I just took the lids off my tree peony (Japanese and Chinese) cages and am a bit worried. They are still sitting in 1.5' of snow around the cages (covered in landscaping paper and burlap). Buds galore. Last year they looked about the same (fewer buds) but this year -- looks like a mouse chewed the bark about 6" up the trunks. Totally gone. The bushes are only about 2' tall. The trunks are green where the old brown bark is gone, and the ends of branches I snipped last fall are also green. Could the bark have split off the trunks naturally? And one has a layer of ice on the bottom of the cage. Also new. I have taken off the tops to allow warm air in and hopefully dry out the surface around the soil surface. But I think I may have a problem with fungus or mold on one of them. I am hoping that fresh air and sun will cure what ails them, but that chewed look is really worrisome. No obvious holes so I don't believe rodents did it. Ideas? Oh, I uncovered them this same time last year. Weather is comparable. Was 19F this morning and will run up to about 45 in the sun. Pond is melting about on schedule also. Peonies bloomed beautifully last year.
It does appear to me that you had some type of small rodent in the cases. Press lightly around the bottom to see if parts cave in.
On one of the pictures it does not appear that what ever caused the damage ate completely down to wood. So that one may survive and form a callus. On the ones that look the worst you might see if the surviving stems are still green. If they are try cutting off and using as experiments. I have had deer damaged portions of tree peonies root if placed in damp soil but have had no luck by placing in any other medium. However moist sand will help other cuttings to root given time.
Very sorry to see this.
As far as bugs doing this type of damage we do have a grain bug of some type, two segmented pencil lead size black/dark brown that can do similar damage but you will find large green cats enclosed in web in the surrounding areas. A heavy warning, if you do have this type of grain bug put all chocolate products under heavy security. Unlike most bugs they love real chocolate products and even will drill holes through those 2 1/2 inch cooking chocolate blocks.
Well, I think I figured it out. Rodents. I dug out a small azalea. This would be the third summer. It bloomed last summer with one or two flowers, so this year it would have been lovely. There was a mound of chewed up burlap making a cozy next for mice, although I didn't find the little ---well, this is a family sort of place --- rats!!! And no azalea. Nothing left. Down to the ground. I got Dcon and bated all three cages. If those rodents get to the buds on my tree peonies I would just absolutely go nutso!!