Friday, July 02, 2010


People unfamiliar with the San Francisco Bay Area's micro-climates find it hard to believe that there is a wide range of diurnal temperatures in the Napa Valley also. A friend, who grows Cabernet sauvignon (Clone 7) up in St. Helena, sent me this photograph last weekend of what he originally thought was a grapevine disease. It turns out that his vineyard, that on any given day can be 5-10 degrees warmer than Vinoland, had just experienced a major hiccup in the transition from flower to berry known as shatter.
Fruit set is the stage of berry development 1 to 3 weeks after bloom when most flowers have fallen and those that remain, about 30-60%, develop into berries. Shatter is the detachment of berries from the cluster at the pedicel base (the dark, necrotic tissue in photograph), after the fruit set stage. It appears that the poor fruit set, in this particular vineyard, was the result of dry conditions and high temperatures at bloom. However, shatter can also be exacerbated by variety (Merlot is particularly susceptible), vine vigour, and disease.
What does all this mean? Well, shatter causes widespread yield losses, which in this instance means a diminished crop from which to make wine at harvest time. The fruit set in Vinoland looks solid so Vinomaker will not be without plenty of grape juice to vinify. But he is mourning the loss of those Clone 7 grapes that fell victim to shatter, especially since the 2009 crop surrendered up the best Cabernet of the vintage.


Vinomaker said...

After talking to the grower last night at a vineyard pre-Fourth of July party, he thankfully confirmed that, despite the higher than normal shatter, the clusters are filling in nicely. He is paying particular attention to cluster quality this year due to the possible appearance of the European Grapvine Moth. I will just cross my fingers and hope for some more of those fantastic grapes!

Vinogirl said...

It was a bit of a relief to hear that good news...the silver lining is that bunch rot sure won't be a problem.

Wartime Housewife said...

Is there any preventative measure that can be taken for shatter or is it just one of the pitflls of viniculture?

Vinogirl said...

Timing of bloom and climatic conditions at time of bloom are impossible to predict. Other than steering clear of susceptible varieties, shatter is just one of the pitfalls of winegrowing!