inception. The history of weed science is not the history of weed management; it is the history of weed control. This is not to say or imply that weed science is diminished because of its history. It is a recognition of reality. The reality is perhaps best exemplified in a statement by the eminent California extension weed specialist W. A. Harvey. Writing in the introductory chapter to Principles of Weed Control in California, Harvey said, “All (in weed science) before 2,4-D became ancient history” (Harvey, 1985).

Any new science is built upon preceding science. Indeed, weed scientists can now see so far because they stand on the shoulders of giants.* However, weed science was not created with a philosophical foundation based on the concepts that will surely be included in the eventual definition of weed management. Weed science was created with a pragmatic, problem-solving orientation. Weed scientists proudly and justifiably claim to be problem solvers and have solved many problems. Harvey (1985) suggests the process of solving those problems helped weed control evolve into weed science. Another way to think about the evolution of weed science is that it has moved from “how” questions to “why” questions.

Available historical accounts of weed science are accurate and are, almost exclusively, histories of chemical weed control (Crafts, 1960; Smith and Secoy, 1975 and 1976; Timmons, 1970; Upchurch, 1969; Zimdahl, 1983). Upchurch (1969) said that “one approach to studying the beginnings of weed control is to examine the appearance of various herbicides.” He is correct, but his approach is the one taken by all writers. Weed science began with herbicides, the technical ability to control weeds, not with a concept of the need to manage crops and their associated weeds.

Many writers cite the early work of Bolley (1908) (a plant pathologist) in North Dakota and the nearly concurrent work of the Frenchmen Bonnet, Martin, and Duclos and the German Schultz (Crafts and Robbins, 1962). Each of these men used solutions of copper salts for selective weed control in small grains; later iron sulfate and sulfuric acid were used.

Succeeding work in Europe observed the selective herbicidal effects of metallic salt solutions or acids in cereal crops. Names encountered frequently include Rabate in France (1911), Morettini in Italy (1915), and Korsmo in Norway (1932). More recent historical accounts almost always cite the synthesis of 2,4-D by Pokorny (1941), the discovery of its growth-regulating properties (Zimmerman and Hitchcock, 1942), and the first field reports of its herbicidal activity (Hamner and Tukey, 1944a,b; Marth and Mitchell, 1946). At the same time, work was under way in England on the herbicidal properties of MCPA (Slade et al. 1945). A short but complete history of the development of the growth regulator herbicides has been written (Kirby, 1980). The first paper on a nonphenoxy acid derivative useful as a herbicide was by Bucha and Todd (1951), who reported the herbicidal properties of monuron, the first of many phenylurea herbicides. The date of the first U.S. patent for several other herbicides of current or historical interest is shown in Table 1. The tabulation does not attempt to list all herbicides ever patented or even most of those patented after 1970. It shows that almost no important herbicides were patented prior to 1940 and most were patented after 1944–1945, with a great surge of development in the 1950s and 1960s, a time coincident with the development of weed science.

Weed science textbooks almost universally note that weeds have been with us since settled agriculture began. Smith and Secoy (1976) state that the harmful effects of weeds were known to early historic humans and cite, as evidence, the hoes and grubbing implements that have been found. Similar tools are still used for weeding and other tasks in many parts of the world and the conclusion is logical. They (Smith and Secoy, 1976) also found that nearly all books from the time of Theophrastus (372?–287? B.C.) to the modern period have mentioned weeds and their detrimental effects. Familiar examples of humans’ battle with weeds are easy to find. The thistles and thorns of Genesis (3:17–18) and the parables of the sower (Matt. 13:17–18) and the tares (Matt. 13:25–30) are among the earliest references.

The importance of weeds is immediately obvious in many third world countries. There, a farmer is a person with a hoe, and weeding is part of the burden of agriculture. It is what farmers do. Weed control, if achieved, is an incidental part of production. Weeding is something the world’s developing country farmers must always do; it is not a task to be completed. If control technology has changed for most of the world’s farmers in developing countries, it has progressed from primitive hand tools to animal powered implements. Weed science, that enabled planned weed control and the thought of annual completion of the task, really began after World War II with the discovery of the herbicidal properties of the phenoxy acid herbicides.

There were herbicides before 2,4-D but none as cheap, as effective, or as selective. Crafts (1960) traces the history of herbicide development from the early workers mentioned to the 1920s discovery of the field bindweed control potential of a dilute solution of sodium arsenite and its apparent translocation in plants. In Colorado, carbon bisulfide was applied as a soil fumigant to control Phylloxera, the root-borne disease of grapes. Carbon bisulfide had been used fi...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Preface
• Contributors
• 1 Introduction
• 2 Ecology of Weeds
• 3 Preventive Weed Management
• 4 Mechanical Weed Management
• 5 Chemical Weed Management
• 6 Herbicide Application Equipment
• 7 Herbicide Formulations, Adjuvants, and Spray Drift Management
• 8 Fate of Herbicides in the Environment
• 9 Biological Weed Management
• 10 Weed Management Systems for Oil Seed Crops
• 11 Weed Management Systems for Grain Crops
• 12 Weed Management Systems for Pastures and Hay Crops
• 13 Weed Management Systems for Rangeland
• 14 Weed Management Systems for Horticultural Crops
• 15 Weed Management Systems for Turfgrass
• 16 Weed Management Systems for Forest Nurseries and Woodland
• Herbicide Index
• Weed Index
• Crop Index
• Subject Index