Are Apple Tree Canker Diseases Impacted by Glyphosate ...shaponline.org/wp-content/uploads/2012/03/Rsnbrgr-Thus-glyphosate.pdf · Are Apple Tree Canker Diseases Impacted by Glyphosate

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.