Thursday, November 5, 2009

Botrytis - Q&A

Hi,

A question for DJ's. Should I spray for botrytis over flowering? We have Shiraz west of McLaren Vale, South Australia - crops up to 12 tonne/ha.

Kym




Dear Kym,
Flowering is an important time in determining your risk of botrytis rot at harvest. In South Australia Shiraz has a low to moderate risk compared to other varieties.

If you protect your vines over flowering it is a case of risk vs. cost of control. Given the predicted prices of grapes this season only use ‘big’ botryticides if you have had issues in the past.

Botrytis cost per hectare (1000lt dilute spray volume)


Filan* = $187
Scala* = $95
Chlorothanonil = $39
Teldor* = $109
Switch* = $129
Captan = $17
Rovral* = $40

*Tradenames in Australian market.

Rain during flowering can lead to botrytis infecting the developing berries through tiny wounds left by the flower caps falling off. This infection is known as ‘latent botrytis’ because the disease waits dormant in the berries as they develop. It will then appear as an infection if weather conditions suit when the fruit ripens.

The best defense against botrytis balanced yields, an early harvest, with an open canopy with loose bunches. A crop of 12 tonne/ha is a moderate tonnage and should not cause over cropping on your vines.

Botrytis in Pinot Noir.
This season canopies will grow larger than last season and with high soil moisture levels berries could be bigger and bunches tighter. This increases botrytis risk.

If your vineyard has a history of botrytis or your variety has tight bunches consider limiting the chances of latent infection with registered botrytis fungicides.

For vineyards operating organically or Bio-Dynamically the best defense against botrytis are techniques that lead to healthy vines with strong berry skins at harvest.

No comments: