Thursday, September 19, 2019

Grape Splitting

One of the things that can happen with some grape varieties is that they are prone to splitting. For those varieties that experience this it happens during the ripening stage and often after a big rain.

As the grapes ripen there are a number of things that happen that collectively can converge in disaster for grapes prone to splitting. First off as the grapes ripen they swell with juice and the skin softens. This is also the same time of sugar accumulation and acids drop in the juice.

The biggest issue is the on-set of bunch rot or sour rot from fungal pressure that a avails itself from the split in the grape skin. This often occurs after a big rain as the vine takes up the moisture and transfers it to already swollen grapes...the result is some of the grapes on the bunch can split open.

Ravat 34 with split grape in centre of the bunch

So this is where the problems start as the same conditions that contribute to the grapes splitting..that is the rain and associated high humidity and cooler weather are the same conditions that spur on the growth of bunch rot and sour rot.

Once the grape splits open, the opening invites the mold spores to grow in the low acid high sugar environment in the ripening grape.

Hard to stop without fungal spray but some cultural practices like shoot thining and bunch area leaf removal are known to help by allowing better air flow and sunlight around the bunches.

Ravat 34 is prone to this, and Colmar a bit as well but less so. So we pull the leaves ftom around the clusters when they start to ripen.

Ravat 34 with leaf removal around clusters