The Effects of Cluster Leaf Zone Removal on Pinot Noir Grapes in the Willamette Valley, Oregon

Grape growers use an arsenal of techniques in the vineyard to help improve grape and ultimately wine quality. One example of such a technique is cluster zone leaf removal. It is understood and has been

Photo by Flickr user  Naotake Murayama (https://www.flickr.com/photos/naotakem/3853875261/)

Photo by Flickr user
Naotake Murayama (https://www.flickr.com/photos/naotakem/3853875261/)

shown to improve air circulation as well as exposure to sunlight and reduction in disease pressure. Studies have shown that having a very leaf-dense canopy can reduce grape and wine quality, while on the other hand too thin a canopy can result in sunburn damage and poor color development in the grapes.

Leaf removal programs also will vary quite widely from location to location. For example, a leaf removal regime in Oregon may not be appropriate for places like Virginia or Arizona, where the weather patterns are significantly different. A location that has more cloudy days will not respond the same as a location that’s in full sun all the time. Thus, understanding the optimum leaf removal amounts in a given area is very important in vineyard management.

A study published earlier this year in the journal Food Chemistry aimed to examine the effect of leaf zone removal on Pinot Noir grape quality in the Willamette Valley in Oregon for a three year period. All results are thus most applicable to vineyards in this and other very similar growing regions.

Methods

This experiment was conducted at two different vineyards in the Willamette Valley in Oregon: the first vineyard in 2010, and the second vineyard in 2011 and 2012.

The vineyard used in 2010 was a commercial vineyard planted in 1995 with 6563 vines/ha Pinot Noir clone 115 grafted onto 3309C rootstock. The rows were planted north to south with 1 x 1.5m spacing.

Photo by Flickr user  David McSpadden (https://www.flickr.com/photos/familyclan/8113120449/)

Photo by Flickr user
David McSpadden (https://www.flickr.com/photos/familyclan/8113120449/)

The vineyard used in 2011 and 2012 was located at Oregon State University’s Woodhall research vineyard planted in 2006 with 3417 vines/ha Pinot Noir clone Pommard grafted onto 101-14 rootstock. The rows were planted north to south with 1.4 x 2.1m spacing.

Both vineyards were pruned to a bilateral Guyot system and were vertically shoot positioned. With the exception of leaf removal, standard viticultural practices applied at both vineyards all three years.

Leaf zone removal was performed using 4 different treatments:

  1. No leaves were removed.
  2. 50% of the leaves were removed. “Half of the leaves from the base of the shoot to the node above the top cluster were removed by choosing leaves on alternating nodes”.
  3. Industry Standard. “Half of the leaves were removed by selecting only those leaves that covered the clusters on the eastern side of the vine canopy for removal.”
  4. 100% of the leaves were removed. “All the leaves from the base of each shoot to the node above the top-most cluster were removed.”

Leaf removal occurred at the same time point each year: when berries were about the size of peas. At the time of leaf removal, all lateral shoots in the cluster zone were removed.

There were 6 vines per plot and a total of 5 replicates per plot (randomized complete block design).

Weather information, including daily temperatures, mean daily temperatures, growing degree days, and daily precipitation was collected.

Canopy size, density, photosynthetically active radiation, grape yield, and dormant pruning weight, percentage of leaf area removed, vine leaf area, whole vine leaf area, incident light (at 10am, solar noon, and 2:30pm), and leaf area index were measured and/or calculated each year.

Grape maturity parameters at harvest were also measured, including: cluster weight, berry weight, berries per cluster, total soluble solids, pH, and titratable acidity.

Grape phenolics were measured by HPLC.

Free volatiles were measured by PDMS-SBSE-GC-MS.

Bound volatiles were measured by SPE-SBSE-GC-MS.

Results

Note: Since this experiment occurred at two different vineyards, it is probably better to focus on the 2011 and 2012 years where the vineyard was the same.

Weather & Harvest

  • 2011 was 1oC cooler than in 2012. There were 63 growing degree days fewer in 2011 than in 2012.
  • Precipitation in 2011 was over double that of 2012.
  • Fruit ripened earlier and harvest occurred earlier in 2012 compared with 2011.
  • In 2011, grapes reached 20oBrix in 45 days after veraison, while in 2012 grapes reached 25oBrix in 39 days after veraison.

