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Alan,
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.
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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. | |
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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!
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----- Original Message -----
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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