Monday, June 5, 2017

Fire Blight!

Fire blight (Erwinia amylovora) is the bane of pear and apple growers.

The front line defense is to choose varieties that have genetic resistance to the disease.  Sadly, the disease evolves more quickly than the plant breeders.

One of the characteristic symptoms of fire blight is that the young shoots take on a "shepherd's crook" bend at the growing end.

Image from Cornell University
The next three images are from the tree that was dying in my young orchard.  In time this shoot would turn brown (apples) or black (if it were a pear).  At that point, a diagnosis of fire blight is a no-brainer.

Another shoot.

And yet another.
The bending over of the growing end of the shoot is not specific to fire blight.  It occurs any time the shoot becomes stressed for moisture.  The end of the shoot is usually turgid because of its internal hydraulic pressure.  In other words, the shepherd's crook occurs because the tip wilts.

Fire blight causes wilting by clogging the vascular tissues of the shoot with cells of  Erwinia amylovora.  It is the vegetable version of anthrax.
Cornell rated the shoots of  Novaspy as highly resistant to fire blight.

I was not considering a diagnosis of fire blight because the rootstock and the scion variety are both reputed to be "very resistant" to fire blight.  I was wrong.

Image from HERE
The protocol for handling fire blight is to remove the infected tissue by pruning at least 6" below the visible infection and then to immediately dispose of the prunings.  Get rid of Typhoid Mary!  I put the prunings into a plastic trash bag and walked it over to my trash dumpster.  I removed the prunings long enough to take some pictures, then rebagged and stuck it into the dumpster which gets picked up today.

Finally, sanitize your hands and your pruning tools to prevent spreading the disease when you use them later.

This is what the tree looks like after surgery.  The tree is the short stick immediately in front of the post.
Now we wait and see what happens.  Do the other trees in the orchard get infected?  Does the tree that was infected throw new shoots and merrily grow as if nothing happened.  Stay tuned!

A final note
Young orchards are particularly vulnerable to fire blight because of the abundance of vigorous growth.  
The area circled in red shows where a growing point was pinched out, i.e., dead-headed.

One of the cultural practices that I was using that contributed to the issue was that I was pinching out the growing points on branches that were not well placed.  I did not want to remove the leaves as they contribute by photosynthesizing but I did not want the tree to invest any more resources into a branch that I knew I was going to have to prune later on.  I wanted all the energy to go into "keepers".

Pinching out the growing point breaches the plant's defenses exactly where it is most vulnerable to fire blight.  Note to self:  No more summer dead-heading on young apples and pears.


  1. I use orchard spray to prevent most things. A combo of insecticide and fungicide. Got a little carried away on getting the pear rust controlled and the pear trees are not wonderful this year but no rust. Think I got the black rot off the grapes too.
    Always something.

  2. Sorry to hear that, hope you can salvage most of your work!


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