Vines & Sun

  • There were no differences between numbers of shoots, clusters per vine, yield, or cluster weight between treatments over the 3 year period.
  • 100% leaf removal treatment removed 25-27% of the total leaf area in 2011 and 2012 (respectively).
  • 50% and Industry Standard treatments removed 15-15% of the total leaf area in 2011 and 2012, respectively.
  • There were no differences in yield, pruning weights, and crop loads between treatments over the 3 year period.
  • The 100% leaf removal treatment experienced the highest levels of photosynthetically active radiation.
  • Leaf removal affected photosynthetically active radiation at 10am and 2:30pm, but not at solar noon.

Grape Chemical Composition

  • Total soluble solids, titratable acidity, and pH were the same during 2011 and 2012. pH was slightly decreased in 2010 (though this could be a vineyard location issue).
  • 100% leaf removal treatment had the highest levels of petunidin-3-monoglucoside in 2010 and 2012 compared with the 0% treatment.
  • There were no differences in any anthocyanins between treatments in 2011.
  • 100% leaf removal treatment had the highest levels of quercetin glycoside compared with the 0% treatments during all years.
  • The Industry Standard and 50% leaf removal treatments had statistically similar levels of quercetin glycoside as the 100% treatment during 2011 and 2012.
  • Quercentin glycoside levels increased with increased cluster exposure and increase photosynthetically active radiation over all three years.
  • There were no differences in flavan-3-ols (including catechin and epicatechin) between treatments over all three years.
  • There were no differences in C6 alcohol or aldehydes between treatments over all three years.
  • Free- and bound- terpenes levels varied by treatment and from season to season.
  • There was a positive correlation between bound-terpenoids and photosynthetically active radiation across all three years.
  • 100% leaf removal treatment had the highest levels of boundβ-damascenone compared with the 0% treatment over all three years.
  • 100% leaf removal treatment had the highest levels of free-damascenone compared with the 0% treatment over two of the three years.

Conclusions

The overall results of this study indicate that leaf removal at the cluster during the time when Pinot Noir grapes are about the size of peas influences the chemical composition of grapes (and thereby the quality of the wine made from those grapes). In general, removing 100% of the leaves from the base of each shoot to the node above the top-most cluster did not affect vine health or vigor, while at the same time seemingly increased some grape phenolics and volatile compounds. None of the grapes appeared to suffer from sunburn during this experiment, even with the 100% leaf removal treatment, indicating that it might be a suitable option for vineyard management in the Willamette Valley in Oregon.

One drawback to this study is related to the duration. It was only three years in length, and only two of them occurring at the same vineyard and thus more directly comparable. For a more long-term analysis of leaf removal, more consecutive seasons should be studied. Perhaps the two and three years were slightly different for one reason or another, and perhaps we’d see different results if a completely different two or

Photo by Flickr user  Ethan Prater (https://www.flickr.com/photos/eprater/3899914942/)

Photo by Flickr user
Ethan Prater (https://www.flickr.com/photos/eprater/3899914942/)

three year period had been chosen. Longer term studies are needed to remedy this.

Also, while the results of this study showed what they showed, I’d be curious to know how the 100% leaf removal recommendation by the authors will hold up over time. Specifically, with climate change, there will likely be significant variations in the weather and general climate of most places, so while 100% leaf removal now might sound like a good idea, is it the best idea in a changing climate? Again, performing a more long-term study would get at this question.

It is important to note that the leaf removal treatments in this study may not yield the same results in a different growing area (and with different grapes), so if you grow grapes outside of the Willamette Valley region of Oregon, take these results with a grain of salt if you plan on performing similar experiments yourself.

Source

Feng, H., Yuan, F., Skinkis, P.A., and Qian, M.C. 2015. Influence of cluster zone leaf removal on Pinot noir grape chemical and volatile composition. Food Chemistry 173: 414-423.

2 comments for “The Effects of Cluster Leaf Zone Removal on Pinot Noir Grapes in the Willamette Valley, Oregon

  1. June 12, 2015 at 11:59 am

    Becca – in a less in-depth review of the same subject, Jason Lett of the Eyrie Vineyards told us about a Swiss family that came to Oregon in the 1980’s and insisted that the Lett’s remove all of the leaves from the fruit zone in their Pinot. In fact, they even stayed to help do the work instead of going to Disney World.

    Video: https://www.youtube.com/watch?v=tVmYN–euss&index=13&list=PLddUmDhg4G_LVdDZ9nz-CCFSXyHfmWkcY

  2. Michael Qian
    September 24, 2015 at 3:11 pm

    Thank you for the comments on long term research on this topic, especially with varied weather conditions

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