Things that change fruit ripening

I've talked about fruit thinning before, and here's another missive.

Common in commercial practice is to do thinning at colour change, so that you can remove the fruit that is less-advanced in ripening - i.e. the stuff that hasn't gone through veraison as soon as the bulk of it.

When you do this, you're advancing the maturty of the harvested fruit. However, this is only so because you have removed that tail end of the fruit -all the stuff that's less ripe, so that the average brix is higher, and that carries on through to harvest.

But, what if you remove fruit randomly at that point in the season? I don't believe you will see much of an effect on Brix at harvest, if at all.

I think this is because regardless of how much fruit is on the vine (within reason!), the rate at which it will accumulate brix won't change much. The conduit for the sugars to pass through is the phloem, and under the conditions in the vine during ripening, sugars are already moving through and into the berry as fast as they can. Removing fruit might mean the vine has more carbohydrates available, but that doesn't mean that the pipes (phloem) leading to the berries can push more sugar into the berry. There is a limit!

In fact, there is evidence that the size of fruit is related to the diameter of the stem that leads to that fruit (i.e. a larger number of pipes leads to a larger fruit), such as this paper working with citrus. This doesn't necessarily mean cause and effect, but it is a logical conclusion.

It might also mean that if you think the fruit early enough (within a couple of weeks post-fruit set), you might be able to enhance the ripening of the fruit because the pedicels can grow larger due to the greater amount of carbohydrate available? I wish I knew the answer to that question!!

Thoughts on thinning - how much does a cluster contribute to yield?

It's such an early season in Canterbury this year!

Just before the nets went on in the Lincoln University Vineyard (the earliest they've gone on in the 13 years I've been here!), we were able to squeeze in some fruit thinning. That prompted me to write the following for the Wines of Canterbury newsletter...

Despite all the heat and promise of a fantastic season, why go through all that trouble when it looks like it will be a year where you can leave all that crop on and get it ripe?

Well, the first thing to check is how much crop you've got! We looked at the Pinot noir and Pinot gris and found that cluster counts were around 20 per metre of row for both of them. Not only that, but the clusters looked pretty big, too, so some more investigation suggested that berry number per cluster was around 125. So figure about 1.1 grams per berry for the productive clones of Pinot noir, and more than that for the Pinot gris, and you're looking at crop loads of around 2.7 or more kilograms per meter of row. Too much!!

For the mythical balanced VSP vineyard (refer to Sunlight into Wine, by Smart and Robinson, 1992), a typical pruning weight per metre of row should be about 0.5kg. Using a yield to pruning weight ratio of about 3 (which, while less than the 5 to 10 figure used by Smart and Robinson, seems to be more appropriate for vines in the Canterbury region) each meter of row should be able to (nicely) ripen 3 multiplied by 0.5kg of fruit, or 1.5kg.

So by doing some quick cluster and berry counts, we can see that there is quite a bit of extra crop on there, to the tune of at least a kilogram per metre of row!

So we need to take off about 44% of the fruit that's on the vine, which could be thought of as slightly fewer than every other cluster.

However, it's important to note that not all clusters are the same. The basal cluster is usually the most advanced in terms of ripening, so it's beneficial to keep as many of those as possible. But if you're removing all the upper clusters, it's important to note that they are also usually smaller, to the tune of about 70%, than the basal clusters. So if a basal cluster is 100g, the cluster above it will be about 70g, and if there's a third cluster on there (which the Chardonnay clone UCD6, for example, has in spades this season), it will be about 50g (it might be a good idea at harvest to do some measurements of this in your vineyard and with your varieties to see if this holds true in your situation).

So if you remove just the top cluster, you're looking at a reduction in yield by about 23% - not a third if you think of the clusters as being all equal. If you remove all but the basal cluster, you've taken off about 54% of the fruit. So to reach the goal of taking off 44% of the fruit, you should be removing all the top clusters, plus most of the secondary clusters.

Whether or not this is an economically feasible thing to do is another matter!!

Good fruitset can equal bad news

Whilst working with some grapevines the other day I was reminded about the problems of having excessively tight clusters. Pinot noir is well known for this, but can be the case for many varieties if you have good conditions at fruit set. It can cause clusters to become so tightly packed as the berries grow and approach harvest, that berries can be popped off the cluster, causing fresh wounds where disease can get established.

As well, tight clusters are undesirable as the interior of the cluster then becomes a very good place for disease organisms to get started, as any pesticide sprays, which are a necessity to producing quality wines in some growing regions, cannot reach inside the cluster.

So while high yields are thought to be a good thing, if this is due to very good fruit set, you can run into problems, usually disease related, later on.

What are some answers to this problem?

As always, when talking about disease control, spray coverage is the most important aspect of fungicide effectiveness. Even if you have the best fungicide in the universe, it isn't any good unless it is delivered to the target. So making sure the sprayer is set up correctly, the nozzles are delivering the appropriate volume of spray and in the correct pattern, the ground speed of the tractor isn't too fast (or slow!) and the canopy is open enough to receive the spray are all important to disease control.

Aside from this, if you have good fruit set, applying a fungicide before the cluster closes up (that is, before the berries swell so much that there is no longer any airflow into and through the cluster) is your best bet to minimising disease later in the season.

If you are in an area known to have high disease pressure in the grapes themselves, choosing a variety or clone that has a more open cluster can be another effective tool.

If you must, absolutely, grow a tight clustered Pinot noir clone in this sort of area and the price you will get for the wine warrants it, then you could consider gibberellin application (if this is an approved chemical for your crop) prior to flowernig - this will cause the rachis to elongate, and thus make the cluster looser.

Another option is to do flower thinning, where flowers are removed prior to flowering. This can be done with comb-like devices, which remove some, but not all the flowers on the cluster.

In some cases, you could also trim the bottom of the flower cluster off, which allows a bit more freedom for berries to poisition themselves.

Early leaf removal has also been experimented with, where the reduced photosynthesis caused by this results in less fruit set.

These last few, though, have traditionally been done before flowering, developed for the table grape industry, where a tight cluster is one that is difficult to remove grapes from and also to pack into shipping containers.

For wine grapes, berry thinning and cluster trimming could be done after fruit set, when you have some idea of whether it was too good or not. This helps since you never really know if a season is going to provide good fruit set or not!

For ultra-premium production, where yields are often kept to very low levels, a reduction in crop is a normal occurrence, and the loss of crop through these methods can result in higher grape quality than through cluster thinning.