Throughout the Vintage Report, Thibaut Scholasch, PhD, co-Founder and VP of Research and Development at Fruition Sciences, highlighted data trends during the 2017 growing season via transitional talks between the Vintage Report’s various speakers. He placed the day’s speakers and topics within the context of the growing season, and shared new findings in vineyard data collected around the Napa Valley.
From the beginning of the season, important parameters to set the stage for vine growth were rain and thermal time accumulation during the winter months. From the period of November 1st to March 1st the Napa Valley saw a large and steady amount of rainfall, similar to 1995, 1998, and 2011. Just like 2011, fields were saturated to field capacity well before and after budbreak. Thermal time during the same period was reduced slightly compared to 2016, 2015, and 2014, but was very similar to both 2012 and 2013. On top of this, thermal time accumulation during the second period of the season, March 1st to June 21st has been steadily rising since the 2013 vintage. 2017 did not deviate from this trend, showing a high thermal time accumulation before the end of June.
So what is the consequence of this high thermal time and abundance of water on leaf area development, vine architecture and physiology?
Field data collected using Dualex, a real-time fluorescence leaf measurement technique to determine plant Nitrogen Biological Index (NBI), revealed that vine leaf Nitrogen content in Napa, reached its peak anywhere from 100-200 GDD earlier than observed in 2016, but with a slightly lower average maximum.
Additionally, seasonal crop coefficient (KCB) variations recorded around the valley revealed high maximum values, or a high vine “horsepower”available for vaporizing soil water into the atmosphere during transpiration. 2017 Kcb values were similar to 2010 and 2011; however, the peak KCB values were reached nearly a month earlier in 2017. The large amount of winter rain, the low rainfall after budbreak, and the high crop coefficient values set up a scenario where the root reservoirs in 2017 were likely depleted faster than expected, sometimes even before veraison when root reservoir size is limited.
All of these trends confirmed the need for winemakers and vineyard managers to assess both Nitrogen and vine water use on a site-specific basis, as each terroir required different operational timing.
Finally, Thibaut highlighted what was possibly the most extreme driver of the 2017 vintage: the high frequency and severe nature of heat events. High heat events increase the risk of cavitation and decrease the chance of green berry survival (with temperatures above 43C).
Recent scientific findings have shown that high temperatures during the month before veraison can lead to a delayed onset of veraison and sugar loading, and reduced anthocyanin levels at fruit maturity (Gouot et al, 2017; Lecourieux et al, 2017; Mori et al, 2007). The extreme heat waves in August and September in Napa were likely responsible for the ripening delays and sudden berry volume accumulation stop that many growers observed across Napa.
Fig 1 : Napa annual vintage map (Fruition Sciences)
In conclusion for 2017, Thibaut Scholasch displayed his annual vintage map, comparing vintages by rain amount, length of dry period, and frequency/intensity of heat waves.
- Gouot, J. Smith, J.; Holzapfel, B.; Barril, C. (2017), Locally Applied High Air Temperature Significantly Altered Bunch Stem and Grape Berry Physiology, Proceedings from 20th GiESCO International Meeting Mendoza, Argentina
November 5th – 10th 2017, pp 333-338
- Lecourieux F., Kappel C., Pieri P., Charon J., Pillet J., Hilbert G., et al. (2017). Dissecting the biochemical and transcriptomic effects of a locally applied heat treatment on developing cabernet sauvignon grape berries. Front. Plant Sci. 8:53
- Mori K., Goto-Yamamoto N., Kitayama M., Hashizume K. (2007). Loss of anthocyanins in red-wine grape under high temperature. J. Exp. Bot. 58 1935–1945.