Here's the information on
cotton root rot. It seems kind of out of the blue as a suggestion for these plants.
More suspect is the relatively recent planting and their failure to thrive. Did you soak the roots in water or compost tea and unwrap roots from inside the container, then plant these each in a shallow hole, stretching out the circling roots and covering them in place with the native dirt? When I first moved into my house I wasn't organic and I didn't know about how to plant properly and lost several shrubs and trees over the next couple of years as they slowly died.
You can dig these up and replant them correctly, even after a year.