Hi Tippy,
I know many times the disease is described as a sort of shot hole appearance on the leaves, but sometimes the disease manifests differently. I was thinking this is possibly the case since the tree is in a greenhouse.
Here is a pic of X disease on a peach
That said, of course I’m not at all certain is X disease, but I thought it a possibility, since X disease just affects different branches at first.
Now that Marc has indicated the other trees are showing symptoms, I’m not sure. I wouldn’t expect X disease to spread that fast.
Marc, is it possible you are over watering the peach trees?