The funny thing is that is is actually good for him. I read an article in a magazine about gross facts. One of them was that picking your nose and eating it, lol, actually keeps one healthier. So those who pick and eat get sick less than those who dont, lol. My son loved it. I would not worry about it.
If it truly does bother you that much just make sure to repeat calmly "Child's Name" we don't put our fingers in our nose. Then give them alternatives to the behavior, such as we can put our fingers on the ball, or on our nose, or something of that nature. If his nose does bother him show him how to blow it when it bothers him, or to tell Mommy that it bothers him.
Good luck!
T.
Founder
www.theparentpack.org