Different Vineyard Training Systems Alter Susceptibility of Grapes to Powdery Mildew

One of the most common pests to vineyards all over the globe is powdery mildew (Erysiphe necator Schwein).  It is responsible for causing widespread destruction in nearly every viticultural area worldwide, and is a fungus that is able to develop in a variety of temperatures and humidity levels.  Though it is present in nearly every corner of the globe, the severity of the infection from vineyard to vineyard is dependent upon a variety of factors, including the variety of grape, the vigor of the vines, the type of protective chemicals applied, and the weather conditions.

http://www.bioseaoz.com.au/images/
DiseaseImages/PowderyMildewOnGrapes.jpg

Some studies have found that the training system used in the vineyard has a significant effect on powdery mildew development, by altering the microclimate in the cluster area.  It appears as though light intensity and UV radiation appear to contribute to the changes in powdery mildew development severity, both of which have also been shown to affect the chemical composition of the grapes themselves.   Specifically, work done by the authors of the paper presented today found that there were significantly lower powdery mildew infections in grapes trained in the free canopy system versus grapes trained in the vertical shoot positioned system.

The article presented today is a very short article with the objective of investigating whether or not the difference in infection incidences as described above were due to light intensity itself, the susceptibility of the berries, or both.

Methods

The study was performed in June 2003 at an experimental vineyard in the Golan Region of Northern Israel.  Grapevines planted in this vineyard were Cabernet Sauvignon and Chardonnay (both with good susceptibility to powdery mildew).

Half of the vineyard was subject to a vertical positioned system, while the other half was left as a free canopy, though topped to one meter in length after fruit set and hedged no more than twice during the growing season.  Dates of bud burst, flowering, and fruit set were the same for both training systems.

Figure 1 from Zahavi and Reuveni, 2012

Experiment 1: Clusters were picked when the diameter of the berries were 3-5mm.  Thirty to forty berries from each training system were selected and placed in plastic boxes.  Berries were then inoculated with powdery mildew.  Twenty more berries were placed in plastic boxes but not inoculated with the fungus to serve as a control to monitor natural infections from the field.  Percent of infected berries was then calculated 7-9 days after inoculation with powdery mildew.

Experiment 2:  Clusters were inoculated in the exact same manner as in Experiment 1, however, 1-2 hours after inoculation, berries were returned to the vineyard and either placed on the cluster zone/vine cordon of their original training system or on vine cordon of the opposite training system for 8 hours.  After this time, berries were brought back to the laboratory and disease development was monitored 7-9 days after.

Results

  • For the first experiment, incidence of powdery mildew was significantly higher on berries originating from the vertical positioned vines than those originating from the free canopy system.
  •  For the second experiment, berries that originated from the vertical positioned vines and then incubated in those same vines were significantly more infected with powdery mildew than those berries that originated from the free canopy vines and incubated in either of the vine position systems.
  • Also in the second experiment, berries that originated from the vertical positioned vines that were incubated in the free canopy system vines had an intermediate level of powdery mildew disease severity.
  • Powdery mildew did not develop on control berries that were not inoculated.

Conclusions

The results of this study found that grapes originating from a free canopy system, which has a greater exposure to light, resulted in lower susceptibility to powdery mildew infection than grapes originating from vertically positioned vines, which have a denser canopy that does not allow in as much light. 

By transferring inoculated free canopy grapes into a vertical positioned set up, powdery mildew development decreased as a result of a pre-conditioning effect on the grapes.  In other words, this means that the grapes were less susceptible to infection after being exposed to higher intensity of light from the free canopy system.  The authors conclude by stating that the conditions in which grapes develop influence the severity of infection by powdery mildew.

Being a short experiment, there are certainly many more questions that these results raised which cannot be answered with the results found.  For example, how do the different training systems affect the chemical and sensory characteristics of the wine?  Are there any differences?  Since it appears grapes grown under a vertical positioned system are more susceptible to powdery mildew than grapes grown under a free canopy system, it suggests that perhaps there are some chemical defense changes within the plant, which may or may not affect the overall sensory characteristics of a wine made from those grapes.

Would the results be the same for each and every variety of grape out there?  Or are Cabernet Sauvignon and Chardonnay more susceptible to powdery mildew invasion under a vertical positioned system while say Riesling and Malbec are more susceptible under a different training system?  I would think it once again boils down to plant defensive chemistry, but we’d need some further studies examining many more grape varieties to be sure.

What about other training systems?  What is the “hierarchy of susceptibility” for powdery mildew in Vitis vinifera grapes? 

The results of this study are not to suggest that one should switch from a vertical positioned system to a free canopy, however without any extra chemical defense (fungicides, etc), it might be recommended that one reconsider the training system that is employed at one’s vineyard.  There are, of course, many other factors that any given training system will affect, thereby requiring one to weigh all the pros and cons before choosing any particular method.

I’d love to hear what you all think of this study!  What questions did this study raise for you?  Please feel free to comment below!

Source: Zahavi, T., and Reuveni, M. 2012. Effect of grapevine training systems on susceptibility of berries to infection by Erysiphe necator. European Journal of Plant Pathology 133: 511-515.

DOI: 10.1007/s10658-012-9938-z



I am not a health professional, nor do I pretend to be. Please consult your doctor before altering your alcohol consumption habits. Do not consume alcohol if you are under the age of 21. Do not drink and drive. Enjoy responsibly!

4 comments for “Different Vineyard Training Systems Alter Susceptibility of Grapes to Powdery Mildew

  1. Jim Baker
    July 27, 2012 at 11:53 am

    As a vinifera grower in western NY state, I am plagued with mildew, particularly in the Chardonnay. I am intrigued by the potential of a different training system. I use a balanced vine approach with VSP and have used leaf plucking to open the area around the grape clusters with moderate success. It is still a battle though. I am unaware of just what a free canopy system looks like. I would have liked to have seen a picture or description of the free canopy system. A quick internet search did not reveal the free canopy system.

  2. July 27, 2012 at 12:07 pm

    Hi Jim!

    Thank you for your comments! As far as the picture goes, since you're comment, I've taken a screen shot of the paper and created a jpeg of the image and uploaded it into the methods section above! Thanks for reminding me of that!

    If you end up trying the free canopy system, I'd love to hear how it ends up going for you (I realize this will be on the order of years potentially ;) ).

    Cheers!

  3. Jim Baker
    July 27, 2012 at 12:20 pm

    I have to admit that this is totally counterintuitive, it goes against everything I know about canopy management. The structure of the canopy needs to let light and air in to keep these humid area diseases under control. Shading is also a big problem with this. I'll have to think about this before I would do a trial. It is a bit of a pardigm shift me. Keep up the good work!

  4. July 27, 2012 at 12:28 pm

    I don't blame you for being hesitant about it. Keep in mind, this paper only looked at this one factor, which doesn't begin to address all the other possible changes that could occur in/on the grapes by switching to this type of canopy. Also remember, the experimental vineyard was somewhere in Northern Israel, which I'm guessing does not have the same climate/conditions as in Western NY. I wouldn't be surprised if the results of this study would be different if they performed it somewhere else in the world.

    Maybe for fun, if you are able and have some to spare, try it on a couple of plants and see what happens ;)

    I definitely wouldn't recommend switching over an entire vineyard based on one study, however, it does raise interesting questions that will hopefully spur more research to get a better understanding of the mechanisms behind it!

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