Tuesday, October 26, 2010

Downy Mildew - Alert for Thursday / Friday - UPDATE 26/10/2010

CropWatch - 101026 Is there a DOWNY MILDEW alert for Thursday / Friday?

CropWatch Adelaide Hills has issued alert for that region. At the point of writing an alert has not been issued by McLaren Vale CropWatch.

Current weather forecasts are predicting conditions will be conducive for a downy mildew Primary Infection (10:10:24) then rains start late Thursday and into Friday.

DJ’S GROWERS ADVISES GROWERS TO TAKE THIS WITH A ‘GRAIN OF SALT’

IN THE ADELAIDE HILLS - VINEYARD CANOPIES ARE VERY SMALL AND BORDERLINE FOR HOSTING DOWNY MILDEW. THEY SHOULD DRY QUICKLY COMPARED TO A LARGE CANOPY LATER IN THE SEASON.

IN MCLAREN VALE – WEATHER CONDITIONS ARE LIKELY TO BE LESS WET THAN THOSE FORECAST FOR THE ADELAIDE HILLS.

WE WILL ADVISE WHAT HAPPENS FROM THIS RAIN EVENT.

WATCH THIS SPACE!!!

Eutypa Dieback -ID Photos.

Eutypa and other trunk diseases have been identified as causing significant problems in South Australian vineyards.

Eutypa is present in many vineyards- of all ages. Pictured below is a grafted vineyard in Willunga, in the McLaren Vale region


Eutypa lata (Dieback) symptoms in spring on Shiraz.
All wine grape varieties are susceptible to Eutypa Dieback along with many other plants including Almonds, pome fruit trees and willows. All can be a source of disease.

For those growers unfamiliar with Eutypa in their vineyard it is often confused with zinc and manganese deficiency and rust mite, both of which also cause stunted shoots and pale leaves.

Note Eutypa dieback is most obvious in early spring when infected vines show stunted shoots with shortened internodes and small leaves that are usually pale in colour, cupped and tattered around the margins.  Bunches on affected shoots appear normal early in the season but after flowering they often shrivel and die. 

Eutypa is caused by the fungus Eutypa lata. The fungus produces ascospores on old infected wood and is spread by rain splash traveling on the wind.

The spores are able to travel large distances and can infect fresh, unprotected wounds, such as those left by pruning cuts. Spores are produced all year but can only infect fresh cuts during wet weather.

Above - Eutypa dieback disease cycle in grapevines(taken from 'Grape Pest Management' Flaherty et al., 1992).

Once inside the vine the fungus slowly grows spreading over a period of years along cordons and down to the trunk. The disease spreads to adjacent parts of the vine and eventually kills affected vine arms. Eutypa moves along the vines water-plumbing (the xylem).

Removal of any infected wood is recommended during spring, the symptoms are easy to see and the vines are naturally pushing sap which will limit infection spread to any fresh cuts you make - SARDI have published work on the problem here.

Thursday, October 14, 2010

Powdery Mildew - Notes on control

The message about Powdery is repetitive but effective. Get good coverage on your vineyard between now and the end of flowering!

The good news is that well protected vineyards remain clean of Powdery Mildew. 

Powdery Mildew Flagshoot.

The weather this week has been good for the development of Powdery. Mild temperatures (20 – 25oC) & cloudy conditions are excellent for the disease to produce spores and spread on unprotected leaves and inflorescences. High humidity and poor airflow will also favours its spread.

Powdery starts from a low level and steadily increases in vineyards without good protection. Monitoring for the disease is difficult, and if protection is not adequate powdery levels can catch growers unawares.

The recent vine growth means that the canopy is beginning to close up and vines are becoming progressively harder to spray. Calibration and set-up of vineyard sprayers is critical at this time.

It is worthwhile checking areas of your vineyard where powdery has been a problem in the past for any signs of powdery development this season.