I just got through pruning out almost 1/4 of one of our pear trees to get rid of fire blight.
Bryant RedHawk wrote:Mark, yes that ring is signifying that the infection goes deeper, I am very sorry to have to tell you that, but I may have a fix since it looks like it is heart wood that is carrying the blight virus.
Make up some dilute (5 parts water to 1 part bleach) bleach solution and apply it by eye dropper directly on the darkened wood, let that soak in and then apply a few more drops.
Be careful to not get it where the wood isn't darkened (or browned) just as a precaution. Do this several times over the next week and observe if the dark color comes back (that means you have to continue the treatment until it goes away) when the ring doesn't come back seal the wound with white Elmer's glue.