Dr. Patty Skinkis, Viticulture Extension Specialist & Associate Professor, OSU
Canopy management, including hedging, leaf and lateral removal, is of paramount importance at this time of year. These practices can change canopy microclimate and thereby influence how fruit develops and how well your fungicides are deposited to control powdery mildew and Botrytis bunch rot. It is important to consider how and when to apply these practices. If canopy management tasks are not done at the correct time, there may be issues that arise. Below are some important considerations with regard to leaf removal, one of the more queried practices in canopy management.
Leaf removal in the cluster zone is an important practice for vineyards with moderate to high vine vigor. Leaves should be removed between fruit set and bunch closure. I often receive reports of berry sunburn due to leaf removal, and in many cases, this was the result of leaf removal at or just prior to véraison. The cluster is relatively resistant to sun exposure in earlier stages of development from bloom to bunch closure. However, once berries begin to ripen (near véraison), the cells of the berry skin become less able to withstand high sun and heat exposure. Studies show that clusters with earlier exposure have more phenolics that likely help prevent damage from exposure.
How much leaf area should be removed? There have been numerous leaf removal studies conducted in Oregon and elsewhere. The industry standard of removing leaves from the cluster zone on only the morning-sun side of the canopy (east side of N-S rows) has been shown to be effective from the standpoint of aroma and color development in Pinot noir. You can read more about this in a recent article by OSU researchers. This research compared no leaf removal to 50% and 100% of leaves removed in the cluster zone and the industry standard of east-side leaf removal. Leaf removal enhanced color and aromas more than no leaf removal (Feng et al. 2015). Several other studies have also been conducted in Pinot noir with 100% leaf removal in the cluster zone where leaves were removed on both sides of the canopy from 2008 to 2015. These studies showed increases in Pinot noir anthocyanin (color) compared to no leaf removal without any issues with sunburn (Lee and Skinkis 2013). Despite complete exposure from shortly after fruit set, there was no excessive sunburn, even in hot seasons like 2014 and 2015 (Reeve & Skinkis, in preparation). Research conducted in eastern Washington’s hot, arid climate with 100% leaf removal of white grape cultivars showed enhanced late season spray coverage and no difference in sunburn compared to no leaf removal (Komm and Moyer 2015). It is important to note that some berry burn may occur due to other factors and not simply from leaf removal itself, including use of certain adjuvants or applying sprays at a certain time relative to the heat of the day.
Although leaf removal is a common and popular practice in western Oregon, it is not necessary in all vineyards and may not result in the same outcomes. Vines that are of low vigor have more well-exposed clusters than high vigor vines, and they may not require additional exposure. Also, leaf removal in low vigor vines may lead to insufficient canopy leaf area for vine productivity and fruit ripening. Furthermore, vines that are under water stress may experience different levels of sunburn/heat stress to the berries with leaf removal, and care should be taken to ensure sufficient coordinated management of irrigation and canopy management.
Feng, H., F. Yuan, P.A. Skinkis and M.C. Qian. 2015. Influence of cluster zone leaf removal on Pinot noir grape chemical and volatile composition. Food Chemistry. 173: 414-423. http://www.sciencedirect.com/science/article/pii/S0308814614015374. Published with permission in Practical Winery & Vineyard Magazine in June 2016: http://files.ctctcdn.com/27fc1a43201/85469b81-aef1-46a9-aa2a-b256e7f2a34b.pdf
Komm, B.L. and M.M. Moyer. 2015. Effect of early fruit-zone leaf removal on canopy development and fruit quality in Riesling and Sauvignon Blanc. American Journal of Enology and Viticulture 66: 424–34. http://www.ajevonline.org/content/66/4/424
Lee, J. and P.A. Skinkis. 2013. Oregon ‘Pinot noir’ grape anthocyanin enhancement by early leaf removal. Food Chemistry. 139:893-901. http://ir.library.oregonstate.edu/xmlui/handle/1957/39412
Skinkis, P.A. and A.J. Vance. 2013. Understanding Vine Balance: An important concept in vineyard management. Oregon State University Extension Service. EM 9068. https://catalog.extension.oregonstate.edu/em9068
Vance, A.J., A.L. Reeve, and P. A. Skinkis. 2013. The Role of Canopy Management in Vine Balance. Oregon State University Extension Service. EM 9071. https://catalog.extension.oregonstate.edu/em9071