[NAFEX] Late fireblight

dmnorton at royaloakfarmorchard.com dmnorton at royaloakfarmorchard.com
Sun Nov 25 23:27:28 EST 2007


I have experienced later season fire blight on Cortland apples as well as Gala and Jonafree on Mark rootstock due to severe thunderstorm activity creating a "trauma" which can 
spread "canker blight", another form of fire blight that results in "shoot blight".  I think i may have posted the different forms of 
fire blight once before last winter.  Here is part of that post that may help.

      In years when blossom infections do not occur, the primary sources of inoculum for the shoot blight phase are the overwintering cankers and, in particular, young water sprouts near these cankers, which become infected as the bacteria move into them systemically from the canker margins. 

            Such systemic shoot infections, called "canker blight", are apparently initiated about 200 DD greater than 55 F (111 DD greater than 13 C) after green tip, although visible symptoms may not be apparent until the accumulation of at least 300 DD greater than 55 F (167 DD greater than 13 C) after green tip. In the absence of blossom infections, the development of shoot blight infections is often localized around areas with overwintering cankers.   
            Although mature shoot and limb tissues are generally resistant to infection by E. amylovora, injuries caused by hail, late frosts of 28 F (-2 C) or lower, and high winds that damage the foliage can create a trauma blight situation in which the normal defense mechanisms in mature tissues are breached and infections occur. Instances of trauma blight are known to occur even on normally resistant cultivars like 'Delicious'.

            Rootstock blight, yet another phase of fire blight, is associated primarily with the highly susceptible M.26, M.9 and Mark rootstocks in apple trees. On these trees, just a few blossom or shoot infections on the scion cultivar can supply bacteria that then move systemically into the rootstock where a canker often, but not always, develops and eventually girdles the tree. Trees affected by rootstock blight generally show symptoms of decline and early death by mid to late season, but may not be apparent until the following spring.

      If you would like any further information on late season fire blight, send me an e-mail and I can forward you the information I have on file.  Hopw this helps!

Dennis Norton
Royal Oak Farm Orchard
  ----- Original Message ----- 
  From: Alan Haigh 
  To: nafex at lists.ibiblio.org 
  Sent: Sunday, November 25, 2007 7:22 AM
  Subject: [NAFEX] Late fireblight

  I have been growing my own and managing for others a wide range of varieties of pears here in the vicinity of southeastern NY for almost 20 years.  Based on what I gathered from the literature, I began with the anticipation of ongoing warfare with fire blight.  Experience has not met anticipation and fire blight has not been a major issue.  On most sites, including my own orchard, I've never seen a single strike.  Knock on wood. 

  There are two sites, however, where this tree-killer has reared its ugly head but the timing of its attacks are strictly Che Guevara-  small attacks when least expected.  I've always read that fire blight occurs in the spring starting in the open blossoms with pollinaters as vector.  In the two orchards where it has appeared the symptoms did not become visible until mid-July.  In one site it hit a Bosc pear for 2 straight seasons while leaving an adjacent Bosc and a Seckel alone.  So far, Ive had to remove about 50% of the tree. 

  In the other site the strikes come about the same time and have also appeared for the 2nd season but have been more widespread 2nd time around.  The first season only the Bosc was badly damaged but this year the quinces, a red Bartlett and a Seckel also had some damage.  There was also a scattering of strikes throughout the various varieties of apples but for these trees the damage was minor. 

  I'm guessing the vector to be leaf-hoppers but that's an uneducated leap.  Does anyone out there have some information about late season fire blight?
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