"Like the build-up to the tropical wet season, or the week before a Grand Final; so too there's electricity in the air a couple of weeks before harvest.
You can see and feel the static. Everyone's on edge, twitchy or downright irritable. These are the weeks of highest tension.
There is no exception to this rule in any winemaking community. It’s all the watching and waiting that heightens anxiety." - Toby & Emmanuel Bekkers.
How much disease is around?
Fortunately the weather this week has not significantly increased the amount of botrytis but there is a real risk of crop loss if rain or heavy dews occur before your crop is safely picked. We have heard reports this week of one vineyard being rejected in Langhorne Creek due to botrytis infection, this shows that it is a threat.
Check your vineyards now for botrytis progression in the thick and dense parts of the canopy where bunches sit in top of each other.
In general the severity is low (1 berry per bunch) with the diseased berries appearing to be drying. Infections are dropping out of the bunch when they are shaken. There are significant infections in Chardonnay and Shiraz that has fruit stacked on top of other fruit. The highest level seen has been in tight bunched varieties (i.e Grenache, Zinfandel, Dolchetto, Sangiovese, Chardonnay) 5 bunches part infected per panel (approx. 1 bunch per meter). View a video of this level of Botrytis activity: (70Mb download).
Why is there some fresh burn to leaves after the rain?
Recent rainfall has caused the mobilization of sodium chloride, more simply called salt, in the soil and the vineyards pictured – right - are showing foliar signs of burn.
As soil moisture reduces during summer vines pull water from the soil. The drier the soil the harder they pull (plants create a negative pressure from the leaves to the roots - pulling harder means a higher negative pressure).
Recent rainfall re-wets the top soil and vines pull up more water from previously dry areas of soil. They take up more salt with the water. Eventually the concentration in the leaves becomes toxic and the leaves 'burn.'
This foliar burn decreases the health of the vines. Sodium and Chloride levels in the developing fruit are also likely to have increased which can have a detrimental effect on wine quality. If you are worried about this request a test of must from your winery.
In high salt situations it is essential that salt is leached from the soil to reduce excessive build-up over seasons. Typical leaching fractions may be in the range of 10 to 20%, and are best applied prior to bud-break if soil testing shows salinity levels were not reduced sufficiently by winter rainfall.