Justin, there is a lot of good advice above, so I really don't have anything completely new to offer, except emphasis.
The best way to avoid fungus is to improve the growing environment.
FANS, soft thin leaves should be gently moving in the breeze, 24 hours a day. This gets air down into the potting mix and helps the roots. You want to feel the air moving.
Good second step is cleanliness, remove all old dead organic matter. Empty old pots that may have once held plants, no dead leaves lying around.
One inexpensive topical sterilant that will help with fungi and bacteria is hybdrogen peroxide at the concentration that is safe for human use on cuts and as a mouth wash. That is 3% concentration from the local grocery store in the section where first aid supplies are sold. It is safe to use as is, both as a spray, or as a drench on your orchids. Its action is only on the surfaces contacted, but there is no damage to healthy leaf tissue. Short action, when the fizzing stops and the plants dry it is gone. It is particularly effective on bacteria, but only bacteria on the tissue surfaces the peroxide touches. Cheap and easy to use for small collections, if you have a lot of plants, it is cheaper to go with other alternatives, but for just a few plants, hydrogen peroxide is cheap and easy to get locally. Safe enough to use "as is" on seedlings coming out of flask. There are commercial grades of stabilized peroxide, one is Zertol (? spelling?) it is more concentrated than over the counter peroxide. It was originally marketed for algae control in swimming pools, plumbing, greenhouse glazing and for cleaning work or lab surfaces. One would need to do the homework to figure out the dose rates.
As mentioned earlier, Physan is another good topical sterilant.
If your rot is slow, taking 5 days or longer to move through a leaf, there is a good chance the disease agent is actually one of the bacterial rots. These bacterial rots usually can not be stopped by a fungicide. Since fungicides can be quite expensive, this distinction is worth noting.
Once when I thought I had a bacterial rot, I tried the anti-biotics sold in the aquarium trade for tropical fish, but to no effect. Tried both gram negative and gram positive. The plants died anyway.
Good air movement, watering in the morning, so the leaves are dry by nightfall, clean growing area, good air voids in the potting mix so the roots can breathe, not drying out plants hard between watering so root tips don't die and provide an entry for pathogens are all key to avoiding rots. The best cures are environmental.
Actually drying plants out too hard between watering, especially Paphs and Phrags can lead to a host of problems, that are the result of the entry of pathogens into the plants from root tips and leaf tissue damaged by drying out too hard. This turned out to be the main cause of my episode with rots back in the day when I thought I knew how to grow orchids. :evil:
Hope this helps.
