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Summer pruning and fire blight

Posted by Peter Fisher 
Summer pruning and fire blight
September 03, 2016 02:58PM
I have have been dealing with a small outbreak of fire blight on 3 pear trees (2 Concorde and a red Bartlet). I read a lot about what to do next season to minimize the spread, but nothing about measures I should be taking now to avoid spreading to other trees, other than pruning off infected branches and burning them. I have avoided summer pruning of water sprouts and root suckers on all my pear trees to avoid creating open wounds, but the infection seems to start on the tips of just such new growth. So I am thinking I might be better off aggressively pruning off this season's unwanted shoot growth now, on the infected trees and on the uninfected ones. Any advice?

Turkey Creek Orchard
Solon, Iowa (zone 5A)
Re: Summer pruning and fire blight
September 04, 2016 06:59AM
Fire blight here this year is just outside the orchard, ironically on a few ornamental specimens like hawthorn and rowan (mountain ash) that have not gotten any holistic spray treatments. The one English hawthorn in Nancy's medicinal herb garden shows nearly what you are describing, Peter. I've been pruning away afflicted brown growth on the tips of whole branches but a week or two later more laterals are turning brown. Sadly, the bacteria are deeper within the vascular system of this tree and it's probably a lost cause. Had I only thought to include it when spraying competitive microbes on open apple and pear blossoms! The "cure" (such as it is) involves making "ugly stub" cuts to suspect limbs. Go back 6 - 12 inches below where you see disease symptoms to make a cut, knowing you need to come back in the dormant season to prune the remaining stub off at a proper branch juncture. This is the time of year to sterilize pruners between cuts, and I suppose you could be all the more fastidious and spray the pruned surface with vinegar as an anti-bacterial treatment. (SPECULATION ALERT on that being a sure-fire step.) What I fear is that the active window of fire blight now stands extended into late summer and even early fall by generally much hotter conditions. The danger in cutting those waterspouts down to the base is that the pruning cut now exposes the larger limb. Leaving short stubs eliminates the growing tip which is apparently being "opened to infection" by wind or aphids which in turn allows bacterial incursion to occur . . . whereas, leaving a transition zone where renewed infection can then be "stored" beyond the limb in the stub . . . protects the deeper vascular system until such time as non-risky dormant cuts can be made.

Lost Nation Orchard
Zone 4b in New Hampshire
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