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Blossom Blast

Posted by Mike Biltonen 
Blossom Blast
December 27, 2017 11:15AM
Blossom blast is a bit of an enigma in apples. It is quite well known in pears, but apparently not so much in apples - at last my experience and according to the literature. The last few years in New York, we've started to notice a collapsing of blossoms and subsequent vegetative growth that never spreads much but kills the section of the affected branch. The pear pathogen is Pseudomonas syringae pv. syringae, which is not supposed to affect apples. Apples do get a malady called blister spot which is called Pseudomonas syringae pv. papulans - most notoriously in Mutsu. To complicate factors, last year we noticed collapsing blossoms that were caused by oriental fruit moth larvae and not a disease, but could create a point of entry. The branches that didn't have OFM, but were assumed to be pathogen were taken to a lab for analysis. The pathologist was able to plate out the disease organism and determine that it was P. spp., but the costs of taking the tests further were too expensive, so we never learned what the species or pathovar (pv) was/is. As well, P. syringae doesn't last long in vegetative tissue, so compared to fireblight, does its damage at the point of infection (and perhaps a bit further in) but doesn't travel into the tree - so all you lose is the branch or the section of the branch. That said, we do not know if the organism is the one that causes blister spot, pear blossom blast, a different Pseudomonas spp., or a more virulent form of any of the known pome fruit bacteria. My thoughts are that the fluctuating late winter temperatures cause sublethal damage to the deacclimated buds, causing small wounds that allow for the bacteria to enter and do its thing. I'm sure there are other factors - but it seems that keeping trees as dormant as possible, as healthy as possible, and spraying a light anti-bacterial spray to fend off the invading bacteria can reduce this. We have seen this problem in Gala, others, but also and mostly SnapDragon (which has Honeycrisp in its gene pool). Prune late, don't fertilize until greentip, spray a light anti-bacterial (not necessarily antibiotic) material. and keep all weak or damaged wood to a minimum in the orchard. Other thoughts?

Mike Biltonen, Know Your Roots
Zone 5b in New York
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