Dog eating conkers

Wonder if anyone has any advise on how stop/ help this for dog? I have a 1 year old springer spaniel who started making a game for himself jumping up to grab conkers off the tree a few months back. this was fine as he could only reach a few but now since it's the time they are falling off he is breaking open shell and chewing on conkers. I tried giving out to him, offering a treat instead but nothing has worked. There are 100s of the blasted things. As soon I have yard cleared( 3 wheel barrows one time) an hour later it's as bad as ever. He has now started vomiting and is off his food and I can't think of what else to do. Any ideas welcome please. He's a very smart dog and quick to learn so I think I'm missing the obvious