Preface

The first synthetic herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D), was discovered in 1942 and its effectiveness and selectivity caused a paradigm shift in weed management practices in agriculture worldwide. Since then, the chemical control of weeds has become the most widely used method in the world because it is efficient, relatively low cost compared to other control methods, easy to use, and professionally appropriate.

However, most growers have an immediate and economic view of weed control, which can create environmental problems in the medium and long term. Repeated applications of herbicides with the same mechanism of action have been common practice in many parts of the globe. Frequently used chemical weed control coupled with target site mutation has led to the emergence of many herbicide-resistant weed biotypes reported worldwide.

This herbicide resistance of weeds is undoubtedly a major concern in modern agriculture, and some mechanisms of action present greater resistance problems than others. The largest number of cases of resistant biotypes belong to the mechanism of action of acetolactate synthase (ALS) inhibitors, followed by photosystem II (PSII) inhibitors. Today, herbicides with new mechanisms of action are necessary to control the evolution of resistance of these biotypes to existing herbicides.

In addition, it is essential that herbicides are properly applied alone or in the mixture to preserve the final quality of the harvested products as well as the natural resources that sustain production, especially soil and water. The correct way to apply these products aims for maximum biological efficacy and minimum damage to neighboring crops, the environment, and humans. The more suitable the equipment and techniques employed, the greater the efficacy. In this sense, herbicide application technology involves economically depositing the correct amount of the biologically active product on the target at the right time in the required quantity with minimal environmental contamination.

In view of this, it is important to study the behavior of herbicides in plants and soil for weed control. This involves estimating the trends to which herbicides are subject, as a function of three main processes: retention, transformation, and transport in the soil. Thus, the mere fact that an herbicide reaches the plant's leaves or is applied to the soil where it develops is not enough for it to exert its action; it must penetrate the plant, translocate, and reach the organelle where it will act. To determine the correct product to be used in each crop and in each soil, the professional must know the product's metabolism characteristics and the plant's sensitivity to the product and/or its metabolites, among other factors, such as the most promising form of application.

*New Insights in Herbicide Science* discusses these issues in six chapters. It is a useful resource for undergraduate and graduate students, technicians, professors, farmers, and all those involved in this area.

> **Kassio Ferreira Mendes** Professor of Biology and Integrated Management of Weeds, Department of Agronomy, Federal University of Viçosa, Viçosa, MG, Brazil

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Section 1

Application History, Mode

of Action and Resistance

Section 1
