Just to clarify, I don't doubt that winter injury was involved in the
bark splitting. The big question that no one can answer at this
point is whether your September glyphosate treatment left trees more
susceptible to winter damage. The differences among rootstocks and
top-worked cultivars could all be due to interactions between
rootstock/scion tendency to absorb or react to glyphosate, internal
water relations within the tree at the time of application,
physiological hardening off times for the cultivars as they affected
rootstocks, winter pruning effects, etc.
I have seen at least 3 cases over the past 25 years where I thought
that glyphosate had probably interacted with cold injury to produce
severe damage on apple trees. In all 3 of these cases, it appeared
that orchards had been sprayed with glyphosate in a manner that allow
fine particles to swirl upward into lower limbs. In the spring that
followed the severe winter cold, entire lower scaffolds either showed
now growth or leaves were sparse and slow in developing. The top
parts of the trees (mature MM.106 size trees) were fine and showed no
symptoms, but many of the lower scaffolds ultimately had to be
removed completely. We never proved that glyphosate was involved,
but we never found any other cause either.
Dave,
Thank you for the interesting information.
I have been using glyphosate, typically once or twice per year,
for many years, but I have difficulty building a case that
glyphosate contributed to the damage. In the past several years I
have used 1 to 1.25 quarts Roundup Weather Max (48.8 % a.i.) per
wetted acre, plus Choice (a Loveland product containing ammonium
sulfate) at rate of 3 pints per 100 gallons of tank mix. The block
containing the Budagovsky roots and trunks received just one Roundup
plus Choice application in 2008, on September 5, at the one-quart
rate of Roundup, applied in a rather dilute mixture of 50 gallons
per wetted acre. On the same day, I used the same mix on another
block of 2 acres. The two-acre block consists of trees mostly 10
years old on MM 106 rootstock, grafted low to Enterprize, and
subsequently topped with one of 6 commercial fruiting varieties at
the 5 foot height, on limbless trunks. Macoun is not included in
that block; but all 600 trees there have remained free of winter
injury. About 200 Macoun trees grafted 12-16 inches high on MM 106
rootstock are included in two other blocks of 30 year old trees that
also get Roundup treatment, typically twice per year. In 2007 they
had Roundup plus Choice ( 1 quart/Acre; 3pints/100 gallons) in about
40 gallons mix per wetted acre. Here, of roughtly 1500 trees,
including perhaps 100 on M26, I saw only one tree (Empire/MM 106)
that had bark cracking essentially identical to those that were so
common in the Bud 54-118 block. The Empire tree had just one crack,
and suffers only cosmetic injury.
I did not mention in my original report that 500 trees of Bud
54-118 growing as a nursery at close spacing, and now about 6 years
from their planting as rooted cuttings, show no bark splitting. All
were given the same Roundup treatment as the injured Bud block, on
the same date last September. I am a bit unsure now about my
original plan to make orchard from these 500.
Southwest winter trunk injury is not terribly uncommon in the
history of my plantings, but the damage to the Macoun/Bud 54-118
trees is rather different in appearance, and far more severe than
any I have seen before. About 8 or 9 years ago, a small number of
Macoun/Bud trees developed a single long bark crack, which did
relatively minor damage. It appeared only on the south-facing side
of the trees. In my current state of uncertainty, I am more
inclined to blame dormant pruning than glyphosate as the
non-weather factor tipping the balance toward winter injury in a
rootstock that may not be suited to the particular use described
here.
David
On Feb 4, 2009, at 11:37 AM, Dave Rosenberger wrote:
Hello, Dave --
Have you been using glyphosate in this orchard? If so, the
e-mail exchange that I am pasting in below may offer an alternative
explanation of what is going on? For whatever reasons, my
observations suggest that there is a unique susceptibility of
Macoun trees to what we think is injury caused by glysphosate. The
following info from the ornamentals industry was passed on to me by
Jon Clements and raises interesting issues that need further
investigation;
Hi, Jon --
Thanks for forwarding this article. It sounds like Hannah
Mathers in Ohio has documented in ornamentals what I have
suspected for a long time in apples, especially Macoun trees. I
summarized some of those concerns in an apple-crop post on
3/15/07, but I never had the time/resources to run trials needed
to prove the association between trunk damage
--
**************************************************************
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/
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