I offer these recipes in altruism, and will not engage in any further context.  TMI.  It’s all from the Yahoo SCA-Herbalist list.

Keeping his feet clean and dry will help. Wearing open toe sandals without socks should help as well as wearing socks  made of natural fibers that breathe as opposed to synthetics. Here’s a recipe for a vinegar foot soak that’s anti-fungal. Soak the feet in vinegar/water solution for 20 minutes.

Foot Vinegar
1-pint orgainc apple cider vinegar
1-teaspoon lavender flowers
1-teaspoon oregano
Allow it to macerate for 2 weeks. Dilute this with water for the
soak.   

Also here’s a recipe for Anti-fungal foot powder
1 part cornstarch
2 parts arrowroot powder
1 part ground calendula
1/2 part ground myrrh
3-4 drops of tea tree essential oil
Allow the mixture to sit 3-4 days before using, shake once a day.Have
him test these formulas on a small area like inside his elbow to be
sure he’s not allergic to them.
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            Toe nail fungus indicates a systemic problem which is the result of an 
imbalance of the flora and fauna of the intestines.  Oil of Oregano, taken  both
internally and applied to the area has the research behind it.  It  often takes
a long time to get rid of too much yeast in the system and would  require a
long-term commitment and dietary changes as well.  Antibiotics  often help
create this imbalance.  So, anti-biotic’ s would be adding to an  existing problem,
though many doctors still pad their wallets by writing these  prescriptions.

Pro-biotics, yogurt with aphodophilus, apple cider vinegar, if tolerated,no 
sugar, no flour, no rice. barley,corn, mushrooms.  Basically, get the white 
out of the diet.  Cleanse with lots of fiber. 

Once this "sympton" has appeared, the condition has been around for a while 
and it will take a while to restore balance.  It is not over when this 
symptom recedes and the program should be followed for months if not up to 3  years.

P’au D’arco and Olive leaf have been used in this course, as well, the oil 
of oregano showing up as the biggest star helper.  Often people react 
differently to herbs, so  trying a little and watching the individual  reaction is the
way to determine which herb is their best ally.