Here is an interesting collection of articles about herbicide use and actions, all in Plant Physiology - important stuff for students to learn about!
Metabolism-based herbicide resistance and cross-resistance in crop weeds: A threat to herbicide sustainability and global crop production (http://www.plantphysiol.org/content/early/2014/08/08/pp.114.242750.abstract)
Herbicides as weed control agents – state of the art.
I. Weed control research and safener technology: the path to modern agriculture (http://www.plantphysiol.org/content/early/2014/08/07/pp.114.241901.abstract)
II. Recent achievements (http://www.plantphysiol.org/content/early/2014/08/07/pp.114.241992.abstract)
And an older but useful background review on their action