I don't experience it here, but I think 'bark split' - it's freeze damage and not a disease. There isn't much you can do now that it's happened, winter protection may have helped.

It's weird, it starts out as a small, oblong area where the bark has pulled away, then it starts appearing all over. I didn't think it was freeze damage as I've got a couple of tropical vireyas that seem to be doing the same thing, but not as badly. On the vireyas the bark has pulled away in a couple of spots but it hasn't completely come away from any branches, so maybe it's just from an injury or something and not the same thing that's killing my outdoor plants. We have definitely had some difficult weather in the past year or so. I'm about to give up on all the rhodies and relatives I think, they're a bit too fussy in these parts for my liking.

Definition, Bark Split

"Freezing temperatures are especially dangerous to unprotected branches and main stems, causing the bark to split and separate from the body of the the stem. In severe cases, a limb will become completely girdled and everything above that point will die; in cases of moderate damage the bark splits and rolls back but not to the point of girdling the branch. Such injury is deceptive in that affected branches may not die until the following Spring or Summer, going unnoticed in the meantime while hidden by foliage.

Sometimes freezing conditions will only split the bark without causing it to separate from the core. These wounds often callous over and allow the plant to function normally, but until the cracks heal they provide easy entry to fungus infections. Grafting wax painted onto these cracks will aid in their healing process and prevent diseases from entering."

Here is a link that might be useful: Photo #8, Bark Split Rhododendron

Here is a picture of what is happening to one of my tropical Rhododendrons. This plant has never even been exposed to frost. I'm not sure that it is the same thing, but I've never seen this type of thing in any of my other plants, just Rhododendrons and relatives.

Here is a link that might be useful: Vireya stem

I can see where that would be confusing - it does look very similar. I have no experience with the tender rhododendrons - but hang on and maybe one of the other members here will chime in and add something of value.

Cutting an example stem and taking it to your county extension agent is always a possibility too - if no plant pathologist in that office they would have access to one.

In the meantime, the ARS does provide a list of rhododendrons and azaleas grown successfully in your area, there may be varieties that would do better for you.

Here is a link that might be useful: Proven Performers, Ozark Chapter

Thanks for your help. I may try contacting the county extension. I hope that it isn't some kind of pathogen, but either way I'm bummed about having so many problems with Rhodies and Azaleas.

Try checking out sudden oak death, Phytophthora ramorum. Rhododendron is a carrier for this disease. It is relatively new and few people have experienced it in rhododendrons. You may be extra unlucky.

Another possibility is too much fertilizer. It the wood was growing too fast it could cause bark split. That is also very unusual. Rhododendrons need very little fertilizer if any at all.

Here is a link that might be useful: Problems in rhododendrons

I'm beginning to think morz8 might have been right about the nature of the problem. We had a terrible freeze in April of last year, and many plants have suffered here, some taking until the past summer and fall to die. It seems like I started having these problems with my Rhodies and Azaleas after this point. The ones in the greenhouse, well, I only have three in there and the extent of the bark damage is limited on them, so I think it's possible that in their case it might be something different, mechanical damage or something.
I contacted the plant diagnostic center of the University of Missouri and they were unable to make a diagnosis based on the pictures that I sent in. I may send in a physical sample to them to rule out Phytophthora or fungal agents.
I'm hoping that it was just damage from the unusual weather that we've had though.

I am not sure what kind of plant it is, but it is mature, have had for 10 years, had on our deck in a large pot and forgot to bring in when temp hit 28. The outer bark has seperated form the inner bark. Do I take off the outer bark or cut the plant back to where there is no seperation [about 1 inch from soil]? Thanks for any help

This is bark split and is caused by the freezing of the plant after the bark has started to rise. I would wait to see how bad it is. Cut off any dying parts or dead parts and leave the rest to see what will stay alive. Sometimes the cambium layer under the bark is still intact. If this is true, the plant should survive with little damage. If the cambium layer is destroyed in a region that basically strangles the plant, then the outward part will die but is should come back from the part closer to the roots for from the roots. If it is only partially strangled, then part of the plant will be OK and part will die back.

Here is a link that might be useful: How to care for rhododendrons and azaleas.

Correction: Bark Split occurs when the pant freezes after the Sap starts to rise under the Bark. That is why a warm spell followed by a cold snap is very destructive to some plants.

I had the same situation on a Kwanzan cherry tree. It was explained to me that this was caused by freezing at night and being exposed to sunlight hitting the bark in the morning and rupturing the cells in the cambium layer of the bark.

This seemed to be the case as the cracking occured on the side which recieved Morning sun. My suggestion would be to plant something low to shade the exposed bark areas or try shading it with a burlap "wall" in the early spring. There was no way to try this with a 15 foot tall tree, so the cherry tree eventually died.