Hello, Art —
What is the strain of McIntosh that has the unusual growth habit and retained
petioles? I’m not certain about the curved shoots, but over the years we have
occasionally noted retained petioles on various strains of Macs as they pass
from the juvenile phase to full bearing. The problem first showed up several
years after Marshal Macs were introduced and has been reported on several of
the newer strains since then. The cause has never been definitively
identified, but I and others suspect that is has been associated with cold
injury in Nov-Dec.
With Marshal Mac, the hypothesis was that this cultivar tended to harden off a
bit later and/or was slightly less winter-hardy than the older Mac strains.
Once trees got past year 8 (and this was on older rootstocks such as M.7,
MM.106, etc.), the trees seemed to recover. However, during the period when
they showed retained petioles, they also developed crotch cankers that may have
(or may not have) been associated with winter damage. The crotches on lower
scaffolds limbs are reputedly the last part of the tree to harden off in the
fall, so it made sense that the crotch cankers noted on these trees may also
have been associated with cold injury. We never noted any particular limb
growth habit with this phenomenon on Marshal Macs, but that may vary with
conditions.
Some otherwise-benign viruses may cause trees to grow a bit differently and may
reduce winter hardiness a bit, but no one ever pinpointed any virus affiliation
with the problem on Marshal Macs. And there is documented evidence that
glyphosate exposure can reduce winter hardiness by a degree or two, but I don’t
think that glyphosate exposure would directly cause the abnormal limb growth or
retained petioles.
So, it would be interesting to know the strain of Mac and the age of the trees
in your block. Also, did you get any rapid temperature declines in Nov or Dec
either this year or in the several previous years that might have contributed
to winter damage. I ask about last year, or even two years ago, because if
your trees have cankers, then the injury started some time ago. Incidentally,
I don’t view “black rot” as a primary cause of cankers: the pathogen causing
black rot canker (Botryosphaeria obtusa) is almost always a secondary pathogen
that can cause damage only if trees were previously injury or compromised by
some other factor.
On the same subject, Michigan had a serious canker outbreak on Linda Mac
several years ago, and I have not heard much about it since then. I’ve
wondered if the canker outbreak in MI might also have been related to cold
injury on trees that had not yet fully settled into mature bearing status. My
suspicion is that when many growers switch to a new strain of Mac at the same
time, the age of those plantings is somewhat synchronous and age-related tree
problems therefore get a lot of attention. As plantings of new strains become
more dispersed over time, the same problems may occasionally show up, but they
don’t generate as much attention because there are fewer plantings of the same
age and problems are therefore more scattered.
****************************************************************************
Dave Rosenberger, Professor of Plant Pathology
Cornell's Hudson Valley Lab, P.O. Box 727, Highland, NY 12528
Office: 845-691-7231 Cell: 845-594-3060
http://pppmb.cals.cornell.edu/people/dave-rosenberger
****************************************************************************
On Feb 12, 2014, at 10:16 AM, Evan B. Milburn
<ebmilb...@yahoo.com<mailto:ebmilb...@yahoo.com>> wrote:
Arthur,
Would it be possible to post some pictures? If and /or when was any roundup
applied?
Evan B. Milburn
http://www.milburnorchards.com/
On Wednesday, February 12, 2014 9:52 AM, Arthur Kelly
<kellyorcha...@gmail.com<mailto:kellyorcha...@gmail.com>> wrote:
I have some McIntosh on M111 that have an unusual growth habit. They grow
shoots in sweeping curves and both the fruit and leaf petioles hang on. There
are petioles out there today. There may be an association with black rot. Any
other thoughts?
--
Art Kelly
Kelly Orchards
Acton, ME
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