Disease Update #V14 - Early Summer

LBAM damage.
Grafted vines.

The weather of  the last week has been atypical for early summer in our region. It has been humid, overcast with frequent light showers that produced less than 1mm of rain.

Disease pressure is high and growers may need to adjust their strategies accordingly. Unseasonal rain and high humidity has increased the disease pressure. Growers are advised to adjust their spray programmes to ensure vineyards have good coverage.


Downy Mildew has sporulated - 9th/12th/2013.
If you have Downy Mildew oilspots in your vineyard they will multiply unless your leaves and bunches were protected with a registered Downy fungicide in the last 7 days. The spread of Downy Mildew can be stopped by an application of Metalxyl (tradenames including Axiomtm and Ridomiltm) if this is applied within 5 days i.e the 14th of December. Seek specific advice for your situation. 


Powdery Mildew pressure is currently very high. Powdery is likely to have increased and spread in your vineyard if your protective programme hasn’t been adequate. Leaf spotting has been seen in an increasing amount of vineyards over the last 7 days confirm that the weather has increased the speed of Powdery Mildew’s spread.

The first signs of Powdery Mildew on grafted vines have been seen this week. Disease spores are transmitted by wind from neighbouring vines onto new grafts. Also powdery can break out on the watershoots that are left on the trunk.   

Grafted vines are now growing very rapidly and have fresh, unprotected foliage that can be easily infected. Powdery infections this season lead to an increased risk in future season as grapevine buds on grafted vines are vulnerable. Once Powdery is inside a grape bud it survives winter to become a flagshoot next season. Growers are advised to keep protection on their grafted vines to prevent Powdery infections. 
Powdery Mildew.


Berries Peasize (EL-31) leads to Bunch Closure (EL-32) which is a key time in protecting fruit from bunch botrytis. Rain during this period increases the risk of bunch botrytis in tight bunched varieties. 

Look for any ‘trash’ or old caps trapped inside your bunches. With humid and wet weather Botrytis can begin on this dead material and become a point of serious infection when grape berries start to ripen (8- 9oBe). 

Hail Damage Dec 2013
Where hail damage has occurred this has increased the risk of Botrytis developing at harvest. Bunch Botrytis infections begin on damaged plant material including old flower caps trapped in bunches, caterpillar damage and other wounds. If Botrytis is present in your bunches now it is likely to increase quickly if we have further wet weather after verasion (EL-35). Monitor closely for bunch damage and if you find some prepare to treat this if wet weather is forecast before harvest. Consult with your winery before any late season sprays  are applied.


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