Evolution of Weed Resistance to Herbicides

Abstract

Chemical control is an efficient method and the most used in agriculture; however, resistant weeds have evolved worldwide due to the selection pressure caused by the repeated use of herbicides with the same mechanism of action. Some mechanisms of action have a greater disposition to evolve resistance, with the Acetolactate Synthase (ALS) and Photosystem II (PSII) inhibitors. Resistant biotypes seriously compromise agricultural crops, making management difficult and increasing control costs; therefore, management alternatives must be adopted to minimize the damage caused by resistant biotypes. For genetically modified varieties, such as glyphosate-resistant soybeans, other herbicides with different mechanisms of action are being included in management programs to control resistant biotypes. The use of herbicides with different mechanisms of action in annual rotations, tank mixes and sequential applications, can delay the evolution of resistance, minimizing the selection pressure imposed by a single specific mechanism of action. Integrated weed management combining different control methods is a viable alternative for controlling resistant biotypes. Thus, the chapter covers the evolution of resistance in the world and in Brazil, the different mechanisms of resistance to tar get and non-target site, methods of identification of resistant biotypes, and alternatives for integrated management of herbicide resistant weeds.