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.