Wash feet; then place 'Clotrimazole 1% w/w cream' on your feet & toes. Allow to semi-dry or pop some socks on. Do this for a week or however long is required (you will need 4 tubes 20g minimum). Everytime you take the boots off, pop some talcum powder into them. These will stop you're feet sweating & help kill the bacteria.
If the OP has manure in his boots he needs to be careful. My mate's 17 year old son joined the Army and grew another foot. He reckoned it was from all the sh*te they put him in.