So you have a moldy saddle... Congratulations! That means you're doing something right.
Mold will not grow on a saddle if there isn't enough oil and moisture in the leather to support it. So your oiling and maintenance routine are spot on.
But nobody wants mold on their saddles and tack, right? Not only is it an eyesore, but it will eventually stain and damage your leather. So head to the kitchen and let's take care of your mold issues.
The Magic Sauce
We're going to create a 50/50 mixture of white vinegar and water. Once you've filled your spray bottle with half vinegar and half water spray the infected area on your saddle. You'll want to wait a couple minutes, then wipe the mixture off. Set the saddle in the sun to dry.
The vinegar will kill the mold spores, but be careful, the mold that has set into the saddle can survive for a number of years. You'll need to be extra careful to make sure it doesn't grow back.
*Test the solution in a hidden spot on your saddle to make sure there will be no darkening or staining before moving on to the more visible areas of your saddle and tack
Preventing Further Mold Growth
The best solution for store your saddle in a mold-free environment is to keep it in your house - along with the rest of your tack. If that's not an option, the next best place is a tack room with a dehumidifier.
Mold flourishes in dark, humid locations, so keeping your saddle in a dry, bright location is key.
Avoid the tack locker in your horse trailer during the most humid seasons for longterm storage. The dark location and damp/humid environment make this quite possibly the worst location you could choose for prolonged saddle storage.