Heat Treatment for Fireblight

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?



One thing i do if a canker is in a trunk is to hit the canker with a blow torch after carving it out. It works!


That gives a whole new meaning to fire-blight!


Maybe we should all grow apples in Phoenix.

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A friend did this to keep pine borers off a very old pitch pine. I wonder what the temperature is underneath when in the sun. Something on a smaller scale might work if temp is high enough.


I did the heat treatment. I wrapped the heating pad around the affected area. It was complicated by multiple branches in the way but finally got it on there solid. Began with a zip loc bag full of water between the pad and trunk but removed that after a few hours struggling to get the temp up. Temps ranged from 115 to 140. It got away from me and heated up hotter than I wanted a few times. Overall I had at least 5 hrs over 115 F. When I started the process only the pruning site was oozing. When I took off the pad there were four spots oozing. I think maybe I just made the FB mad :grimacing:. After 24 hrs there was no more oozing despite a bunch of rain. Bark is starting to look discolored. Maybe I cooked the bark? Anyway I’ll keep monitoring and update. I hate losing this tree I just grafted it over to winesap which is a really good apple here - one of the few.

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Update, it didn’t work. Well, I have not seen any ooze since shortly after the heat treatment, but all of the tree above where I put the heating pad is stone cold dead. So I’m not sure if the heat killed it or if the FB just ran its natural course and girdled the tree. There are three branches still alive that originate below where the dead starts. I need to decide whether to pull the plug on this tree or cut back below the bad part and see if by some miracle the FB has not stealthily moved down.

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