vintage summary 2011

8/7/2019 Vintage Summary 2011

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Vintage 2011 - Botrytis Bunch Rot in McLaren ValeThis seasons harvest was affected by Botrytis Bunch Rot, botrytis cinerea (and other Bunch secondarymoulds). There are two times when grapes are susceptible to botrytis infection at flowering, and atripening. Weather conditions during harvest were ideal for the development of bunch rot.

We can summarizes the conditions that suit botrytis as,- High Humidity- Leaf and bunch wetness- Warm temperatures (20-24 oC).

By looking at the weather conditions this season during those times we can look at why vintage 2011 washeavily affected.

Flowering

All of South Australia had rainfall during spring. Even a small amount of rain or free moisture, allied withhigh humidity can cause botrytis infection of grape vine flowers ( below right ).

Botrytis infection at flowering causes latentinfection. This infection lies latent as it enters a resting stage until the berries ripenproviding a source of food for further growth.

The wet weather during flowering allowedbotrytis to be inside fruit lying dormantwaiting for sugar to develop.

This is not uncommon and occurs in manyseasons. What made this season differentwas the weather during March saw thislatent botrytis develop into a full infection.The wet weather at that time meant thatbunch rots were active at both flowering andripening.


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MarchLow levels of botrytis were seenin some vineyards in earlyMarch caused by some rain inFebruary. This level of botrytis

was fairly low and limited tovarieties with very tightbunches.

Pictured left on March 20th is abunch of Riesling with an earlyinfection of botrytis . Thisvineyard was assessed ashaving 1.1% botrytis severity ordinarily we would considerthis was a low level and unlikelyto affect harvest.

Unfortunately the weatherconditions changed.

McLaren Vale had a three day rain event, from the 20 th to the 23 rd of March that produced long periods of leaf wetness. Conditionswere warm and the windwas still. Furthermoreheavy dews ( right ) were

experienced in manylocations which createdconditions inside thegrapevine canopy thatwere warm, wet andhumid.

Download the March Weather Data here.


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The steamy, wet weather caused low lying cloud toshroud the valley.

Immediately after the rain event some Botrytis wasevident across the majority of vineyards.

After the rain it then became a case of how closevineyards were to harvest ripeness. In hindsight we canconsider the district in 3 areas. 1- south of McLarenVale 2- north of McLaren Vale and 3- McLaren Flat,Blewitt Springs & Clarendon.


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1 - McLaren Vale, Willunga & 2 - North of McLaren Vale

In generally little fruit was lost in these areas - some vineyards had already been harvested and wereunaffected, other were close to harvest and were immediately picked still in good condition with less than1% bunch bot. Much of this fruit was A & B grade Shiraz and wineries looked to pick as much as they couldimmediately. These vineyards were sitting around 12.5 13.5 baume when the rain occurred.

Initially the better C Grade Shiraz vineyards also held together us recording 1-5 single berries of bunchinfection, ie less than 2%. In vineyards that had a heavier canopy and where canopy manipulation,irrigation management was not focused on Shiraz crops were immediately in trouble.

Grenache vineyards with tight bunches also showed significant botrytis after the March rain event.

At this point any berry damage by Light Brown Apple Moth caterpillars, Grapevine Weevil, Downy mildewor Powdery mildew also increased the chances of seeing botrytis. All of these factors cause of damage toberry skin tissue that weakens its natural defense against botrytis.

Cabernet Sauvignon vineyards also showed low levels of bunch rots and other weather related problems.

3 - McLaren Flat, Blewitt Springs & north to Clarendon

None of the red varieties were close toharvest and all had to hold together intoApril in order to be harvest ready thisresulted in bunch rot levels building up.Continued heavy dews into April keptwetting up vineyard canopies and this leadto the high humidity, warm temperatureconditions that favoured botrytis.

Left - The spores of the fungus show thatthe recent conditions have been warmand humid. The berries next to theinfection have gone slippery because theenzyme, laccase, botrytis produces hasspread around the bunch.


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AprilFruit that was tobe picked at thestart of April faceda battle against

the affects of botrytiss enzyme ,laccase .

This enzymedegrades the ligninin the berry skinand oxidizes thered colourpigments. Laccase

causes slipperyskins left , whichwas the mainreason fruit wasrejected duringApril.

In wine, this enzyme causes a reaction that turns the wine brown and detrimentally affects it smell andtaste. Browning of the red pigments is caused by an oxidation reaction, which laccase catalyses or speedsup.

Laccase is a difficult problem for wine makers to manage as the enzyme can survive the fermentationprocess, has low sensitivity to sulphur dioxide (this is added to many wines as a preservative) and thrives inthe natural pH of wine. This means the laccase enzyme will be present in the wine end product.

Download the April Weather Data here.


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Conclusions

Many vineyards elected to spray either, conventional fungicides eg. Rovral, or the surface sterliants PMS orHydrogen Peroxide eg. Peratec. All of these options are only of marginal effectiveness when weatherconditions are wet.

The potential of getting botrytis is equally the weather, the canopy and bunch size you grow and what youspray.

The weather events this season wereinfluenced by the La Nia effect, ameteorological system controlled by thetemperature on either side of the PacificOcean. When the sea temperature is up onthe western Pacific (near Australia), we getwet seasons, like the 201011 one. When thetemperatures are down, we tend to have

drier summers. At the moment, the La Niaeffect is neutralising, meaning we are likely tohave more-like average rainfall over winter.

The high rainfall season, with wet weatherboth during flowering and critically duringharvest, caused widespread botrytis.

Early next season assess the weather conditions to determine the risk of bunch infection by botrytis inparticular. Sprays during flowering may be warranted but because the bunch rot organisms need warmthand moisture for infection, they will not be a major problem next season if the weather stays dry.

Vineyards that grow big canopies, have big bunches, or are grown in areas without natural air movementare most at risk of botrytis . We consider McLaren Vale C-Grade, or D-Grade Shiraz in this high riskcategory.

Techniques that make vines have more open canopies which dry quicker, or produce thicker grape skinsare just as important as chemical application.

vintage summary 2011

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