My favorite leather reins are growing penicillian !!!!!!!!!!!!!!!!!!?

White vinegar on a damp sponge/cloth, and then lay the tack in the sun for a little bit. It'll kill off the mold you can't see, so it won't come back. Throw out the cloth you used. Go over your tack one more time with saddle soap.

The reason the mold keeps coming back is because it's nearly impossible to manually remove every last bit of the mold spores by cleaning with the usual stuff. All you need is for one measly spore to be left behind to cause trouble.

The vinegar might work but I'd wonder how good that would be for the leather.

Mold needs dampness and darkness to thrive so what I do is clean it the best I can then leave it out in the sun to dry out as much as it can (mold hates UV light) and then leave it to dry even more. Move it around some to get all surfaces exposed to that deadly UV light. When you start to think that leaving it out in the sun any longer would ruin the leather, give it another day then give it a good oiling or two to bring the leather back to life.

Once I left all my Leather tack in the trailer over night and when I was getting ready for a rodeo, ALL my tack was covered in that nasty green mildew!

Take moldy leather out of the tack room and clean it outdoors. That way, you'll avoid filling the air in the tack room with mold spores that will simply 'infect" other items in the confined space. After each use, clean dirt and sweat off of tack and allow the undersides of saddles and headstalls to dry thoroughly before they go back into the tack room. Dry saddle pads and blankets, preferably in the sun, before folding them and putting them away.

Clean them with saddle soap and oil them. The only way to prevent mildew is to store tack away from humidity (which can be difficult in some areas). I usually have to do some de-greening after every winter.

Wipe them down with white vinegar. It will kill the mold spores (at least most of them - you might have to do it more than once to get them all).