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A Technical Guide for Wine Producers
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RECENT ARTICLES | WYNBOER HOME
Shiraz Decline
Nico Spreeth
The symptoms of Shiraz Decline must not be confused with those of Shiraz disease . The symptoms can be clearly distinguished and although the causative pathogens are unknown, two different viruses are associated with the symptoms.
The extent of Shiraz decline in France was extensively discussed in the April 2004 issue of the well-known French viticultural magazine "Le Progrès Agricole et Viticole No 15 - 16" and conveyed to the French wine growers. In France the symptoms have been observed for the past 10 years and Professor Denis Boubals, editor of the magazine, contends that all Shiraz vineyards older than 15 years display between 1 and 15% symptoms of the disease, depending on the location and the cultivation conditions of the vineyard.
Symptoms have been observed in vineyards as young as three years old, but these are the exception, seeing that symptoms usually appear five to six years after planting. The symptoms are thickened graft joints with cracks on the graft joint and red discoloration of the leaves from middle to late summer. The symptoms are similar to those usually observed in girdled vines or shoots. The bark thickens above the graft joint and deep cracks can be seen on the stem and cordon arms. The vines weaken and usually die back between five to ten years.
Up to now no correlation has been found between the disease and any fungus, bacteria, mycoplasma , soil type, climate, rootstock, clone or virus disease.
The symptoms are currently found only on the imported French Shiraz clone 99 in South Africa, whereas the locally selected clones 1, 21 and 22, as well as clones 5 and 9, imported from Argentina, show no symptoms in neighbouring blocks. The propagation of clone 99 has been discontinued by Vititec and any further use of this clone will take place at the producer's own risk.
In France the intensity of the symptoms differs and it appears as though the clone and the rootstock cultivar do play a role.
The symptoms were worst on clones 73, 381 and 383 which displayed cracks on 38 - 43% of the live vines, while 46 - 48% vines had already died.
The symptoms of clones 99 and 174 varied depending on where the block was situated.
Clones 470, 524 and 471 appear to be less sensitive, while 73, 301, 381 and 383 are more sensitive.
Only 1,54% symptoms were observed in clone 300, compared to the 9,12% symptoms in clone 301 on the same premises.
All new French Shiraz clones are therefore suspect until such time as more information about the clones becomes available in South Africa.
Stemgrooving strains that differ at RNA level have been found in material displaying the symptoms on Shiraz in California and France. These two strains also differ from the stemgrooving strain that has been found in Pinot noir vineyards. The Pinot noir vines often have thick graft joints and show dieback from 2 - 3 years after establishment ("Syrah Decline by James A Stamp - Wine Business Monthly, February 01, 2004, Volume XI, Issue 2").
All Pinot noir clones imported from France test positive for stemgrooving and similar symptoms are being observed in South African Pinot noir vineyards where the material has not yet been subjected to virus elimination .
For more information about the symptoms contact me on (021) 807-3017 or Spreeth@kwv.co.za.
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