Most likely those tunnels are from cabbage root maggots, which are a problem in my garden. They are the larvae of a small fly which lays its eggs on the stems of radishes, turnips and other cole crops. The best defense I have found is floating row cover, although I can get some clean radishes from unprotected rows just by harvesting them when they are very young.

Jim

Thanks for the fast response, I appreciate it. I've heard of those before but I wrongly assumed they attacked only the cabbages! Guess they go for anything. I'm going to have to do some research! Thanks. Marg