This is a fine guide from Breeden, Brosnan, and Vargas at the University of Tennessee: Understanding how turfgrass herbicides work. It's about herbicide active ingredients and the associated mechanism of action class for those herbicides. It's important to know this so herbicide mechanism of action can be rotated. This is something you want to do before a problem develops. From the guide:
"Developing weed management programs utilizing herbicides that employ different mechanisms of action is critical to both preventing and managing herbicide resistant weeds. It is recommended to rotate herbicides that employ different mechanisms of action as often as possible, as well as implementing cultural practices that maximize turf competition and limit weed encroachment."
This guide lists the mechanisms of action and tells you how to do it. One to add to the #TurfReads list and to keep handy as a reference.