Hello, Mark --
The symptoms you describe sound exactly like a problem that
appeared on Marshall McIntosh trees in New York and New England soon
after that strain of Mac was introduced. On the Marshall Macs, the
problem also appeared when trees were about 5-7 yr old. No one ever
made a definitive diagnosis of the problem, but there was some
evidence that trees at this stage (could we call them adolescents?)
were particularly susceptible to winter damage following years that
allowed them to grow late into the fall. Some folks in MA thought
that fire blight might have been involved, but I think that
hypothesis was mostly discarded. I thought that perhaps
Botryosphaeria dothidea was involved in some of the die-back, perhaps
by extending the cankers beyond the tissue that would have died from
winter-kill, but I never proved that hypothesis either. Many growers
in the Hudson Valley attacked this problem by apply a dormant copper
spray in spring just as they would have done for fire blight, and I
believe that some of them also used a copper spray in late fall. The
problem disappeared after the copper sprays were applied, but we
never had a controlled trial and it may well be that the problem
would have disappeared without the copper applications. Folks have
continued to plant some Marshall Macs and I've not seen this problem
in later plantings. Thus, it seems that it was probably a
combination of "adolescent" tree age and weather conditions that
contributed to the problem.
Hello all,
In 08 a neighbor with a 5 yr old Pioneer Mac block on G30 saw
extensive amounts of die-back in his trees, starting with trees
hanging onto their leaves going into late fall. Spring of 09 showed
that the most vigorous trees were affected to the greatest degree
with whole limbs, leaders and some entire trees dying.
Everything looked good in the spring of 09 in our orchard, which is
7 yr old P-Mac on M26. We wondered if our neighbor had a problem
because of G30. Many "experts" looked at his trees and the
consensus was "winter injury". In early October we harvested our
block and noticed nothing of concern (except scab). In mid-November
we saw trees throughout the block with dark leaves that refused to
fall. The most vigorous trees seem to be the most affected. Whole
limbs seem to die from the tip to or near the truck. Leaders often
turned dark brown down to just above the lower scaffold limbs.
Trunks below this point are mostly unaffected. Most trees seem to
be O.K. at this point in time but nearly 20% of the block has some
degree of this malady.
None of our other varieties have this problem.
Does anyone have experience with this sort of situation? Any ideas
would be appreciated.
Mark Evans,
Northwest Michigan
--
**************************************************************
Dave Rosenberger
Professor of Plant Pathology Office: 845-691-7231
Cornell University's Hudson Valley Lab Fax: 845-691-2719
P.O. Box 727, Highland, NY 12528 Cell: 845-594-3060
http://www.nysaes.cornell.edu/pp/faculty/rosenberger/
