Grass eating isn't just to induce vomiting. Many dogs eat it as a 'salad'. It's also learned behaviour from other dogs.
Re ticks, Bung. Not sure what the vet did - sounds like a 'spot on', but try & keep him clear of ticks through spot-on, Ivomec injections, whatever. They are the leading cause of E Canis, which is a huge killer and can be unnoticable until too late. Also keep up with heartworm prevention - another silent killer. Both can be kept at bay by cheap Ivermectin injections every couple of months.