Botrytis - UPDATE 15/1/09

No Botrytis has been seen in McLaren Vale vineyards at this stage. It pays to think of botrytis in terms of rain events different varieties can sustain before showing signs of the disease.

This is a simple rule or thumb. There is more in determining why botrytis a problem at harvest in some vineyards and not others.

Botrytis level is dependent on three things in equal parts.

1= Canopy and bunch size.
2= An effective spray plan.
3= The weather conditions pre-harvest.

Late season chemical control is a protective measure and best applied before wet weather is forecast. Late season botrytis sprays reduce the spread of rot during wet weather.
Once established, botrytis is difficult to kill. Only sustained hot, dry weather will dry out the damaged and infected fruit.

Late in the season always consult your winery about your actions.

Non Chemical Options

Botrytis is suited by warm, wet conditions. Varieties with open canopies, thick berry skins and loose bunches dry much quicker then heavy canopies after rain events.

During the season there are several techniques that can be used to reduce the risks of botrytis. Pruning, irrigation and the use of foliage wires can reduce the bunch & canopy density improving the speed of bunch drying after rain or heavy dews. Good nutrition (low to moderate Nitrogen + high Calcium) helps thicken up berry skins.

Late in the season trimming can be used to increase airflow around bunches and decrease the amount of time canopies take to dry out. When considering trimming big canopies remember leaves ripen fruit! Sunburn is a real concern for fruit quality and it reduces crop yield. Vines need leaves and good cover from the afternoon sun.

One solution that has been used for vigorous Chardonnay in Blewitt Springs has been trimming the morning side of the canopy only. This is done late in the season after the vines have stopped growing. Trimming the eastern side only has the positive effect of increasing airflow around bunches, while leaving the west reduces sunburn risk, and leaves enough leaf area for ripening.

Please consult your winery about trimming pre-harvest.


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