My cold storage area is a ''well house'' that was built before municipal water was installed in the area. It is an underground room, accessible from my basement, that is under the back yard patio. It is about 6 foot x 6 foot by 4 foot tall, I have to crouch to get int there, but I don't have to crawl. All winter it hovers at soil temp, between 40 F and 32 F, occasionally during very cold spells it will get to 29 F. when it is well below zero outside. It is concrete block, which is not totally water tight, humidity hovers close to 100% all winter. First year I used it, fungus and mold destroyed almost everything. Second winter I added an inexpensive fan, just a little 9 inch diameter fan from local box store, maybe a $12 fan on sale. It is pointed at the ceiling, runs 24/7 while room is in use. I have not had a problem at all with mold in the well house ever since. I do need to check for water, and will probably have to water once a month, to once every 3 weeks.
Seriously, adding a fan to your growing area or your wintering area will help the health of your trees, and may eliminate the need to use fungicides completely.