Are Apple Tree Canker Diseases Impacted by Glyphosate Herbicide?

Transcription

1 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

2 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.

3 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.

4 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.

5 The heartwood pathogens are usally bract fungi that sporulate only after killed tissue extends to the plant surface.

6

7 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.

8 Canker development in apple trees 6. When the pathogen reaches the limb surface, a canker appears. 7. As the bark is weakened from within, it becomes susceptible to Botryosphaeria obtusa, the pathogen that causes black rot canker.

9 Canker development Botryosphaeria dothidea Causes white rot canker. Enabled by drought-stress.

10 Basal trunk cankers appear on apples. Damage in NY was first noted around 2001 on Cortland, then reported in 2004 after it began showing up in many Macoun blocks. Rosenberger, D. A. and Fargione, M. J Apple tree deaths attributable to herbicides? Scaffolds Fruit Journal 13(13): 3-5.

11 Macoun/M.9 photographed 22 Oct 04

12 Basal trunk cankers appear on apples. Hypothesis: Basal trunk cankers are caused by Botryosphaeria dothidea invading bark that was injured when glyphosate was applied to waterstressed trees.

13 Background on glyphosate 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.

14 What happened on apples? When the glyphosate patent expired around Prices dropped and use on apples increased. 2. Manufacturers changed to different glyphosate salts and started adding surfactants to speed weed kill on Roundup-ready crops.

15 What happened on apples? 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.

16 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.

17 Background on glyphosate Glyphosate mode of action: Glyphosate does not break down in plants. Sublethal levels of glyphosate can be detected in trees for at least two years after exposure. Dr. Hannah Mathers group at Ohio State showed that exposed trees have reduced winter hardiness.

18 Problems on Apples Thus, winterinjury noted in orchards may be glyphosaterelated.

19 The link between glyphosate and trunk cankers remains unproven because: 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. 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.

20 More Problems? Bark-cracking on young trees has appeared in some orchards. We have not determined if glyphosate is involved.

21 Internal Browning on Apples L 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.

22 Internal Browning on Apples L The shikimate pathway is involved in many aspects of fruit ripening. Glyphosate blocks this pathway. Is glyphosate contributing to the internal browning problem?

23 Effects of glyphosate exposure in incidence of flesh browning: L

24 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 Glyphosate exposure contributes to internal browning of apples during long-term storage. N.Y. Fruit Quarterly 18(3):15-18

25 General conclusions: 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 ( work in NY). Probably causes basal trunk cankers on some cultivars in some orchards. Other potential impacts on tree health remain uncertain.

26 Immediate cautions to consider: 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.

27 Immediate cautions to consider: 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. CORNELL S Hudson Valley L A B O R A T O R Y