I found a paper describing a study that heated apple scions to 45 or 50 C (113 or 122 F) for a range of durations to test whether the treatment would eliminate the FB bacteria from the twigs.
It appeared to have worked at least for the longer durations (3+ hrs). This study gave me an idea for a possible treatment of FB cankers that have reached the main trunk or larger scaffold branch. What if one were to wrap the infected area of the trunk with a heating pad for several hours - maybe overnight? I ran a test with my heating pad on the lowest setting wrapped around one of my outdoor temperature sensor units and it produced a constant temperature of around 140 F (60C).
This spring i grafted the branches of my yates apple tree to winesapleaving the main yates trunk in tact. One of the grafts became infected with FB at the end of the 2’ of new winesap growth. I broke off the entire graft and peeled back the bark on the end of the 12" yates stub coming off the trunk. I could see no visual signs of FB so I decided to call it an “ugly” stub and come back and cut if off in the hot summer once the FB settled down. Fast forward to this week. We’ve been having 95+ temps and pretty dry with no FB observed for two months, so I fugured this is as good a time as any to cut off the ugly stub. I cut it off and it appears that FB had run down the center of the stub and into the main trunk. Not good. The cut is discolored in the middle and this morning there was a tiny bead of golden ooze in the center of the pruning cut - right on the discolored wood. Really not good.
My options are a) to leave it be and see what happens. I’ve seen this story enouogh to know what is likely to happen. The FB will come back with a vengeance this fall or next spring, b) cut the main trunk all the way back to well below this infection - basically a stump with just enough yates left to get a new tree going, or c) try the wacky heat treatment idea. I think I’m going with option c.
Question: Has any one done something like this? How did it go? What temp did you acheive and for how long? I’m guessing my 140F heating pad could damage the cambium although I’m not cerain. So I’ll probably need to bring that temp down somehow - maybe a plug in thermostat. Any idea how hot is too hot?