Hi sharkie, poor woofer. Not sure on doggy conjunctivitis, but human conjuctivitis means a sticky yellow goo that turns into a crust normally; his eye will be itchy, and he will be irritated. You say he's been in long grass, so it may well be a grass seed that's caught in his eye and stayed there, causing discomfort and irritation. If I were you I would get to the vet, it may become infected, and I am sure that could lead to a number of complications.
In the meantime, I am told cold teabags are good for wiping eyes, but be careful, as if it is a grass seed you don't want to embed it further, and if it is conjunctivitis then you don't want to spread it-it's v. contagious, certainly in human form anyway. Keep him away from other dogs, JIC.