In dry climates, hoof wall fungus is somewhat rare. It ususally will happen when the paddock gets flooded, the horse prefers to stand in the manure and urine pile, or when the stalls aren't kept clean. You can fix the problems by exposing the fungus to air and they will usually go away.
In moist climates, this problem can be a never ending cycle. Dawn Jenkins, a barefoot trimmer and therapeutic shoeing practitioner, works in both Southern California and Hawaii and encounters such issues. She wrote a great article that appeared in the Holistic Horse magazine, issue Oct/Nov 2008.
In this article, she discusses ways to prevent and treat hoof fungal problems in moister climates. She also mentions some facts and poses the question....Could there be a difference in the individual immune system, not just the environment?
Read this article for some really good information and education that makes quite a bit of sense. She also gives some natural remedies and general instructions for helping to eliminate some of the fungal problems that your horse may experience at the wetter times of the year. Some of the natural fixes could certainly incorporate hoof boots and soaker boots. EasyCare has many boot styles such as, Easyboots, Epics, Bares, Old Mac and Boas, to help you keep your hooves clean and dry during the moister times. We have the Soaker boots to use for soaking with the remedies that are mentioned. Especially the Apple Cider Vinegar and water mixture, which I know works as I use this soak for my horses occasionally.
Check out the Holistic Horse magazine for several great articles on horse care and holistic answers to some of your horse's needs.