Workinonit, you've pointed out the reason I am trying a gravity fed drip system first. The weeds I wish to target (dandelions and thistles, etc.) are not all standing higher than the grass. Some are, but not all of them. For that reason, I will be using a herbicide which targets broadleaf weeds. Because of the wind factor I spoke of in my first post, I don't want to spray as that invites drift. Another consideration is the mix rate. Can I dilute the herbicide a bit more since the drip should be applying more liquid than the spray? I'll have to look up Johnson Grass to see if that's the same as what we call Crab or Couch Grass.