Herbicide Resistance Action Committee (HRAC): Herbicide Classification, Resistance Evolution, Survey, and Resistance Mitigation Activities

Abstract

Crop losses and quality depreciation, due to harmful organisms, especially weeds, can be substantial and can be significantly reduced or even prevented by crop protection measures [1]. In combination with agronomic measures, herbicides are necessary tools of weed control in modern crop production systems; however due to natural selection process, herbicide-resistant weed populations can evolve rapidly [2]. The first cases of herbicide resistance (HR) were reported in 1957 on wild carrot (Daucus carota) resistant to 2,4-D [3]. Then during the second half of the 1970s, new cases were reported. Since then, resistance of monoand dicotyledonous weeds to herbicides has become an increasing problem worldwide [4]. In September 2018, the International Survey of herbicide-resistant weeds (http://weedscience.org/; [4]) recorded 495 unique cases (species × site/mode of action (MoA)) of herbicide-resistant weeds globally, representing 255 species (148 dicotyledonous and 107 monocotyledonous) [4]. Weeds have evolved resistance to 23 of the 26 known herbicide sites/MoA and to 163 different herbicides. Herbicide-resistant weeds have been reported in 92 crops in 70 countries [4]. The relatively constant increase in the number of new cases of resistance since about 35 years accounts for the increasing importance of HR in weed control in the major agricultural regions (Figures 1.1 and 1.2). During the period 1970–1990, a significant number of documented cases of resistance concerned the triazine resistance. The introduction of new herbicides with different MoAs that resulted in the evolution of new resistance cases related to acetolactate synthase (ALS) and acetyl-CoA carboxylase (ACCase)-resistant weeds, especially in grass weeds present in cereal-based cropping systems, has been reported (Figure 1.3). Since 1996, the introduction of glyphosate-tolerant maize, soybean, and cotton in North and South America and the extensive and repeatedly use of glyphosate Herbicide Resistance Action Committee (HRAC): Herbicide Classification, Resistance Evolution, Survey, and Resistance Mitigation Activities Roland Beffa, Hubert Menne, and Helmut Köcher 2