are apple tree canker diseases impacted by glyphosate...
TRANSCRIPT
Are Apple Tree Canker Diseases
Impacted by Glyphosate Herbicide?
2012 Mid-Atlantic Fruit and Vegetable Convention
Hershey, PA
2 February 2012
Dave Rosenberger
Cornell University‟s Hudson Valley Lab
Highland, NY 12528
Defining the Components
1. Background on canker development in
apple trees.
2. Background on what glyphoste does in
plants.
3. Can glyphosate exposure predispose trees
to canker diseases.
Canker development in apple trees
1. Most of the fungi that cause cankers in
apple trees are “weak” pathogens:
They appear only after other factors have
compromised tree health.
Black rot canker is the
end product from a
whole cascade of
events within the tree.
Apple trees do not
develop “heart wood.”
A completely healthy
apple tree/limb has no
brown center.
Brown discoloration of
old xylem indicates
invasion by wood-decay
pathogens: bacteria,
yeast, fungi.
The heartwood pathogens
are usally bract fungi that
sporulate only after killed
tissue extends to the plant
surface.
Canker development in apple trees
2. Trees have defensive
mechanisms that limit
invasion by fungi.
3. Trees expend energy on
these defenses.
4. Trees under stress may be unable to
maintain their defenses.
5. Wood decay pathogens can
grow through barrier zones
and colonize more wood.
Canker development in apple trees
6. When the pathogen
reaches the limb
surface, a canker
appears.
7. As the bark is weak-
ened from within, it
becomes susceptible to
Botryosphaeria obtusa,
the pathogen that
causes black rot canker.
Botryosphaeria dothidea
• Causes white rot canker.
• Enabled by
drought-stress.
Canker development
Damage in NY was first
noted around 2001 on
Cortland, then reported in
2004 after it began
showing up in many
Macoun blocks.
Basal trunk cankers appear on apples.
Rosenberger, D. A. and
Fargione, M. J. 2004. Apple
tree deaths attributable to
herbicides? Scaffolds Fruit
Journal 13(13): 3-5.
Macoun/M.9 photographed 22 Oct „04
Hypothesis:
Basal trunk cankers are
caused by Botryo-
sphaeria dothidea
invading bark that was
injured when glyphosate
was applied to water-
stressed trees.
Basal trunk cankers appear on apples.
Glyphosate:
• Systemic herbicide originally sold as
Roundup.
• Today there are >45 trade names and
formulations.
• Widely used in apple orchards, especially
to control problem weeds such as poison
ivy, sumac, Asian bittersweet,
brambles, etc.
Background on glyphosate
When the glyphosate patent
expired around 1990 —
1. Prices dropped and use on
apples increased.
What happened on apples?
2. Manufacturers changed to
different glyphosate salts
and started adding surfactants
to speed weed kill on
Roundup-ready crops.
When the glyphosate patent
expired —
3. Surfactants enhanced uptake
into apple tree bark and
exposed leaves (e.g., on root
suckers).
4. Trunks hit with glyphosate in
repeated applications year
after year developed cankers.
What happened on apples?
Background on glyphosate
Glyphosate mode of action:
• Broad-spectrum chelator:
Ca, Mg, Cu, Fe, Mn, Ni, Zn.
• Inactivates enzymes that require
Mn and other ions as co-factors.
• Blocks shikimic acid pathway which is
important for fruit ripening and plant
defense mechanisms.
Background on glyphosate
Glyphosate mode of action:
• Glyphosate does not break down in plants.
• Dr. Hannah Mathers‟ group at Ohio State
showed that exposed trees have reduced
winter hardiness.
• Sublethal levels of glyphosate can be
detected in trees for at least two years
after exposure.
Thus, winter-
injury noted in
orchards may be
glyphosate-
related.
Problems on Apples
1. There is no cheap and simple assay for presence of
glyphosate in plant tissue, so we can‟t easily
document glyphosate content in damaged trees.
The link between glyphosate and trunk
cankers remains unproven because:
2. Effects of non-lethal glyphosate exposure in plants
are complex because of the interactions involved.
3. Effects are subtle, often interlinked with other factors
such as cold injury, nutrition, pathogens that are
enabled by decreased host defenses.
Bark-cracking on young
trees has appeared in
some orchards.
We have not determined
if glyphosate is involved.
More Problems ?
L
Internal Browning on Apples
• Physiological disorder that
develops after 7-10 months of CA
storage.
• Severity varies by year, with
greatest severity following cool
summers.
• Variable from block to block.
• Extensive trials have failed to
identify reliable predictors of
occurrence or methods for
reducing losses.
L
Internal Browning on Apples
The shikimate pathway is
involved in many aspects of
fruit ripening.
Glyphosate blocks this
pathway.
Is glyphosate contributing to
the internal browning problem?
Effects of glyphosate exposure in
incidence of flesh browning:
L
Conclusion after Year 1:
Glyphosate exposure in late
summer can increase the incidence
and severity of both flesh and core
browning in Empire apples.
Rosenberger, D. Watkins, C., Miranda Sazo,
M., Kahlke, C., and Nock J. 2010. Glyphosate
exposure contributes to internal browning of
apples during long-term storage.
N.Y. Fruit Quarterly 18(3):15-18
Sub-lethal levels of glyphosate in apple trees
affects tree physiology:
• Can reduce winter hardiness (Mather lab).
• Reduces storage life of Empire apples in
some years (2009-11 work in NY).
• Probably causes basal trunk cankers on
some cultivars in some orchards.
Other potential impacts on tree health remain
uncertain.
General conclusions:
1. NEVER ever apply glyphosate
to Macoun trees.
2. Try to identify and use
glyphosate formulations that
are similar to the original
Roundup (i.e., with few or no
surfactants).
3. Minimize exposure of trunks
and root suckers, especially
after May.
Immediate cautions to consider:
Immediate cautions to consider:
CORNELL‟SHudson ValleyL A B O R A T O R Y
4. Always include a chemical drift
inhibitor in the spray tank
when spraying glyphosate so
as to minimize small droplets
that drift to low limbs.
5. If possible, apply only with
hooded boom sprayers.
6. Never apply with controlled
droplet applicators that
generate super-fine droplets.