Suggested Citation:"Appendix D: Herbicide Classifications and Mechanisms of Action." National Research Council. 2012. National Summit on Strategies to Manage Herbicide-Resistant Weeds: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/13518.
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Appendix D
Herbicide Classifications and Mechanisms of Action
Table D-1 contains the herbicide classifications and mechanisms of actions for herbicides discussed in the proceedings. It is based on Appendix A of the National Research Council report The Impact of Genetically Engineered Crops on Farm Sustainability in the United States (2010). Readers can find more information on herbicides, herbicide classifications, and mechanisms of action in that appendix and on the websites of the Weed Science Society of America (www.wssa.net) and the Herbicide Resistance Action Committee (www.hracglobal.com).
TABLE D-1 Selected Herbicide Classifications and Mechanisms of Action
| Herbicide Classification | Abbreviation or Herbicide Example | Mechanism of Action |
| Acetyl COA carboxylase inhibitors | ACCase inhibitors (e.g., fluazifop) | Inhibitor of acetyl coenzyme-A carboxylase, a pivotal enzyme in plant fatty acid biosynthesis. |
| Acetolactate synthase inhibitors | ALS inhibitors (e.g., sulfonylurea and chlorimon) | Inhibition of the acetolactate synthase enzyme, resulting in cessation of the biosynthesis of essential branched chain amino acids (leucine, valine, and isoleucine). |
| Enolpyruvyl shikimate-3-phosphate (EPSP) synthase inhibitor | Glyphosate | Inhibits the EPSP synthase, which leads to depletion of essential aromatic amino acids (tryptophan, tyrosine, and phenylalanine). |
| Hydroxyphenylpyruvate dioxygenase inhibitors | HPPD inhibitors (e.g., mesotrione) | Inhibition of hydroxyphenylpyruvate dioxygenase, an enzyme involved in the synthesis of plastoquinone and tocopherol (vitamin E). |
| Photosynthesis II inhibitors | Symmetric and asymmetric triazines (e.g., atrazine) | Inhibit photosynthesis by binding with a specific protein in the photosystem II complex. |
Suggested Citation:"Appendix D: Herbicide Classifications and Mechanisms of Action." National Research Council. 2012. National Summit on Strategies to Manage Herbicide-Resistant Weeds: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/13518.
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| Protoporphyrinogen oxidase inhibitors | PPO inhibitors (e.g., lactofen) | Inhibits protoporphyrinogen oxidase, which is in the chlorophyll synthesis pathway. The PPO inhibition starts a reaction in the cell that ultimately causes the destruction of cell membranes. The leaking cell membranes rapidly dry and disintegrate. |
| Synthetic auxins | Plant growth regulators (e.g., dicamba and 2,4-dichlorophenoxyacetic acid) | Mimics a plant growth regulator. The specific mode of action is not well defined; however, these herbicides mimic endogenous auxin (IAA) and appear to negatively affect cell wall plasticity and nucleic acid metabolism. |
