Sorry about the FB. What variety is in your picture? Thanks, Bill
Bosc pear. Store bought trees. I’m thinking of removing all store bought trees in my orchard because I don’t know the rootstock and a lot of them were disease prone varieties. Looks like I’m gonna be digging these pears up.
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Summer Pruning and Fire Blight: I like to lower the height of my apple trees in summer to eliminate ladder work and to calm their growth rate.
What temperature is it safe to do this without fire blight entering the cut surface? I see various ranges on internet: blight is active 60 to 80 degrees then another says 75 to 90 degrees. Then U of Md says prune out blight in winter below 40 degrees, implying blight can spread above 40 degrees.
Can anyone sort this out?
Update: Dr. Kari Peter at Penn State, advocate of Prof. Steiner’s Ugly Stub Method, says blight is active from 50 degrees to 90 degrees. He says do any summer pruning in Aug to early Sept during a dry spell. I suppose 95 degrees in July would also work, right? By August trees have already stored a lot of energy which defeats the purpose of trying to de-invigorate. I have experienced apple friends who summer prune to reduce height at the Summer Solstice in fire blight country, saying that has greatest effect to calm down tree growth before it has had a chance to store energy during summer months. If those Solstice cuts are into say three year old wood, blight may have hard time taking hold against all the carbohydrates stored in older wood. Maybe that’s how you can get away with Solstice cuts to lower height.
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Good question. I’m looking forward to hearing the replies.
Here’s diagram from U of Md showing Ugly Stub Blight Pruning Method. It’s not as clear as it could be but if you study you’ll get the drift. The top diagrams are the incorrect method of cutting off the blight flush with next branch and the bottom diagrams show correct stub method.
![drawing of ugly stub pruning method|498x388]
(file:///sites/default/files/_images/programs/hgic/Diseases/uglystub0001editsm.jpg)
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This is not a straightforward answer but the truth is fireblight is active anytime the tree grows. You will hear people say the rule is 65 degrees and 65% humidity the fireblight bacteria is active which is more the guidelines but not exactly the rules. Fireblight is never active when the tree tissue is not growing and that’s the only time your 100% safe. You can prune in dormancy without fear of fireblight but use good cleaning techniques on your saw blade. If the cells are rapidly multiplying e.g… blooming or new leaf shoots are forming the fireblight bacteria multiplys rapidly. Thats why the rainy season during a warm spring is so dangerous because trees grow like crazy which is perfect breeding ground for fireblight bacteria. To make matters worse some people fertilize which causes rapid growth like throwing gasoline on a fire that really provokes fireblight to multiply. If you have a spreading agent e.g. cicada, grasshoppers, birds etc. A orchardist like us grafting from tree to tree with fireblight juice all over their hands cutting non dormant trees then we have big trouble. I paid dearly over the 17 year cicada 17 year cicada's woke up hungry . I’m no longer naive about insects and fireblight and though its been years ago i remember it well Late season Fireblight
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Clark- Re: cleaning your saw during/after dormant pruning- do you mean cleaning it between cuts (which I thought was unnecessary during dormancy) or cleaning it after you’re finished with dormant pruning?
The late Prof. Steiner, University of Maryland (Ugly Stub method author) said you don’t need to clean your tools because in winter it’s impossible to spread blight and in summer it’s impossible not to spread blight if temps are 50 degrees to 90 degrees, even if you disinfect. Blight is in the air, on every inch of bark of the tree already- there is no way to avoid introducing it on to the pruned cut surface. That’s the whole rationale behind leaving an ugly stub.
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My opinion is clean the blade during cuts in an orchard where fireblight is uncontrolled or particularly bad. Fireblight oozes a syrupy mixture and though its not the case in my orchard if fb is left unchecked for years and you cut through that sap it does spread it in my opinion. In my orchard I remove fireblight as it comes up so it does not winter over. I have neighboring farms who’s trees are covered in fireblight top to bottom and don’t die and I cringe when I think of my blade touching those trees. Dormant or not that oily tar like substance is the bacteria spreading agent that winters over year after year until someone puts a torch to it or it dies and drys up.
