One year Lee’s orchard got hit really hard with fireblight. With so many varieties and the right conditions it can run amok and overwhelm even the most resistant ones.
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Some varieties have to be typhoid Marys. I know that here, quince brings FB to orchards that likely would otherwise not get it on apples and pears.
I’m quite sure too much vigor (too much nitrogen in most cases) is responsible for a lot of the fireblight in apple trees. I suspect stress in general may also mean less resistance in a plant.
Alan made a good point that some light damage on tips of limbs is not same as having a tree killed. (I’ve never had a large tree killed…but younger ones I have.)
The vigorous seem to be most at risk of getting a strike (but also seem to recover).
Stayman/winesaps get fireblight pretty easily here…but only current year shoots seem to get killed…(unsprayed trees).
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Compact spacing with low to the ground trees are tailor made for fireblight.
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Fireblight on apple is not usually that big a deal around here, but this year I saw a fair amount of it in one particular area. This was on very old trees that had been recently and heavily pruned. It looked like the damage was limited to certain branches on the trees, but I couldn’t tell anything more than that. We’ll see how they do this year.
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Here fireblight is present. A local orchard lost their crops on Northern Spy one year. I haven’t really seen fireblight on my apple trees with the exception of one tree that suddenly died but I suspect that was probably a root issue of some type but it is hard to be sure.
On the other hand I have a large Cleveland pear ornamental tree right next to the orchard. This year it was covered with fireblight strikes but nothing showed up on the apple trees. I did pick apple trees and rootstocks that had resistance to fireblight and that probably helped. Also my trees are almost all on dwarf rootstocks… I don’t have large trees that tend fare well with fireblight strikes.
If you have fireblight in your area I think you would want to pick trees and rootstocks that have some resistance to fireblight. Also resistance does not mean immunity. A resistant tree can die from fireblight if the disease pressure is intense, or it is weakened by poor health. Here are some charts that list fireblight resistance.
However, I will caution you sources don’t always agree on the level of resistance. I think this is due to various factors, field studies being done in different areas of the country, different fireblight strains, etc. But the charts are still pretty useful.
Disease Susceptibility Ranking of Apples – Database of Apple Diseases
https://www.extension.purdue.edu/extmedia/BP/BP-132-W.pdf
Table of Apple Cultivar Fire Blight Susceptibility – Apples
https://treefruit.wsu.edu/article/fire-blight-susceptibility-of-apple-cultivars/
https://blogs.cornell.edu/khanlab/extension/fire-blight-susceptibility-of-common-apple-cultivars/
I think Alan already posted the last one from Cornell but I went ahead and included it as it was on my list. Plus I think the WSU link above is a really good study with lots of detail.
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I think I"ll order one of the ‘Mutus’ apples on that “Table of…” link.
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2024 Spray Bulletin (VA, WVA, MD) out. Fireblight instructions have changed a bit - more emphasis on application of heavy concentration of copper during dormant season. I think this will help. Key is to apply with dormant oil at least twice, gets the scale and reduces FB issues in my experience. Even then you have to watch for it. Since we should be pruning soon, if you see damage remove it.
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