If you have to prune for disease (fb) or damage, would dusting the cut with streptomycin be of any benefit?
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It really does not help unfortunately. Spraying with copper is the best bet before infection occurs.
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Rats!
The results of my methods though highly controversial have produced very good results Here comes the 2016 apple and Pear harvest! & Here comes the 2018 apple & pear harvest!. Deer pressure and their browsing has challenges. What works in Kansas may not be the best methods in other places. Fireblight will destroy an orchard in a place like Kansas if pruning is done at the wrong time.
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I live in southern Louisiana. We have severe and constant fireblight issues. This spring I tried a slightly new approach to antibiotic application - I only sprayed the trunk of the tree. It worked, or at least I had no fireblight until the end of May, and then not much. Trees that I did not spray are heavily infected. So, my question is, does fireblight overwinter in the stem and then get translocated to the leaves in the xylem?
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Yes fireblight can be stored in lesions on the tree your observation is very accurate. Antibiotic does work and used it myself for years but i wouldnt looking back on it. Things build tolerance to antibiotics. Try using copper for your spray its highly effective. Better yet like your thinking remove the lesion areas and you removed the next infection. Fireblight is dormant when the tree is not growing it needs actively growing tissue to spread. Some pears like leadbetter are highly resistant to fireblight but intended just for canning.
Thanks for your quick reply. My training is plant anatomy so I gravitate to consideration of anatomical factors that might affect fireblight. While it appears that many people believe that fireblight is principally spread via an external route, i.e. insects etcā¦, I wonder if it can travel through the xylem. Angiosperm xylem is a series of cells that are connected to each other via large pores. Could it be possible that a resistance factor would be the diameter of the pores? i.e. a variety with relatively small diameter pores would be resistant.
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Anything is possible ofcourse but your theory will need additional research. You will need to put it under the microscope so to speak. We know the cambium layer is the only part of the trunk thats growing which is why we use it for grafting. Trees such as farmingdale in my area show no strikes at all. Keep in mind pears such as kieffer and pineapple get fireblight but they dont typically die its their ability to not uptake the bacteria systemically that keeps them alive. Many antibacteria compounds exist such as copper. Years ago i had a very bad fireblight infection on a row of pears they were all turning black all over the leaves and leaf tips as it was everywhere that year. I sprayed the trees with a very diluted vinegar which is ill advised because its a herbicide. Vinegar is also antibacterial and i knew the trees would die if i did not do something. The next year i sprayed with copper and looked for lesions and removed any i found with a knife from the trunk. There has never been fireblight on those trees since which is over 5 years. Bacteria such as fireblight are not well understood. The #1 problem is people donāt understand fungicides are not intended to kill fireblight since its a bacteria. That means 99% of home orchards go untreated and spread the bacteria to us by bird and insect. That is why fireblight is such a problem. In addition wild callery are everywhere and though very tolerant themselves to fireblight they sometimes act as a host for the bacteria. If you need tissue samples from different pears the usda corvalis program is excellent for research such as yours. Iāve researched pears many years and find them fascinating. My area has no commercial pear orchards as they are challenging to grow here but easy in comparison to your location. Iāve done lots of research which i post for future generations that they can use for growing pears in Kansas or similar climates.
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Thank you for your insights. I certainly have plenty of raw material to work with!
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Consider an approach that i use on your pears. I grow callery and BET rootstocks many years and once they get several feet of growth i cut them off several feet high and graft them. So i leave the bottom of the tree callery. So i do that for many reasons one which is applies to you. If fireblight does not kill callery and only the top part of your tree is tame the roots are not killed. I bring this up because if fireblight kills the top of my tree im back in commision producing pears in just 2 years typically. The roots are also more tolerant to drought and other things so i get pears when others donāt. There are home users growing pears who get crops every few years. If the pear has a poor root system it drops pears during drought but mine dont drop.
Cutting them high also has the benefit of putting the graft out of deer range. Plus established roots and all that you said. I tried a couple BET here but they donāt seem to like clay much. Most of my pears are on callery and they love clay.
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Based on my own experience it seems like most fireblight strikes are from the environment. I had many trees getting fireblight every year but one year I removed all my quince and highly susceptible apples and had almost no fireblight the next year (or any later year). Also, I noticed trees with a few late blooms were more likely to get infected on those late blooms which is consistent with external forces (eg bees).
Cutting open fireblight infections it is clearly traveling through the wood (the wood is discolored) and overwintering there so spraying the trunks could help limit the initial outbreaks perhaps. Maybe try spraying all of the trunks or all but one next yearā¦
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The critical need to cut out over-wintering blight lesions or cankers is just one reason I urge new growers to limit tree height to whatever you can easily inspect every square inch of bark in winter for cankers.
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Yes there is some truth to that in the South especially. In my area nature prunes them for me more than i like.
Orcas is a variety that really produces for me. Most of our varieties produce well. We are the pear state after all.
John S
PDX OR
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My lack of pruning pays off again and again year after year. That said remember nature prunes for us in Kansas. We have significant wind storms and several branches can be lost in one storm. That natural cycle here invigorates the trees more than enough. You can see this Duchess Dā Angoulme though badly damaged in a storms heavy with pears
Improved Kieffer
Douglas. Harrow sweet, Harrow delight, ayers , drippin honey and many others were very heavy with pears this year in 2021 as well. The trick is trying to get the heavy fruit off the tree prior to a big storm. Sometimes trees are damaged by strong storms with no fruit on the trees.
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Clark! Wowie. Zowie. Thatās a LOT of pears! That is pretty amazing! 
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Same experience here with an Anjou and a Bartlett bought from Southern States. They had fairly severe fireblight the first season they were planted. Then I cut back all the fireblight I could find - and grafted other varieties to those scaffold branch āstubsā. It seems to have worked well. And even though I left a few original variety scaffold branches - no fireblight appeared this summer. ? I was expecting to have to get rid of the trees despite the surgery! But so far - fingers crossed - no more fireblight. I will continue to spray as a precaution, of course.
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Thank you ! Iām not sure what happened it frosted repeatedly on the blossoms. That surgery you did I have done with other pear trees and it works. Had a seedling Bartlett that was a big problem I grafted over to fireblight resistant type pears about 10 years ago and my problems are gone.
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As pointed out we have had heavy wind damage in recent years so the pruning gets done for us so this year there is lots of extra work. In your zone you may not have my problems! Donāt overdue it with your pruning if you want fruit.
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