I really shouldn’t say things out loud.
Cast your mind back a couple of weeks to when I stupidly said this…
We’ll have to wait and see what the next few weeks has in store weather-wise. BUT… what we don’t want now is either:
1. a significant heatwave which will cause soil moisture stress and sunburn of the leaves and bunches
2. a heap of rain which will cause the berries to split and make them more susceptible to disease.
Come on 2021… we know you can do better than 2020!!
Since I said that we had a rainfall event on January 26th where over 30mm of rain fell at Mount Lofty (which thankfully put out the fires at Cherry Gardens). And then on February 5th, there was a second big fall of almost 25mm.
And it looks like the amount of rain was variable across the region. We recorded 39mm at home (in Heathfield) on Feb 5th and according to a social media post by a winery in Carey Gully, they recorded 68mm between February 4th and 7th!
Now, don’t get me wrong… that’s great news for soil moisture (and my garden!). As you can see in this table from the Bureau of Meteorology, we’ve had next to nothing all January. In fact, ignoring the 26th Jan, we had a total of 2.8mm at Mount Lofty for the whole month!
According to the latest CropWatch report (dated 5th February… the same day of our last big rainfall event)…
All varieties are now developing sugar and colour and the earliest varieties are at E-L 36 (berries with intermediate sugar values) and later varieties are at E-L 35 (berries beginning to colour and enlarge).
Remembering that E-L 38 signifies that the grapes are ready to harvest. That means we are very close to the end of the season and the grapes are soft and at risk of splitting from that large amount of rain over a short period of time.
Split berries are a problem for a couple of reasons…
- once the skin is broken, the berries lose moisture quickly, die and fall off. This obviously impacts yield. For example, if 10% of the berries on a vine are split, then you can expect to harvest 10% fewer berries from that vine.
- split skins are a perfect infection site for Botrytis infections.
Here is a quick reminder of what Botrytis is…
Botrytis (bunch rot)
Botrytis spores are almost always present in vineyards.
Infection can be initiated from spores carried over from the previous season. The fungus can rest in a quiet state and then resume growth when the developing berry begins to soften. Once that happens it can then spread from berry to berry. This process is usually pretty quick especially in compact bunches of thin-skinned varieties. Botrytis also spreads readily from bunch to bunch in crowded fruit zones.
Botrytis needs about 8 hours of moisture to set off an infection period. It infects grapevine tissue via wounds (like split berries) and natural openings. Spore germination is stimulated by sugars and amino acids in the ripening berries.
Here is a fun fact… botrytis grows 8 times faster in grape juice than in water!
The only way to combat botrytis is to apply fungicides and to increase the aeration in the canopy.
All that being said, we have been lucky this season. So, if this is the worst of it then I guess we should be grateful (again, why do I insist on saying these things out loud?!).
Smoke taint update
Before I go, I mentioned a couple of weeks back that I would give you an update on the effect of smoke taint from the Cherry Gardens bushfire.
I’d love to have something to tell you but it really is just too early to tell.
There was a call out to any growers who were worried to submit samples for analysis. It will just be a matter of time to tell if there were any effects on the small number of vineyards in the vicinity of the fires.