Cluster Counts and Fruit Set Evaluation: Taking a Guess

Posted on June 16, 2010 by Aaron Lange

June has arrived and with that comes the ending of bloom and fruit set, which means that we have reached the second stage in evaluating the size and quality of the upcoming harvest.

If you remember, we first counted tiny clusters in April (before bloom) which gave us an idea of our cluster counts and our potential cluster size.  I say potential because we never know what effect the environmental and growing conditions during bloom will have on the eventual set of the fruit.

Grape Pest Management, Second edition, University of California, 1992.

The individual berries are “set” when successful fertilization occurs of the ovules.  Wind, rain, temperature, disease, and genetics are some of the major factors that can hamper the pollen from successfully germinating and fertilizing all ovules present.  So, even though we may see a large cluster with lots of berries before bloom, it’s very possible that a significant percentage of potential berries never develop, especially in sensitive varieties like Merlot.

These undeveloped berries are called “shot berries“, and as winegrape growers, we generally do not like to see them!

However, a “shattered” bunch can be a benefit to some varieties that have extremely large or dense clusters, allowing the bunch to be looser and therefore decreasing the chance of berries rubbing and splitting.

In the pictures below, you can see a Chardonnay bunch which set a couple of weeks ago and this is evident by the larger size of the berries. The cluster looks a little smaller than normal years.

The other picture is a Cabernet Sauvignon cluster which is still finishing set, as you can see by the presence of the old flowers. Notice the cluster is looser (but still not as developed) as the Chardonnay.

So, long story short: We are evaluating the fruit set now to make predictions on the crop size.  This is very important to not only regulate our crop and canopy correctly with proper fruit thinning, irrigation, leaf pulling, and trimming techniques, but also for winery tank management for the 2010 crush: do we have enough tank space for the grapes?

At the end of the day, it is nothing more than an educated guess, because the harvest always has a way of throwing unpredictable curveballs at us!

  • http://www.panthos.com Jon Bjork

    So what’s your guess for crop size for the different varieties in 2010?

  • http://www.langetwins.com Aaron Lange

    Ah, the million dollar question Jon! We are still working through the numbers on this. I think Chardonnay is lower than normal, mostly due to smaller cluster size and some vineyards have fewer than average clusters. I’m still evaluating each vineyard block individually because each one will be different depending on location, varietal clone, micro-climate, pruning styles, etc….so I can’t really give you the specifics you’re looking for. There are a lot of decent techniques through which to predict crop size, but I still don’t trust any “prediction” of my crop size until the fruit has passed the scales in the winery! Nature has a way of throwing curve balls at us, and sometimes the best crop estimating tools and techniques are off by significant percentages. I try to use a scientific method to make a prediction, but sometimes the old-school method of the experienced farmer walking into his field and making an “precision eyeball” guess is just as effective!

  • http://www.panthos.com Jon Bjork

    I hear you, Aaron, regarding trying to reduce crop prediction to a science. I’m sort of hoping that an old farmer will always be as reliable (or moreso) than a bunch of people spending hours looking at bunches. My guess is that even those old guys, when younger, spent vintages trying to figure it out to the point where they taught themselves the most important clues to look for in the vineyard and then gave up trying to improve their precision.

    Thanks for your shot at Chard being less. I’ll get out my chisel and carve that in stone. Just kidding…

    I appreciate your great information, as always, Aaron!