The dreaded F word (Fireblight) is showing up in our orchards


I know what you mean about the smell. It was awful. I put the bags in my big trash can, come trash pick up day it was terrible sitting in there baking in the hot sun.


Interesting discussion of fireblight on apples, use of copper, proper pruning by Steve Wood, well known cider maker:

Over the years, we’ve lost thousands of trees to fireblight – we take it
pretty seriously. We’ve learned that season-long applications of a low
rate of copper work pretty well to suppress fireblight. In cider trees, you
aren’t worried about fruit finish – a little copper russeting has no
effect on the value of a cider crop. In any event, a little copper
phytotoxicity doesn’t hold a candle to a fireblight infection – fireblight
is the grim reaper.

There are a few newer formulations (eg. Badge, Cueva)
that contain much lower concentrations of elemental copper than the older
compounds (less metal left in the soil), and appear to be equally
effective, and gentler on the trees and fruit. Spray the whole orchard
(not just the infected trees). One of of copper’s chief functions is to
make an inhospitable environment for the pathogen on the surface of the
trees. Fireblight lives (in part) as an epiphyte on all the plant
surfaces, so the main thing you’re doing with copper is to reduce the
viable surface population of the bacterium in the whole orchard. Spraying
the infected trees alone won’t accomplish that. The most important copper
sprays of the season are the early ones (too late this year…), when old
cankers first start to ooze. Foraging insects pick up that nutritious,
photosynthate-rich goop, and spread it all over the place – that’s the
chief source of innoculum for blossom blight. Of course, nothing is more
effective than thorough removal of infected tissue during the dormant
season (those days are gone, this year). I think that a lot of infections
that are attributed to blossom blight are actually vascular – i.e. are the
result of internal translocation within the tree.

Thorough dormant pruning removes that source. But you’ll never get it all with your saw in the
winter – copper is the best backup we have, at the moment. Well-timed
antibiotic sprays during bloom will do a lot to protect against blossom
infection, but if you use antibiotics, be sparing – if you don’t time them
perfectly, they’re useless, and if you use frequent antibiotics, you’ll
contribute to the development of resistance, which affects all of us (just
like over-use of human medicine).

For what it’s worth, Paul Steiner (RIP)
always laughed at the practice of sanitizing tools between cuts – since
fireblight is on the surface of everything during the growing season
(epiphyte), you can’t avoid infecting every new cut, if you prune in those
days. So sanitizing tools between cuts is a waste of time. If you decide to
cut during the growing season, leave an ‘ugly stub,’ i.e. make a bad
pruning cut, below the point of infection, but nowhere near a healthy trunk
or main branch.

This is cool: early in the season, fireblight thrives on
sorbate and other photosynthates, but later in the season, the trees are
producing so much of that stuff that the concentration becomes toxic to it.
The bacterium will advance another couple of inches below the cut, and then
stop (die). It’s sort of like other complex carbos for the rest of us
(think about alcohol) – a little bit enlivens us; too much kills us. The
‘ugly stubs’ are easy to find and remove during dormant pruning, when you
don’t need to worry about moving the bacterium around with your tools.
Steiner also laughed at the notion of hauling all the infected wood out of
the orchard – if it is removed from the tree, mashed up with a mower or
flail on the orchard floor, and left to dry, the fireblight dies, pretty

Steiner died in 2000, and for years, other talks about fireblight
were mostly regurgitation of his work. More recently, Kari Peter (PA),
George Sundlin (MI), and others have done very good work on fireblight –
their stuff is very much worth reading. And google Steiner – every spring,
I re-read a couple of his articles, just to reset myself before getting
back into the battle. Meanwhile, there’s a lot of lame ‘information’ about
fireblight out there – don’t act on everything you hear or read,
especially if it doesn’t comport with what you learn from Steiner, Peter,
and Sundlin."


@scottfsmith Is there a way to edit the topic name to include the word fireblight? When I search using “fireblight” this topic string does not come up. Help please.


Put in “F word”! :flushed: At the end of the thread change the topic controls to “watching” then you will get notified if anyone posts to it.


Thanks but I want other people searching “fireblight” to be able to see this string/topic/conversation. And say two years from now and I’m wondering where is that Steve Wood post on fireblight, I want to be able to find it again too.


Fireblight. It has been added. Great idea. Let me know if this is what was needed. Bill


I wasn’t sure if I could still change it. I typed in fireblight under the search and it came up. Hopefully this is what was needed.


Thanks Bill!




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.


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.


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]



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


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.


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.


(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.