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Lesson Outline Auxin and Auxinic Herbicide Mechanism(s) of Action - Part 1 - Introduction - Overview and Objectives History and Uses - Introductory Level Mimics a Natural Plant Hormone Injury Symptoms Advanced Level Mechanism of Action or How Do Plants that are Sensitive Die? Summary - Auxin and Auxinic Herbicides - Part 1 - Introductory Lesson Media Objects Overall Picture of Auxinic Herbicide Action

Auxin and Auxinic Herbicide Mechanism(s) of Action - Part 1 - Introduction Rate Me 1 2 3 4 5 History and Uses - Introductory Level The auxinic herbicides were among the first selective organic herbicides developed and were first discovered independently by British and American scientists during the 1940s. The selective control of broadleaf weeds in cereal grain crops by auxinic herbicides has made this group one of the most widespread and important herbicide families. Table 1 contains the four major classes of the auxinic herbicides, their trade names and the crops on which they are used. Figure 1 shows their structures. They are applied postemergence. Depending on the class, they may have soil as well as foliar activity (Table 2). Common features among the auxinic herbicides are: They are applied POST emergence for the control of broadleaf weeds in grass crops or systems, Their soil residual activity varies with individual herbicides, Some are volatile, They translocate from leaves or roots to growing points, and Selectivity in tolerant grasses is due to restricted translocation, enhanced metabolism, and the lack of a vascular cambium. Selectivity in broadleaf species is due to metabolism of the herbicide to a non-toxic form. Table 1. Auxinic herbicides belonging to different chemical families and the crops in which they are used. Herbicide Class Active Ingredient Trade Name Major Use Phenoxyalkanoic acids 2,4-D Various Corn, wheat, barley, turf, etc. 2,4-DB Butyrac Soybeans, peanuts, forage legumes Dichlorprop (2,4-DP) Various Brush control MCPA Various Wheat, barley, corn, turf, sorghum, flax MCPB Various Peas Mecoprop MCPP Various Cereals, turf Benzoic acids Dicamba Banvel, Clarity, Banvel SGF Corn, wheat, barley, fallow, sorghum, range Pyridinecarboxylic acids Clopyralid Stinger, Reclaim, Transline, Lontrel Wheat, barley, canola, range, corn, oats, sugar beets Fluroxypyr Starane, Attain Wheat, barley Picloram Tordon Wheat, barley, range Triclopyr Garlon, Grandstand, Remedy Rangeland, turf, rice Quinolinecarboxylic Acids Quinclorac Facet, Paramount Rice Table 2. Foliar and soil activity of auxinic herbicides. Herbicide Class Foliar Activity Soil Activity Phenoxyalkanoic acids 2,4-D 2,4-DB MCPA Little to none Benzoic acids Dicamba Dicamba (very little) Pyridinecarboxylic Acids Clopyralid Picloram Triclopyr Clopyralid (< one year) Picloram (> one year) Triclopyr (very little) Quinolinecarboxylic acids Quinclorac About one year Fig. 1: Structures for the Four Major Chemical Groups of Auxinic Herbicides (click on images to enlarge) Comments Be the first to write a comment... Add Comment

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This project was supported in part by the National Research Initiative Competitive Grants CAP project 2011-68002-30029 from the USDA National Institute of Food and Agriculture, adminstered by the University of California-Davis and by the National Science Foundation (NSF), Division of Undergraduate Education, National SMETE Digital Library Program, Award #0938034, administered by the University of Nebraska. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the USDA or NSF.
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