Powdery Mildew - UPDATE - 15/12/2014

Powdery Mildew: Notes from behind the scenes.

For your information. I have been informally gathering grapegrowers feedback and want to pass this on to you all. I have been receiving mixed reports about how we are reporting Powdery Mildew in CropWatch this season. Some sources are saying that CropWatch is overstating Powdery Mildew problems. i.e ‘scaremongering’. Other reports are that we are downplaying disease levels and simplifying.

I am comfortable that, in my professional opinion, the following statements are a factual summary of the current situation;

CropWatch McLaren Vale Vol 12 Issue 20. Summary; FUNGAL DISEASE:  

    
Where growers have had good coverage disease levels continue to be low. There are increasing amounts of Powdery Mildew being found, but in most cases these disease colonies are inactive. 

The earliest vineyard sites are at EL-33 Berries - Hard & Green.  In general these hard berries are now resistant to disease as they are highly acidic and have a ‘tough’ surface.'

Report Text:

'Vintage 2015 has been a generally dry growing season and most growers have been able to keep disease levels down. There are some exceptions to note though; 

 

Leaf spotting from Powdery Mildew. This vineyard is near a neglected site and is likely being exposed to windblown Powdery spores from that unsprayed vines.

POWDERY MILDEW: levels are increasing. At present in approximately 25% of vineyards as inactive leaf spots. These can be found every 10-100m of vine row. A much lower percentage of vineyards, typically Chardonnay, have bunch infections. Active Powdery Mildew colonies appear to be white or light grey. Inactive colonies (i.e. dead) appear dark grey, brown and black. If you find Powdery it is important to identify why you have a problem. Has your coverage been adequate?'
 

Light Powdery Mildew Infections on the surface of berries. This is called a diffuse infection. McLaren Vale - 15/12/2014 (c) James Hook

Previous issues have given both warnings to look for Powdery, pictures and the information that general pressure is low to moderate. It is always a challenge to convey complex information. CropWatch in no way, or was it ever intended to replace looking at growers specific vineyards. As the disclaimer on the reports states information is general in nature’.

Grapevines have reached the growth stage of Bunch Closure / Berries Hard & Green EL-32 / EL-33. Reports from monitoring scouts and agronomists are showing that there are only a few sites with significant disease issues. Where they have been found they have been serious and grapegrowers are needing to act.

Fortunately the vast majority of sites are clean and on the way to a successful harvest.

Regards,

James Hook