Last week, the Oregon Wine Symposium was held in Portland Oregon at the Oregon Convention Center. Vitis Terra Vineyard Services had a trade show booth at the symposium for the first time. In addition Chemeketa Community College also had a booth and a large number of students attended event. It was fun to see everyone at the event and luckily I did manage to go to several talks that were quite interesting.
I attended the “Ebb & Flow: The Dynamics of Water Availability and Vine Use” by the new Oregon State University Southern Oregon researcher Dr. Vinay Pagay. We had just covered water relations in my Vine Physiology class at Chemeketa so it was a nice review.
He discussed the grapevine growth cycle and talked about the impact of the previous season and the water status on the development of the compound bud that will produce the following season’s crop. He also discussed the grapevine water potential that involves the soil plant atmosphere continuum and is driven by transpiration.
He reviewed what controls the negative water potential gradient which includes a number of variables such as environmental conditions, soil characteristics, soil moisture and resistances in the plant. Two of the main factors driving water use are canopy size and evapotranspiration. These are two factors used in calculating the amount of water to irrigate with on a weekly basis. In grapevines the greatest resistance or control of water loss is through the stomata on the undersides of the leaves. If these close in response to drought stress it will also slow down photosynthesis and grape ripening.
While excessive water can lead to high vigor, he also discussed the negative impacts drought stress can have on fruit quality such as the loss of the aromatics in white wines and stressed vine off aromas in red wines. In Oregon we often have too much vigor early in the spring due to our rainfall and then late in the summer and fall many vineyards have high levels of drought stress. We could improve our fruit and wine quality by understanding and managing irrigation better. Growers and winemakers get concerned about using irrigation between veraison and harvest but this is the time that it can have the greatest impact on wine quality.
He mentioned that a grapevine typically uses 1000 gallons of water per vine per season. During the summer in our cool climate a grapevine can typically use 8 gallons per day. I think it is very important to keep this in mind because when we do provide irrigation, it is a very small amount compared to the total number of gallons used in a year or even a given week! If you do a 3 to 5 gallon irrigation set you are lucky if you’re replacing 50% of the water used that week.
As far as when irrigation has the greatest impact on berry size, the greatest impact is from bloom through fruitset as this is when cell division is occurring. Before veraison water moves into the berries through the xylem. Consequently there can be a greater impact on berry size related to water status before veraison. After version the xylem becomes nonfunctional for water moving into the berries, however; the most recent research suggests there could be xylem back flow of water out of the berry.
At veraison, water and sugar move into the berry through the phloem. When this occurs, the berry becomes more isolated from the vine. Keller’s research shows that at this point irrigation can help prevent shrivel but once shrivel has occurred it can’t be used to reverse the shrivel but only to prevent more shrivel.
Another talk at the symposium, “Water into Wine: The Downstream Effects of Vineyard Water Management on Wine Quality” presented some interesting information on the changing water content in berries due to rain events. This relates to what we experienced during harvest in 2013. Watch for the next blog on this topic.
Markus Keller, Jason P. Smith and Bhaskar R. Bondada. Ripening grape berries remain hydraulically connected to the shoot. Journal of Experimental Botany, Vol. 57, No. 11, pp. 2577–2587, 2006.