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(answered my own question)
Visible Sign of Blight
My dear old Virginia Beauty apple (8 years old) is riddled with blight. I recently learned Century Farm’s David Vernon warns against VB in coastal plain. As I gradually saw back into older and older wood, will the inside appearance of the branch tell me if blight has penetrated that far? In other words does blight discolor the inside of the wood? If so I plan to cut back until I see “clear” wood.
Many thanks for help on this. I’d like to save and graft four or five limbs vs cut at two feet and start over from scratch.
If you see discoloration it’s definitely in there. If it looks clear, it may or may not be there, in my experience. I’m 1 out of 6 for cutting the trunk low to save the tree from fb in the trunk. In the 5 failures, the blight always got deep into the center of the trunk or branch and ran a long way before I even realized it was there.
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Thanks Barry. Is the discoloration black? I’m hoping six year old wood has extreme resistance to blight. Going on the theory that younger wood is more susceptible to blight.
How old was the tree or trees you lost?
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Mostly brown. My trees were around 3 yrs old. I let a lot of flowers bloom on 1 yr old wood with no antibiotic spray, and fb tore through that young wood. Hopefully your older tree holds up better. I hope you can do a modest cutback instead hacking it off low.
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Does this look like fireblight in the heartwood and sapwood? I sawed below it where wood is clear, no sign of discoloration. Will bark graft and find out soon enough if I cut low enough. Caney Fork Limbertwig and Kentucky Limbertwig (shown in photo) have turned out to be blight magnets here with blah/meh taste, so they are now officially gone. Ditto Virginia Beauty.
Note to Limbertwig collectors: All three Royals show excellent blight resistance here in 7B: Royal LT; Red Royal LT and Myers Royal LT. Black LT gets its share of bight but so far is manageable. Too early to say for Swiss LT and Victoria LT, but so far so good. Guy Ames in Arkansas says Royal LT resists all major diseases. I think it was Calhoun who raved about Red Royal LT as one of his favorite eating apples.
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We have been fighting FB for a long time. Don’t believe it can be controlled in my area when it rains a lot during bloom. Young dwarf trees are the most susceptible. The worst place for a FB infection is on the leader of a young dwarf tree.
We had very little FB for the first 3 years but we got clobbered in year 4. We removed the worst trees. Cut the leaders on many more which survived but were stunted. Cut out about and destroyed about 2 pickup trucks of infected material on about 400 trees.
Now in year 8, we decided to remove most trees with cankers on the leaders. Some trees were in slight decline but producing some fruit, but lots were productive and looked normal except for 1 major canker on the leader. Some of the cankers may have been some form of Bot rot.
Just 1 FB canker contains enough bacteria to infect an entire acre of apples and hopefully removing most of the infected trees will reduce the amount of available FB bacteria and will help us in the future.
This year we plan to spray copper and oil a little late and not worry about the russet then spray strep based on the cougar blight model through NEWA. This model uses weather info from my local airport to make predictions about a coming FB infection. I try to spray strep ahead of the infection, but when it rains everyday its impossible to spray in time to kill the FB bacteria. Probably use some Apogee for shoot blight on some varieties, but not Stayman where it promotes splits. It may promote splits on Goldrush too, so no Apogee on Goldrush this year.
The label for Lime Sulfur has been extended to some mid Atlantic states for bloom thinning and perhaps FB control. Its often used in Washington for both purposes.
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The inside of a tree is not alive. The outside layer of the tree aka cambium layer is the living part of the tree. Fireblight only attacks living tissue.
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Thanks Clark. Any idea what this discoloration is in the photo? It peters out the farther away I cut from blight cankers.
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I’m not sure what’s causing it but it could be death of cambium that is allowing water to get to internal wood.
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That’s how my fb trees looked inside when I cut them down. My $ is on that being fb but I’m no expert.
Thanks for your ideas guys. I’m going to cut below it just to be on the safe side. It seems to peter out pretty fast as I head South down the leader.
I should never prune when I’m tired or in a hurry. Today I accidentally cut off a three year grafted branch of Royal Limbertwig that was all spurred up. Damn. Really want to taste it. So I cut up scions and will graft them back on!! A lesson in patience, Time and care, etc.
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