The condition could be one of two things: It could either be mange (which is serious, but can be treated), or it could be a flea infestation and they are congregating in the long fur on the neck area. Both conditions can become intolerable for your dog because of the itching, scratching, scabbing over of scratched-raw areas, and these open sores (at least until they scab over) can become infected. Either way, it is not pleasant for the dog going through all that. I would strongly recommend that you take your dog to your vet to be checked over thoroughly. Both are treatable conditions, and your dog will thank you for relieving his/her discomfort.