Hi Roy- I threw a response at you on the other board, just in time for the whole crew to jet.
I’m no plant biologist, but I know a couple of them.
Dormancy is a plant response to conditions. Preservation of life and all. It is essential in some plants for fruit production, but AFAIK, not in grapes. In fact, in many parts of the world grapevines, even vinifera, never go dormant. In places like Thailand, for example. Whether or not they can make great wine from it is certainly debatable, but is also a chicken and egg argument due to their climate.
During dormancy, the phloem is inactive and there’s no appreciable transfer of carbs around the plant. When we talk about sap running, the concern is that this means the vasculature is still working. The concern there is that this takes energy…energy that is better preserved.
In grapevines, there are many contributing factors to the end of dormancy, including sunlight incidence and day length, rainfall, and temperature. Probably the biggest determinant would be soil temperature, which, when raised a bit sparks a root flush and we’re off to the races before you know it. If we get a warm rain now, for example, that may spark some budbreak. As you probably know, soil temperature is very, very stable, so it takes some extreme conditions to make significant changes.
How does dormancy effect wine quality?
AFAIK, it doesn’t, except that the end (and beginning) of dormancy determine the growing season. Bud differentiation and flower cluster production occur in the Spring of the previous year, so I don’t think dormancy affects potential yield much.
What can be done to ensure better dormancy (if anything?)
Nothing I know of. I don’t think “better” is the key; “longer” might be for us here, but other places are twiddling their thumbs praying for budbreak because every day the start is delayed is another day of risk for rain at the end of the season.
Does pruning have any effect on dormancy?
There is certainly an effect on the vine when pruning, much as we respond to cuts. AFAIK, pruning will prolong dormancy. In other crops, there are only ways to hasten dormancy…Dormex is a spray often used in cherries, for example, that tightens up bloom and reduces ripeness variability. AFAIK, there isn’t a way to prolong dormancy.
So, all in all, the biggest concern with a shortened dormancy will be that budbreak in February puts us at risk for more frosting, potentially bad bloom weather and the lion’s share of the ripening occurring in the summer. These are symptoms of short dormancy, though, and not necessarily related to dormancy itself.