According to the attached UGA link, maybe it can be stopped with fungicides, maybe not. Hope this publication helps.

Here is a link that might be useful: UGA Root Rot

I've stopped root rot on aquatic houseplants using a capful of hydrogen peroxide per quart of water. It gets rid of the green slime that grows on the sides of the glass containers, too. I've never tried this outdoors.

I've also read that azaleas and rhododendrons get root rot more easily that some other plants. My county extension service office told me that they now recommend to plant these raised above ground level to help prevent root rot. She said an easy way to plant them is to take them out of the container, place them on top of the ground, and pour a bag or two of milled pine bark organic soil conditioner, pine bark mini-nuggets, or shredded pine bark mulch. Keep watered until the roots invade the pine bark, then they do great. I planted two new azaleas using this method about a month and a half ago under a large oak shade tree. They are doing great, so far. And I didn't have to dig a hole into the dirt with all of those tree roots! I went to Lowes and bought a 2 cu. ft. bag of Garden Plus Organic Soil Conditioner and a 3 cu. ft. bag of Garden Plus pine bark mini-nuggets and mixed those together in a couple of large wheelbarrows.